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Aviation History
1976
1976 - 3003.PDF
1786 OFF TO THE PLANETS for high-resolution views of selected regions. Resolution is normally about 0 • 1km when the' vehicles are near the lowest parts of their orbits, about 1,500km above the surface, but this will be improved to about 0 08km when the low points are dropped to 900km next year. Each orbiter can store about 100 pictures, and tape can accept television loads at the rate of 2,112,000 bits/sec, which can be transmitted at such a rate as to synthesise one picture every 4-48sec, compared with 42sec for Mariner 9. More than 8,000 pictures had been taken by early November, when the craft went on a six-week standby owing to inter ference from the Sun. If the craft remain operational until June 1978, Nasa expects to secure as many as 40,000 pictures. Demands for electrical power have increased to satisfy continually more ambitious flights. Mariner 4 had 194W available for its Mars fly-by in 1965, and Mariner 5 (Venus fly-by) two years later had 198W. Mariners 6 and 7 (Mars fly-by) called for 450W apiece and Mariner 10 (Venus/ Mercury fly-by) 540W. Mariner 9's greater capacity required 500W and the Viking orbiters each generate 620W. Total science data returned per mission has increased from 40 million bits (Mariner 4) to 54,000 million bits SUCCESSFUL LUNAR AND PLANETARY FLIGHTS Vehicle Country Luna 1 Pioneer 4 Luna 2 Luna 3 Mariner 2 Ranger 7 Mariner 4 Ranger 8 Ranger 9 Zond 3 Luna 9 Luna 10 Surveyor 1 Lunar Orbiter 1 Luna 11 Luna 12 Lunar Orbiter 2 Luna 13 Lunar Orbiter 3 Surveyor 3 Lunar Orbiter 4 Venus 4 Mariner 5 Explorer 35 Lunar Orbiter 5 Surveyor 5 Surveyor 6 Surveyor 7 Luna 14 Venus 5 Venus 6 Mariner 6 Mariner 7 Venus 7 Luna 16 Luna 17 Mars 2 Mars 3 Mariner 9 Luna 19 Luna 20 Pioneer 10 Venus 8 Luna 21 Pioneer 11 Explorer 49 Mars 5 Mariner 10 Luna 22 Venus 9 Venus 10 Viking 1 Viking 2 Luna 24 USSR US USSR USSR US US US US US USSR USSR USSR US US USSR USSR US USSR US US US USSR US us us us us us USSR USSR USSR US US USSR USSR USSR USSR USSR US USSR USSR US USSR USSR US US USSR US USSR USSR USSR US US USSR Launch date 2/1/59 3/3/59 12/9/59 4/10/59 27/8/62 28/7/64 28/11/64 17/2/65 21/3/65 18/7/65 31/1/66 31/3/66 30/5/66 10/8/66 24/8/66 22/10/66 6/11/66 21/12/66 5/2/67 17/4/67 4/5/67 12/6/67 14/6/67 19/7/67 2/8/67 8/9/67 7/11/67 7/1/68 7/4/68 5/1/69 10/1/69 24/2/69 27/3/69 17/8/70 12/9/70 10/10/70 19/5/71 28/5/71 30/5/71 28/9/71 14/2/72 3/3/72 27/3/72 8/1/73 6/4/73 10/6/73 26/7/73 3/11/73 29/5/74 8/6/75 14/6/75 22/8/75 9/9/75 9/8/76 Launch weight (lb) 796 ? 860 959 448 807 575 809 808 1,962 3,490 3,528 2,194 853 3,616 3,583 860 3,617 849 2,282 860 2,439 540 229 360 2,216 2,223 2,293 3,561 2,492 2,492 838 838 2,602 12,789 12,789 10,253 10,253 2,271 12,789 12,789 569 2,602 12,789 571 723 9,150, 1,111) 12,789' 11,025 11,025 7,585 7,585 12,789 Planet Moon Moon Moon Moon Venus Moon Mars Moon Moon Moon Moon Moon Moon Moon Moon Moon Moon Moon Moon Moon Moon Venus Venus Moon Moon Moon Moon Moon Moon Venus Venus Mars Mars Venus Moon Moon Mars Mars Mars Moon Moon Jupiter Venus Moon Jupiter Saturn Moon Mars Venus Mercury Moon Venus Venus Mars Mars Moon Mission Fly-by Fly-by Impact Fly-by Fly-by Impact Fly-by Impact Fly-by Fly-by Soft-land Orbiter Soft-land Orbiter Orbiter Orbiter Orbiter Soft-land Orbiter Soft-land Orbiter Probe Fly-by Orbiter Orbiter Soft-land Soft-land Soft-land Orbiter Probe Probe Fly-by Fly-by Probe-lander Sample return Roving vehicle Orbiter Probe Orbiter Orbiter Sample return Fly-by Probe-lander Roving vehicle Fly-by Fly-by Orbiter Orbiter Fly-by Fly-by (X 3) Orbiter Soft-land/Orbiter Soft-land/Orbiter Soft-land/Orbiter Soft-land/Orbiter Sample return FLIGHT International, 18 December 1976 (Mariner 9) between 1965 and 1972. Accumulated data from the four Viking spacecraft is expected to exceed this by a wide margin when operations cease, probably in June 1978. Scientific instruments and sensors have evolved along with spacecraft equipment, and a progression from fly-by to orbiter and subsequently lander missions has enabled the first "quick look" data to be increasingly refined and expanded. Apart from the single television camera, Mariner 4 carried equipment to measure inter planetary magnetic fields, solar particles and high-energy cosmic rays. Mariners 6 and 7 concentrated on the Mars environment, with an infra-red spectrometer for studying the composition and temperature of the atmosphere, ultra violet spectrometers for identifying gases in the upper atmosphere and infra-red radiometers for measuring surface temperatures. Mariner 9's task was to investigate atmospheric composition and temperature, surface con tours and temperatures, weather and cloud features. Viking studies atmospheric and surface pressures and temperatures, and measures the total water content in the atmosphere and the amount of water vapour near the surface which is capable of condensing out as water, frost or snow. The investigation of Venus has followed a slightly different path, with emphasis on the temperatures, pres sures and structure of the very thick, hot atmosphere. Television views of the surface from orbiting spacecraft are impossible due to the permanent blanket of cloud which obscures the entire planet. The 95-atmosphere, 590°C environment close to the surface poses great diffi culties to the designers of landing spacecraft, and the successful landing of Russia's Venus 9 and 10 capsules last year was a very fine achievement. The necessarily slow descent through the dense atmosphere, permitting a lengthy period for heat to reach the interior of the craft, called for extensive heat-shielding, which must have severely cut into the science payload. Techniques for the transmission of pictures from the surface through the atmosphere may find application in future attempts to probe the deeper layers of the atmosphere surrounding Jupiter. Target Jupiter While Mariners have successfully scanned the planets of the inner solar system, the increasing emphasis on outer-planet research has stimulated development of a new vehicle for fly-by missions to Jupiter and Saturn. This is Pioneer, latest in a line of successful Sun-orbiting probes which have contributed immense quantities of information about the solar wind and the environment of the inner solar system. Requirements for spacecraft visiting the outer planets are so different from those for missions to Mercury, Venus or Mars that a completely new approach is necessary. Photo-voltaic generation of electrical energy calls for impossibly large solar panels because the Sun's energy is so weak at these great distances. Instead, small nuclear generators must be used. Pioneer 10 and 11, the first emis saries to the middle realms of the solar system, each carried four 30W-40W generators fuelled with plutonium- 238, the heat from which was converted into electrical power by means of banks of thermocouples surrounding the fuel core. Carried on 6ft truss assemblies to isolate experiments from damaging heat and radiation, their radioisotope thermo-electric generators (RTGs) will continue to power these Pioneer craft out to the distance of Neptune (2,700 million miles from Earth or 30 astronomical units, 1 a.u. being the Earth-Sun separation). The attitude-control system also represents a major departure from Mariner design. Instead of locking on to Sun and star alignments Pioneer spins continually at 4-5 r.p.m. with the 9ft-diameter parabolic dish antenna pointing at Earth. Precession of the spin axis to maintain Earth lock is achieved by firing sets of attitude-control thrusters on the outer edge of the dish and these hydrazine jets are also used for course corrections. Communication power is 8W, permitting a data-rate of 1,024 bits/sec at the distance of Jupiter compared, for
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