Mar 24 1975
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Radio transmissions from Mariner 10 ceased after attitude control gas was depleted and flight controllers at Jet Propulsion Laboratory sent the command for the spacecraft to stop operations at 8:20 am EDT. Before shutdown, spacecraft engineering tests were conducted to try to open the stuck door on the plasma science experiment, rotate the solar panels to various positions, stow the scan platform at 180°, operate the stuck tape recorder, and provide data for future spacecraft design.
During its more than 16 mo in heliocentric orbit, Mariner 10 (launched 3 Nov. 1973) had traveled more than 1.6 billion km and made four planetary encounters, one of Venus and three of Mercury. It had passed within 5800 km of Venus 5 Feb. 1974, and transmitted to earth the first closeup photographs ever taken of the cloud-shrouded planet.
Mariner 10 had confirmed the high-speed circulation of Venus' upper atmosphere and revealed circulation patterns that swirled from the equator toward the poles. It had also revealed along tail of charged particles trailing behind the planet and away from the sun; verified the presence of a bow shock wave created by the solar wind acting upon the dense atmosphere; detected hydrogen, helium, and argon in the Venusian atmosphere; and discovered temperature-inversion zones suggestive of deeper stratiform cloud layers.
First spacecraft to use the technique, Mariner 10 used the gravity of Venus to speed it on toward Mercury. The probe flew by that planet three times, on 29 March and 21 Sept. 1974 and 16 March 1975. At Mercury, Mariner 10 photographed a highly cratered lunar-like surface with large scarps hundreds of kilometers long and over 1.6 kilometers high. Mariner 10 data also revealed the existence of a chemically differentiated light crust, lunar-like near the surface and earth-like at its interior, and an unexpected magnetic field 100 times smaller than earth's. A slight but measurable atmosphere was found, in addition to streams of high-energy electrons and protons on the planet's dark side. On' its last encounter with Mercury [see 16 March] Mariner 10 came within 327 km of Mercury to take the closest photographs ever made of another primary planet. (NASA MOR, 7 April 75 NASA Activities, April 75, 12-13; NASA Release 75-59; A&A 1974)
The Saturn IB scheduled to launch the Apollo spacecraft for the Apollo Soyuz Test Project in June left the Vehicle Assembly Building on its crawler to begin the 5-km journey to Launch Complex 39 Pad B. Witnessed by 6000 people, the rollout was completed at 3:15 pm, followed by a ceremony attended by the ASTP astronauts and KSC Deputy Director Miles Ross commemorating this as the last Saturn IB and Apollo rollout. Then the slow journey was resumed. (NASA PAO audio news service, 24 March 75; KSC Release 48-75)
Assembly of the first main engine of the Space Shuttle had been completed by Rockwell International Corp.'s Rocketdyne Div. I mo ahead of schedule, NASA announced. After assembly the engine was automatically checked out-for the first time in history-by the engine's internal controller and integral digital computers for functional, electrical, and mechanical operations. Known as the Integrated Subsystems Test Bed, this engine was not built for flight but for static firing tests at the National Space Technology Laboratories.
The Space Shuttle would use 3 of the liquid-hydrogen/liquid-oxygen engines. Designed to perform at high internal pressures for greater specific impulse, each engine would produce more than 2.1 million newtons thrust and would be used for up to 55 missions before overhaul, with between-mission maintenance comparable to techniques used by commercial airlines. (NASA Release 75-83; Rocketdyne Release RD-7)
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