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Aviation History
1969
1969 - 1705.PDF
458 fUGHT International, 20 March 1969 to the five sites, selected from Lunar Orbiter photographs, along the Moon's equator. After the critical rendezvous and docking manoeuvre on March 6 (see Flight last week) the further tests in Earth orbit of the command and service modules seemed tame by com parison. But these were very important and, in any case, a full ten-day flight gives valuable statistical experience. In fact the exercise scheduled for the latter half of the mission was a simulated return flight from the Moon. The main activities for this period included exercises in landmark tracking and space craft systems, and multi-spectral ground photography for Earth- resources studies. Almost no problems were encountered. One source of worry—the clouding of the windows—has apparently been licked, hopefully for all time. The recovery of the three Apollo 9 astronauts—McDivitt, Schweickart and Scott—provided a classical comedy touch. In the top scene, Scott sprawls headlong into the life raft, followed (centre picture) equally ungracefully by Schweickart. Finally, urged on by the downwosh from a helicopter, a liferaft is upended Mariners to Mars (continued from page 437) It is just possible that the enigmatic Phobos, the innermost of Mars' two satellites, may appear in one of the approach photographs, although the conditions necessary for the best views would have added to the already long list of fly-by constraints and no special effort will be made to detect it. Both cameras will be used during the fly-by to photograph the surface. Each camera will take one picture every 84.48sec. in a series of 24 close-up photographs at ranges of between 6.000 and 2,000 miles. They will be operated alternately so that the overlapping of the wide- and narrow-angle pictures will allow both interpretation of the photograph and location of the areas on the planet to be made. The trajectories of the two spacecraft have been chosen so that the close-up photographs will cover as many as possible of the various types of feature observed. These include the permanent dark markings, oases, "blue" maria, canals, polar caps, "wave of darkening," white markings on crater rims (discovered in the Mariner 4 pictures) and circular light areas which vary in colour. The intra-red spectrometer will ascertain, or otherwise, the presence (in the lower levels of the atmosphere) of molecules which suggest that biochemical activities may be taking place, or which may affect the surface temperature and limit the amount of ultra-violet reaching the surface, or which may detect variations in the composition of the atmosphere related to specific surface details. Specifically the instrument can detect the presence of water, carbon dioxide, methane, ethylene, acetylene and a number of other molecules. The presence of sulphur dioxide and hydrogen sulphide might indicate recent volcanic activity. By contrast the ultra-violet spectrometer will identify gases in the upper atmosphere of Mars. This experiment may be able to determine whether the atmosphere is the result of the condensation of solar material (i.e., if it is of primordial origin) or whether it was formed by the outgassing of rocks. Ultra violet studies of Mars are not possible on Earth because these wavelengths are absorbed in the Earth's atmosphere, and UV experiments have been flown only briefly on sounding rockets. The infra-red radiometer will provide surface temperature data from which a thermal map may be prepared. The instrument is boresighted with the TV cameras to allow correlation of surface temperatures with clouds and ground features. It is expected that this experiment will help to clear up the uncertainty concerning the composition of the southern ice cap. Tt may also determine whether the white rims seen on craters in the Mariner 4 photographs are due to carbon dioxide or water ice. The S-band occulation experiment was first performed at Mars by Mariner 4. from which new values of atmospheric pressure, density and electron density were derived. In particular it is now thought that the surface pressure may be as low as 9mb—less than one per cent of that at the surface of the Earth. This particular measurement is not just of academic interest; at these low pressures the deposition of landing payloads by parachute is uncertain and retro-rockets have to be provided. The 1969 experiment will refine the 1965 data and will in addition enable precise measurements of the radius of Mars to be made (the currently accepted value is 2,120 miles). The experiment uses radio signals transmitted from the spacecraft and does not require special on-board equipment. As the spacecraft moves behind the planet, the frequency and strength of radio signals vary with the increasing depth of atmosphere through which they pass, the changes being directly related to characteristics of the atmosphere. Finally the celestial mechanics experiment also uses radio equipment which is part of the standard on-board system. By accurately tracking the spacecraft in the vicinity of the planet a better value of the mass of Mars may be derived. The immediate object also includes a better determination of the Earth-Moon mass ratio, and the distance from the Earth to Mars at encounter. The long-range objectives are to give a better ephemeris (predicted future positions) and an attempt to measure general relativity effects on the solar orbit of the 1969 Mariners.
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