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Aviation History
1969
1969 - 1586.PDF
Above, folded for mounting inside the Centaur heat-shield, the Mariner 6 spacecraft spreads its cruciform solar-cell array soon after separation from the Centaur stage. Right, the Mariner 6 and 7 spacecraft in the cruise configuration. Although similar to Mariner 4, the 1969 spacecraft lay be identified from the earlier Mars probe by the deletion of the four passive stabilisation vanes. The 7ft 4in mast acts as a wave guide for the low-gain omni-directional antenna, while the 40in dish is Earth- pointing for deep-space communications. The spacecraft spans 19ft, with the octagonal structure accounting for 4ft 6%in of this. Directly under this compartment is a scan platform in which the experiments can be slewed to track the planet without "losing" the Earth the basis for experiments in the two 1971 Mariner-Mars orbiters (which will circle the planet for a period of three months) and the two 1973 Viking spacecraft which will land instrumental packages. The l%9 flights will not establish the existence of biological activity on Mars but will assist in determining the suitability of the environment to support life. Two television cameras on each spacecraft (Mariner 4 had one) will photograph the disc and surface of the planet during the approach and flyby. While the best resolution obtainable from Earth-based studies is only about 100 miles (due to the great distance involved—Mars never comes closer than 36 mil lion miles to the Earth—and to atmospheric blurring) the resolution expected from the Mariner transmissions during approach and flyby—the latter at a minimum of about 2,000 miles—is 15 miles and 900ft respectively; the best resolution from the 21 Mariner 4 pictures was about two miles: Data-handling has been an area of intense development since START RECORDING SCIENCE AND TV \ CLOSEST APPROACH EQUATORIAL PASS the Mariner 4 flight and the two new spacecraft show sig nificant improvements in this area. The picture content is now 3.9 million bits/frame against 240,000 bits/frame for the 1965 mission. In order to return this in a reasonable time and avoid committing the nine deep space networks and. particu larly, the 210ft Mars antenna at Goldstone. for an excessive period, the basic data-transmission rate has been increased from 8J; bits/sec to 270 bits/sec. while there is an experimental ability to transmit 16,200 bits/sec in the vicinity of Mars. Whether or not the latter rate can be used will depend on the condition of the spacecraft after their five-month journeys, and also on the availability of the 210ft antenna. The programme is managed for NASA by the Jet Propulsion Laboratory and the total cost of the 1969 Mariner project is $148 million, of which $20 million is accounted for by the two Atlas Centaurs and launch facilities. To be continued NASA SELECTS VIKING SCIENCE TEAMS NASA has announced the selection of 38 scientists organised into eight teams to assist with the design and development of the soft-landing instrumented capsule for the two 1973 Viking flights to Mars. The final selection of the experiments for both the landing capsules and the orbiteTS which comprise the Viking spacecraft will be made in December, by which time the initial results of the 1969 Mariner flybys will be available. NASA's Langley Research Centre. Virginia, has overall project management for Viking and direct responsibility for the landing capsule, while the Jet Propulsion Laboratory, Pasadena, is responsible for the orbiter. The eight areas of investigation include active biology (an instrument capable of providing data which may be inter preted as verifying, or otherwise, biological activity): imagery (optical and thermal representation of the landing site using a landed camera system); surface sampler/pyrolysis/gas analysis (detection and investigation of organic compounds and water content, and composition of the atmosphere using a surface sampler/pyrolyser/gas analyser); entry science (derivation of atmospheric density and composition profiles by radio during the descent of the lander, using both direct and indirect measurement techniques); meteorology (investigation of meteorology from the lander capsule with direct-measure ment instruments and applicable data from engineering and housekeeping daita on the spacecraft); radio (the study of the planet and its atmosphere by radio techniques using a system on the entry and landed spacecraft); ultraviolet studies (using a lightweight two-channel photometer); and seismometry (the investigation of internal structure using a seismometer). Each Viking, including the orbiter and the lander modules. will weigh 6,0001b. The orbiters are understood to be similar to those which will be flown in the 1969 missions. The soft- landing spacecraft will weigh about 8001b and the instrument capsule about 1501b. The latter will place 301b-401b of experi ments on the surface and data from these will be transmitted to the orbiter for relay to Earth. By this means the landed telemetry system is kept as simple as possible, thus reducing the weight and complexity of the lander.
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