Apollo 16 was originally scheduled to launch in March 1972 but NASA postponed it to the next launch window on 16 April 1972. The postponement is to enable modification of the Lunar Module’s batteries, modification of the spacecraft docking collar jettison mechanism (which is thought to be faulty), modification of the Lunar Module Pilot’s space suit and to allow the Lunar Module Pilot to recover from an illness. The crew for the mission are: Charles Duke (Lunar Module Pilot), Thomas “Ken” Mattingay (Command Module Pilot) and John Young (Commander).
NASA has selected a landing site in the mountainous highland region North of the crater Descartes at selenographic latitude 9° E, longitude 16° S. Near the landing site of Apollo 16 are two young craters about 0.8 km across where the astronauts will acquire documented samples. The craters support two distinct primary sampling objectives which are expected to provide material to fill gaps in current models of the lunar surface. The first sampling objective is material of volcanic appearance which floods many of the old highland craters; geological evidence indicates that this material is older than that at the Apollo 11 and Apollo 12 landing sites, but younger than the samples of ejecta from Mare Imbrium returned by Apollo 14. Studies of material from Apollo 16, when combined with samples from Apollo 15 taken from Hadley Apennine will help to develop theories of lunar evolution more fully. The second sampling objective is material from a hilly, grooved and furrowed area thought to be volcanic and of similar age but different composition to the material filling the highlands basins. This uplands volcanic terrain may yield data on interior composition of highlands material.
Young and Duke will use Lunar Roving Vehicle 2 (LRV-2) to explore the landing site. They will deploy the Apollo Lunar Surface Experiments Package (ALSEP), containing an active seismic experiment, a far ultra-violet camera / spectroscope, a comic-ray detector, a portable magnetometer and other instruments. The Command Module will also carry orbital sensors to study the lunar environment, including cameras, geo-chemical indicators, etc.
Apollo 16 will largely follow the lines of Apollo 15. The latter was the first fully operational Apollo, using the up-rated version of the Saturn 5 rocket, up-rated version of the Lunar Module and LRV, and a Scientific Instruments Bay (Sim-bay) in the Service Module. Apollo J is the name for these up-rated Apollos. Apollo 16 and Apollo 17 (due to be launched in December 1972 or January 1973) will also be Apollo J missions.
NASA hoped to launch a probe called the Grand Tour in 1977, followed by a second Grand Tour in 1979. Grand Tour 1 would have travelled via Jupiter, Saturn and Pluto and Grand Tour 2 via Jupiter, Uranus and Neptune. However, for financial reasons, NASA has cancelled this exciting project. The next opportunity to use gravity assist from the planets for this long journey will not occur for another 180 years. It is therefore unfortunate that NASA has cancelled Grand Tour; however it is likely that the USSR will try to launch a Grand Tour probe.
By way of compromise, NASA will launch a single probe in 1977 to fly past only Jupiter and Saturn, but this will not obtain badly needed information on Uranus, Neptune and Pluto (about which we know little compared with the rest of the solar system).
Although Grand Tour will be cancelled, preparations are still going on for the launch of the first probe to Jupiter, Pioneer‑F. Launch date for Pioneer‑F is set for 27 February 1972. Pioneer‑G will be launched towards Jupiter in March 1973.
In November 1971, the USSR landed two capsules on Mars. In the same year, the USA placed its orbiting probe, Mariner 9, into orbit around the planet and the USSR placed a further two spacecraft into orbit around the planet. As of February 1972, the three orbiters are still functioning and providing a great deal of data.
NASA has scheduled the launch of Pioneer-F to Jupiter for 27 February 1972. Pioneer-F weighs 250 kg. NASA intends to launch a twin probe, Pioneer‑G, towards Jupiter in March 1973. The Pioneers are also known as Pioneer 10 and Pioneer 11. Both Pioneers are equipped with scientific apparatus to undertake the following measurements:
- Detecting and counting meteoritic material by recording punctures made by particles weighing more than 10 -9 grams.
- Detecting and counting larger meteoritic material by examining the sunlight which it reflects.
- Analysis of the composition of the solar wind.
- Measurements of interplanetary magnetic fields.
- Counting charged particles.
- Counting cosmic rays.
- Measuring the intensity of particles in Jupiter’s magnetic field.
- An ultraviolet photometer.
- An infrared radiometer to analyse Jupiter’s atmosphere and to record temperatures on the planet’s cloud tops.
- Finally, a novel device, an imaging photopolarimeter, will photograph the disk of the planet. This instrument consists of a telescope of 25 mm aperture that will sweep out a cone as the spacecraft spins slowly at about five revolutions per minute. The light entering the telescope will be split to produce separate red and blue images. The image will be obtained in the form of scan lines (as in television) along the viewing cone and will provide an image of the raster type with a resolution of 200 kilometres.
The total weight of the 11 scientific instruments is 28 kg and none draws more than 4.2 watts. The Pioneers will return digital data to Earth at the rate of 1 kb/s. NASA will use three dish antennae of 64 m diameter at Goldstone, California, in Spain and in Parkes, Australia to receive the data. The spacecraft transmitter has a power of only eight watts. The power for operating the transmitter and other instruments will come from two thermoelectric generators (the probe will be too far from the Sun to use solar cells) each capable of supplying 40 watts at the start of the mission and 30 watts after five years. The spacecraft have to reach a speed of 32,000 mph to reach Jupiter; to do this an Atlas-Centaur rocket with an added solid fuel third stage is being used. This will be the fastest velocity achieved by a spacecraft and will allow Pioneers F and G ultimately to leave the solar system and head into interstellar space.
Pioneers F and G will take about two years to reach Jupiter. En route , they will spend more than six months passing through the asteroid belt, and should return much valuable information on the asteroids. Once in the vicinity of Jupiter they should transmit much interesting and valuable information about the giant planet and some of its 12 moons. The spacecraft will pass within 160,000 km of Jupiter’s surface and will examine the planet for about a fortnight.
We know something of Jupiter’s external appearance and of its gaseous atmosphere but there is still tremendous mystery about atmospheric phenomena such as the Great Red Spot, the tremendous radio noise storms, the question whether the planet has any surface at all and why it sends out more energy than it receives from the Sun. The Pioneers should throw light on these matters.
First Lunar Astronomy Observatory
Apollo 16 will set up and operate on the Moon a telescope-camera system to obtain ultraviolet and radiation data on Earth’s upper atmosphere, magnetic field, aurorae, the solar corona and solar wind, interplanetary, interstellar and intergalactic hydrogen, nebulae, galactic clusters, the lunar atmosphere and, possibly, lunar volcanic gases.
The observation programme allows for extensive observations to be made by a tripod-mounted telescope camera (to be deployed in the shadow of the Lunar Module) of the M31 Galaxy in Andromeda, the Magellanic Clouds and the Coma cluster of galaxies. During each lunar surface exploration period, astronauts Young and Duke will re-align the camera several times in elevation and azimuth and activate the automatic exposure sequencer. Before entering the Lunar Module for the last time, the astronauts will remove the exposed film for return to Earth; the telescope itself will remain on the Moon. The experiment is expected to provide information on the feasibility of remote-controlled, unmanned, lunar surface astronomical observatories.
Project Moonglow And Apollo 16
There are three main types of TLP (Transient Lunar Phenomenon).
- Very brief, brilliant white flashes.
- Obscuration of lunar detail covering several square kilometres, lasting from a few minutes to several hours, perhaps due to dust or gas clouds, normally colourless.
- Red or occasionally blue glows lasting from several minutes to, more rarely, several hours, covering several square kilometres. This is the type of TLP on which most attention has been concentrated recently.
Type 3 TLPs can be easily detected by using contrasting colour filters, e.g. red/green for red type 3 phenomena and blue/yellow for blue type 3 phenomena.
The S-IVB 3 rd stage of Apollo 16’s Saturn 5 rocket should hit the Moon, with a force equivalent to 10 tonnes of TNT, about half an hour after Apollo 16 enters lunar orbit. Once the astronauts have finished with the Lunar Module, they will also send it to crash onto the Moon. We hope that members of OASI will attempt to observe the impact of S-IVB and the Lunar Module to determine whether they cause TLPs. Observations are required not only of the impact sites but also of any known, nearby TLP-prone areas from a few minutes before to a few hours after each impact. Times of impact will be publicised later.
Russia has recently launched several lunar probes to the Moon:
- Luna 16 landed on a lunar plain at latitude 0° 41′ S, longitude 56° 18′ E in Mare Fecunditatis and returned a sample of moonrock.
- Luna 17 landed in Mare Imbrium in November 1970 and unloaded Lunokhod 1, an unmanned lunar roving vehicle.
- Luna 18 crashed in a mountainous region at latitude 3° 34′ N, longitude 56° 30′ E on the edge of Mare Fecunditatis. Luna 18 was probably meant to retrieve a sample of rock from a lunar mountain to compare with the sample obtained from the lunar plain by Luna 16.
- As of March 1972, Luna 19 is orbiting the Moon and transmitting to Earth TV pictures and useful data.
- The most recent probe, Luna 20, was launched on Tuesday 14 February 1972. It reached the Moon five days later on Saturday 19 February and went into lunar orbit at an altitude of 100 km with a period of 118 minutes. On Monday 21 February, Luna 20 fired its rocket for a few minutes to slow its orbital speed, then descended by free-fall to an altitude of 750 m before firing its rocket again to soften its landing on the Moon, which occurred at 19:19 GMT. The landing site was at latitude 3° 32′ N, longitude 56° 33′ E in a mountain plateau region on the north-east edge of Mare Fecunditatis, about 130 km north of the landing site of Luna 16, very close to the landing site of Luna 18. Luna 20 was probably a backup mission to replace the failed Luna 18.
Shortly after landing, Luna 20 started using a drill to bore into the Moon. The drill was at the end of an arm and was in the form of a hollow cylinder which collected a core sample as it drilled, being an improved version of the drill on Luna 16. The rock was the hardest yet encountered on the Moon, and operators on Earth had to switch off the drill at intervals, to allow it to cool down before recommencing drilling. The operators monitored the operation via the TV camera on Luna 20. After finishing drilling, the drill arm retracted and placed the drill bit and its moonrock sample into a hermetically sealed, spherical container at the top of the spacecraft. The upper section of the spacecraft, carrying its precious cargo, then blasted off for Earth at 10:25 GMT on 22 February. The spherical container of moonrock successfully re-entered the Earth’s atmosphere, landed by parachute and was recovered as planned in Kazakhstan in the USSR on Friday 25 February amidst blizzard conditions.
The lunar sample collected by Luna 20 was formed from ejecta scattered from the formation of the crater Apollonius C. It is thought to be lunar bedrock 100 million years older than any moonrock yet returned to Earth.
The following map shows the landing sites of Luna 16 and Luna 20, marked by large arrows.
|Earth orbit insertion||16||18:06||0:12||N|
|Lunar orbit insertion||19||19:57||74:03||N|
|Descent orbit insertion||19||23:55||78:01||N|
|Separation of LM from CM||20||–||–||Y|
|LM lunar orbit circularisation||20||19:00||97:06||N|
|Stand up EVA||20||–||–||N|
|EVA 1 start (moonwalk)||20||23:59||102:05||Y|
|EVA 1 end||21||06:59||109:05||Y|
|EVA 2 start (moonwalk)||21||21:59||124:05||Y|
|EVA 2 end||22||04:59||131:05||Y|
|EVA 3 start (moonwalk)||22||21:59||148:05||Y|
|EVA 3 end||23||04:59||155:05||Y|
|LM launch from Moon||23||21:04||171:10||Y|
|LM lunar orbit insertion||23||21:19||171:17||N|
|LM – CM docking||23||22:50 approx||172:50 approx||Y|
|LM jettison & lunar impact||24||–||–||N|
|Transearth EVA (spacewalk)||26||19:14||241:20||Y|
Two American and three Russian probes were launched towards Mars in 1971. In order of launch they were:
- Mariner 8/H (USA; failure),
- Cosmos 419 (USSR; failure),
- Mars 2 (USSR; partial success),
- Mars 3 (USSR; success),
- Mariner 9 (USA; success).
Mars 2 reached Mars on 7 November 1971 and then split into two sections. One section parachuted to the Martian surface but crashed because its final retro-rocket failed to provide a soft-landing. The other section successfully entered elliptical orbit around Mars with the following characteristics: altitude 1380-25,000 km; period 18 hours; inclination to the Martian equator 48° 54′.
On 02 December 1971, Mars 3 arrived at Mars and, like its predecessor, split into two sections. One section plunged into the Martian atmosphere and began its descent, heating up due to friction with the planet’s atmosphere. However, unlike its predecessor, the parachute opened successfully and the retro-rocket fired to cushion the landing, and Mars 3 became the first man-made object to land intact on the surface of Mars. However, it transmitted from the surface for only 20 seconds after which ground controllers were unable to regain contact. Mars 3 landed at Martian co-ordinates latitude 45° S, longitude 158° W, between the regions Electris and Phaetonis. The other section of Mars 3 entered orbit around Mars with a period of 11 days and a minimum altitude of 1450 km (the apapsis was not announced). At the time of writing, the two orbiters are still functioning, sending back data on composition, pressure and properties of the Martian atmosphere, day and night surface temperatures, surface characteristics and composition of the Martian soil.
Mars 2 and 3 carried the following equipment:
- Infra-Red (IR) radiometer. This measured temperatures down to -100° C via IR emission at wavelengths 8-40 microns. It comprised two tiny telescopes, one pointing towards Mars, the other towards outer space. The instrument weighed little more than 1 kg.
- An instrument to measure the surface relief of Mars by measuring the optical thickness of the planet’s atmosphere in the carbon-dioxide absorption band.
- Visible light photometer with coloured filters.
- An instrument to measure faint water absorption lines in spectra of the Martian atmosphere. Evidence of such absorption lines would indicate the presence of water vapour in the atmosphere. Note that water vapour in the Martian atmosphere is thought to be much less dense than in the Earth’s: the amount of water vapour in a column one metre high at sea level on Earth would be present in an equivalent column on Mars spanning the entire thickness of the atmosphere.
- Radio telescopes to receive radio waves from Mars in the 3-metre band and to measure their intensity and polarisation.
- Multi-channel Ultra-Violet (UV) photometers measuring the intensity of airglow in the Martian upper atmosphere, and capable of resolving the airglow into resonance lines of hydrogen, oxygen and argon.
The two Mars probes are performing tasks similar to Mariner 9 (which was shut down on 18 March until early June). They are returning many photographs taken by two cameras, one fitted with a narrow-angle (4°) telescopic lens, the other a wide-angle mapping camera. The probes automatically develop the film, scan each image then transmit it to Earth in electronic form.
The temperature (electron movement) of the Martian atmosphere is much less than that of the Earth. The probes have measured very little water vapour in Mars’ atmosphere but have detected atomic hydrogen and oxygen in the upper layers: a hydrogen corona at an altitude of 10,000-20,000 km and oxygen at 600-1000 km.
The probes found individual areas on Mars’ sunlit side to have temperatures not exceeding -15° C. One of the probes sent a radio transmission to Earth detailing measurements of temperature along a strip from latitude 58° S, longitude 330° to latitude 30° N longitude 190°. The highest temperature in this region was -20° C, in a region close to local noon! Some locations on the night side of the planet were as cold as -90° C. On the night side, there are some “hot spots” with temperatures 20-25° C warmer than the surrounding regions.
The photometers, using red, blue and near-UV filters (in the range 300-700 nm), detected large differences in brightness of the surface. Measurements in red light showed a sharp fall in brightness near Mars’ limb and a gradual decrease near the terminator. The instrument also detected a large bright cloud (a dust storm?), some hundreds of kilometres in length, at latitude 15° S longitude 220°.
Sources: Flight International 02 March 1972, vol. 101, no. 3286, page 334; Science Horizons , February 1972, no. 131; New Scientist 20 January 1972, vol. 53, no. 779, page 128; New Scientist 24 February 1972, vol. 53, no. 784, page 420.
In April 1972, the USSR’s probe Venera 8 took off from Earth and began its journey to Venus. On 06 April 1972, it undertook a mid-course correction to ensure arrival on Venus at the required time and place. Ground controllers held a total of 86 communications sessions with the probe while it was in flight towards Venus. On 22 July 1972 the probe entered the atmosphere of Venus after a journey of 300 million km undertaken in 117 days.
Shortly after Venera 8 arrived at Venus and entered the planet’s atmosphere, a landing capsule separated (at 10:40 am on 22 July, Moscow time). aerodynamic braking slowed the landing capsule from 11.6 km/s to 250 m/s, causing the vehicle to heat up. The landing capsule slowed its descent by deploying a parachute, and undertook some experiments during its descent. It set down on Venus’ daylight side and returned data to Earth about the rocks on the planet’s surface, temperature and atmospheric pressure for 50 minutes after landing.
November & December 1972
Apollo 17 is the last Apollo mission scheduled to land on the Moon. (There is a remote possibility that Apollo 18 may orbit the Moon in 1974). BBC and ITV coverage of previous Apollo flights, although adequate for most purposes, has not been extensive enough for the true spaceflight enthusiast. The Voice of America (VoA) radio station provided coverage of the missions when British radio and TV were off the air. For example, at one point during the Apollo 16 mission, when the spacecraft was in lunar orbit a few hours prior to landing, the landing guidance computer became troublesome and mission controllers postponed the landing. If the fault were not corrected within a few orbits, mission controllers would have found it necessary to cancel the landing. The problems occurred in the evening after British radio and TV had gone off the air; nevertheless, VoA continued to provide coverage with an extremely informative commentator (better than those on the BBC, with all due respect to Patrick Moore and colleagues who do a really good job!) and live feed from the spacecraft. Listeners to VoA were thus among the first to learn of the correction of the fault.
VoA can be heard on medium wave (AM) at 1190 kHz, 245 m (very close to BBC Radio 1). It can be found easily in the early morning (breakfast shows start at 6.00am and 7.30am GMT) and in the evening (9.00pm GMT onwards). VoA can also be heard on 790 kHz, 349 m medium wave (AM) and several short wave wavelengths but reception is best at 245 m. VoA is broadcast to Europe via a relay, which means that the voices sound as if spoken over a telephone, but they are quite comprehensible.
The following is the timetable for Apollo 17. Launch will take place just after new moon. The Apollo 17 S-IVb Saturn rocket stage will impact the Moon sometime in the evening of 10 December 1972, when the Moon is a crescent visible in the south-west around sunset. Impact is expected to take place in Mare Crisium and it is just possible that the 26 cm refractor at Orwell Park Observatory may be able to see a TLP (Transient Lunar Phenomenon) catalysed by the impact.
|Enter lunar orbit||10||19:49||N|
|EVA 1 start (moonwalk)||11||23:33||Y|
|EVA 2 start (moonwalk)||12||22:13||Y|
|EVA 3 start (moonwalk)||13||21:33||Y|
|Start journey to Earth||16||23:33||N|
|Transearth EVA (spacewalk)||17||–||Y|
Apollo 17 will be manned by Eugene Cernan (Commander), Harrison H Schmidt (Lunar Module Pilot) and Thomas (Ken) Mattingly (Command Module Pilot). Harrison Schmidt is the first scientist to go into space (apart from two Russians in 1965). Mattingly will remain in the command module orbiting the Moon while Cernan and Schmidt land on the Moon in the region of the Taurus Mountains near the crater Littrow, towards the north-east edge of the lunar disk visible from Earth. Cernan and Schmidt will undertake three moonwalks (EVAs) while on the Moon, each lasting for up to seven hours. The Apollo 17 lunar roving vehicle is expected to cover a total distance of some 37 km during the three EVAs.
Note that Apollo 17 will lift off at night time on 07 December, and this will be well worth watching on a colour television if possible. The lift off, although of no inherent scientific value, will provide a fitting visual end to a truly magnificent human achievement.
The American space probe orbiting Mars, Mariner 9, has run out of fuel for its manoeuvring rockets and has been shut down by mission controllers. Mariner 9 took a total of 7329 pictures, covering the whole surface of Mars; it took its last on 27 October 1972. The two Russian Mars orbiters, Mars 2 and Mars 3, were shut down in August 1972.
The next chance to launch space probes to Mars comes in August 1973. The USSR is expected to launch two soft-lander probes but America will not launch any.
The Russian spaceprobe Luna 19, in orbit around the Moon, is still operating, taking photos and making measurements. It has made over 4000 lunar orbits. Ground controllers say that it is nearing the end of its useful lifetime.
The next manned American space programme is Project Skylab. If all goes well, the Americans will launch the Skylab Orbiting Laboratory (or Skylab) at the beginning of March 1973. A few days later, they will launch a small rocket, carrying a crew of three, to dock with Skylab, and the crew will spend 28 days in orbit. One of the major experiments aboard Skylab is associated with the Apollo Telescope Mount which will enable astronomers to make the first continuous photographic study of the Sun and stars in X-ray and Ultra-Violet (UV) wavelengths. The unmanned Orbiting Astronomical Observatories (OAS) 2 and 3 have previously made UV observations and the unmanned Uhuru satellite has previously made X-ray observations. Sounding rockets have also been used to obtain observations, but they only observe for a matter of minutes whereas satellites and manned spacecraft can make observations over a period of many months.
Stratoscope Observes Uranus
Stratoscope 2, a balloon-borne, 91 cm reflector, observed Venus from an altitude of 24 km. The telescope provided a resolution of 0.15 arcsec, some ten times better than that of a similar instrument on the Earth’s surface. The telescope also took 17 photographs of Uranus, which showed no detail whatsoever, even after computer processing to improve contrast. The photographs confirm that Uranus does not have the prominent belts associated with Jupiter and Saturn.
From analysis of the distribution of brightness across the planetary disk of Uranus, it seems that the planet is uniformly shrouded by a thick layer of methane clouds topped by a semi-transparent atmosphere composed of molecular hydrogen gas. The estimated equatorial diameter of the planet is 51,800 km (in excellent agreement with earlier estimates) and it has a mean density of 1.2 gcm -3 , only about one quarter that of the Earth. The lack of global circulation belts in the atmosphere of Uranus may be important in understanding its atmosphere. The axis of rotation of Uranus is almost in its orbital plane, as if the planet had fallen over. This causes very strange seasonal effects and the resulting uneven heating of the planet may inhibit the establishment of stable wind zones.
Lunar Orange Soil Not Volcanic After All
The orange soil discovered by the Apollo 17 mission was not, after all, created by volcanic action. Under electron and visible light microscopes, the soil was found to consist of many tiny glass spheres. The orange colour is likely due to high iron and titanium content. This means that none of the Apollo missions succeeded in finding any direct evidence of lunar volcanism (either active, dormant or extinct). However, since almost all the rocks returned by the Apollo missions are volcanic, this raises the obvious question: where did all the volcanic rock come from?
Pioneer 10 has left the asteroid belt and completed half of its journey to Jupiter. It will reach the planet in December 1973 and several years later will leave the Solar System. NASA will launch Pioneer 11 towards Jupiter in April 1973 and the probe will reach the planet in early 1975.
The USA will launch Skylab A on 14 May 1973, to be followed by three men in an Apollo capsule on 15 May to dock with the vehicle. The crew will stay aboard Skylab for about 28 days. Skylab is crammed with scientific equipment, full details of which are outlined in the October 1970 edition of the BAA Journal and Analog magazine.
The USSR launched Salyut 2 on 03 April 1973, but have not yet sent a crew to man the station. There is, as yet, no explanation for this. The Salyut space stations are similar to, but smaller than, Skylab.
The USSR launched the Salyut 2 space station on 03 April 1973. After launch, the orbit of the space station was too eccentric and ground controllers adjusted it on 04 and 08 April. The orbital corrections should have permitted the USSR to launch cosmonauts to the space station on 09 or 10 April, but it did not do so. On 14 April another orbital correction was carried out. Subsequently, ground radar detected fragments, suggesting that either Salyut 2 or the launcher Proton rocket had suffered an explosion. The USSR announced that the space station had “terminated its mission” on 28 April.
The attempt by the USSR to beat America to a long duration space laboratory, Salyut 1, was launched in 1970. Two teams of cosmonauts visited the craft: the first could not get inside, and the second died of decompression before landing after 23 days (a record) in space.
The Americans launched the space laboratory Skylab A, packed full of scientific equipment and somewhat larger than Salyut 1, at 17:30 UT on 14 May 1973. Skylab A successfully entered Earth orbit; however, because of excessive vibration by the Saturn V launch vehicle, a shield against micro-meteors and solar radiation was torn, and interfered with the mechanism to deploy one of the solar panels. As a result, the solar cells could not generate electricity and the cabin, unprotected from solar radiation, became very hot, reaching temperatures in excess of 40° C. Ground controllers postponed the launch of a three-man crew in an Apollo Command Service Module on a Saturn 1b launch vehicle because the cabin of Skylab A was too hot. It was impractical for the crew to attempt to repair the damaged shield and solar panel because their umbilicals, providing water and air during spacewalks, were not long enough to reach the faulty parts. In addition, mission controllers worried that unexploded bolts close to the damaged components might detonate, or the solar panel might suddenly deploy, causing injury to a spacewalker.
Pioneer 10 was launched in February 1972 and should reach Jupiter in early December 1973, where it will return TV coverage of two thirds of the planet’s disc. It has successfully passed through the Asteroid Belt between the orbits of Mars and Jupiter. Measurements by the spacecraft indicate that the density of asteroids in the Belt is not enough to cause a serious hazard to spacecraft passing through the region. Indeed, a spacecraft in orbit around the Earth is in greater danger from meteors than a spacecraft passing through the Asteroid Belt is from asteroids.
Pioneer 11 was launched on 05 April 1973. It passed the orbit of the Moon after 11 hours and within a few days had travelled over one million kilometres. In early Summer 1973, it will cross the orbit of Mars. In August 1973, it will cross the Asteroid Belt and it will reach Jupiter on 05 December 1974 after a journey of 609 days (this is the minimum journey time associated with the most favourable launch window). Pioneer 11 is identical to Pioneer 10. The two spacecraft were launched 13 months apart in order to provide an equivalent gap in their arrival dates at Jupiter. The planet generates a great deal of radio noise. If this interferes with radio transmissions from Pioneer 10 when it is near Jupiter, the 13 month gap will provide an opportunity for ground controllers to re-programme Pioneer 11 to overcome the problem before it arrives at the planet.
Jupiter has an equatorial diameter of 142,800 km and a polar diameter of 133,500 km. Pioneer 10 will pass the planet at a distance of 140,000 km and will be accelerated by the gravitational field to a speed of 125,000 km/hr. If Pioneer 10 experiences no problems associated with radiation or radio noise through such a close passage to Jupiter, ground controllers may send Pioneer 11 even closer to the planet, perhaps as close as 35,000 km, which would accelerate it to a speed of 173,000 km (over 1/400 th the speed of light). Pioneer 11 may also pass close to one of Jupiter’s four Galilean moons. If Pioneer 11 does pass close to Jupiter, its trajectory will then bring it close to Saturn in 1980. However, if Pioneer 10 suffers difficulties with a close passage to Jupiter, ground controllers will send Pioneer 11 along a trajectory similar to that of Pioneer 10, and it will cross the orbit of Saturn four years after its Jupiter flyby.
Future Launches Of Space Probes
The launch window for sending probes to Mars in 1973 is from 15 July to 10 August. The USA will not launch a probe to the planet in 1973, but it is likely that the USSR will attempt to launch one or more soft-landers. The next launch window for Mars is September 1975; during this window it is likely that the USA will launch two Viking soft-lander probes and the USSR will launch its second generation soft-lander, probably a Mars roving vehicle similar to Lunokhod.
Later in 1973, the USA will launch a space probe which will pass Venus and Mercury in 1974. Mercury is a planet about which little is known, so information returned by the probe will be very valuable. The space probe will be called Mariner 10 Venus/Mercury .
The USA will launch a Pioneer probe in 1977 towards Jupiter and Saturn. In the same year occurs the launch window for the Grand Tour, whereby a space probe could follow a trajectory to visit all the outer planets except Pluto. The USA will not attempt to launch a probe on the Grand Tour, but the USSR may attempt to do so, to survey the outer planets during the 1980s.
Possible Russian Manned Spaceflight?
The USSR launched Salyut I in April 1971, and subsequently sent two manned Soyuz spacecraft to dock with it. On 03/04 April 1973, the USSR launched the space station Salyut II, and is likely soon to send a manned spacecraft to dock with it.
More space probes will likely be despatched to Mars in 1973. Until now, only the Americans have sent probes to Mars, but this may change as the USSR now also has a flourishing Mars programme.
The first American probe to Mars was Mariner 3; unfortunately ground controllers lost control of it before it landed on the planet. In November 1964, NASA launched Mariner 4. It reached Mars in 1965 and returned 22 TV pictures, the first ever from close range. Although blurred and with poor focus, they showed for the first time that Mars was cratered. Mariner 4 also sent to Earth the first data on the Martian atmosphere. Mariner 4 completely changed our views on Mars.
In 1969, NASA launched Mariners 6 and 7 to Mars. (NASA had previously sent Mariner 5 to Venus.) The spacecraft provided even better information than Mariner 4 on Mars, using improved equipment to return clearer TV pictures and to investigate the temperature and composition of the Martian atmosphere and surface.
In 1971, Mars approached closer to Earth than it had since the 1920s. In that year, the USA launched Mariners 8 and 9 to Mars. Unfortunately, Mariner 8 enjoyed a ten minute journey culminating in a dive into the Atlantic! However, Mariner 9, launched in May 1971, reached Mars in November 1971 and became the first ever artificial satellite of the planet. The spacecraft orbited the planet twice a day, carrying out long term experiments: it mapped the entire surface of Mars in great detail, discovering huge volcanoes, vast canyons and features resembling dried river beds. NASA shut down the spacecraft in October 1972, after it had exceeded the Administration’s wildest dreams.
After analysis of the results from Mariner 9, NASA tentatively selected potential landing sites for the Viking probes which are intended to soft-land instrument packages onto Mars in 1976. NASA selected four potential landing sites (although there are only two Viking probes):
- Chryse, 4500 km long canyon, 19.5° N, 34° W (close to the Martian Equator).
- Tritonis Lacus, 20.5° N, 252° W (backup for Chryse).
- Cydonia, 44.3° N, 10° W (Martian arctic).
- Alba, 44.2° N, 110° W (backup for Cydonia).
There is some controversy about the choice of sites. NASA appears definite about site 1/2 for Viking 1. However, there is some doubt as to what the Viking 2 landing site should be. Once of the main aims of the Vikings is to search for life on Mars. Geologists wanted Viking 2 to land at a geologically interesting site, either 73° N or 9° S (one site polar, the other equatorial). However, biologists consider the former site to be too cold for life and the latter to be too dry; they would instead prefer Viking 2 to touch down on the edge of the North Polar Cap at about 44° N, which is, they believe, the only site with much chance of finding life. Even so, the dryness of the biologists’ favoured site is comparable to that of a terrestrial desert, and its coldness to that of the terrestrial North Pole. The biologists have won the day, and both sites 3 and 4 are at a latitude of approximately 44° N.
Each Viking will carry equipment to detect the presence of life on Mars (thought to be a remote possibility) and also a TV camera, seismometer, meteorology experiment and rock analyser to return data on Mars to ground controllers.
The USA will not launch any more spaceprobes towards Mars during 1973. So let’s turn now to the USSR. The USSR launched its first Mars probe, Mars 1, in 1962, but unfortunately ground controllers lost contact with it shortly before it reached the planet. A similar fate befell Zond 2, which had a trajectory very similar to that of Mariner 4.
The first successes for the USSR came with Mars 2 and 3, which operated at the same time as Mariner 9. Mars 2 and 3 were each in two parts: each spacecraft comprised an orbiter and an instruments package designed to crash-land on the surface of Mars: the package from Mars 3 became the first man-made object to reach the planet. The USSR sent two more spaceprobes to orbit Mars in August 1972. The media gave far less publicity to the Russian probes than to Mariner 9; this was due in part to the fact that the Russians released hardly any images of Mars whereas the Americans released all 10,000 or so Mariner 9 images of the planet. The USSR did, however, release many of the interesting findings of the two probes Mars 2 and 3 (see entry for April 1972 above).
It is likely that the USSR will launch Mars 4 and 5 towards the planet in August 1973, to arrive in late 1973 or early 1974. It is likely that these spacecraft will orbit Mars and send landers to the surface.
The Russians have been optimistically talking about landing Lunokhod-type vehicles on Mars. It is likely that they could land a second generation Mars lander, complete with surface rover, on the planet at about the same time as the American Viking probes; there is therefore a possibility that the Russians will pull ahead of the Americans in the field of Mars exploration.
American Manned Space Programme
Recent TV pictures from Skylab were fantastic (and in colour)! Particularly impressive was the sequence of the rendezvous of the Skylab A mission with Skylab, showing the massive, brilliant white space station hanging in space and close-ups of its exterior from all angles. Images of the surface of the Earth, some 430 km below, with the space station in the frame, showed remarkable detail. First pictures of the interior of the space station, including an astronaut propelling himself the entire length of the craft by “swimming” in weightless conditions, were also interesting. The view from inside the space station of the deployment of the sun-shade was spectacular: an orange foil suddenly burst out into its deployed position.
All that remains now is to await the return of the three-man crew to Earth. The crew should return scientific data, including astronomical material and photographs of the Earth, Sun, stars and Skylab which will be examined in detail on their arrival. Articles in Flight International, Nature and New Scientist should provide detail as the mission continues.
Failure of one of the main solar panels of Skylab to deploy fully after orbital insertion depleted the electrical capacity of the craft. An extra-vehicular activity (EVA, or spacewalk) on 07 June 1973 by crew members Charles Conrad, Jr and Joseph Kerwin appears to have succeeded in releasing the jammed panel and, if it thaws in the sunlight, should restore electrical capabilities to nominal levels. However, Skylab frequently passes into Earth’s shadow, during which time its solar cells cannot generate electricity. A television report indicated that the orbit of Skylab would be altered in June 1973, likely by firing the Service Propulsion System (SPS) of the Apollo Service Module (Skylab proper is not equipped with a large manoeuvring rocket), to increase the time during which the space station is in sunlight, allowing more time for electricity to be generated.
The launch date of the second Skylab mission has been brought forward from August to 28 July. After Skylab, there will not be another American astronaut in space until 1975 when a joint Russian-American spaceflight is scheduled. Plans for this enture are well under way and it has been announced that the mission will begin as follows: an Apollo Command Service Module will take off from America with three Americans on board. It will rendezvous and dock with a Russian Soyuz spacecraft carrying two Russians. It is clear that there will be some differences to the usual arrangements: for example, for the first time, the Russians will have to announce in advance the exact time of a launch and give live coverage of the lift-off. Also for the first time, there will be Russians stationed at Houston Mission Control and Americans at Tyuratam/Biakonur Mission Control in Russia. Diagrams of the mission spacecraft have been published labelled in both Russian and English.
The Americans have announced two of their three crewmen:
- Tom Stafford, a veteran of Apollo 10 and Gemini 9 missions. Tom is also due to visit Skylab. He will be Mission Commander.
- Deke Slayton. Deke was one of the original seven American Mercury astronauts chosen in 1961, but was grounded because of suspected heart trouble. He has at last received medical clearance!
Russian mission controllers have provided an unprecedented amount of information about the crews of the mission. They have announced the crew of their spacecraft before the mission and have also announced the back-up and support crews, something that they have rarely done before, even after a mission. The crews are:
- Primary crew: Alexei Leonov (first man to walk in space, in 1965) and Valery Kubasov (veteran of Soyuz 6).
- Back-up crew: Anatoly Filipchenko (veteran of Soyuz 7) and Nokolai Rukavishnikov (veteran of Soyuz 10, Salyut 1).
- Support crew 1: Vladimir Dzhanibekoz (born in South Kazakhstan in 1942, entered cosmonaut training in 1970 but has not been into space yet) and Boris Andreyev (born in Moscow in 1940 and commenced training in 1970).
- Support crew 2: Yuri Romanenko (born in 1944 and started training in 1970) and Alexander Ivanchenkov (born 1940 near Moscow and started training in 1970).
Both Boris Andreyev and Alexander Ivanchenkov were born in 1940 in Moscow and both worked in design bureau then entered cosmonaut training in 1970: could they be friends?
After the joint Soyuz-Apollo mission, NASA does not plan to send men into space again until the first manned tests of the Space Shuttle in the 1980s.
Some indications in early 1973 were that Skylab would not be visible from East Anglia. However, by late June of the year, first reports began to circulate around members of OASI of sightings of the space station. In fact, Skylab, a cylinder some 36 m in length, is the largest satellite visible from Britain. It is visible from southern England travelling west via south to east. Charles Radley was one of the first members of OASI to see Skylab, observing the following objects on 23 June 1973:
73/027/19 Skylab object K, possibly one of the fairings from the craft, or the associated Saturn 1b rocket.
Other members of OASI observing Skylab in June 1973 were: Roy Cheesman, Alan and John Cox, John Easty and David Bearcroft.
Other objects associated with Skylab visible from Earth are:
73/027/02 The second stage of the Saturn V used to launch Skylab.
73/027/05 Fragment E, a piece of debris associated with Skylab.
73/027/12 Object M, another fragment of debris.
The orbit of Skylab is inclined at 51° to the Earth’s equator, so Skylab does not come North of the English Channel. However, because Skylab orbits at an altitude of some 430 km, it can be seen from more northerly latitudes.
The Russians launched Mars 4 at 22:21 on 21 July 1973 and Mars 5 at 21:56 on 25 July 1973. At 02:00 on 26 July, the probes were at the following distances from Earth: Mars 4 – 1,460,000 km; Mars 5 – 66,000 km. The Russians launched Mars 6 on 06 August and Mars 7 on 10 August. Mars 6 carries a French-made solar radio experiment, similar to that carried on Mars 3 in 1971. According to the Russians, Mars 6 will co-operate with equipment on Mars 4: this has resulted in speculation that that one of the probes will soft-land and use the other as an orbiting radio relay station. The probes are now all coasting towards the Red Planet. Mars 4 and Mars 5 are due to arrive in mid-February 1974 and Mars 6 and Mars 7 in March 1974. (Times above refer to Moscow time.)
If a rescue launch is necessary it cannot be made before 05 September 1973. The three-man crew of Skylab-2 are due to return to Earth on or about 22 September.
America will launch Mariner 10 Venus/Mercury in December 1973. It will flyby Venus between 03 and 06 February 1974, depending on the launch date, and will take approximately 3000 TV pictures of the clouds surrounding the planet. It should reach Mercury on 30 March 1974; it will flyby the planet rapidly and will capture approximately 2000 pictures of in a two hour period. It will map Mercury in resolution similar to that provided of the Moon by Earth-based telescopes, capturing details as small as 100 m across. After 18 months, in August 1975, it will encounter Mercury again and, if still working, will perform further investigations. There is a possibility that the probe may still be functional for a third Mercury encounter.
Little is known about Mercury. It is the planet with greatest density apart from the Earth, its lighter elements having boiled away into space due to the intense heat and low surface gravity. Its surface has the lowest albedo (reflectivity) of all the planets and is composed of hard, dark rock: radar suggests granite.
Visual observations of Mercury and Venus rarely show significant detail, so scientists eagerly await pictures from the TV cameras on Mariner 10.
Pioneer 10 will reach Jupiter in December 1973.
As of September 1973, there should be a three-man crew aboard Skylab. They are scheduled to return to Earth on or about 22 September. The final Skylab mission is due to be launched on 09 November and return to Earth on 05 January 1974.
The period and inclination of the orbit of Skylab mean that the craft is visible from Ipswich at most three times a day. For the first week or so of September 1973, the craft will be visible (weather permitting) each night in the evening sky, appearing as a bright point of light moving quickly from west via south to east, taking a few minutes to pass from horizon to horizon, at least once, sometimes twice and occasionally three times. When it is visible three times in an evening, the first and third passes will be unfavourable but the second will be very favourable. Later in September, Skylab will be visible at most twice a night. Skylab was last well-placed for visibility from Ipswich in mid-late June, early July, and 11 August onwards. Often its passages occur in daylight and are not visible.
Effects of Weightlessness
The effects of weightlessness can be drastic! The first long spaceflight was in December 1965, when Frank Borman and James Lovell spent 14 days in space aboard Gemini 7, in a mission intended to examine the effects of long-duration space voyages on the human body. Neither man suffered significant ill-effects from the journey. The next long flight was by cosmonauts Andrian Nikolayev and Vitali Sevastyanov in Soyuz 9; their flight, in June 1970, of almost 18 days, broke the record for human endurance in space. Unfortunately, both men lost calcium from their bones, suffered muscle-shrinkage, were unable to stand without assistance after landing and subsequently found difficulty re-adapting to terrestrial gravity. The next long-duration flight was by Soyuz 11 in June 1971. The crew, Georgy Dobrovolsky, Vladislav Volkov and Viktor Patsayev entered the Salyut 1 space station but, unfortunately, after 23 days in space, perished when the capsule depressurised prior to re-entry. The next long duration flight, of length 28 days, was Skylab 2, to visit the orbiting space station Skylab. At the time of writing, early August 1973, the three-man crew, Pete Conrad, Joseph Kerwin Paul Weitz, have still not fully recovered after more than a month back on solid ground. Their hearts shrank slightly but measurably in size and they lost many red blood cells.
The current mission to the space station, Skylab 3 (crewed by Alan Bean, Owen Garriott and Jack Lousma), is scheduled to last twice as long as Skylab 2. What will be the effects on the crew?
And extrapolating from the above, what would be the physiological damage to the crew during a two year weightless flight to, say Mars?
The Russian Mars probes are still going strong! They executed scheduled course corrections as follows (times are Moscow Time):
- Mars 4 and Mars 5: 30 July and 03 August.
- Mars 6: 2.45 am on 13 August 1973.
- Mars 7: 11:00pm on 16 August 1973.
The following table gives the distances of the probes from Earth on 17 August 1973 and the estimated arrival dates at Mars.
|Distance (km) From Earth on 17 Aug 1973|
|Mars 4||mid-February 1974||8,770,000|
|Mars 5||mid-February 1974||7,420,000|
|Mars 6||early March 1974||4,110,000|
|Mars 7||mid-March 1974||2,760,000|
The crew of Skylab 2 returned to Earth after a very successful mission, bringing with them some 77,000 photographs, many of them of the Sun and Earth, revealing much new information.
Skylab is now becoming visible in skies over the UK once more. Predictions of its visibility are available to members of OASI from Charles Radley and are occasionally published in the Evening Star . The Skylab 3 mission is due to start on 11 November 1973 and return to Earth in January 1974. It is possible that the Skylab 3 mission will be delayed and/or extended to allow it to cover the period when Comet Kohoutek reaches greatest brilliance, in early January 1974.
Mariner 10 Venus/Mercury was scheduled for launch on 03 November 1973. During its journey towards Venus and Mercury it will monitor interplanetary space conditions, which will help to explain the appearance of Comet Kohoutek. The probe is scheduled to reach Venus in February 1974 and Mercury in March 1974. When the probe reaches Mercury, it will increase our knowledge of the planet hugely: a few dozen photographs from close range would provide more information than the entire data on the planet amassed during the course of human history to date.
There are currently seven space probes en route to various planets as follows:
- Mariner 10 Venus/Mercury was launched on 03 November 1973 and is the first two-planet mission. It will pass Venus on 02 February 1974 and swing around Mercury on 23 March 1974. Its camera and other instruments will monitor both planets as it passes. It will attempt to return images of the surface of Mercury with a resolution of 0.1 km (better than we can achieve with the lunar surface through the 26 cm refractor at Orwell Park!) The space probe is then scheduled to return to Mercury on 22 September 1974 and 17 March 1975; if its instruments are still functioning on these later passes, they will return more information. If all goes well, Mariner 10 will provide more information about Mercury in a fortnight than has so far been obtained in the course of human history!
- Four Russian space probes, Mars 4, 5, 6 and 7 are scheduled to reach Mars at approximately weekly intervals in February-March 1974. The USSR has indicated that at least one soft-landing will be attempted. Note: Mars 3 soft-landed on the planet in November 1974 but its transmitter failed 90 seconds after touchdown.
- Pioneers 10 and 11 are en route to Jupiter. Pioneer 10 is due to reach the planet in December 1973 and Pioneer 11 in early 1975.
February and March 1974 should be two very interesting months:
- In early February, Mariner 10 should pass Venus and take the first close-up photos of the planet’s cloud mantle.
- In mid- to late February, and perhaps early to mid- March, the four Russian probes Mars 4, 5, 6 and 7 should arrive one after another at Mars. They are likely all to orbit the planet, and two of them may attempt soft landings on the surface.
- In late March, Mariner 10 will arrive at Mercury.
On 18 December 1974, the crew of Soyuz 13, Pyotr Klimuk and Valentin Lebedev, ended an eight-day mission during which they performed many astronomical observations. Their mission had been concurrent with Skylab 3. They took X-ray photographs of the Sun (as did Skylab 3). They used a telescope named Orion 2 , with a wide angle quartz crystalline lens (to withstand the extreme temperatures of space) to obtain hundreds of ultra-violet spectrograms of stars brighter than magnitude 9.5.
No doubt the two cosmonauts also observed Comet Kohoutek. The Skylab 3 crew reported seeing the comet by naked eye in early December 1973.
The record duration of the Sklab 3 mission (over 80 days) is likely to remain unsurpassed for several years, for the Americans are not planning any more long duration spaceflights until the 1980s at the earliest, and the Russians are still in the experimental stage with their Salyut space station.
NASA launched Mariner 10 on 03 November 1973. The craft passed Venus on 05 February 1974 and then used the “slingshot” effect of Venus’ gravity to set course for Mercury, which it will reach on 29 March 1974. Mariner 10 is intended to pass within 1000 km of Mercury at its closest approach.
Mariner 10 carries television cameras to observe Venus and Mercury and scientific instruments to make measurements of atmospheric composition, surface temperature, magnetic field and cosmic radiation at both planets. Secondary objectives of the mission include measurement of the interplanetary environment. The probe hosts two TV cameras, fitted to Cassegrain telescopes. Scientists expect that analysis of the TV pictures taken at Venus will show a dense cloud blanket in visible light and ultra-violet wavelengths. Current theories suggest that clouds visible in ultra-violet light orbit Venus every five days.
Mariner 10 is expected to beam back to Earth pictures of Mercury with a resolution similar to that of the Moon taken through an Earth‑based instrument. Such images will increase overnight Mankind’s knowledge of Mercury, supplying information which is not accessible to terrestrial observers. Scientists hope to receive 2740 images from Mariner 10 at Mercury, where the TV camera will be capable of producing a frame every 42 seconds.
Mariner 10 carries the following scientific instruments:
- Scanning electronic analyser. This measures ions (charged particles) thus helping to understand how the solar wind interacts with Mercury and Venus. NASA will correlate data from this instrument with that from Pioneers 10 and 11.
- Two magnetometers, to measure magnetic fields during the flight.
- Ultraviolet spectrometer. This will take direct measurements of airglow, which together with occultation techniques should yield the likely structure and composition of Venus’ atmosphere and should contribute to the search for an atmosphere around Mercury. The instrument will also monitor galactic and inter-planetary background radiation and observe the Earth’s corona.
- Infra-red radiometer, to measure thermal emissions from the planets.
Data from Mariner 10 should be interesting and enlightening, especially concerning Mercury, a planet about which our current knowledge is so limited. For further information see New Scientist , 14 February 1974.
So, eventually the Skylab missions are over! There were three missions, lasting 28, 56 and finally, a record-breaking 85 days. The final 85 day mission is likely to remain unbeaten for many years, perhaps until the Russians make their own Soyuz/Salyut spacecraft fully operational. The Skylab programme, although less dramatic than Apollo, has in many ways yielded much more data about spaceflight. It is now clear that the main limitations to Man’s endurance in space will be political and financial rather than physiological. The question now arises: what is left for NASA to do? A manned mission to Mars, perhaps? Skylab has yielded enough data on long manned spaceflights to make a trip to Mars possible, but it is unlikely that America will launch a manned Mars mission before the turn of the century at least, although it would be technologically possible in the 1980s. It is known that the Russians are very interested in sending men to Mars, but are unlikely to attempt a mission until they have resolved problems with their Soyuz and Salyut spacecraft (two Soyuz missions ended in the death of the crews and Salyut 2 disintegrated after a short period in orbit).
The next scheduled American spaceflight is in June 1975, when an Apollo capsule will dock in orbit with a Soyuz capsule. After that, no more American spaceflights are planned until the Space Shuttle, which will become operational in the 1980s. Without doubt the Space Shuttle will extend man’s horizon’s in space at relatively low cost, but there do not appear to be any plans for missions beyond the Space Shuttle, largely due to uncertainty about the financial climate that will prevail in the future. There was talk of closing down NASA, but Congress has now granted funding.
NASA plans to launch an advanced space probe to Venus in 1978 and an another advanced probe to Jupiter and Saturn, to replace the cancelled Grand Tour mission.
European Space Agency (ESA)
ELDO (European Launch Development Organisation) and ESRO (European Space Research Organisation) are well on the way to merging to form the European Space Agency (ESA). ESA will have three main initial programmes:
- Development of a European orbital launch rocket, to reduce Europe’s dependence on the USA for satellite launches.
- Spacelab, where the USA will depend on ESA to design and build an advanced version of Skylab to be launched by the Space Shuttle in the 1980s. The Spacelab missions may be crewed by a joint US-Europe crew, so we may see a Briton in space at last!
- Development and launch of a European communications satellite for shipping.
The crew of Soyuz 13 used a telescope named Orion 2 , with a wide angle quartz crystalline lens, to obtain hundreds of ultra-violet spectrograms of stars brighter than magnitude 9.5 (see above, February 1974, for more details). Orion 2 was in fact a successor to the earlier Orion 1 ultra-violet spectrograph telescope, which flew in the Salyut space station in 1971. In the course of eight days, Orion 1 obtained 10,000 spectrograms of more than 3000 stars. It provided clear spectrograms of stars down to magnitude 10, and in one case, in the sky around Capella, to magnitude 11. The spectrograms provided important information for solving many topical problems of astrophysics and cosmology. Pointing accuracy of Orion 1 was achieved by an unique three axis stabilised platform.
Source: Soviet News , 29 January 1974.
Space Probes Arrive At Mars
The four space probes launched by the USSR in Summer 1973 to Mars have met mixed fates. Mars 4 approached Mars on 10 February 1974, but missed its target orbit by 2200 km, went straight past the planet and was lost. It was intended to work with Mars 6 and it is unclear to what extent, if any, its compromises the latter mission. However, Mars 5 successfully entered Mars orbit. If Mars 7 can successfully enter Mars orbit, the USSR may subsequently attempt to soft land it on the surface of Mars, working together with Mars 5. Mars 6 and Mars 7 are due to reach Mars in mid-March 1974.
The USSR recently admitted using over 1700 American Mariner 9 images of Mars for planning their Mars probes, without releasing any of their own images to NASA.
The July-August 1973 launch window saw the USSR launch four probes towards Mars. Unfortunately on arrival at Mars in February-March 1974, the probes met with limited success. The entire USSR Mars programme can be described as unlucky, as the following brief summary indicates.
Mars 1, launched in 1961 and scheduled to reach Mars in 1962, broke several space endurance records but was lost before arrival at the planet.
Zond 2, launched during the same launch window in November 1964 as Mariner 3 and the famous Mariner 4 (the first probe to return TV pictures of Mars from close range), failed at an earlier stage in its journey than did Mars 1.
The USSR then concentrated on exploration of Venus until the very favourable 1971 Mars launch window, when it launched Mars 2 and Mars 3. Both probes went into orbit around Mars in November 1971. Mars 2 then attempted a landing on the planet’s surface, which involved braking by a parachute and a descent rocket: the former appeared to deploy correctly but the rocket did not, and the probe crashed on the surface. Mars 3 had better luck! On 02 December 1971, Mars 3 became the first spacecraft to soft-land on Mars, at co‑ordinates latitude 45° S, longitude 158° W. It transmitted from the surface for 90 seconds, then the signals stopped. The orbiter sections of Mars 2 and Mars 3 remained in orbit and gathered much interesting data about the planet before being shut down after some months.
Mars 4 reached the vicinity of Mars on 10 February 1974. Unfortunately, its retro-rocket failed to ignite, and instead of entering Mars orbit, it shot straight past the planet at a distance of 2200 km, taking pictures as it went. On leaving the planet, Mars 4 entered heliocentric orbit.
Mars 5 reached the vicinity of Mars on 12 February 1974 and successfully entered Mars orbit at 06:45 (Moscow Time). The retro-burn went perfectly, and Mars 5 acquired the planned orbital parameters: apareon 32,500 km, periareon 1760 km, period 35 hours, inclination to Mars equator 35°. Mars 5 has an orbital period slightly longer than the Martian day (24h 37m 23s). This means that it will be in a not-quite synchronous orbit, moving backwards around the planet by approximately 5° per Martian day. Thus, provided its cameras are functional, it will have an opportunity to photograph every feature on Mars under its orbit at close range every 76 Martian days (every 75 orbits). The USSR is releasing photographs taken by Mars 5 from orbit: there is one in Flight International , vol 105, no 3395, 04 April 1974, page 440. The picture quality is not good, although slightly better than that obtained by Mariner 4 a decade earlier; it shows some craters which appear to have suffered erosion by wind and sand.
Mars 7 approached Mars on 09 March 1974. However, according to the USSR, because of a hitch in the operation of one of the onboard systems , the probe released its descent module at too great a velocity as a result of which it did not approach closer to the surface of Mars than 1300 km. Mars 7 joined Mars 4 in heliocentric orbit.
Mars 6 reached Mars on 12 March 1974, some three days after Mars 7. Mars 6 met with some success: the lander separated from the main craft at a distance of approximately 80,000 km from Mars and, after a descent through the atmosphere lasting 148 seconds, touched down on the surface of the planet. Mars 6 took photographs of as it descended, providing the first close-up photographs of the surface, but these have not been released at present. The USSR issued a statement: For the first time information about the Martian atmosphere, obtained by direct measurement during the module’s descent, was transmitted back to the Earth . The data showed several times more water vapour in the atmosphere than had been expected. Mars 6 touched down at co-ordinates latitude 24° S, longitude 25° W and, like Mars 3 over two years earlier, shut down for reasons unknown.
Details of Soviet spaceprobes are not readily available, and information on recent Mars probes has been particularly confused. The following information has been pieced together from Soviet reports and the interpretations of western spaceflight experts. Mars 4 and 5 are orbiter vehicles, intended to perform experiments in Mars orbit similar to those of Mariner 9. Mars 6 and 7 are lander vehicles, with flight programmes more similar to the Soviet Venera probes than the anticipated American Viking probes. That is, they each consist of a main bus and a descent module . The main bus provides interplanetary transportation from Earth to Mars and then flies past Mars (it does not enter planetary orbit). The descent module is intended to land on the planet. Flight plans call for the descent module to separate from the main bus before arrival at the planet, slow down by using a retro-rocket and then atmospheric braking and then descend by parachute to the surface. Mars 2 and 3 were more similar to the planned American Viking probes: each comprised a Mars orbiter and a lander.
NASA’s probe Mariner 10 worked perfectly at Venus. It returned pictures of Venus’ cloud deck in ultra-violet light, showing swirling clouds. The pictures of Mercury were fabulous, if a little blurred at first.
Since Mariner 10 and Mercury are both in heliocentric orbits relatively close to the Sun (compared to the Earth), they both have short orbital periods and will re-encounter one another from time to time. The first re-encounter will occur on 22 September 1974, when flight controllers hope that the probe will return more pictures of the planet. There is a second re-encounter on 17 March 1975, but flight controllers are unsure whether the probe will still be operational by then.
During the 05-20 September 1974 launch window, NASA will launch two Viking probes to land on Mars. They should arrive in March/April 1976, and touch down on the surface a few weeks later. The average atmospheric pressure on the surface of Mars is around 6 mb, the minimum atmospheric pressure for water to be present as a liquid. Viking B is targeted to land in Cydonia, close to the North polar cap, where the average atmospheric pressure is 7.6 mb, and therefore liquid water (and perhaps life!) may exist.
Pioneer 11 emerged from the Asteroid Belt on 20 March 1974. It should reach Jupiter on 05 December 1974. Following the successful voyage of Pioneer 10, fight controllers have adjusted the trajectory of Pioneer 11 to a more ambitious route. The probe performed a mid-flight manoeuvre at the end of March to set course to pass within 40,000 km of Jupiter. (Pioneer 10 passed Jupiter at a distance of 130,000 km.) The close passage of Pioneer 11 to Jupiter will bring it deeper into the planet’s radiation belts than Pioneer 10 ventured. However, Pioneer 11 will accelerate to 160,000 km/h at Jupiter and will pass through the radiation belts more quickly than Pioneer 10, so the dose of radiation that the probe receives should be acceptable. Pioneer 11 will approach Jupiter at a much steeper angle than Pioneer 10, and pass closer to the the pole of the planet, covering a greater range of latitudes than its predecessor.
The close approach of Pioneer 11 to Jupiter will result in it attaining a high exit velocity and will sharply alter its trajectory, setting the probe on course for a rendezvous with Saturn. On leaving Jupiter, it will move inwards towards the Sun, reaching perihelion in 1976, then move outwards again, re-crossing the orbit of Jupiter (but with the planet a long way behind!) in 1977. It will reach Saturn on 05 September 1979, some 6.5 years after its launch. The probe was not designed for an extended operational life, but there is a good chance that at least some of its systems will be operational at Saturn and able to send useful data, including images, to Earth.
The information which Pioneer 11 returns from Jupiter is intended to pave the way for the 1981 Jupiter orbiter probe.
Factors such as weather and launch windows influence when the Russians launch manned or planetary probes. There are no launch windows in the near future except for Jupiter and Saturn, but Russian technology is not currently advanced enough to launch a probe to these planets. The Russians’ normal launch season for manned spacecraft is April – September; they tend not to launch manned spacecraft in winter, but have occasionally done so, for example Voskhod 1 and Soyuz 3, both of which landed in blizzards, hampering recovery operations.
Therefore, if Russia intends to launch any manned spacecraft during 1974, it will probably start to do so soon. Of course, it could launch an unmanned probe to the Moon at any time.
Soyuz-Apollo Docking Flight
June 1975 will see the joint USSR-USA, Soyuz-Apollo docking flight. This has greater political value than scientific, but is very promising for hopes of future co-operation in space.
Russia launched Luna 22 on 29 May 1974. It entered lunar orbit on 02 June, and was in orbit for the lunar eclipse on 04 June. There is no further information on the probe at present.
Salyut 3 – Soyuz 14 Linkup
On 25 June 1974, Russia launched Salyut 3, an orbiting space station similar to America’s Skylab. The vehicle is about 20 metres long and weighs approximately 20 tonnes. The Russians placed it into an orbit with period 90 minutes, inclination 52°, perigee 260 km and apogee 275 km.
At 18:15 UT on 03 July, Russia launched, from the Baikonur Space Centre, two cosmonauts, Colonel Popovich and Lieutenant Colonel Yuri Artyukhin, aboard the Soyuz 14 spacecraft. Soyuz 14 docked with Salyut 3 after a 35,000 km orbital chase lasting some 30 hours. On entering Salyut 3, the cosmonauts first checked it, then for the next 14 days performed various experiments involving observation of Earth resources; observation of the atmosphere; examination of the biological effects of prolonged weightlessness; and studies of radiation and particle fields.
The crew re-entered Earth’s atmosphere on 20 July. There was some speculation that Russia would attempt a maritime recovery, but in fact Soyuz 3 came down on land just two kilometres from the landing site of Dzhezkazgan.
The mission of Soyuz 11 in 1971 ended with the tragic death of three cosmonauts. Soyuz 12 and 13, launched in September and December 1973 respectively, tested new designs of the Soyuz vehicle. Soyuz 14 was the third of the modified Soyuz craft, so the Russians expressed relief that its mission had been a success. The fact that Russia used the Soyuz 14 craft for the mission to Salyut 3 probably indicates that the craft is cleared for operational use.
Salyut 3 was at first visible from the UK but its orbit has now shifted, and it is no longer visible. However, in a few months time, due to further orbital changes it should become visible once more.
The date for the Apollo-Soyuz Test Project (ASTP) has been set. The Soyuz rocket will lift-off at 12:30 UT on 15 July 1975. Seven and a half hours later, once the Russian rocket has been confirmed to be functioning satisfactorily, a three-man Apollo crew will blast off from Cape Kennedy. The Russians will have a duplicate rocket and crew standing by should the first Soyuz flight go wrong.
Once in orbit, the Apollo crew will have 32 hours locate and dock with the Soyuz craft. To assist with the location of the Soyuz vehicle, the Russians are building US transponders into it. Once the craft have docked, the Apollo commander, Tom Stafford, will crawl through the airlock to greet Alexei Leonar and Valery Kubasov in Russian. No special experiments are planned, but the mission will signify the first internationally manned spaceflight. The Soyuz-Apollo craft should be visible from the UK.
Pioneer 11 To Visit Saturn
Pioneer 11 safely crossed the Asteroid Belt in March 1974 and is now speeding towards Jupiter with all its equipment functioning satisfactorily. During April 1974, NASA announced that it had executed a mid-course trajectory adjustment which will result in the craft approaching Jupiter on 04 December 1974. The encounter will result in the velocity of the craft being greatly increased by the gravity of Jupiter, and it will swing round in a tight curve behind the planet and head off almost at right angles to its original course on its way to rendezvous with Saturn on 05 September 1979. Pioneer 11 will make a much closer approach to Jupiter than did Pioneer 10, which is now heading out of the Solar System.
NASA is currently planning two Pioneer-type space probes for launch in 1978. Previous expeditions to the inner Solar System have used Mariner-type spacecraft. However, NASA is very pleased with the performance of the Pioneer 10 and 11 craft. The current plan is to launch the first Pioneer (#1) craft in May 1978 and a second (#2) three months later. Pioneer #2 will overtake Pioneer #1 and go into orbit around Venus in December 1978. Some 10-20 days before Pioneer #1 reaches Venus it will launch one large probe and three small probes which will enter Venus’ atmosphere approximately one week after Pioneer #2 enters orbit. The four probes will transmit information back to Earth about the composition of the cloud layers which surround the planet and the characteristics of its magnetic field. Pioneer #1 will itself enter the atmosphere of Venus and transmit information before burning up or crashing onto the planet.
Luna 22 is still orbiting the Moon. On 09 June 1974 it executed a manoeuvre which brought its orbit to within 25 km of the lunar surface at closest approach. For four days, the probe obtained high resolution photographs of the lunar surface. The photographs may be used to choose a landing site for a future Moon probe. On 13 June, ground controllers raised the probe’s orbital altitude to 299×181 km.
Skylab was visible from the UK during August. The Ipswich Evening Star newspaper sometimes publishes satellite predictions.
In December 1974, Pioneer 11 should send back more pictures of Jupiter, then swing around behind the planet and start its journey to Saturn, arriving in September 1979.
Russia launched Soyuz 15 on 26 August 1974. The craft landed just three days later having failed to dock with the orbiting space station Salyut 3. Soyuz 15 appears to have had difficulty catching up with Salyut 3 in orbit, and in fact only reached to 100 km of the space station. Ground controllers became concerned about the drain on the power supplies aboard the spacecraft and terminated the mission.
NASA plans to launch two Viking unmanned robot spacecraft to Mars between mid-August and mid-September 1975. The spacecraft will each use a Titan III rocket as launch vehicle. The Viking probes will arrive at the planet approximately one year later. Each probe will first orbit the planet surveying possible landing sites, then release a landing craft to descend to the surface and (it is hoped!) transmit information back to Earth via the orbiting spacecraft.
The Russians have tried to land the probes Mars 2, 3, 4, 5, 6 and 7 on the planet without much success: perhaps the little green men have been shooting at them!
Russia launched Luna 23 on 28 October 1974. The craft entered lunar orbit on 02 November. The original mission appears to have been to land on the surface, collect soil samples and return them to Earth, but recent reports mention that the craft was too badly damaged on landing to continue with the mission as planned.
Apollo-Soyuz Test Project (ASTP)
Preparations are well advanced for the launch of an Apollo spacecraft on 15 July 1975 as part of the joint Soviet-American space mission, ASTP (Apollo-Soyuz Test Project). The docking module of ASTP is now at NASA’s Kennedy Space Center, where it has joined the Apollo Command and Service Module CSM III which arrived from Rockwell’s plant at Downey, California, in Summer 1974.
When the Apollo and Soyuz craft dock in orbit, Apollo will be at one end of the docking module and Soyuz at the other. Apollo will be pressurised with pure oxygen at 34 kPa. Soyuz is normally pressurised with an oxygen/nitrogen mix at 101 kPa; however on ASTP it will be pressurised with an oxygen/nitrogen mix at 69 kPa. The docking module of ASTP, which is 3 m long and 1.5 m in diameter, is an air-lock, first equalising pressure in Soyuz and Apollo and then enabling astronauts to pass between them.
The Apollo-end of the docking module carries a drogue fitting of the type used on the lunar module so that the probe on the CSM III can achieve a rigid docking with it. The Soyuz-end carries an androgynous system whereby either Apollo or Soyuz can be active during linkup so that both craft can move about. It is intended that all future manned space missions will employ the new androgynous system.
Russia has made several modifications to the Soyuz spacecraft to suit ASTP. At the forward end of the spacecraft is an orbital module for the crew to inhabit during work and rest. It is 2.2 m in diameter and 2.7 m in length and weighs 1.2 t. Behind this lies the descent module with flight controls and two couches for use during launch and re-entry: it is 2.1 m in diameter, 2.2 m in length and weighs 2.8 t. The instrument module at the rear is 2.3 m in length, carries propulsion equipment and weighs 2.7 t. Two solar panels are attached to it, positioned diametrically opposite one another, and spanning more than 10 m. The complete Soyuz vehicle is 7.2 m long, 2.2 m in maximum diameter and weighs 6.7 t.
Russia will launch the ASTP Soyuz at 12:20 GMT on 15 July into a 123×101 km orbit at inclination 51.8°. Ideally, only a single manoeuvre will be required to configure the path of the spacecraft for rendezvous, this being an apogee burn to circularise the orbit at a radius of 123 km on revolution 17. A small trim burn may be necessary on the fourth revolution to compensate for orbital insertion errors: flight controllers will use post-launch information from Russian and American tracking stations to determine whether or not this is needed.
Meanwhile, NASA will launch the ASTP Apollo at 19:50 GMT on 15 July into a 90×81 km orbit. The Apollo will consist of the CSM III atop a Saturn 1B SA-210 rocket. Sixty-four minutes after launch the CSM III will separate from the S-IVB stage adaptor, turn around and dock with the drogue on the docking module; 2 hours and 34 minutes into the flight, the CSM III will extract the drogue from its truss assembly mounting. Around 21:36 GMT Apollo will begin a series of complex manoeuvres to prepare for rendezvous with Soyuz at 121 km altitude at 15:52 GMT on 17 July.
By 17 July, the orbit of Soyuz will have decayed three kilometres from its circular 123 km orbit. Docking should occur at 16:15 GMT. The first transfer from one craft to another will begin when the Apollo astronauts pressurise the docking module to 34 kPa, then remove the CSM III command module hatch and stow it under a couch. They will then open the hatch at the Apollo end of the docking module, and two of them will enter the module, close the hatch behind them and re-pressurise the module to 69 kPa. The cosmonauts in Soyuz will then open the hatch at their end of the docking module and equalise the pressure. The Americans will then enter the Russian craft. The crews will adopt the reverse procedure when the Americans return to Apollo.
The two spacecraft will separate at about 16:35 GMT on 19 July after 48 hours and 20 minutes of joint activity. The Soyuz de-orbit burn is timed for 10:06 GMT on 21 July with landing at 12:51 GMT. In the meantime, Apollo will conduct an extensive programme of experiments before performing its de-orbit burn at 18:06 GMT on 27 July. Apollo will jettison the docking module five minutes later and CSM III will splash-down at 18:55 GMT. The Apollo flight will last for 11 days 23 hours and 5 minutes; it will be America’s 32 nd manned spaceflight and will also be its last, for the time being.
Radio enthusiasts may like to note that the following frequencies will be used during ASTP. Soyuz and the Russian ground stations will use VHF amplitude-modulated radios operating on the 121.75 MHz band. AST 6 satellite stations will relay 2256 MHz and 2077 MHz feeds from synchronous orbit, and this will improve voice and television coverage.
Source: Flight International .
Reports are coming in that the US Viking probe currently en route to Mars is suffering some technical difficulties with its soil analysis equipment. Strangely enough, the fault appears to have developed in the same region of space as many incidents involving Russian space probes.
According to a film produced by NASA and shown recently on The Sky At Night (BBC1) it is possible that a form of organic life might exist on Mars, so it will be interesting to see what results the Viking probe will achieve if it arrives on the planet with its equipment intact.
The biology experiments on Viking 1 have given ambiguous results. Upon wetting some Martian soil, a large volume of oxygen was released; however it is unclear whether this was of biological or chemical origin (peroxides locked in the soil). Scientists will not resolve the question definitively for some time, weeks, or maybe years. However, whatever the eventual conclusion, there is now known to be an abundant supply of oxygen locked in the Martian soil which could be used by colonists in future decades.
Viking 2 lands on Mars on 04 September 1976.
Source: New Scientist , 12 August 1976.
The Viking Mission To Mars
NASA has sent two automatic Viking probes to Mars. They have two main objectives:
- To search for evidence of life on Mars, either existing now or in former times.
- To obtain information that will improve mankind’s understanding of how planet Earth developed as a body able to support life, and how best to preserve and protect its environment.
If a Viking probe found evidence of life on Mars, that would be an incredible achievement in itself, butwould also mean that the chances of finding life among the 100,000,000,000 or so stars in our galaxy were also greatly increased.
The Viking spacecraft are designed to make three basic types of scientific study of Mars:
- The orbiting module of the Viking spacecraft will continue mapping Mars, supplementing the pictures taken by the earlier Mariner spacecraft. The orbiters will also undertake thermal mapping of the surface of Mars, to detect hot spots and cold spots and general heat-flow anomalies.
- The lander will search directly for life on Mars. The lander will also identify elements and compounds in the Martian soil.
- Both Viking spacecraft will obtain information about Mars’ physical features and the constituents of its atmosphere. The landers will determine whether Mars is geologically “active” by using seismometers to detect “Marsquakes”, if there are any. If the seismometers do detect “Marsquakes”, analysis of detailed recordings should enable scientists to deduce the internal structure of Mars and compare it with that of the Earth and Moon.
The Viking project is managed by NASA’s Langley Research Centre, Hampton, Virginia. The Martin Marietta Corporation designed and built the landers and the two Titan III launch vehicles. The Jet Propulsion Laboratory, California was responsible for building the orbiters and is now responsible for craft tracking and mission control. Eighty scientists in thirteen science teams are responsible for the science projects.
The Viking Landing Capsule (Lander) is a cuboid-shaped object with three protruding legs. Its main features are:
- The uppermost part, an S-band high-gain antenna.
- At the sides, two radio-isotope thermo-electric generators (RTGs) which together provide power for the craft’s scientific operations.
- Two cameras, each containing a slit and a moving mirror, and producing a strip picture of Mars as seen through the slit. The two cameras can be moved, so that it is possible to build up a picture of the Martian landscape as a set of contiguous strips.
- The all-important soil boom which has caused so much trouble on Viking 1 by twice jamming. (The boom is located close to the two cameras.) The boom extends, scoops a sample of Martian soil, retracts and deposits the soil into two soil-receiving funnels which lead to the crucial biology experiments package.
- Propellant tanks for the descent engines. These are located one each under the RTGs.
- The landing legs. Prior to landing, there was much controversy as to whether the Vikings would land on permafrost, sand or rock, as the surface upon which the spacecraft landed could mean the difference between a successful landing and a failed landing which damaged the craft.
The Orbiter is the larger of the two modules of the Viking spacecraft, attached by a truss to the lander. The orbiter is a larger version of the successful Mariner orbiter, and the lander separates from it prior to entry into the Martian atmosphere. The orbiter has a large surface of solar panels which supply 620 watts of electric power for its systems. It also has a large parabolic antenna which it keeps pointed towards Earth to provide communications with NASA’s worldwide Deep Space Network.
Recently, NASA rolled out the first Space Shuttle from the Palmdale facility in California. Gerald Ford named the first Shuttle Enterprise , after the Starship Enterprise in the TV series Star Trek . Enterprise is only one third of the height of a Saturn V, yet it represents a new stage in space techniques, rocketry and technology.
The Space Shuttle comprises the Orbiter, an external tank that contains the ascent propellant used by the Orbiter’s main engines, and the Solid Rocket Boosters (SRBs). The Orbiters and SRBs are reusable, whereas the external tank is expended on each mission.
A typical Space Shuttle mission proceeds as follows. The mission begins with the installation of the mission cargo into the Orbiter. The SRBs and the Orbiter’s main engines fire simultaneously at lift-off. The Shuttle jettisons the SRBs at an altitude of 50 km. The SRBs descend on parachutes and drop into the sea approximately 300 km from the launch site; they are subsequently recovered, re-conditioned, and re-used. After the Space Shuttle jettisons the SRBs and is set on the correct ascent path, it jettisons the external tank, which falls in either the Indian Ocean or South Pacific Ocean (depending on the launch site). The Orbiter then continues into orbit. It uses the Orbital Manoeuvring System (OMS) to attain the desired orbit and to undertake any required orbital manoeuvres (e.g. to approach a faulty satellite to undertake a repair). Once in orbit, as soon as the payload doors are open, the crew begins payload operations. When payload operations are complete, the crew initiates de-orbit manoeuvres and commences re-entry into the Earth’s atmosphere. The de-orbit trajectory enables the Orbiter, when it reaches low altitude, to glide to a landing much like conventional plane. NASA aims for a best turnaround time for the Orbiter of two weeks.
The current Orbiter vehicle is designed to carry a crew of seven into orbit (although the initial baseline crew is four) including scientific and technical personnel and payload specialists. While the Orbiter is in orbit, it is powered by rocket motors, with fuel tanks in the rear of the Orbiter. During atmospheric flight, the Orbiter is controlled and stabilised by the aerodynamic surfaces on its wings and the vertical stabiliser (tail fin).
An Orbiter on standby status can attain orbit within 24 hours of the decision to launch. An Orbiter can accommodate a maximum of 10 astronauts, so it is possible to launch a second Orbiter to rescue the crew of an Orbiter which becomes disabled while in orbit.