Sep 20 1974
From The Space Library
20-23 September: Mariner 10 (launched 3 Nov. 1973) encountered the planet Mercury a second time, with its closest approach on 21 Sept. at 48 069 km. The objective of the second flyby was to extend photographic coverage of the sun side of Mercury. The spacecraft obtained some 500 TV science photos of Mercury, with 350 additional TV pictures to support an optical navigation experiment. Encounter TV pictures were transmitted in real time at the rate of 117.6 kilobits per second. New photo mosaics would correlate incoming and outgoing portions of Mercury photographed during the first encounter (25 March-5 April) and pro-vide additional views of the south polar area. In the two encounters, Mariner 10 had photographed 45% of Mercury's surface. Ultraviolet airglow scans were also made to obtain more information about Mercury's atmosphere.
The spacecraft did not pass through either sun or earth occultation, and communications with the Deep Space Network stations were uninterrupted. The second flyby was adjudged successful 3 Oct. A third flyby was planned for March 1975.
Preliminary results, presented at a 23 Sept. press briefing at Jet Propulsion Laboratory, indicated that scarps and evidence of volcanism observed on the first flyby were pervasive and not localized. The scabby hills detected on the first encounter in an area opposite the Caloris Basin did not reappear, suggesting that such terrain was peculiar to that site. (NASA MOR, 3 Oct 74; NASA Release 74-248; NASA proj off, interview, 30 June 75 ; Sullivan, NYT, 24 Sept 74)
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