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Spaceflight Insider

SpaceX successfully launches CRS-20, recovers their 50th Falcon 9 Booster

Northrop Grumman Successfully Completes Cold Static Test of Second Stage for OmegA Rocket

SpaceX successfully launches fourth batch of Starlink satellites

Crew Dragon In-Flight Abort’s successful completion clears way for crewed flights

Boeing’s Starliner capsule begins much-delayed first flight: UPDATE

Northrop Grumman’s NG 12 paints the sky in honor of an American legend

Delta IV Medium ends 17-Year run with 100% success

CRS-18 Falcon and Dragon brave storms to begin 18th ISS flight

Night time is the right time for SpaceX STP-2 mission

Anomaly occurs during OmegA first stage static fire test

Boeing CST-100 Starliner Testing Deficiencies Identified

Michael McCabe March 9th Cape Canaveral, FL – Details are emerging about exactly what and how testing was performed prior to Boeing launching their Starliner test capsule on December 20, 2019, a flight which resulted in a mixed outcome instead of what was supposed to be a resounding and highly anticipated success.

Northrop Grumman Successfully Completes Cold Static Test of Second Stage for OmegA Rocket

Patrick Attwell February 28th PROMONTORY, Utah – Feb. 28, 2020 – Northrop Grumman has successfully completed a cold static test of the second stage of its OmegA rocket in Promontory, Utah, completing the full-duration (approx. 140 seconds) firing on the afternoon of February 27.

New Horizons parallax project seeks public participation

Laurel Kornfeld February 21st NASA’s New Horizons mission is seeking public participation in a project aimed at imaging the two closest stars, Proxima Centauri and Wolf 359, from Earth on April 22 and 23, the same day the spacecraft will photograph them from almost five billion miles (eight billion km) away.

Pluto’s heart feature controls its winds

Laurel Kornfeld February 20th Pluto’s iconic heart feature, named Tombaugh Regio, functions as a “beating heart” that controls the small planet’s winds and might even play a role in shaping its surface features.

Arrokoth data sheds light on planet formation

Laurel Kornfeld February 19th Data returned by NASA’s New Horizons spacecraft taken during its January 2019 flyby of Kuiper Belt Object (KBO) Arrokoth, also known as 2014 MU 69, located four billion miles from Earth, supports the theory that planet formation in the solar system occurred in a gentle rather than violent process.

ULA successfully launches Solar Probe aboard Atlas V

Theresa Cross February 10th CAPE CANAVERAL, FL – A United Launch Alliance Atlas V rocket launched a NASA probe its way to our Sun. At 11:03 p.m. EDT, February 9, the rocket left Space Launch Complex 41 (SLC-41) located at Cape Canaveral Air Force Station, Florida.

Pluto’s hazy atmosphere is similar to that of Titan

Laurel Kornfeld February 2nd Pluto is often compared to Neptune’s largest moon Triton, but its hazy atmosphere is actually more akin to that of Saturn’s largest moon Titan, which is sometimes viewed as an analog of early Earth.

Artemis I Orion spacecraft advancing through tests at Plum Brook Station

Michael Cole January 31st SANDUSKY, OHIO — Testing is fully underway on the Orion spacecraft for the upcoming Artemis I test flight mission at NASA’s Plum Brook Station testing facility in Sandusky, Ohio. The Orion crew capsule, integrated with its European Service Module, is currently inside the facility’s Space Environments Complex undergoing thermal vacuum tests in the largest thermal vacuum chamber in the world.

SpaceX successfully launches fourth batch of Starlink satellites

Theresa Cross January 29th CAPE CANAVERAL, Fla. – SpaceX launched their fourth batch of approximately 60 satellites for the Starlink broadband network at 9:06am EDT, January 29, after carefully “evaluating extreme weather in the recovery area,” according to SpaceX.

NASA broadcast celebrates Spitzer telescope’s accomplishments

Laurel Kornfeld January 24th In a live broadcast on Wednesday, January 22, NASA celebrated 16 years of incredible accomplishments by the Spitzer Space Telescope, one of its four “Great Observatories” in space.

Spitzer telescope to be decommissioned after 16 years

Laurel Kornfeld January 20th NASA’s Spitzer Space Telescope, which has studied the universe in infrared light since its launch in August of 2003, will be decommissioned on Thursday, January 30, 2020.

Gallery: SpaceX’s Dragon clears safety check paving way for crewed missions

Michael McCabe January 19th CAPE CANAVERAL, Fla. — Images from the Jan. 19 test of SpaceX’s Crew Dragon spacecraft which successfully demonstrated the vehicle’s ability to pull astronauts away from the rocket in the event of an accident on its way to orbit.

Boeing CST-100 Starliner Testing Deficiencies Identified

Michael McCabe March 9th Cape Canaveral, FL – Details are emerging about exactly what and how testing was performed prior to Boeing launching their Starliner test capsule on December 20, 2019, a flight which resulted in a mixed outcome instead of what was supposed to be a resounding and highly anticipated success.

Northrop Grumman Successfully Completes Cold Static Test of Second Stage for OmegA Rocket

Patrick Attwell February 28th PROMONTORY, Utah – Feb. 28, 2020 – Northrop Grumman has successfully completed a cold static test of the second stage of its OmegA rocket in Promontory, Utah, completing the full-duration (approx. 140 seconds) firing on the afternoon of February 27.

Artemis I Orion spacecraft advancing through tests at Plum Brook Station

Michael Cole January 31st SANDUSKY, OHIO — Testing is fully underway on the Orion spacecraft for the upcoming Artemis I test flight mission at NASA’s Plum Brook Station testing facility in Sandusky, Ohio. The Orion crew capsule, integrated with its European Service Module, is currently inside the facility’s Space Environments Complex undergoing thermal vacuum tests in the largest thermal vacuum chamber in the world.

SpaceX successfully launches fourth batch of Starlink satellites

Theresa Cross January 29th CAPE CANAVERAL, Fla. – SpaceX launched their fourth batch of approximately 60 satellites for the Starlink broadband network at 9:06am EDT, January 29, after carefully “evaluating extreme weather in the recovery area,” according to SpaceX.

Crew Dragon In-Flight Abort’s successful completion clears way for crewed flights

Theresa Cross January 19th SpaceX successfully completed yet another milestone under NASA’s Commercial Crew Program to send astronauts to the International Space Station – the In Flight Abort Test.

SuperDraco engines set to be tested during SpaceX in-flight abort

Theresa Cross January 19th KENNEDY SPACE CENTER, Fla. — With the in-flight Crew Dragon abort test set to launch in less than an hour, let’s take a look into the incredibly powerful and spacecraft specific SuperDraco engine.

SpaceX, NASA monitoring weather ahead of in-flight abort test.

Sean Costello January 19th CAPE CANAVERAL. Fla. — As the sun rises and the shorelines of the Space Coast communities fill with eager spectators, SpaceX and NASA engineers have their attention focused on the early Sunday morning weather systems.

SpaceX poised to take large step toward human space flight

Cullen Desforges January 17th SpaceX is ready to check off another box on the list of requirements that need to be completed before the company can send crewed missions to the International Space Station.

NASA graduates its newest class of Astronauts

Sean Costello January 10th As NASA prepares to send astronauts to destinations far beyond Earth, a new breed of space flyers has joined the elite cadre of the agency’s astronaut corps.

New Year, new headquarters for Blue Origin

Laurel Kornfeld January 9th With Blue Origin opening its new headquarters, 2020 appears to be a year of further expansion for NewSpace.

SpaceX starts 2020 with Starlink launch

Patrick Attwell January 6th SpaceX’s Starlink constellation just got a major boost.

What’s in a name? Mars 2020 wouldn’t know, it doesn’t have one – yet

James Rice December 30th NASA’s Mars 2020 rover is on the verge of traveling to the Red Planet and beginning its search for evidence of Martian life. But it’s missing something very important.

Launch of Shijian 20 lights up Chinese skies and exploration ambitions

SpaceFlight Insider December 28th China has big plans for its space program. But before it can achieve them, it needed to make sure a key launch vehicle was up to the task. A recent mission suggests that it is.

Russia launches final Rockot with trio of communications satellites

SpaceFlight Insider December 27th Russia launched its final mission on the nation’s 2019 manifest when it sent three communications satellites to orbit on Friday, Dec. 27. The flight marked the close of a vehicle designed for violence.

Boeing Blunder! Starliner timing failure prevents ISS rendezvous

SpaceFlight Insider December 20th “Unplanned but stable.” That’s how Boeing referred to the first flight of its Starliner “space taxi.” In layman’s terms, the spacecraft was placed in the wrong orbit and won’t be going to the International Space Station.

Boeing’s Starliner capsule begins much-delayed first flight: UPDATE

Cullen Desforges December 20th CAPE CANAVERAL, FL – After almost a year of continued delays, Boeing’s CST-100 Starliner has finally launched. It is the culmination of years of development, but there’s still a ways to go before astronauts will be soaring aloft in the vehicle.

New Horizons parallax project seeks public participation

February 21st
NASA’s New Horizons mission is seeking public participation in a project aimed at imaging the two closest stars, Proxima Centauri and Wolf 359, from Earth on April 22 and 23, the same day the spacecraft will photograph them from almost five billion miles (eight billion km) away.

Pluto’s heart feature controls its winds

February 20th
Pluto’s iconic heart feature, named Tombaugh Regio, functions as a “beating heart” that controls the small planet’s winds and might even play a role in shaping its surface features.

Arrokoth data sheds light on planet formation

February 19th
Data returned by NASA’s New Horizons spacecraft taken during its January 2019 flyby of Kuiper Belt Object (KBO) Arrokoth, also known as 2014 MU 69, located four billion miles from Earth, supports the theory that planet formation in the solar system occurred in a gentle rather than violent process.

ULA successfully launches Solar Probe aboard Atlas V

February 10th
CAPE CANAVERAL, FL – A United Launch Alliance Atlas V rocket launched a NASA probe its way to our Sun. At 11:03 p.m. EDT, February 9, the rocket left Space Launch Complex 41 (SLC-41) located at Cape Canaveral Air Force Station, Florida.

Pluto’s hazy atmosphere is similar to that of Titan

February 2nd
Pluto is often compared to Neptune’s largest moon Triton, but its hazy atmosphere is actually more akin to that of Saturn’s largest moon Titan, which is sometimes viewed as an analog of early Earth.

NASA broadcast celebrates Spitzer telescope’s accomplishments

January 24th
In a live broadcast on Wednesday, January 22, NASA celebrated 16 years of incredible accomplishments by the Spitzer Space Telescope, one of its four “Great Observatories” in space.

Spitzer telescope to be decommissioned after 16 years

January 20th
NASA’s Spitzer Space Telescope, which has studied the universe in infrared light since its launch in August of 2003, will be decommissioned on Thursday, January 30, 2020.

Gallery: SpaceX’s Dragon clears safety check paving way for crewed missions

No in-flight abort for SpaceX’s Crew Dragon spacecraft today

January 18th
SpaceX has been forced to stand down from today’s attempt to test out a critical element of the company’s crew-rated spacecraft.

Boeing releases video from recent OFT mission

January 16th
Boeing has released video from its failed attempt to send its “Starliner” spacecraft to the International Space Station.

Processing of Starlink 2 booster underway, following return to Port Canaveral

January 11th
SpaceX’s B1049.4 returned to Port Canaveral January 9, 2020 after the completion of its fourth flown mission delivering the third set of Starlink satellites into low-Earth-orbit (LEO). This is Spacex’s first launch supported by the newly-created U.S. Space Force and its forty-eighth successful booster recovery.

CRS-19 Dragon wet and waiting for next mission

January 7th
After spending nearly a month berthed to the International Space Station, a SpaceX Cargo Dragon capsule left the Station and splashed down marking the successful completion of its mission.

OPINION: 2019 – Numbers and Names

January 1st
Well that happened. 2019 was a roller-coaster of ups and downs that will have far-reaching consequences for future space exploration efforts.

SpaceX prepares for first of many Starlink launches in 2020

December 31st
2020 looks to be a big year for space. The next twelve months could see the U.S. regain a long-lost capability and another rover should be sent on its way to the Red Planet. SpaceX is planning to kick off 2020 with the launch of the next batch of Starlink satellites.

NASA Mars 2020 rover passes driving test

December 27th
Remember how stressful it was taking your first driver’s test? Now imagine driving a car that’s worth $2.5 billion.

Space Flight Archives – Universe Today

Category: Space Flight

SpaceX Has Requested Permission to Fly Starship as Early as March

In September of 2019, SpaceX unveiled the first Starship prototype, the first of several test vehicles that would validate the design of the next-generation spacecraft that would fulfill Musk’s promise of making commercial flights to the Moon and Mars. And while there was a bit of a setback in November of 2019 after the Mk. 1 suffered a structural failure, Musk indicated that the company would be moving forward with other prototypes.

As Musk explained at the time, this would consist of the Mk. 3 prototype conducting an orbital test flight to an altitude of 100 km (62 mi) sometime in 2020. According to recent filings made with the FCC, this test could be happening as early as mid-March and will involve the vehicle launching from the company’s test facility in Boca Chica, Texas, and flying to an altitude of 20 km (12.6 mi) before landing.

Record-Setting Space Travelers Return to Earth

A trio of space travelers returned to Earth this morning from the International Space Station, including NASA astronaut Christina Koch, who set a record for the longest single spaceflight by a woman, at 326 straight days. Also coming home was ESA astronaut Luca Parmitano, who has now spent a total of 367 days in space (in two missions), more days than any ESA astronaut in history.

The crew of Expedition 61 also included Russian cosmonaut and Soyuz Commander Alexander Skvortsov, who completed his third mission for a total of 546 days in space, placing him 15th on the all-time time-in-space list.

LightSail 2 is Still Solar Sailing, But it’s Getting Lower and Lower with Each Orbit

LightSail 2 deployed it solar sail five months ago, and it’s still orbiting Earth. It’s a successful demonstration of the potential of solar sail spacecraft. Now the LightSail 2 team at The Planetary Society has released a paper outlining their findings from the mission so far.

Spaceflight Stories Expected for 2020

The year two thousand and twenty is almost upon us. And as always, space agencies and aerospace companies all around the world are preparing to spend the coming year accomplishing a long list of missions and developments. Between NASA, the ESA, China, SpaceX, and others, there are enough plans to impress even the most curmudgeonly of space enthusiasts.

Starliner Launches But it Can’t Reach the Station

Boeing’s Starliner crew capsule launched successfully, but a mishap prevented it from docking with the ISS. The ship is undamaged and will return and land at its designated location, according to officials. This could delay the planned crewed flight of the Starliner next summer.

A Private Company in China Plans to Launch Reusable Rockets by 2021

A Chinese company is planning to launch a rocket with a reusable booster in 2021. The company is called i-Space, and the rocket is called Hyperbola-2. They’ve already developed and launched another rocket, called Hyperbola.

NASA Tests Autonomous Lunar Landing Technology

In anticipation of many Moon landings to come, NASA is testing an autonomous lunar landing system in the Mojave Desert in California. The system is called a “terrain relative navigation system.” It’s being tested on a launch and landing of a Zodiac rocket, built by Masten Space Systems. The test will happen on Wednesday, September 11th.

The Light Sail is Working… It’s Working!

Good news from The Planetary Society: LightSail 2’s solar sail is functioning as intended. After launching on June 25th, then deploying its solar sail system on July 23rd, mission managers have been working with the solar sail to optimize they way LightSail 2 orients itself towards the Sun. Now The Planetary Society reports that the spacecraft has used its solar sail to raise its orbit.

Check Out This Super-Cool Quad Video of the Falcon Re-Entry. Two Sonic Booms!

Elon Musk has posted a four-panel video of the Falcon re-entry on his Twitter feed and it’s driving even jaded space-watchers into a frenzy.

LightSail 2 is Sending Home New Pictures of Earth

LightSail 2, the brainchild of The Planetary Society, has gifted us two new gorgeous images of Earth. The small spacecraft is currently in orbit at about 720 km, and the LightSail 2 mission team is putting it through its paces in preparation for solar sail deployment sometime on or after Sunday, July 21st.

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Universe Today Podcast

In this week’s questions show, I explain why we should be excited for both Starship and Artemis. Do we have a cognitive bias when thinking about advanced civilizations? Should humans or robots explore space? And more.

Follow Dr. Pamela Gay on Twitter:

00:30 Why should Artemis bother? Starship is better

04:34 Do we have a cognative bias when thinking about aliens?

08:55 Do I have a bobble-head?

17:04 Can we land without fuel?

19:55 Can we see farther into the Universe?

21:48 Could superearth inhabitants launch rockets?

23:47 What if my content is wrong?

25:50 Can we predict when a supernova will happen?

Want to be part of the questions show? Ask a short question on any video on my channel. I gather a bunch up each week and answer them here.

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Karla Thompson – @karlaii /

Support Universe Today podcasts with Fraser Cain

Virginia Space Flight Academy, Wallops Island VA

Virginia Space Flight Academy | Wallops Island VA

Our Mission

Virginia Space Flight Academy is a non-profit 501(c)(3) organization whose mission is to offer and inspire young people in programs that enhance their interest in science, technology, engineering and math and related career opportunities.

If it’s “brain-stretching” fun you seek this summer and thrive on the science of space adventure, check out the Virginia Space Flight Academy’s Summer Camps. For middle school students, ages 11-15, it’s an opportunity to build and launch model rockets. You also build and program robots to perform specific tasks. Add some drone flying to the mix, and you have the formula for a fun week at summer camp.


Taking Lego Robotics to the Next Step with Arduino Coding

STEM Initiatives on the Easter Shore

VSFA’s residential space camps bring young people from around the country to Wallops Island every summer.

Our Newest initiative is to build off season programs offering a variety of STEM-based programs that will build enthusiasm and inspiration for the next generation of home-grown space scientists, technicians, and engineers, sharing the many career opportunities that are right next door at Wallops Island.

Now Hiring Summer Camp Counselors

Registration is Open


It’s almost a wrap! Remember, when you finish your holiday shopping at, AmazonSmile donates to Virginia Space Flight Academy at no cost to you!

No Time to Be Bored!

I just picked up my 13 yr old son. It was his first time away ever and I had to drive 4 hrs to bring him. He roomed with a friend from school. I can’t say enough great things about the program and staff! Highly recommended! He learned so much this week and is talking about next year. I felt very comfortable leaving him there. The program is well tuned with no time to be bored!

Looking Forward to Returning Next Summer

What an amazing week for my daughter. It proved to be beyond what we had expected. She hasn’t stopped talking about her experience and adventures or the friends she’s made and is already looking forward to returning next summer.

Enriching Program

From the time we left him, to the time we picked him up, until now. he continues to tell us so much of what he has learned, you have truly satisfied his appetite and ignited his passion even more just like the rocket he created and launched. It is an absolute honor to be a part of this enriched program. Thank you all for everything.

Walking to the Rocket Launch Pad

Fantastic week last week for my 12 year-old! He was so enthusiastic about everything they did, and the first thing he said was that he wants to go back next year. He loved seeing the hangar where they build the rockets and walking over to the rocket launch pad. Great week!

A 10 out of a 10

My daughter has attended many camps in her 15 years but this is the first time she has come home raving. She gave her experience ‘a 10 out of 10’ which never happens! Thank you for giving her that.

Good mix of field trips, presentations, hands-on activities

I’ve enjoyed checking in on this site during the week to see what types of activities my son has been doing. It seems like a good mix of field trips, presentations and hands-on activities. I like that evening meals are at various sites that helps the local economy and allows my son to see parts of this area as if he’s on vacation. Good value for the money.

Both My Boys LOVED this camp

I can not say enough about this camp. Both of my boys LOVED it and want to go back next year. I am blown away by all of the things they got to do. I am also thankful for the pictures that were taken and the Facebook updates. I felt like I was there with them and was glad to see their smiling faces! THANK YOU VSFA!!

Thank you!

My 13 year old son just finished his week at VSFA, he loved it! A big thank you to all the supporters, organizers and camp counselors who make this possible.

Great Experience

Great experience for our son and the other campers!

Rocketry & Robotics

Amazing opportunity for adolescents to learn about rocketry and robotics. Wonderful program.

I would love to work at NASA or NOAA one day

“When I passed security and entered the NASA facility, I was absolutely astonished at what I saw. So many complex buildings; people working; huge planes and rockets! I would love to work at NASA or NOAA one day.”

Are Like Me

“The people here at Space Camp are like me; it’s kinda hard to find people like that outside of Space Camp.”

Creating Robots

“This camp was very fun and educational. My favorite part was creating a robot and battling them against the other kids and also making/launching the rockets.”

Virgin Galactic s Next Space Plane Should Begin Test Flights in 2020, Space

Virgin Galactic’s Next Space Plane Should Begin Test Flights in 2020

SpaceShipTwo Serial No. 3 is nearing completion.

Virgin Galactic will soon have two space planes plying the sky, if all goes according to plan.

The company’s newest six-passenger SpaceShipTwo vehicle, known as VSS Unity, is nearly ready to fly tourists to suborbital space and back. Unity reached space on its two most recent test missions, and the craft is being prepped for a move to Spaceport America in New Mexico, the hub for Virgin Galactic’s commercial operations.

Virgin Galactic’s manufacturing subsidiary, The Spaceship Company, is currently building two additional SpaceShipTwos in Mojave, California. And one of them is almost ready to go, Virgin Galactic President Mike Moses told last week at the unveiling of the company’s Gateway to Space building at Spaceport America.

“We expect to see test flights in 2020,” Moses said, speaking about the vehicle known as Serial No. 3. (VSS Unity is Serial No. 2. The first SpaceShipTwo, VSS Enterprise, was destroyed during a test-flight accident in October 2014 that killed co-pilot Michael Alsbury and wounded pilot Peter Siebold.)

Serial No. 4 is in production as well. And that’s how we’ll have to refer to these two future space planes, at least for now.

“They have internal names, but we’re not revealing them yet,” Moses said.

Now that the wing structure is complete, the next major step will be to join it to the completed fuselage. Exciting to see our next spaceship starting to take shape! 2, 2019

Closing out the wing of the next spaceship in our fleet consisted of integrating both structures and systems before finally bonding the lower skins and completing the main wing structure. Great job, @TheSpaceshipCo! 1, 2019

We have completed the wing of the next spaceship in our fleet, a major milestone in its manufacture. Watch as our teammates bond the internal structures together to complete the internal frame 31, 2019

SpaceShipTwo is designed to be lofted by a carrier plane called WhiteKnightTwo. At an altitude of about 50,000 feet (15,000 meters), the space plane separates from the carrier; then, SpaceShipTwo engages its onboard rocket motor to make its own way to suborbital space.

Passengers aboard the vehicle will experience a few minutes of weightlessness and get to see the curvature of Earth against the blackness of space before coming back down to Earth for a runway landing.

A ticket for this ride currently costs $250,000, and more than 600 people have put down deposits to reserve a seat, Virgin Galactic representatives have said.

Unity’s test flights to date have all originated from the Mojave Air and Space Port in Southern California, near The Spaceship Company’s headquarters. But the final missions in the test campaign will lift off from Spaceport America. Virgin Galactic’s one and only WhiteKnightTwo plane, VMS Eve, will haul Unity to the spaceport in the next few months, after technicians finish outfitting the space plane’s cabin, company representatives said. (VSS stands for “Virgin Spaceship” and VMS for “Virgin Mothership,” by the way.)

The Gateway to Space will be able to fit the new SpaceShipTwos when they’re ready, with plenty of room to spare. The building’s hangar can accommodate two WhiteKnightTwos and five SpaceShipTwos simultaneously, Virgin Galactic representatives said.

And that cavernous space provides an insight into the company’s long-term plans: Virgin Galactic aims to eventually achieve a rapid cadence of commercial flights, perhaps even launching multiple missions per day out of Spaceport America, company representatives have said.

Airplanes and Coronavirus: How to Disinfect Your Space – The New York Times

How to Disinfect Your Space on an Airplane

Here are some tips for cleaning your area of a plane and keeping healthy on a flight.

When a video of Naomi Campbell cleaning her airplane seat and wearing a mask and gloves was shared online last year, it made the rounds because her behavior seemed exaggerated. (“Clean everything you touch,” Ms. Campbell said in the video.)

Major airlines, including Delta Air Lines and American Airlines, say they clean their planes to varying degrees between flights, and that plane cleanliness is a priority. But some travelers, including apparently Ms. Campbell, prefer the comfort of knowing they’ve also taken measures of their own to sanitize their airplane space.

There’s been increased attention on this in recent weeks, with the unsettling spread of the coronavirus around the world.

“The airplane and airplane seat is a public space, and we know that germs can live on surfaces for a long time, so it doesn’t hurt to clean it,” said Aaron Milstone, associate hospital epidemiologist at the Johns Hopkins Hospital.

Here are some tips for cleaning your area of a plane and keeping healthy on a flight.

Keep your hands clean and stop touching your face

“Wiping down surfaces on a plane won’t hurt, as long as it doesn’t give you a false sense of security,” Andrew Mehle, associate professor of medical microbiology and immunology at the University of Wisconsin Madison, said, stressing that sanitizing your space on a plane should be done in conjunction with washing hands and following other best practices.

Get an informed guide to the global outbreak with our daily coronavirus newsletter.

Viral particles, the transmission vehicle of the coronavirus, must travel within mucus or saliva, and they must enter through eyes, nose or mouth. While the coronavirus can last on surfaces like tray tables, touch screens, door handles and faucets — one study found that other coronaviruses, like SARS and MERS stay on metal, glass and plastic for up to nine days — a disinfectant on a hard surface, or soap while washing your hands, will kill the virus.

However, most people tend to touch their faces more often than they realize. Doing so after touching a surface where there are droplets from when someone sneezed or coughed can lead to the virus being passed on.

So first things first: Wash your hands.

“It’s just as important to think about where your hands have been and to wash your hands,” said Dr. Mehle.

Wash your hands with soap and water for 20 seconds or long enough to sing “Happy Birthday” twice, and if that’s not possible, then use a generous amount of hand sanitizer.

Choose a window seat

A study from Emory University found that during flu season, the safest place to sit on a plane is by a window. Researchers studied passengers and crew members on 10 three- to five-hour flights and observed that people sitting in window seats had less contact with potentially sick people.

“Book a window seat, try not to move during the flight, stay hydrated and keep your hands away from your face,” said Vicki Stover Hertzberg, a professor at Emory University’s School of Nursing and director of the Center for Nursing Data Science at Emory, and one of the lead researchers on the study. “Be vigilant about your hand hygiene.”

Disinfect hard surfaces

When you get to your seat and your hands are clean, use disinfecting wipes to clean the hard surfaces at your seat like the head and arm rest, the seatbelt buckle, the remote, screen, seat back pocket and the tray table. If the seat is hard and nonporous or leather or pleather, you can wipe that down too. Using wipes on upholstered seats could lead to a wet seat and spreading of germs rather than killing them.

“It’s not bad to wipe down the area around you, but it’s worth remembering that the coronavirus is not going to jump off the seat and get into your mouth,” Dr. Milstone said. “People should be more careful of touching something dirty then putting their hands on their faces.”

Disinfecting wipes typically say on the packaging how long a surface needs to stay wet in order for them to work. That time can range from 30 seconds to a few minutes. In order for the wipes to work, you need to follow those time requirements.

Dr. Hertzberg added that if there’s a touch-screen television, you should use a tissue when touching the screen. Using a paper towel or tissue ensures that there’s a barrier between a surface that might have droplets and your hands, which will likely make their way to your face.

“Someone who has been sick and coughing might have touched the door and the faucet, so use wipes in the bathroom then use paper towels to open the door and to close the faucet then throw those in the trash on the way out,” said Bernard Camins, the medical director for infection prevention at the Mount Sinai Health System.

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Quickstart Guide to Military Space-A Flights, Poppin – Smoke

Quickstart Guide to Military Space-A Flights

Military Space-A flights have been a major element of our strategy for saving money on our frequent travels since my husband retired from the Army in 2015. We’ve flown Space-A to Europe, Hawaii, Alaska, Japan, Korea, and many places within the continental U.S.

I estimate that during our last 4+ years of world travel, we’ve saved more than $20,000 by taking military hops. Our experiences have been overwhelmingly positive, and whenever it’s a viable option, Space-A is my preferred way to fly.

Talking with others about our travels, we were surprised to realize how few military folks knew about Space-A travel, let alone had used it. Even those who knew it was an option were reluctant to give military flights a shot. They heard you have to wait around too much, the aircraft have too many maintenance issues, or the flights are canceled at the last minute.

The bottom line is yes, those things do happen. Flying Space-A requires patience and flexibility, and it’s not a good choice for all circumstances. But if you’ve flown a civilian airline lately, you know all those inconveniences happen with regular flights, too. The difference is, Space-A flights are free!

This Quickstart Guide explains everything you need to know about how to fly Space-A. After reading it and following the related links within the article, you should be all set to take your first Space-A journey!

If you’re NOT new to military Space-A travel, you should still read these lessons learned from our experiences and our recommended strategies for having a successful journey when using military hops.

This page contains affiliate links. For more information, please see our disclosure.

How Space-A Flights Work

Space-available flights, a.k.a “MAC flights” or “military hops,” are military operational flights that have extra seats. The military mission is the priority, and the Space-A passengers are essentially cargo.

Eligible travelers may “hop” the flight (free of charge), but the system is based on priority.

Space-A Travel Categories: Who Can Fly Space-A?

Travelers are divided into six Space-A categories or “Cats:” 1 is the highest and 6 is the lowest.

Available seats on the aircraft are first offered to travelers in lower-numbered categories. Any remaining seats can be used by travelers in higher-numbered (lower priority) categories. Priority within a category is based on signup date, as discussed below.

In the context of leisure travel, active duty service members traveling with or without dependents on accompanied environmental and morale leave (EML) are Cat 2 and on regular leave are Cat 3.

Military retirees and veterans with a permanent service-connected disability rated as total (100% disabled veterans) are Cat 6.

Certain travelers within Cat 6 have restrictions on where they can fly Space-A. “Gray Area” retirees (retired Guardsmen and Reservists who served 20 years but are under the age of 60) and 100% disabled veterans are not eligible to fly Space-A to foreign countries. They can take military hops within the continental United States (CONUS) and to U.S. states and territories outside the continental United States (OCONUS).

Please note that the list above is not exhaustive. Other passengers may be eligible to use military space-available travel under various circumstances. For a complete list and more information on eligibility by category, view Table 3 in Section 4.11 of DOD Instruction 4515.13.

Military Dependent Space-A Travel Eligibility

Dependents of active duty service members are eligible to fly Space-A without their sponsor under certain circumstances explained here.

A retiree’s dependents are eligible to fly Space-A, but only when accompanied by their sponsor.

The following dependents and family members are NOT eligible to fly Space-A at all:

  • Dependents of Gray Area retirees (defined above)
  • Dependents and caregivers of 100% disabled veterans
  • Ex-spouses or spouses of deceased service members or retirees
  • A service member’s or retiree’s parents, siblings, or any other family members who are not the sponsor’s dependents

Dependent children can fly Space-A with their sponsor or eligible unaccompanied parent. They are not authorized to travel with other military families.

Pets may not fly Space-A unless they are registered service animals.

The Space-A Flying Process: How to Take a Military Hop

Here is a summary of how to fly Space-A. For more details and links to the required forms, visit the Air Mobility Command (AMC) website.

1. Space-A Signup

Sign up with every military passenger terminal from which you might originate travel (including your destination). Keep in mind that you are not signing up for a particular flight. You are signing up to compete for any flight with Space-A seats at a given terminal.

You can sign up in one of several different ways:

  • Via e-mail
  • Using the Space-A travel app, Take-a-Hop (the app has a one-time cost of $6.99)
  • Through the AMC website’s online form
  • In person at the terminal

E-mail and the Take-a-Hop app allow you to sign up with multiple terminals at once.

If you sign up via e-mail, you must include all of the information listed in the Space-A Sign-Up section of the AMC website’s Space Available Travel page (see screenshot below).

Space-A Travel Sign-Up info on the AMC website

You can find a link to a document containing current e-mail addresses for all military passenger terminals at the bottom of the Space-A Sign-Up Section (highlighted in red in the screenshot above).

Many terminals will not reply to confirm receipt of your signup. Remember to retain and print copies of the e-mails you send, because they serve as proof of your signup date.

Priority within a Space-A category is based on signup date, so the earlier you sign up (maximum 60 days before your travel date at most locations, 45 days or less at some Navy locations), the better. Active duty cannot sign up for Space-A travel until they are on leave.

Visit for more information about signup.

2. Tracking Space-A Flight Schedules

Track flights (also referred to as “missions”) from your desired departure base(s). Flight schedules and tentative seat counts are available up to 72 hours before a flight.

If you monitor flight schedules out of your departure base for several weeks or months prior to travel, you may see patterns in how often they have missions to particular destinations and how many Space-A passengers get seats.

Most military passenger terminals maintain a Facebook page on which they publish flight information for the upcoming 3 days. A Space-A flight schedule lists the destinations, anticipated number of Space-A seats, and the “Roll Call” time, which is the time at which passenger terminal staff announce the names of passengers selected for the flight.

Many passenger terminals also publish data on recently-departed flights, including the number of Space-A seats released.

You can obtain information on Space-A seats by calling the terminal directly, but if a passenger terminal has a Facebook page, Facebook is an efficient way to monitor flight schedules.

Click here for a detailed explanation of the information on passenger terminal Facebook pages, including a guide to understanding the Space-A flight schedules.

3. Check-In or “Marking Yourself Present”

Within 24 hours of your target flight’s Roll Call, go to the terminal and speak with the staff to mark yourself present.

Bring your military ID, passport (if traveling to/from a foreign country), and any required paperwork, such as your leave form if you are active duty or the memo from your sponsor’s command if you are a dependent traveling unaccompanied.

You should also bring a copy of your signup e-mail in case the terminal does not have you in their system. Most terminals will accept your e-mail as proof of your signup date and time.

You must mark yourself present before Roll Call starts. As long as you have signed up in advance, there is no advantage to marking yourself present earlier than other passengers. Arriving one or two hours prior to Roll Call is usually sufficient, but in the 12 hours or so before your flight, check the schedules frequently to ensure Roll Call hasn’t changed.

Many passenger terminals have a screen or printed document near the terminal desk that displays a list of passengers who are marked present and are “competing” for the flight. Make sure your name is on that list along with the accurate number of dependents traveling with you and your correct date of signup. If not, speak with the terminal staff.

4. Roll Call

The time listed on the Space-A flight schedule on Facebook is usually the Roll Call time. When Roll Call begins, terminal staff announce how many Space-A seats are available and read the names of the passengers selected. They begin with the passengers in the lowest-numbered (highest priority) category and work their way down the list.

The AMC terminal at Travis AFB

When they call your name, go to the desk and confirm that you and any dependents traveling with you are present. Show your and your dependents’ military ID cards along with the aforementioned paperwork.

ID cards are required for all passengers over the age of 10. If you are traveling with children younger than 10 who do not have an ID card, bring their passport or a MilConnect printout that shows their DOD ID number.

After Roll Call, you might go directly to luggage check, or you may wait several more hours, but you won’t know the schedule in advance.

At the time of Roll Call, you must be in the terminal with all of your luggage. Don’t plan on waiting until after Roll Call to go back to your hotel or return your rental car, because you might not have time.

Note: If you’re not selected during Roll Call, stay in the terminal, at least until the flight boards. Sometimes additional Space-A seats are released at the very last minute.

Virtual Roll Call

Some passenger terminals offer Virtual Roll Call (VRC) for select missions. In theory, having VRC means passengers do not have to be present at the terminal for Roll Call. When there is a VRC for a particular flight, that information is noted on the Facebook slide.

With VRC, you must still go to the terminal within 24 hours of Roll Call to mark yourself present (and verify that they have your e-mail address). About an hour before the in-person Roll Call, the terminal sends you a “Roll Call Notification” e-mail.

If you don’t respond promptly, they take you out of the running. If you do respond, they eventually send you one of two e-mails: a “Flight Selection Notification” with instructions to go directly to the terminal to check your bags, or a “Non-Selection Notification,” which means you should activate Plan B (always have a Plan B when flying Space-A!).

In our limited experiences with VRC, it has not worked quite as planned. We had to go to the terminal for Roll Call anyway. VRC is a relatively new process, so they may still be working out the kinks. In the meantime, showing up in person is the best way to ensure you don’t miss any communication.

5. Bag Check

When it’s time to check bags, you, your dependents, and all of your luggage must be present.

Space-A passenger luggage on a C-17

On most Space-A flights, each passenger can check two bags of up to 70 lbs each. You can also check car seats, which do not count towards your baggage allowance.

Weight limits on some smaller aircraft may be as low as 30 lbs. If you cannot meet those requirements on the weight-restricted aircraft, you are not eligible for the flight.

The AMC website has more information about baggage for Space-A travelers in their FAQs starting with question #24.

You cannot access your checked luggage during the flight, even though you may see it strapped down right in front of you. Make sure you have everything you’ll need in your carry-on bag.

During baggage check, you can request a meal, (if meals are offered — usually a box lunch with sandwich, chips, cookie, and drink), which costs $5 – $10, depending on the base.

After you’ve checked your bags and have your boarding passes, you are “manifested” on the flight. Terminal staff will tell you the estimated boarding time, but keep in mind that it often changes without notice, so stay in the terminal.

6. Boarding

When boarding begins, all passengers go through security. Military passenger terminals follow TSA regulations, so you have the same restrictions for carry-on items as on civilian planes.

You sit in a secure area of the terminal until it’s time to board. At most locations, a bus takes you to the aircraft, and you board the plane from the tarmac.

If you are on a Patriot Express flight, your boarding pass will list your assigned seat. On other military aircraft, you select your own seats on a first-come, first-served basis. The crew may allow passengers with small children to board first, but not always.

7. Flight

Unless you are on a Patriot Express, which has full in-flight service, most Space-A flights are “no-frills.” The crew provides foam earplugs, water, and sometimes chips or cookies, but you must get those refreshments yourself.

Depending on the type of aircraft and how much space there is, you may be able to stretch out across a few seats or even sleep on the floor (see the section on Military Aircraft below).

8. Arriving at Your Destination

After landing, you take a bus from the aircraft to the terminal, where you collect your checked bags. Passenger terminals generally have information and phone numbers for local rental cars, base lodging, and other resources. You can also use UJ Space A Info to quickly search for local information related to any base in the world.

If you’ve flown to a foreign country, you may pass through customs, or you may have to go to an off-site location to have your passport stamped. The process varies by country and base.

Use Poppin’ Smoke’s Space-A Location Guides to research the customs and immigration process at your destination. The Guides also have detailed information about lodging, ground transportation, and other logistics for major Space-A hubs worldwide.

When (and When Not) to Fly Space-A

So now you know how Space-A travel works when all goes smoothly. Of course, it doesn’t always happen that way.

There are many situations when flying Space-A is not the best option. If you are going on a short vacation (less than 2 weeks) with little flexibility or you are traveling during major holidays, relying on Space-A is risky.

Most experienced Space-A travelers also avoid flying Space-A during summer PCS season (late May through early September), particularly to OCONUS destinations.

In those situations, it’s better to plan ahead and try to find cheap military flights from airlines that offer discounts or use a site like Skyscanner to find the best commercial fares.

If you are traveling solo, you have a better chance of getting a seat, even during busy periods. Many other Space-A travelers are couples or families, and even if those groups are in a higher category, when there is only one seat left, a solo traveler will get it.

Packing light also increases your chances of getting a seat. Some flights have baggage weight restrictions that will take most other passengers out of the running.

You can take some of the risk out of flying Space-A and boost your chances of having a successful trip by following these strategies and tips and monitoring the Space-A flight schedules on Facebook to make informed decisions about what flights are most promising.

How to Prepare for Space-A Travel

Knowing what to expect at the passenger terminal and on the planes can help you have a more comfortable journey.

What to Expect at Military Passenger Terminals

Passenger terminals vary widely in terms of their hours, services available, and rules. Some have a USO, a snack bar, a children’s area, and showers, while others have little more than a check-in desk and a few chairs. has information on specific services available at each terminal.

Most terminals discourage passengers from getting too comfortable and falling asleep. The chairs generally have fixed armrests that prevent you from stretching out across the seats. Also, there are often signs requesting that you not lie on the floor. Be prepared with a good book and plenty of activities for the kiddos!

Many military passenger terminals have WiFi, but it’s not always very strong, so remember to download any books, movies, or activities you may want ahead of time.

I recommend saving the contact information for the passenger terminals you anticipate using so that you have it handy if you need to call or e-mail with questions.

Finally, keep in mind that most passenger terminals are NOT open 24 hours, so you cannot spend the night there. Even if you arrive on an aircraft that has an overnight layover, staying in the terminal is not an option. Click here to read tips and tricks for reserving base lodging.

What to Wear and Bring on Military Aircraft

Depending on the type of aircraft and how it’s configured, you have different considerations for comfort. If it’s a Patriot Express (a.k.a. a “rotator”), it’s simply a regular passenger plane. Most other Space-A flights will be “organic aircraft,” a.k.a. military planes.

For all organic aircraft, three tips apply:

  • Dress in layers. It can be very cold or very warm, depending on the type of aircraft, where you’re sitting, and pilot preference. We use this layering system so that we can easily adjust to the temperature. I occasionally see passengers (especially children) wearing shorts, but I don’t recommend it unless you have a pair of sweatpants handy.
  • Bring a small, inflatable mat and a blanket or sleeping bag. You can use an inflatable mat like this one to lie on the floor or stretch out across multiple seats. The blanket/sleeping bag is important for warmth.
  • Bring hand wipes. The lavatory sinks generally don’t have running water. Instead, there is a pile of antiseptic wipes, but often not enough to last for the entire flight. Bring your own stash of hand wipes.

While you could fly on one of more than a dozen different types of aircraft, the ones below are the most common:

C-5: This is the largest aircraft in the Air Force. If the Facebook slide indicates there are 73 seats available, the aircraft is probably a C-5. Seats are configured just like a commercial airplane, but they face the rear of the aircraft, and you have more legroom. If the plane isn’t crowded and you are lucky enough to have your own row, you can stretch out (unlike in the passenger terminals, you can raise the armrests!).

C-17: The first time we traveled Space-A on a C-17, all passengers were sitting in jump seats along the sides of the aircraft (facing the middle). With this configuration, you can lie down after the plane reaches altitude if there is room on the floor and the crew authorizes you to do so. On our first Space-A flight from Andrews AFB to Germany we didn’t plan ahead and had to sleep on a wool blanket provided by the crew (it was still more comfortable than sitting in the economy section of a commercial flight).

Flying Space-A on a C-17

The next time we flew in a C-17 with that configuration, we were prepared with a couple of inflatable pool rafts. The rafts provided much more cushion than the wool blankets and were pretty inexpensive. Unfortunately, they were exhausting to blow up and nearly impossible to drain and fold down to an easily-transportable size.

Now we have this small easily-inflatable sleeping pad. It weighs only 18.6 oz, inflates with 10 – 15 breaths, and easily deflates to fit back in its carrying bag.

We also flew in a C-17 configured with regular passenger seats filling most of the bay. Some passengers chose to sit along the sides anyway, but we preferred real seats to jump seats. With that configuration, there was very little space to lie on the floor.

C-130: This a prop plane, so it is noisier, slower, and bumpier than a C-17. It has the same open bay configuration with web seating along the sides. If there is room on the floor, you can lie down like on a C-17.

KC-10/KC-135: These are tankers used to fuel jets while in the air, and they may perform that mission with Space-A passengers aboard. The KC-10 usually has regular airline seats and about twice the passenger capacity of the KC-135. The latter generally has web seating along the sides of the aircraft.

“VIP” aircraft (C-9/C-12/C-21/C-40): These aircraft have regular passenger seats and generally do not have space to lie on the floor. The baggage weight limit may be much lower (usually 30 lbs. for C-12 and C-21, 50 lbs. for C-9 and C-40) due to aircraft baggage storage limitations and/or fuel requirements to the destination.

Final Advice

Think of Space-A travel as an adventure. Along the way, you will meet other travelers who remind you how helpful and supportive the military community can be.

Hitching a ride with a military mission is a privilege and, for dependents who have never flown in a military aircraft, a very unique experience. If you think of your journey in this way, you will be better-prepared to handle any parts of the process that don’t go as planned.

Recommended Reading

If you’re looking for more information about flying Space-A, these articles are good reading:

Trying to keep all this Space-A jargon straight? Get the list of terms you need to know.

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The WIRED Guide to Commercial Human Space Flight, WIRED

The WIRED Guide to Commercial Human Space Flight

On the morning of December 13, 2018, the Virgin Galactic WhiteKnightTwo wheeled down a stark runway in Mojave, California, ready to take off. Whining like a regular passenger jet, the twin-hulled catamaran of an airplane passed by owner Richard Branson, who stood clapping in an aviator jacket on the pavement. But WhiteKnightTwo wasn’t just any plane: Hooked between the two hulls was a space plane called SpaceShipTwo, set to be the first private craft to regularly carry tourists away from this planet.

WhiteKnightTwo rumbled along and lifted off, getting ready to climb to an altitude of 50,000 feet. From that height, the jet would release SpaceShipTwo; its two pilots would fire the engines and boost the craft into space.

“3 … 2 … 1 …” came the words over the radio.

SpaceShipTwo dropped like a sleek stone, free.

“Fire, fire,” said a controller.

On command, flame shot from the craft’s engines. A contrail smoked over the folds of the mountains as the spaceship flew up and up and up. Soon, both contrail and fire stopped: SpaceShipTwo was simply floating. The arc of Earth curved across its window, up against the blackness of the rest of the universe. A hanging dashboard ornament, shaped like a snowflake, wheeled in the microgravity of the cabin.

“Welcome to space,” said base. And with that, Virgin Galactic had flown its first astronauts, who were not the government-sponsored heroes of old but private citizens working for a private company.

For most of the history of spaceflight, humans have left such exploits to governments. From the midcentury Mercury, Gemini, and Apollo days to the 30-year-long shuttle program, NASA has dominated the United States’ spacefaring pursuits. But today, companies run by powerful billionaires—who made their big bucks in other industries and are now using them to fulfill starry-eyed dreams—are taking the torch, or at least part of its fire.

Projection range of potential revenue from space tourism in 2022.

Virgin Galactic, for its part, styles itself as a tourism outfit, and space-hopefuls of this sort often speak of the philosophical uplift—the perspective shift that happens when humans view Earth as an actual planet in for-real space. Other companies want to help set up permanent residence on the moon and/or Mars, and they sometimes speak of destiny and salvation. There’s much gesturing toward the strength of the human spirit and the irrepressible exploratory nature of our species.

But let us not forget, of course, that there’s the money to be theoretically made; and the federal government isn’t itself actually flying astronauts anymore. After the closure of the space shuttle program in 2011, the US no longer had the ability to send humans to space and has since relied on Russia. But that’s about to change: Today, two private companies—Boeing and SpaceX—have contracts to fly humans to the International Space Station.

But even before NASA’s programs for sending people to space started to dwindle, business magnates recognized what they could do if they had their own private rockets. They could ferry supplies to the Space Station for the budget-conscious government. They could launch satellites. They could take tourists on suborbital jaunts. They could foster industrial infrastructure in deep space. They could settle the moon and Mars. Humans could become the spacetime-defying species they were always meant to be, and travel often—or even live long-term—away from Earth. It’s exciting: After all, science fiction—that great predictor and creator of the future—has told us for decades that space is the next (the final) frontier, and we should (will, can) not just go but also live there.

Global launch industry revenue in 2017

The private space companies are taking small steps toward that long-term, large-scale presence in space, and 2019 holds more promise than most years. But the deadlines keep slipping: Like cold fusion, private human space travel is perpetually just around the corner. Perhaps part of the lag is because private human space travel—and especially extended private human space travel—is a nearly untested business model, and most of these companies make much of their money on enterprises that have little to do with humans: Often, the operations that generate revenue in the here and now involve schlepping satellites and supplies close by, not sending humans far off. But because the most promising plans are backed by billionaires with big agendas—and are, in some sense, aimed at other rich people—science fiction could nevertheless become space fact.

Today, the capitalists of the space-jet set call their industry New Space, although in earlier days forward-thinkers spoke about “” You could say it all started in 1982, when a company called Space Services launched the first privately funded rocket: a modified Minuteman missile, which it christened Conestoga I (after the wagon, get it?). The flight was just a demonstration, deploying a dummy payload of 40 pounds of water. But two years later, the US passed the Commercial Space Launch Act of 1984, clearing the pad for more private activity.

Human passengers climbed aboard in 2001, when a financier named Dennis Tito bought a seat on a Russian Soyuz rocket and took a $20 million, nearly eight-day vacation to the Space Station. Space Adventures, which arranged this pricey flight, would go on to send six more astro-dilettantes to orbit through the Russian Space Agency.

That same year, some guy named Elon Musk, about to be rich from selling PayPal, announced a plan called Mars Oasis. With his many monies, he wanted to amp up public support for human settlement on the Red Planet, so that public pressure would impel Congress to mandate a mission to Mars. Through an organization he founded called the Life to Mars Foundation, Musk proposed the following privately funded opening shot: a $20 million Mars lander, carrying a greenhouse that could fill itself with martian soil, to be launched maybe in 2005.

Potential value of NASA’s contracts with SpaceX and Boeing to take astronauts to and from the Space Station.

This, let us note, never happened—in part because the cost of launching such a future-garden was so high. A US rocket would have cost him $65 million (around $92 million in 2018 dollars), a reconstituted Russian ICBM around $10 million. A year later, Musk set out to lower the rocket barrier. Switching from “foundation” to “corporation,” he started SpaceX, a rocket company with the explicit end-goal of Mars habitation.

In the early aughts, Musk wasn’t the only one who wanted to send people to space. Pilot (and then astronaut) Mike Melvill flew SpaceShipOne, which resembled a bullet that grew frog legs, to space in 2004. After that test flight and two subsequent trips, SpaceShipOne won a $10 million X-Prize. These flights brought together two New Space dreams: a privately developed craft and private astronaut pilots. After the victory, Virgin Galactic and Scaled Composites developed the high-flying technology into SpaceShipTwo. Unveiled by Virgin in 2009, this passenger vessel was intented to send tourists to space … for the cost of an average house. (After all, why have a home forever when you can go to space for five minutes??)

Value of NASA’s first contracts with SpaceX and Orbital Sciences (now part of Northrop Grumman) to deliver supplies to the ISS, from 2009 to 2016

Virgin Galactic has always kept its focus close to home and on short but frequent flights that stay suborbital. Musk, though, has stuck to his original martian mission. After launching its first rocket to orbit in 2008, SpaceX won a NASA contract to bus supplies to and from the Space Station, and it’s still shuttling cargo there for the agency. But the startup really got its legs in 2012 and 2013, when it launched a squatty rocket called the Grasshopper. Though it didn’t hop high into the air, it landed back on the launch pad, from where it could go up again (like, say, a grasshopper). This recyclability paved the way for today’s reusable Falcon 9 rockets, which have gone up and down and helped transform the ethos of rocket science from one of dispensability to one of recyclability.

From Virgin Records to the airline Virgin Atlantic to the cell provider Virgin Mobile, Richard Branson has made money around the block.

The beknighted Virgin Galactic plane carries a space plane that can ferry up to six passengers and two pilots just over the border of space, so they can experience a few minutes of weightlessness and an incredible view. Richard Branson hopes to go up himself toward the middle of this year, with tourists soon to follow.

Musk’s goal, since the failure of Mars Oasis, has always been to cut launch costs. Today, SpaceX’s Falcon 9 reusable rockets cost $50–60 million—still a lot, but less than the $100 million-plus of some of its competitors. Getting to space, the thinking goes, should not be the biggest barrier a would-be space-farer faces. If SpaceX can accomplish that, the company can—someday, theoretically—send to Mars the many shipments of supplies and humans that are necessary to fulfill Musk’s “MAKE LIFE MULTIPLANETARY” tagline.

But the road to multiplanetarity hasn’t always been smooth for SpaceX. Its reusable rockets have crashed into the ocean, tipped over in the sea, crashed into barges, tipped over on ships, tumbled through the air, spun out, exploded midflight, and exploded on the launch pad.

The course of true New Space, though, never did run smooth, and SpaceX is far from the only company that has experienced crashes. Virgin Galactic, for instance, faced tragedy in 2014 when pilot Pete Siebold and copilot Michael Alsbury were in SpaceShipTwo underneath the WhiteKnight jet.

Jeff Bezos, of Amazon fame and fortune, is still very much married to space pursuits.

Blue Origin’s reusable rocket will take crews and payloads on 11-minute suborbital flights, landing as softly as the feather painted on its body. The goal is to send the first crew up this year.

Blue Origin says it wants this heavy-lift, recyclable rocket to “build a road to space.” This launcher will likely debut in 2021.

The flight of SpaceShipTwo did not go as planned. SpaceShipTwo has a “feathering mechanism” that, when unlocked and enabled, slows the ship so that it can land safely. But Alsbury unlocked it early, and it dragged the craft while its rockets were still firing. The aerodynamic forces ripped SpaceShipTwo apart, killing Alsbury. Siebold parachuted, alive, to the ground. A few customers canceled. Most still wanted to go to space, even though the industry has higher-risk and lower-regulation than lower-altitude commercial flights.

Meanwhile, another major corporation—Blue Origin—was quietly crafting its human-mission plans. This celestial venture, funded by Amazon founder Jeff Bezos, started in 2000—before Musk started SpaceX—but stayed pretty stealthy for years. Then, in an April 2015 test launch, the would-be-reusable New Shepard rocket lifted off. It successfully deployed a capsule but failed to land. That November, though, a New Shepard did what it was supposed to: touched back down, beating SpaceX to that launch-and-land goal.

Blue Origin, like Virgin Galactic, wants to use its little rocket to send up suborbital space tourists. And it wants, with bigger dick–lookalike rockets, to help facilitate a permanent moon colony. Bezos has suggested heavy industry should happen off this planet, in places that kind of suck already but have minable resources. The first lunar touchdown, he says, could be in 2023, facilitating an Earth that’s zoned mostly residential and light-industrial.

SpaceX, too, has big 2023 plans. The company announced last September that in 2023 it will send Japanese magnate Yusaka Maezawa and a passel of artist companions on a trip around the moon. NASA has also contracted with the company, and with Boeing, to shuttle astronauts to and from the ISS as part of the commercial crew program, which begins human testing later this year.

Still, for all the hype around these wider-vision companies, Virgin Galactic remains the only private enterprise that has actually sent a private someone to space on a private vehicle.

The way these companies see the future, they (humbly, of course) will be the ones to normalize space travel—whether that travel takes you just over the Karman line or to another celestial body. Space planes will ferry passengers and experiments to suborbital spots, touching back down in less time than it takes to watch The Right Stuff. Rockets will launch and land and launch again, sending up satellites and ferrying physical and biological cargo to an industrial base on the moon or the martian home base, where settlers will ensure the species persists even if there’s an apocalypse (nuclear, climatic) on terra firma. Homo sapiens will have manifested its destiny, shown itself to be the brave pioneer it always knew it was. And the idea that we don’t have to be stuck in one cosmic spot forever is exciting!

But all of these enterprises are businesses, not philanthropic vision boards. Is making life casually spacefaring and seriously interplanetary actually a plausible financial prospect? And—more important—is it actually a desirable one?

Let’s start with low-key suborbital space tourism, of the type Virgin Galactic and Blue Origin would like to offer. Some economists see this as fairly feasible: If we know one thing about the world, it’s that some subset of the population will always have too much money and will get to spend it on cool things unattainable for the plebs. If such flights become routine, though, their price could go down, and space tourism could follow the trajectory of the commercial aviation industry, which used to be for the wealthy and is now home to Spirit Airlines. Some also speculate that longer, orbital flights—and sleepovers in cushy six-star space hotels (the extra star is for the space part)—could follow.

After there’s a market for space hotels, more infrastructure could follow. And if you’re going to build something for space, it might be easier and cheaper to build it in space, with materials from space, rather than spending billions to launch all the materials you need. Maybe moon miners and manufacturers could establish a proto-colony, which could lead to some people living there permanently.

Or not. Who knows? I can’t see the future, and neither can you, and neither can these billionaires.

But with long journeys or permanent residence come problems more complicated than whether money is makeable or whether it’s possible to build a cute town square out of moon dust. The most complicated part of human space exploration will always be the human.

We weak creatures evolved in the environment of this planet. Mutations and adaptations cropped up to make us uniquely suited to living here—and so uniquely not suited to living in space, or in Valles Marineris. It’s too cold or too hot; there’s no air to breathe; you can’t eat potatoes grown in your own shit for the rest of your unnatural life. Your personal microbes may influence everything from digestion to immunity to mood, in ways scientists don’t yet understand, and although they also don’t understand how space affects that microbiome, it probably won’t be the same if you live on an extraterrestrial crater as it would be in your apartment.

Plus, in lower gravity, your muscles go slack. The fluids inside you pool strangely. Drugs don’t always works as expected. The shape of your brain changes. Your mind goes foggy. The backs of your eyeballs flatten. And then there’s the radiation, which can deteriorate tissue, cause cardiovascular disease, mess with your nervous system, give you cancer, or just induce straight-up radiation sickness till you die. If your body holds up, you still might lose it on your fellow crew members, get homesick (planetsick), and you will certainly be bored out of your skull on the journey and during the tedium and toil to follow.

Maybe there’s a technological future in which we can mitigate all of those effects. After all, many things that were once unimaginable—from vaccines to quantum mechanics—are now fairly well understood. But the billionaires don’t, for the most part, work on the people problems: When they speak of space cities, they leave out the details—and their money goes toward the physics, not the biology.

They also don’t talk so much about the cost or the ways to offset it. But Blue Origin and SpaceX both hope to collaborate with NASA (i.e. use federal money) for their far-off-Earth ventures, making this particular kind of private spaceflight more of a public-private partnership. They’ve both already gotten many millions in contracts with NASA and the Department of Defense for nearer-term projects, like launching national-security satellites and developing more infrastructure to do so more often. Virgin, meanwhile, has a division called Virgin Orbit that will send up small satellites, and SpaceX aims to create its own giant smallsat constellation to provide global internet coverage. And at least for the foreseeable future, it’s likely their income will continue to flow more from satellites than from off-world infrastructure. In that sense, even though they’re New Space, they’re just conventional government contractors.

Elon Musk made his first fortune on PayPal.

SpaceX will also be ferrying astronauts and accessories to the International Space Station for NASA, and after its journey, the Falcon will land itself, while the Dragon capsule will splash down. Bonus: The company boasts that passengers can set the internal temperature anywhere from 65 to 80 degrees Fahrenheit. Its first crewed test could occur in mid-2019.

Formerly called BFR (Big Falcon Rocket or Big Fucking Rocket, depending on what kind of person you are talking to), this SpaceX craft and its human capsule are supposed to take 100 people and 150 tons of cargo to the Red Planet. Musk unveiled a smaller, suborbital prototype in January, and its shiny silver sides and vintage sci-fi shape look like if a ‘50s diner dreamed it became a rocket. Its first test should take place sometime this year.

So, if the money is steadier nearby, why look farther off than Earth orbit? Why not stick to the lucrative business of sending up satellites or enabling communications? Yes, yes, the human spirit. OK, sure, survivability. Both noble, energizing goals. But the backers may also be interested in creating international-waters-type space states, full of the people who could afford the trip (or perhaps indentured workers who will labor in exchange for the ticket). Maybe the celestial population will coalesce into a utopian society, free of the messes we’ve made of this planet. Humans could start from scratch somewhere else, scribble something new and better on extraterrestrial tabula rasa soil. Or maybe, as it does on Earth, history would repeat itself, and human baggage will be the heaviest cargo on the colonial ships. After all, wherever you go, there you are.

Maybe we’d be better off as a species if we stayed home and looked our problems straight in the eye. That’s the conclusion science fiction author Gary Westfahl comes to in an essay called “The Case Against Space.” Westfahl doesn’t think innovation happens when you switch up your surroundings and run from your difficulties, but rather when you stick around and deal with the situation you created.

No billionaire here. Just the military-industrial complex joining forces with itself. Within the past 15 years, this rocket has had a 100 percent success rate.

The Atlas V rocket made by United Launch Alliance, a joint venture of Lockheed Martin and Boeing, will join with Boeing’s CST-100 Starliner capsule to send astronauts and science experiments to the ISS. The Starliner can fly 10 times, as long as it gets a six-month refractory period—for refurbishing and tests—between each trip. Its first crewed test could occur in mid-2019.

Besides, most Americans don’t think big-shot human space travel is a national must-do at all, at least not with their money. According to a 2018 Pew poll, more than 60 percent of people say NASA’s top priorities should be to monitor the climate and watch for Earth-smashing asteroids. Just 18 and 13 percent think the same of a human trip to Mars or the moon, respectively. The People, in other words, are more interested in caring for this planet, and preserving the life on it, than they are in making some other world livable.

But maybe that doesn’t matter: History is full of billionaires who do what they want, and it’s full of societal twists and turns dictated by their direction. Besides, if even a fraction of a percent of the US population signed on to a long-term space mission, their spaceship would still carry the biggest extraterrestrial settlement ever to travel the solar system. And even if it wasn’t an oasis, or a utopia, it would still be a giant leap.

It’s Time to Rethink Who’s Best Suited for Space Travel
The definition of the “right stuff” has changed since the military test-pilot astronauts of old became the first US astronauts. Maybe it should expand to include people with disabilities.

Meet the Astronauts Who Will Fly the First Private “Space Taxis”
Soon, NASA will be sending up its first cohort of commercial astronauts. Here’s who they are.

The Race to Get Suborital Tourists to Space Is Heating Up
There’s a new space race, and this time you’re not paying for it with your tax dollars but with your discretionary income.

The Japanese Space Bots That Could Build “Moon Valley”
If humans do develop a long-term presence in space, they’ll definitely need to help of a few good robots.

Jeff Bezos Wants Us All to Leave Earth—for Good
A billionaire’s got to dream, right? Here’s what Bezos and his money see in space’s future.

Last updated January 30, 2019

Enjoyed this deep dive? Check out more WIRED Guides.

Space-A Travel for Military Families

Space-A Travel for Military Families

Plan Your Trip With Space-A Travel

Service members and their families can use Space-Available flights – formally known as Military Airlift Command or MAC flights – to travel around the country and world at little to no cost. Though sometimes unpredictable, military flights are perfect for families with flexible plans and limited travel budgets. With the right planning and documentation, Space-A travel can be the best way to take a trip with your family.

Space-A Tips and Tricks

Learn how to take Space-A flights like a seasoned pro with these seven tips.

Space-A travel basics

These flights are not commercial, but rather military flights with a mission. That means there are certain restrictions to travel, including:

  • Only service members, retirees and their families are eligible. Only with certain qualifications are reservists, National Guardsmen and family members without an accompanying active-duty sponsor permitted.
  • Flights are typically free of charge, but you should contact your closest Air Mobility Command, or AMC, passenger terminal or the terminal at the location you intend to depart from for specific information.
  • Most terminals have a Facebook page where they post flight information, including their 72-hour flight schedule.

Space-Available travel eligibility

Once you sign up for a Space-A journey, you’ll be put into a category that determines your priority for a flight. A complete listing of eligible passengers by category is contained in DoD Instruction 4515.13. For the most recent instruction, search the DoD Directives Division website for “Air Transportation Eligibility.” Categories include:

  • Category I: Emergency Leave Unfunded Travel.
  • Category II: Accompanied Environmental and Morale Leave, or EML.
  • Category III: Ordinary Leave, Relatives, House Hunting Permissive Temporary Duty, Medal of Honor Holders and Foreign Military.
  • Category IV: Unaccompanied EML.
  • Category V: Permissive Temporary Duty (Non-House Hunting), Students, Dependents, Post Deployment/Mobilization Respite Absence and Others.
  • Category VI: Retired, Dependents, Reserve, Reserve Officers’ Training Corps, Nuclear Propulsion Officer Candidate Program and Civil Engineer Corps members.

Prepare for your Space-A flight

AMC has a travel page that includes the following important information about Space-A travel. You should review this travel page for up-to-date information, including what type of identification is required for you and your family, baggage allowance for checked and hand carried baggage, and prohibited items.

  • Travel instructions: travel eligibility; locations; required travel documents; registration, flight schedule and checking-in information.
  • AMC Form 140, Space Available Travel Request (fill out a form online and email it to your desired AMC passenger terminal)
  • Listing of Facebook pages for stateside and overseas locations.
  • AMC passenger terminal contact information.
  • Various travel information links.
  • Legal information for Space-A travel.
  • Operations security for social media and travelers.

Fly commercial with TSA Precheck

If Space-A travel isn’t right for your plans, take advantage of TSA Precheck to expedite your time at the airport when flying commercial. Use your Department of Defense ID as your known traveler number.

You’ll bypass long security lines without removing your shoes or jacket or taking your laptop from your bag. Family members under the age of 12 can pass through expedited screening with you.

Basics of Space Flight: Orbital Mechanics

Space a flight

Orbital mechanics, also called flight mechanics, is the study of the motions of artificial satellites and space vehicles moving under the influence of forces such as gravity, atmospheric drag, thrust, etc. Orbital mechanics is a modern offshoot of celestial mechanics which is the study of the motions of natural celestial bodies such as the moon and planets. The root of orbital mechanics can be traced back to the 17th century when mathematician Isaac Newton (1642-1727) put forward his laws of motion and formulated his law of universal gravitation. The engineering applications of orbital mechanics include ascent trajectories, reentry and landing, rendezvous computations, and lunar and interplanetary trajectories.

A conic section, or just conic, is a curve formed by passing a plane through a right circular cone. As shown in Figure 4.1, the angular orientation of the plane relative to the cone determines whether the conic section is a circle, ellipse, parabola, or hyperbola. The circle and the ellipse arise when the intersection of cone and plane is a bounded curve. The circle is a special case of the ellipse in which the plane is perpendicular to the axis of the cone. If the plane is parallel to a generator line of the cone, the conic is called a parabola. Finally, if the intersection is an unbounded curve and the plane is not parallel to a generator line of the cone, the figure is a hyperbola. In the latter case the plane will intersect both halves of the cone, producing two separate curves.

We can define all conic sections in terms of the eccentricity. The type of conic section is also related to the semi-major axis and the energy. The table below shows the relationships between eccentricity, semi-major axis, and energy and the type of conic section.

Conic Section Eccentricity, e Semi-major axis Energy
Circle 0 = radius
Ellipse 0 > 0
Parabola 1 infinity 0
Hyperbola > 1 > 0

Satellite orbits can be any of the four conic sections. This page deals mostly with elliptical orbits, though we conclude with an examination of the hyperbolic orbit.

To mathematically describe an orbit one must define six quantities, called orbital elements. They are

    • Semi-Major Axis, a
    • Eccentricity, e
    • Inclination, i
    • Argument of Periapsis,
    • Time of Periapsis Passage, T
    • Longitude of Ascending Node,

    An orbiting satellite follows an oval shaped path known as an ellipse with the body being orbited, called the primary, located at one of two points called foci. An ellipse is defined to be a curve with the following property: for each point on an ellipse, the sum of its distances from two fixed points, called foci, is constant (see Figure 4.2). The longest and shortest lines that can be drawn through the center of an ellipse are called the major axis and minor axis, respectively. The semi-major axis is one-half of the major axis and represents a satellite’s mean distance from its primary. Eccentricity is the distance between the foci divided by the length of the major axis and is a number between zero and one. An eccentricity of zero indicates a circle.

    Inclination is the angular distance between a satellite’s orbital plane and the equator of its primary (or the ecliptic plane in the case of heliocentric, or sun centered, orbits). An inclination of zero degrees indicates an orbit about the primary’s equator in the same direction as the primary’s rotation, a direction called prograde (or direct). An inclination of 90 degrees indicates a polar orbit. An inclination of 180 degrees indicates a retrograde equatorial orbit. A retrograde orbit is one in which a satellite moves in a direction opposite to the rotation of its primary.

    Periapsis is the point in an orbit closest to the primary. The opposite of periapsis, the farthest point in an orbit, is called apoapsis. Periapsis and apoapsis are usually modified to apply to the body being orbited, such as perihelion and aphelion for the Sun, perigee and apogee for Earth, perijove and apojove for Jupiter, perilune and apolune for the Moon, etc. The argument of periapsis is the angular distance between the ascending node and the point of periapsis (see Figure 4.3). The time of periapsis passage is the time in which a satellite moves through its point of periapsis.

    Nodes are the points where an orbit crosses a plane, such as a satellite crossing the Earth’s equatorial plane. If the satellite crosses the plane going from south to north, the node is the ascending node; if moving from north to south, it is the descending node. The longitude of the ascending node is the node’s celestial longitude. Celestial longitude is analogous to longitude on Earth and is measured in degrees counter-clockwise from zero with zero longitude being in the direction of the vernal equinox.

    In general, three observations of an object in orbit are required to calculate the six orbital elements. Two other quantities often used to describe orbits are period and true anomaly. Period, P, is the length of time required for a satellite to complete one orbit. True anomaly, , is the angular distance of a point in an orbit past the point of periapsis, measured in degrees.

    For a spacecraft to achieve Earth orbit, it must be launched to an elevation above the Earth’s atmosphere and accelerated to orbital velocity. The most energy efficient orbit, that is one that requires the least amount of propellant, is a direct low inclination orbit. To achieve such an orbit, a spacecraft is launched in an eastward direction from a site near the Earth’s equator. The advantage being that the rotational speed of the Earth contributes to the spacecraft’s final orbital speed. At the United States’ launch site in Cape Canaveral (28.5 degrees north latitude) a due east launch results in a “free ride” of 1,471 km/h (914 mph). Launching a spacecraft in a direction other than east, or from a site far from the equator, results in an orbit of higher inclination. High inclination orbits are less able to take advantage of the initial speed provided by the Earth’s rotation, thus the launch vehicle must provide a greater part, or all, of the energy required to attain orbital velocity. Although high inclination orbits are less energy efficient, they do have advantages over equatorial orbits for certain applications. Below we describe several types of orbits and the advantages of each:

    Geosynchronous orbits (GEO) are circular orbits around the Earth having a period of 24 hours. A geosynchronous orbit with an inclination of zero degrees is called a geostationary orbit. A spacecraft in a geostationary orbit appears to hang motionless above one position on the Earth’s equator. For this reason, they are ideal for some types of communication and meteorological satellites. A spacecraft in an inclined geosynchronous orbit will appear to follow a regular figure-8 pattern in the sky once every orbit. To attain geosynchronous orbit, a spacecraft is first launched into an elliptical orbit with an apogee of 35,786 km (22,236 miles) called a geosynchronous transfer orbit (GTO). The orbit is then circularized by firing the spacecraft’s engine at apogee.

    Polar orbits (PO) are orbits with an inclination of 90 degrees. Polar orbits are useful for satellites that carry out mapping and/or surveillance operations because as the planet rotates the spacecraft has access to virtually every point on the planet’s surface.

    Walking orbits: An orbiting satellite is subjected to a great many gravitational influences. First, planets are not perfectly spherical and they have slightly uneven mass distribution. These fluctuations have an effect on a spacecraft’s trajectory. Also, the sun, moon, and planets contribute a gravitational influence on an orbiting satellite. With proper planning it is possible to design an orbit which takes advantage of these influences to induce a precession in the satellite’s orbital plane. The resulting orbit is called a walking orbit, or precessing orbit.

    Sun synchronous orbits (SSO) are walking orbits whose orbital plane precesses with the same period as the planet’s solar orbit period. In such an orbit, a satellite crosses periapsis at about the same local time every orbit. This is useful if a satellite is carrying instruments which depend on a certain angle of solar illumination on the planet’s surface. In order to maintain an exact synchronous timing, it may be necessary to conduct occasional propulsive maneuvers to adjust the orbit.

    Molniya orbits are highly eccentric Earth orbits with periods of approximately 12 hours (2 revolutions per day). The orbital inclination is chosen so the rate of change of perigee is zero, thus both apogee and perigee can be maintained over fixed latitudes. This condition occurs at inclinations of 63.4 degrees and 116.6 degrees. For these orbits the argument of perigee is typically placed in the southern hemisphere, so the satellite remains above the northern hemisphere near apogee for approximately 11 hours per orbit. This orientation can provide good ground coverage at high northern latitudes.

    Hohmann transfer orbits are interplanetary trajectories whose advantage is that they consume the least possible amount of propellant. A Hohmann transfer orbit to an outer planet, such as Mars, is achieved by launching a spacecraft and accelerating it in the direction of Earth’s revolution around the sun until it breaks free of the Earth’s gravity and reaches a velocity which places it in a sun orbit with an aphelion equal to the orbit of the outer planet. Upon reaching its destination, the spacecraft must decelerate so that the planet’s gravity can capture it into a planetary orbit.

    To send a spacecraft to an inner planet, such as Venus, the spacecraft is launched and accelerated in the direction opposite of Earth’s revolution around the sun (i.e. decelerated) until it achieves a sun orbit with a perihelion equal to the orbit of the inner planet. It should be noted that the spacecraft continues to move in the same direction as Earth, only more slowly.

    To reach a planet requires that the spacecraft be inserted into an interplanetary trajectory at the correct time so that the spacecraft arrives at the planet’s orbit when the planet will be at the point where the spacecraft will intercept it. This task is comparable to a quarterback “leading” his receiver so that the football and receiver arrive at the same point at the same time. The interval of time in which a spacecraft must be launched in order to complete its mission is called a launch window.

    Newton’s laws of motion describe the relationship between the motion of a particle and the forces acting on it.

    The first law states that if no forces are acting, a body at rest will remain at rest, and a body in motion will remain in motion in a straight line. Thus, if no forces are acting, the velocity (both magnitude and direction) will remain constant.

    The second law tells us that if a force is applied there will be a change in velocity, i.e. an acceleration, proportional to the magnitude of the force and in the direction in which the force is applied. This law may be summarized by the equation

    where F is the force, m is the mass of the particle, and a is the acceleration.

    The third law states that if body 1 exerts a force on body 2, then body 2 will exert a force of equal strength, but opposite in direction, on body 1. This law is commonly stated, “for every action there is an equal and opposite reaction”.

    In his law of universal gravitation, Newton states that two particles having masses m1 and m2 and separated by a distance r are attracted to each other with equal and opposite forces directed along the line joining the particles. The common magnitude F of the two forces is

    where G is an universal constant, called the constant of gravitation, and has the value 6.67259×10 -11 N-m 2 /kg 2 (3.4389×10 -8 lb-ft 2 /slug 2 ).

    Let’s now look at the force that the Earth exerts on an object. If the object has a mass m, and the Earth has mass M, and the object’s distance from the center of the Earth is r, then the force that the Earth exerts on the object is GmM /r 2 . If we drop the object, the Earth’s gravity will cause it to accelerate toward the center of the Earth. By Newton’s second law (F = ma), this acceleration g must equal (GmM /r 2 )/m, or

    At the surface of the Earth this acceleration has the valve 9.80665 m/s 2 (32.174 ft/s 2 ).

    Many of the upcoming computations will be somewhat simplified if we express the product GM as a constant, which for Earth has the value 3.986005×10 14 m 3 /s 2 (1.408×10 16 ft 3 /s 2 ). The product GM is often represented by the Greek letter .

    For additional useful constants please see the appendix Basic Constants.

    For a refresher on SI versus U.S. units see the appendix Weights & Measures.

    In the simple case of free fall, a particle accelerates toward the center of the Earth while moving in a straight line. The velocity of the particle changes in magnitude, but not in direction. In the case of uniform circular motion a particle moves in a circle with constant speed. The velocity of the particle changes continuously in direction, but not in magnitude. From Newton’s laws we see that since the direction of the velocity is changing, there is an acceleration. This acceleration, called centripetal acceleration is directed inward toward the center of the circle and is given by

    where v is the speed of the particle and r is the radius of the circle. Every accelerating particle must have a force acting on it, defined by Newton’s second law (F = ma). Thus, a particle undergoing uniform circular motion is under the influence of a force, called centripetal force, whose magnitude is given by

    The direction of F at any instant must be in the direction of a at the same instant, that is radially inward.

    A satellite in orbit is acted on only by the forces of gravity. The inward acceleration which causes the satellite to move in a circular orbit is the gravitational acceleration caused by the body around which the satellite orbits. Hence, the satellite’s centripetal acceleration is g, that is g = v 2 /r. From Newton’s law of universal gravitation we know that g = GM /r 2 . Therefore, by setting these equations equal to one another we find that, for a circular orbit,

    Click here for example problem #4.1
    (use your browser’s “back” function to return)

    Through a lifelong study of the motions of bodies in the solar system, Johannes Kepler (1571-1630) was able to derive three basic laws known as Kepler’s laws of planetary motion. Using the data compiled by his mentor Tycho Brahe (1546-1601), Kepler found the following regularities after years of laborious calculations:

    1.&nbsp All planets move in elliptical orbits with the sun at one focus.
    2.&nbsp A line joining any planet to the sun sweeps out equal areas in equal times.
    3.&nbsp The square of the period of any planet about the sun is proportional to the cube of the planet’s mean distance from the sun.

    These laws can be deduced from Newton’s laws of motion and law of universal gravitation. Indeed, Newton used Kepler’s work as basic information in the formulation of his gravitational theory.

    As Kepler pointed out, all planets move in elliptical orbits, however, we can learn much about planetary motion by considering the special case of circular orbits. We shall neglect the forces between planets, considering only a planet’s interaction with the sun. These considerations apply equally well to the motion of a satellite about a planet.

    Let’s examine the case of two bodies of masses M and m moving in circular orbits under the influence of each other’s gravitational attraction. The center of mass of this system of two bodies lies along the line joining them at a point C such that mr = MR. The large body of mass M moves in an orbit of constant radius R and the small body of mass m in an orbit of constant radius r, both having the same angular velocity . For this to happen, the gravitational force acting on each body must provide the necessary centripetal acceleration. Since these gravitational forces are a simple action-reaction pair, the centripetal forces must be equal but opposite in direction. That is, m 2 r must equal M 2 R. The specific requirement, then, is that the gravitational force acting on either body must equal the centripetal force needed to keep it moving in its circular orbit, that is

    If one body has a much greater mass than the other, as is the case of the sun and a planet or the Earth and a satellite, its distance from the center of mass is much smaller than that of the other body. If we assume that m is negligible compared to M, then R is negligible compared to r. Thus, equation (4.7) then becomes

    If we express the angular velocity in terms of the period of revolution, = 2/P, we obtain

    where P is the period of revolution. This is a basic equation of planetary and satellite motion. It also holds for elliptical orbits if we define r to be the semi-major axis (a) of the orbit.

    A significant consequence of this equation is that it predicts Kepler’s third law of planetary motion, that is P 2

    Click here for example problem #4.2
    Click here for example problem #4.3

    In celestial mechanics where we are dealing with planetary or stellar sized bodies, it is often the case that the mass of the secondary body is significant in relation to the mass of the primary, as with the Moon and Earth. In this case the size of the secondary cannot be ignored. The distance R is no longer negligible compared to r and, therefore, must be carried through the derivation. Equation (4.9) becomes

    More commonly the equation is written in the equivalent form

    where a is the semi-major axis. The semi-major axis used in astronomy is always the primary-to-secondary distance, or the geocentric semi-major axis. For example, the Moon’s mean geocentric distance from Earth (a) is 384,403 kilometers. On the other hand, the Moon’s distance from the barycenter (r) is 379,732 km, with Earth’s counter-orbit (R) taking up the difference of 4,671 km.

    Kepler’s second law of planetary motion must, of course, hold true for circular orbits. In such orbits both and r are constant so that equal areas are swept out in equal times by the line joining a planet and the sun. For elliptical orbits, however, both and r will vary with time. Let’s now consider this case.

    Figure 4.5 shows a particle revolving around C along some arbitrary path. The area swept out by the radius vector in a short time interval t is shown shaded. This area, neglecting the small triangular region at the end, is one-half the base times the height or approximately r(rt)/2. This expression becomes more exact as t approaches zero, i.e. the small triangle goes to zero more rapidly than the large one. The rate at which area is being swept out instantaneously is therefore

    For any given body moving under the influence of a central force, the value r 2 is constant.

    Let’s now consider two points P1 and P2 in an orbit with radii r1 and r2, and velocities v1 and v2. Since the velocity is always tangent to the path, it can be seen that if is the angle between r and v, then

    where vsin is the transverse component of v. Multiplying through by r, we have

    or, for two points P1 and P2 on the orbital path

    Note that at periapsis and apoapsis, = 90 degrees. Thus, letting P1 and P2 be these two points we get

    Let’s now look at the energy of the above particle at points P1 and P2. Conservation of energy states that the sum of the kinetic energy and the potential energy of a particle remains constant. The kinetic energy T of a particle is given by mv 2 /2 while the potential energy of gravity V is calculated by the equation -GMm/r. Applying conservation of energy we have

    From equations (4.14) and (4.15) we obtain

    Click here for example problem #4.4
    Click here for example problem #4.5

    The eccentricity e of an orbit is given by

    If the semi-major axis a and the eccentricity e of an orbit are known, then the periapsis and apoapsis distances can be calculated by

    The launch of a satellite or space vehicle consists of a period of powered flight during which the vehicle is lifted above the Earth’s atmosphere and accelerated to orbital velocity by a rocket, or launch vehicle. Powered flight concludes at burnout of the rocket’s last stage at which time the vehicle begins its free flight. During free flight the space vehicle is assumed to be subjected only to the gravitational pull of the Earth. If the vehicle moves far from the Earth, its trajectory may be affected by the gravitational influence of the sun, moon, or another planet.

    A space vehicle’s orbit may be determined from the position and the velocity of the vehicle at the beginning of its free flight. A vehicle’s position and velocity can be described by the variables r, v, and , where r is the vehicle’s distance from the center of the Earth, v is its velocity, and is the angle between the position and the velocity vectors, called the zenith angle (see Figure 4.7). If we let &nbspr1, v1, and 1 be the initial (launch) values of &nbspr, v, and , then we may consider these as given quantities. If we let point P2 represent the perigee, then equation (4.13) becomes

    Substituting equation (4.23) into (4.15), we can obtain an equation for the perigee radius Rp.

    Multiplying through by -Rp 2 /(r1 2 v1 2 ) and rearranging, we get

    Note that this is a simple quadratic equation in the ratio (Rp/r1) and that 2GM /(r1 × v1 2 ) is a nondimensional parameter of the orbit.

    Like any quadratic, the above equation yields two answers. The smaller of the two answers corresponds to Rp, the periapsis radius. The other root corresponds to the apoapsis radius, Ra.

    Please note that in practice spacecraft launches are usually terminated at either perigee or apogee, i.e. = 90. This condition results in the minimum use of propellant.

    Equation (4.26) gives the values of Rp and Ra from which the eccentricity of the orbit can be calculated, however, it may be simpler to calculate the eccentricity e directly from the equation

    To pin down a satellite’s orbit in space, we need to know the angle , the true anomaly, from the periapsis point to the launch point. This angle is given by

    In most calculations, the complement of the zenith angle is used, denoted by . This angle is called the flight-path angle, and is positive when the velocity vector is directed away from the primary as shown in Figure 4.8. When flight-path angle is used, equations (4.26) through (4.28) are rewritten as follows:

    The semi-major axis is, of course, equal to (Rp+Ra)/2, though it may be easier to calculate it directly as follows:

    If e is solved for directly using equation (4.27) or (4.30), and a is solved for using equation (4.32), Rp and Ra can be solved for simply using equations (4.21) and (4.22).

    Orbit Tilt, Rotation and Orientation

    Above we determined the size and shape of the orbit, but to determine the orientation of the orbit in space, we must know the latitude and longitude and the heading of the space vehicle at burnout.

    Figure 4.9 above illustrates the location of a space vehicle at engine burnout, or orbit insertion. is the azimuth heading measured in degrees clockwise from north, is the geocentric latitude (or declination) of the burnout point, is the angular distance between the ascending node and the burnout point measured in the equatorial plane, and is the angular distance between the ascending node and the burnout point measured in the orbital plane. 1 and 2 are the geographical longitudes of the ascending node and the burnout point at the instant of engine burnout. Figure 4.10 pictures the orbital elements, where i is the inclination, is the longitude at the ascending node, is the argument of periapsis, and is the true anomaly.

    If , , and 2 are given, the other values can be calculated from the following relationships:

    In equation (4.36), the value of is found using equation (4.28) or (4.31). If is positive, periapsis is west of the burnout point (as shown in Figure 4.10); if is negative, periapsis is east of the burnout point.

    The longitude of the ascending node, , is measured in celestial longitude, while 1 is geographical longitude. The celestial longitude of the ascending node is equal to the local apparent sidereal time, in degrees, at longitude 1 at the time of engine burnout. Sidereal time is defined as the hour angle of the vernal equinox at a specific locality and time; it has the same value as the right ascension of any celestial body that is crossing the local meridian at that same instant. At the moment when the vernal equinox crosses the local meridian, the local apparent sidereal time is 00:00. See this sidereal time calculator.

    Geodetic Latitude, Geocentric Latitude, and Declination

    Latitude is the angular distance of a point on Earth’s surface north or south of Earth’s equator, positive north and negative south. The geodetic latitude (or geographical latitude), , is the angle defined by the intersection of the reference ellipsoid normal through the point of interest and the true equatorial plane. The geocentric latitude, ‘, is the angle between the true equatorial plane and the radius vector to the point of intersection of the reference ellipsoid and the reference ellipsoid normal passing through the point of interest. Declination, , is the angular distance of a celestial object north or south of Earth’s equator. It is the angle between the geocentric radius vector to the object of interest and the true equatorial plane.

    R is the magnitude of the reference ellipsoid’s geocentric radius vector to the point of interest on its surface, r is the magnitude of the geocentric radius vector to the celestial object of interest, and the altitude h is the perpendicular distance from the reference ellipsoid to the celestial object of interest. The value of R at the equator is a, and the value of R at the poles is b. The ellipsoid’s flattening, f, is the ratio of the equatorial-polar length difference to the equatorial length. For Earth, a equals 6,378,137 meters, b equals 6,356,752 meters, and f equals 1/298.257.

    When solving problems in orbital mechanics, the measurements of greatest usefulness are the magnitude of the radius vector, r, and declination, , of the object of interest. However, we are often given, or required to report, data in other forms. For instance, at the time of some specific event, such as “orbit insertion”, we may be given the spacecraft’s altitude along with the geodetic latitude and longitude of the sub-vehicle point. In such cases, it may be necessary to convert the given data to a form more suitable for our calculations.

    The relationship between geodetic and geocentric latitude is,

    The radius of the reference ellipsoid is given by,

    The length r can be solved from h, or h from r, using one of the following,

    And declination is calculated using,

    For spacecraft in low earth orbit, the difference between and ‘ is very small, typically not more than about 0.00001 degree. Even at the distance of the Moon, the difference is not more than about 0.01 degree. Unless very high accuracy is needed, for operations near Earth we can assume ‘ and r ≈ R + h.

    It is important to note that the value of h is not always measured as described and illustrated above. In some applications it is customary to express h as the perpendicular distance from a reference sphere, rather than the reference ellipsoid. In this case, R is considered constant and is often assigned the value of Earth’s equatorial radius, hence h = r – a. This is the method typically used when a spacecraft’s orbit is expressed in a form such as “180 km × 220 km”. The example problems presented in this web site also assume this method of measurement.

    where Mo is the mean anomaly at time to and n is the mean motion, or the average angular velocity, determined from the semi-major axis of the orbit as follows:

    This solution will give the average position and velocity, but satellite orbits are elliptical with a radius constantly varying in orbit. Because the satellite’s velocity depends on this varying radius, it changes as well. To resolve this problem we can define an intermediate variable E, called the eccentric anomaly, for elliptical orbits, which is given by

    where is the true anomaly. Mean anomaly is a function of eccentric anomaly by the formula

    For small eccentricities a good approximation of true anomaly can be obtained by the following formula (the error is of the order e 3 ):

    The preceding five equations can be used to (1) find the time it takes to go from one position in an orbit to another, or (2) find the position in an orbit after a specific period of time. When solving these equations it is important to work in radians rather than degrees, where 2 radians equals 360 degrees.

    Click here for example problem #4.13
    Click here for example problem #4.14

    At any time in its orbit, the magnitude of a spacecraft’s position vector, i.e. its distance from the primary body, and its flight-path angle can be calculated from the following equations:

    And the spacecraft’s velocity is given by,

    The orbital elements discussed at the beginning of this section provide an excellent reference for describing orbits, however there are other forces acting on a satellite that perturb it away from the nominal orbit. These perturbations, or variations in the orbital elements, can be classified based on how they affect the Keplerian elements. Secular variations represent a linear variation in the element, short-period variations are periodic in the element with a period less than the orbital period, and long-period variations are those with a period greater than the orbital period. Because secular variations have long-term effects on orbit prediction (the orbital elements affected continue to increase or decrease), they will be discussed here for Earth-orbiting satellites. Precise orbit determination requires that the periodic variations be included as well.

    The gravitational forces of the Sun and the Moon cause periodic variations in all of the orbital elements, but only the longitude of the ascending node, argument of perigee, and mean anomaly experience secular variations. These secular variations arise from a gyroscopic precession of the orbit about the ecliptic pole. The secular variation in mean anomaly is much smaller than the mean motion and has little effect on the orbit, however the secular variations in longitude of the ascending node and argument of perigee are important, especially for high-altitude orbits.

    For nearly circular orbits the equations for the secular rates of change resulting from the Sun and Moon are

    Longitude of the ascending node:

    where i is the orbit inclination, n is the number of orbit revolutions per day, and and are in degrees per day. These equations are only approximate; they neglect the variation caused by the changing orientation of the orbital plane with respect to both the Moon’s orbital plane and the ecliptic plane.

    Perturbations due to Non-spherical Earth

    When developing the two-body equations of motion, we assumed the Earth was a spherically symmetrical, homogeneous mass. In fact, the Earth is neither homogeneous nor spherical. The most dominant features are a bulge at the equator, a slight pear shape, and flattening at the poles. For a potential function of the Earth, we can find a satellite’s acceleration by taking the gradient of the potential function. The most widely used form of the geopotential function depends on latitude and geopotential coefficients, Jn, called the zonal coefficients.

    The potential generated by the non-spherical Earth causes periodic variations in all the orbital elements. The dominant effects, however, are secular variations in longitude of the ascending node and argument of perigee because of the Earth’s oblateness, represented by the J2 term in the geopotential expansion. The rates of change of and due to J2 are

    where n is the mean motion in degrees/day, J2 has the value 0.00108263, RE is the Earth’s equatorial radius, a is the semi-major axis in kilometers, i is the inclination, e is the eccentricity, and and are in degrees/day. For satellites in GEO and below, the J2 perturbations dominate; for satellites above GEO the Sun and Moon perturbations dominate.

    Molniya orbits are designed so that the perturbations in argument of perigee are zero. This conditions occurs when the term 4-5sin 2 i is equal to zero or, that is, when the inclination is either 63.4 or 116.6 degrees.

    Drag is the resistance offered by a gas or liquid to a body moving through it. A spacecraft is subjected to drag forces when moving through a planet’s atmosphere. This drag is greatest during launch and reentry, however, even a space vehicle in low Earth orbit experiences some drag as it moves through the Earth’s thin upper atmosphere. In time, the action of drag on a space vehicle will cause it to spiral back into the atmosphere, eventually to disintegrate or burn up. If a space vehicle comes within 120 to 160 km of the Earth’s surface, atmospheric drag will bring it down in a few days, with final disintegration occurring at an altitude of about 80 km. Above approximately 600 km, on the other hand, drag is so weak that orbits usually last more than 10 years – beyond a satellite’s operational lifetime. The deterioration of a spacecraft’s orbit due to drag is called decay.

    The drag force FD on a body acts in the opposite direction of the velocity vector and is given by the equation

    where CD is the drag coefficient, is the air density, v is the body’s velocity, and A is the area of the body normal to the flow. The drag coefficient is dependent on the geometric form of the body and is generally determined by experiment. Earth orbiting satellites typically have very high drag coefficients in the range of about 2 to 4. Air density is given by the appendix Atmosphere Properties.

    The region above 90 km is the Earth’s thermosphere where the absorption of extreme ultraviolet radiation from the Sun results in a very rapid increase in temperature with altitude. At approximately 200-250 km this temperature approaches a limiting value, the average value of which ranges between about 700 and 1,400 K over a typical solar cycle. Solar activity also has a significant affect on atmospheric density, with high solar activity resulting in high density. Below about 150 km the density is not strongly affected by solar activity; however, at satellite altitudes in the range of 500 to 800 km, the density variations between solar maximum and solar minimum are approximately two orders of magnitude. The large variations imply that satellites will decay more rapidly during periods of solar maxima and much more slowly during solar minima.

    For circular orbits we can approximate the changes in semi-major axis, period, and velocity per revolution using the following equations:

    where a is the semi-major axis, P is the orbit period, and V, A and m are the satellite’s velocity, area, and mass respectively. The term m/(CDA), called the ballistic coefficient, is given as a constant for most satellites. Drag effects are strongest for satellites with low ballistic coefficients, this is, light vehicles with large frontal areas.

    A rough estimate of a satellite’s lifetime, L, due to drag can be computed from

    where H is the atmospheric density scale height. A substantially more accurate estimate (although still very approximate) can be obtained by integrating equation (4.53), taking into account the changes in atmospheric density with both altitude and solar activity.

    Perturbations from Solar Radiation

    Solar radiation pressure causes periodic variations in all of the orbital elements. The magnitude of the acceleration in m/s 2 arising from solar radiation pressure is

    where A is the cross-sectional area of the satellite exposed to the Sun and m is the mass of the satellite in kilograms. For satellites below 800 km altitude, acceleration from atmospheric drag is greater than that from solar radiation pressure; above 800 km, acceleration from solar radiation pressure is greater.

    At some point during the lifetime of most space vehicles or satellites, we must change one or more of the orbital elements. For example, we may need to transfer from an initial parking orbit to the final mission orbit, rendezvous with or intercept another spacecraft, or correct the orbital elements to adjust for the perturbations discussed in the previous section. Most frequently, we must change the orbit altitude, plane, or both. To change the orbit of a space vehicle, we have to change its velocity vector in magnitude or direction. Most propulsion systems operate for only a short time compared to the orbital period, thus we can treat the maneuver as an impulsive change in velocity while the position remains fixed. For this reason, any maneuver changing the orbit of a space vehicle must occur at a point where the old orbit intersects the new orbit. If the orbits do not intersect, we must use an intermediate orbit that intersects both. In this case, the total maneuver will require at least two propulsive burns.

    The most common type of in-plane maneuver changes the size and energy of an orbit, usually from a low-altitude parking orbit to a higher-altitude mission orbit such as a geosynchronous orbit. Because the initial and final orbits do not intersect, the maneuver requires a transfer orbit. Figure 4.11 represents a Hohmann transfer orbit. In this case, the transfer orbit’s ellipse is tangent to both the initial and final orbits at the transfer orbit’s perigee and apogee respectively. The orbits are tangential, so the velocity vectors are collinear, and the Hohmann transfer represents the most fuel-efficient transfer between two circular, coplanar orbits. When transferring from a smaller orbit to a larger orbit, the change in velocity is applied in the direction of motion; when transferring from a larger orbit to a smaller, the change of velocity is opposite to the direction of motion.

    The total change in velocity required for the orbit transfer is the sum of the velocity changes at perigee and apogee of the transfer ellipse. Since the velocity vectors are collinear, the velocity changes are just the differences in magnitudes of the velocities in each orbit. If we know the initial and final orbits, rA and rB, we can calculate the total velocity change using the following equations:

    Note that equations (4.59) and (4.60) are the same as equation (4.6), and equations (4.61) and (4.62) are the same as equation (4.45).

    For example, we may specify the size of the transfer orbit, choosing any semi-major axis that is greater than the semi-major axis of the Hohmann transfer ellipse. Once we know the semi-major axis of the ellipse, atx, we can calculate the eccentricity, angular distance traveled in the transfer, the velocity change required for the transfer, and the time required to complete the transfer. We do this using equations (4.59) through (4.63) and (4.65) above, and the following equations:

    Another option for changing the size of an orbit is to use electric propulsion to produce a constant low-thrust burn, which results in a spiral transfer. We can approximate the velocity change for this type of orbit transfer by

    where the velocities are the circular velocities of the two orbits.

    To change the orientation of a satellite’s orbital plane, typically the inclination, we must change the direction of the velocity vector. This maneuver requires a component of V to be perpendicular to the orbital plane and, therefore, perpendicular to the initial velocity vector. If the size of the orbit remains constant, the maneuver is called a simple plane change. We can find the required change in velocity by using the law of cosines. For the case in which Vf is equal to Vi, this expression reduces to

    where Vi is the velocity before and after the burn, and is the angle change required.

    From equation (4.73) we see that if the angular change is equal to 60 degrees, the required change in velocity is equal to the current velocity. Plane changes are very expensive in terms of the required change in velocity and resulting propellant consumption. To minimize this, we should change the plane at a point where the velocity of the satellite is a minimum: at apogee for an elliptical orbit. In some cases, it may even be cheaper to boost the satellite into a higher orbit, change the orbit plane at apogee, and return the satellite to its original orbit.

    Typically, orbital transfers require changes in both the size and the plane of the orbit, such as transferring from an inclined parking orbit at low altitude to a zero-inclination orbit at geosynchronous altitude. We can do this transfer in two steps: a Hohmann transfer to change the size of the orbit and a simple plane change to make the orbit equatorial. A more efficient method (less total change in velocity) would be to combine the plane change with the tangential burn at apogee of the transfer orbit. As we must change both the magnitude and direction of the velocity vector, we can find the required change in velocity using the law of cosines,

    where Vi is the initial velocity, Vf is the final velocity, and is the angle change required. Note that equation (4.74) is in the same form as equation (4.69).

    As can be seen from equation (4.74), a small plane change can be combined with an altitude change for almost no cost in V or propellant. Consequently, in practice, geosynchronous transfer is done with a small plane change at perigee and most of the plane change at apogee.

    Another option is to complete the maneuver using three burns. The first burn is a coplanar maneuver placing the satellite into a transfer orbit with an apogee much higher than the final orbit. When the satellite reaches apogee of the transfer orbit, a combined plane change maneuver is done. This places the satellite in a second transfer orbit that is coplanar with the final orbit and has a perigee altitude equal to the altitude of the final orbit. Finally, when the satellite reaches perigee of the second transfer orbit, another coplanar maneuver places the satellite into the final orbit. This three-burn maneuver may save propellant, but the propellant savings comes at the expense of the total time required to complete the maneuver.

    When a plane change is used to modify inclination only, the magnitude of the angle change is simply the difference between the initial and final inclinations. In this case, the initial and final orbits share the same ascending and descending nodes. The plane change maneuver takes places when the space vehicle passes through one of these two nodes.

    In some instances, however, a plane change is used to alter an orbit’s longitude of ascending node in addition to the inclination. An example might be a maneuver to correct out-of-plane errors to make the orbits of two space vehicles coplanar in preparation for a rendezvous. If the orbital elements of the initial and final orbits are known, the plane change angle is determined by the vector dot product. If ii and i are the inclination and longitude of ascending node of the initial orbit, and if and f are the inclination and longitude of ascending node of the final orbit, then the angle between the orbital planes, , is given by

    The plane change maneuver takes place at one of two nodes where the initial and final orbits intersect. The latitude and longitude of these nodes are determined by the vector cross product. The position of one of the two nodes is given by

    Knowing the position of one node, the second node is simply

    Orbital transfer becomes more complicated when the object is to rendezvous with or intercept another object in space: both the interceptor and the target must arrive at the rendezvous point at the same time. This precision demands a phasing orbit to accomplish the maneuver. A phasing orbit is any orbit that results in the interceptor achieving the desired geometry relative to the target to initiate a Hohmann transfer. If the initial and final orbits are circular, coplanar, and of different sizes, then the phasing orbit is simply the initial interceptor orbit. The interceptor remains in the initial orbit until the relative motion between the interceptor and target results in the desired geometry. At that point, we would inject the interceptor into a Hohmann transfer orbit.

    Similar to the rendezvous problem is the launch-window problem, or determining the appropriate time to launch from the surface of the Earth into the desired orbital plane. Because the orbital plane is fixed in inertial space, the launch window is the time when the launch site on the surface of the Earth rotates through the orbital plane. The time of the launch depends on the launch site’s latitude and longitude and the satellite orbit’s inclination and longitude of ascending node.

    Once in their mission orbits, many satellites need no additional orbit adjustment. On the other hand, mission requirements may demand that we maneuver the satellite to correct the orbital elements when perturbing forces have changed them. Two particular cases of note are satellites with repeating ground tracks and geostationary satellites.

    After the mission of a satellite is complete, several options exist, depending on the orbit. We may allow low-altitude orbits to decay and reenter the atmosphere or use a velocity change to speed up the process. We may also boost satellites at all altitudes into benign orbits to reduce the probability of collision with active payloads, especially at synchronous altitudes.

    V Budget

    To an orbit designer, a space mission is a series of different orbits. For example, a satellite might be released in a low-Earth parking orbit, transferred to some mission orbit, go through a series of resphasings or alternate mission orbits, and then move to some final orbit at the end of its useful life. Each of these orbit changes requires energy. The V budget is traditionally used to account for this energy. It sums all the velocity changes required throughout the space mission life. In a broad sense the V budget represents the cost for each mission orbit scenario.

    The discussion thus far has focused on the elliptical orbit, which will result whenever a spacecraft has insufficient velocity to escape the gravity of its primary. There is a velocity, called the escape velocity, Vesc, such that if the spacecraft is launched with an initial velocity greater than Vesc, it will travel away from the planet and never return. To achieve escape velocity we must give the spacecraft enough kinetic energy to overcome all of the negative gravitational potential energy. Thus, if m is the mass of the spacecraft, M is the mass of the planet, and r is the radial distance between the spacecraft and planet, the potential energy is -GmM /r. The kinetic energy of the spacecraft, when it is launched, is mv 2 /2. We thus have

    which is independent of the mass of the spacecraft.

    A space vehicle that has exceeded the escape velocity of a planet will travel a hyperbolic path relative to the planet. The hyperbola is an unusual and interesting conic section because it has two branches. The arms of a hyperbola are asymptotic to two intersecting straight line (the asymptotes). If we consider the left-hand focus, f, as the prime focus (where the center of our gravitating body is located), then only the left branch of the hyperbola represents the possible orbit. If, instead, we assume a force of repulsion between our satellite and the body located at f (such as the force between two like-charged electric particles), then the right-hand branch represents the orbit. The parameters a, b and c are labeled in Figure 4.14. We can see that c 2 = a 2 + b 2 for the hyperbola. The eccentricity is,

    If we let equal the angle between the periapsis vector and the departure asymptote, i.e. the true anomaly at infinity, we have

    If we know the radius, r, velocity, v, and flight path angle, , of a point on the orbit (see Figure 4.15), we can calculate the eccentricity and semi-major axis using equations (4.30) and (4.32) as previously presented. Note that the semi-major axis of a hyperbola is negative.

    The true anomaly corresponding to known valves of r, v and can be calculated using equation (4.31), however special care must be taken to assure the angle is placed in the correct quadrant. It may be easier to first calculate e and a, and then calculate true anomaly using equation (4.43), rearranged as follows:

    Whenever is positive, should be taken as positive; whenever is negative, should be taken as negative.

    The impact parameter, b, is the distance of closest approach that would result between a spacecraft and planet if the spacecraft trajectory was undeflected by gravity. The impact parameter is,

    Closet approach occurs at periapsis, where the radius distance, ro, is equal to

    p is a geometrical constant of the conic called the parameter or semi-latus rectum, and is equal to

    At any known true anomaly, the magnitude of a spacecraft’s radius vector, its flight-path angle, and its velocity can be calculated using equations (4.43), (4.44) and (4.45).

    Early we introduced the variable eccentric anomaly and its use in deriving the time of flight in an elliptical orbit. In a similar manner, the analytical derivation of the hyperbolic time of flight, using the hyperbolic eccentric anomaly, F, can be derived as follows:

    Whenever is positive, F should be taken as positive; whenever is negative, F should be taken as negative.

    If you give a space vehicle exactly escape velocity, it will just barely escape the gravitational field, which means that its velocity will be approaching zero as its distance from the force center approaches infinity. If, on the other hand, we give our vehicle more than escape velocity at a point near Earth, we would expect the velocity at a great distance from Earth to be approaching some finite constant value. This residual velocity the vehicle would have left over even at infinity is called hyperbolic excess velocity. We can calculate this velocity from the energy equation written for two points on the hyperbolic escape trajectory – a point near Earth called the burnout point and a point an infinite distance from Earth where the velocity will be the hyperbolic excess velocity, v. Solving for v we obtain

    Note that if v = 0 (as it is on a parabolic trajectory), the burnout velocity, vbo, becomes simply the escape velocity.

    It is, of course, absurd to talk about a space vehicle “reaching infinity” and in this sense it is meaningless to talk about escaping a gravitational field completely. It is a fact, however, that once a space vehicle is a great distance from Earth, for all practical purposes it has escaped. In other words, it has already slowed down to very nearly its hyperbolic excess velocity. It is convenient to define a sphere around every gravitational body and say that when a probe crosses the edge of this sphere of influence it has escaped. Although it is difficult to get agreement on exactly where the sphere of influence should be drawn, the concept is convenient and is widely used, especially in lunar and interplanetary trajectories. For most purposes, the radius of the sphere of influence for a planet can be calculated as follows:

    where Dsp is the distance between the Sun and the planet, Mp is the mass of the planet, and Ms is the mass of the Sun. Equation (4.89) is also valid for calculating a moon’s sphere of influence, where the moon is substituted for the planet and the planet for the Sun.

    Compiled, edited and written in part by Robert A. Braeunig, 1997, 2005, 2007, 2008, 2011, 2012, 2013.

  • Virgin Galactic completes crewed space test, more flights soon

    Virgin Galactic completes crewed space test, more flights soon

    MOJAVE, Calif. (Reuters) – A Virgin Galactic rocket plane reached space on Thursday and returned safely to the California desert, capping years of testing to become the first U.S. commercial human flight to breach Earth’s atmosphere since America’s shuttle program ended in 2011.

    The successful test flight presages a new era of civilian space travel that could kick off as soon as next year, with Richard Branson’s Virgin Galactic battling billionaire-backed ventures such as Inc founder Jeff Bezos’ Blue Origin, to be the first to offer suborbital flights to fare-paying tourists.

    Branson, who said he personally put up $1 billion toward the roughly $1.3 billion development costs for Virgin’s space businesses, told Reuters he viewed competition with Bezos and others as a race, though passenger safety was the top priority.

    “Today we get to enjoy the fact that we have put people into space before anybody else,” Branson said.

    Virgin’s twin-fuselage carrier airplane holding the SpaceShipTwo passenger spacecraft took off at 7:11 a.m. local time (1511 GMT) from the Mojave Air and Space Port, about 90 miles (145 km) north of Los Angeles.

    British billionaire Branson, wearing jeans and a leather bomber jacket with a fur collar, attended the take-off along with hundreds of spectators on a crisp morning in the California desert.

    After the rocket plane, also called the VSS Unity, reached an apogee of 51.4 miles (83 km) above Earth, a crying Branson hugged his son and high-fived and hugged other spectators. The plane reentered the atmosphere at 2.5 times the speed of sound and landed a few minutes later to cheers and applause, concluding roughly an hour’s journey.

    One of the pilots handed Branson a small Earth stress ball when the two hugged.

    Thursday’s test flight – the fourth mission during which VSS Unity flew under its own power – had pilots Mark Stucky and Frederick Sturckow onboard, four NASA research payloads, and a mannequin named Annie as a stand-in passenger.

    The next flight test is within the next couple of months, depending on data analysis from Thursday’s flight, Virgin Galactic said. Branson has said Virgin’s first commercial space trip with him onboard would happen “in months and not years.”


    The carrier airplane hauled the SpaceShipTwo passenger rocket plane to an altitude of about 45,000 feet (13.7 kms) and released it. Seconds later, SpaceShipTwo fired, catapulting it to more than 51 miles above Earth, high enough for the pilots to experience weightlessness and see the curvature of the planet.

    The ship’s rocket igniting and vertical ascent through a cloudless sky could be seen from the ground.

    Virgin’s latest flight test comes four years after the original SpaceShipTwo crashed during a test flight that killed the co-pilot and seriously injured the pilot, dealing a major setback to Virgin Galactic, a U.S. offshoot of the London-based Virgin Group.

    “It’s been 14 long years to get here,” Branson told reporters after the landmark flight. “We’ve had tears, real tears, and we’ve had moments of joy. So the tears today were tears of joy.”


    Nearly 700 people have paid or put down deposits to fly aboard Virgin’s suborbital missions, including actor Leonardo DiCaprio and pop star Justin Bieber. A 90-minute flight costs $250,000. Virgin Galactic has received about $80 million in deposits from future astronauts, Branson said.

    Short sightseeing trips to space aboard Blue Origin’s New Shepard rocket are likely to cost around $200,000 to $300,000, at least to start, Reuters reported in July. Tickets will be offered ahead of the first commercial launch, and test flights with Blue Origin employees are expected to begin in 2019.

    Branson added that he “would be delighted to offer Bezos a flight on Virgin” and for Bezos “to maybe offer me a flight” on New Shepard.

    Bezos’ New Shepard has already flown to the internationally recognized boundary between Earth’s atmosphere and outer space known as the Karman line at 62 miles (100 km) – though the Blue Origin trip did not carry humans.

    Virgin’s Thursday launch did not go as high as the Karman line. Its pilots were aiming to soar 50 miles into the sky, which is the U.S. military and NASA’s definition of the edge of space and high enough to earn commercial astronaut wings by the U.S. Federal Aviation Administration.

    Other firms planning a variety of passenger spacecraft include Boeing Co, Elon Musk’s SpaceX and late Microsoft Corp co-founder Paul Allen’s Stratolaunch.

    In September, SpaceX said Japanese billionaire Yusaku Maezawa, founder and chief executive of online fashion retailer Zozo, would be the company’s first passenger on a voyage around the moon on its forthcoming Big Falcon Rocket spaceship, tentatively scheduled for 2023.

    Musk, the billionaire CEO of electric carmaker Tesla Inc, said the Big Falcon Rocket could conduct its first orbital flights in two to three years as part of his grand plan to shuttle passengers to the moon and eventually fly humans and cargo to Mars.

    Looking to the future after the successful flight, Branson talked about the possibility of using his space plane to link international cities, offering orbital space flights, or potentially even building a Virgin hotel in space.

    “One thing leads onto another. I forever dream,” he told Reuters. “Actually, I said to my son today, we were sitting in the cockpit (before the flight), and I said sometimes I think life is just one incredible dream.”

    Reporting by Eric M. Johnson in Mojave, California; Additional reporting by Irene Klotz in Cape Canaveral, Florida; Writing by Nick Zieminski; Editing by Leslie Adler