Dec 15 1973
From The Space Library
December 15-20 NASA launched Explorer 51 (AE-C) Atmosphere Ex-plorer on a two-stage, thrust-augmented Thor-Delta launch vehicle from Western Test Range at 10:18 pm PST (1:18 am Dec. 16 EST) . The satellite entered an almost perfect elliptical orbit with a 4304-km (2674.4-mi) apogee, 157-km (97.6-mi) perigee, 132.5-min period, and 68.1° inclination. Explorer 51, third of five AE missions and first of second-generation AE spacecraft designed to extend the knowledge of energy absorption and photochemical processes of the atmosphere, would obtain data relating solar ultraviolet activity to atmospheric composition in the lower atmosphere, extending measurements down to altitudes where most solar extreme uv radiation was absorbed by the upper atmosphere. Onboard propulsion would vary perigee and apogee altitudes on command, permitting excursions into the largely unexplored region of the lower thermosphere.
By Dec. 19 command and telemetry systems were checked out, the memory of the onboard computer was loaded and read out, and the tape recorder, atmosphere density accelerometer, and cylindrical electro-static probe were switched on, All spacecraft systems were checked out by Dec. 20 and were functioning normally. Experiment instrumentation checkout would be completed by Dec. 31. The Explorer 51 mission would consist of two phases. During Phase 1, excursions would be made at two- to four-week intervals, each lasting several days. The spacecraft perigee would be lowered in steps through a range of 150 to 125 km (95 to 80 mi) . At each perigee step, telemetry data would be acquired. Phase 2 would begin after eight months and last four months; the spacecraft would be placed in a series of circular orbits ranging between 250 and 800 km (155 and 500 mi) in altitude. Explorer 51 carried 14 scientific instruments provided by a research team of scientists from nine institutions. In addition to the investigation of solar uv activity, the instrumentation would examine particle fluxes, airglow intensities, plasma densities, and temperatures and magnetic fields at low altitudes. To use the full spacecraft and instrument capabilities, a new rapid-response data system would provide data reduced to physical parameters, allowing the spacecraft to operate as a laboratory-in-space periodically reprogrammed to make optimum measurements in the light of interim results rather than gathering data in predetermined modes. Explorer 17 (launched April 2, 1963), the first AE satellite, had con-firmed that the earth was surrounded by a belt of neutral helium. The second, Explorer 32 (launched May 25, 1966), was placed in a higher orbit than planned but the higher altitude enhanced the resolution of the measured atmospheric parameters. The spacecraft continued to return useful data for 10 mos. The AE program was managed by Goddard Space Flight Center under the direction of the NASA Office of Space Science. (NASA prog off; NASA Release 73-269)
December 15: President Nixon issued Proclamation 4257 calling for nationwide observance of Wright Brothers Day Dec. 17: "It is both fitting and proper . . . , on this 70th anniversary of powered flight, that we should commemorate the achievements of two resourceful and farsighted men who have come to symbolize America's inventive genius." (PD, 12/17/73, 1462)
More than 100 Congressmen had endorsed legislation to start a $50-million, five-year program to find practical ways of harnessing solar energy to heat and cool U.S. buildings, according to an Associated Press report quoted in NASA Activities. Several senators planned to introduce identical and similar versions of the bill. House hearings would start in two weeks, and sponsors hoped Congress would pass the bill by early 1974. (NASA Activities, 12/15/73, 237)
President Nixon signed H.R. 11324 into law, placing the U.S. on daylight saving time for approximately two years beginning Jan. 6, 1974. The action was taken to alleviate the energy crisis. (PD, 12/17/73, 1462)
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