May 7 1975
From The Space Library
An Italian launch crew launched Explorer 53 (SAS-C) Small Astronomy Satellite for NASA from San Marco launch platform, located in the Indian Ocean off the coast of Kenya, at 6:45 pm EDT (1:45 am local time 8 May) on a Scout launch vehicle. The spacecraft entered near-equatorial orbit with a 523.35-km apogee, 502.18-km perigee, 94.88-min period, and 2.995° inclination.
Primary objectives of the Explorer 53 mission were to measure the x-ray emission of discrete extragalactic sources, to monitor the intensity and spectra of galactic x-ray sources from 1.0 kev to 50 kev, and to monitor the x-ray intensity of the star Sco X-1.
During a preliminary in-orbit checkout, controllers noticed that a stuck nutation damper was causing the spacecraft nutation, or coning, angle to be 4° rather than the planned 0.2°. Energizing the z-axis coil reduced the coning angle to 0.5°. Although the damper could not be freed despite repeated attempts, the nutation could be kept within reasonable limits so that scientific objectives could be achieved. A committee would evaluate the problem.
Other spacecraft anomalies included intermittent operation of the spinning digital solar-aspect detector, and irregular and noisy operation of the spacecraft star sensor. Neither problem was expected to seriously degrade the mission.
The 195-kg satellite was designed to extend and complement the capabilities of Explorer 42 (Uhuru, launched 12 Dec. 1970 as the first satellite dedicated entirely to the study of x-ray sources in space) and Explorer 48 (launched 16 Nov. 1970 to study galactic and extragalactic gamma radiation). Explorer 53, with its broad spectral range, provided higher energy resolution than previous satellites and permitted a study of physical conditions near an x-ray source. The spacecraft's quasi-three-axis stabilization system allowed much longer continuous observation of sources. Data from Explorer 53 would provide the basis for the more detailed x-ray studies to be made by High Energy Astronomy Observatories A and B scheduled for launch in 1977 and 1978.
The experiment aboard Explorer 53 was designed and built by the Center for Space Research of the Massachusetts Institute of Technology. The spacecraft control section was designed by the Applied Physics Laboratory of the Johns Hopkins Univ. Goddard Space Flight Center managed the program for the Office of Space Science. Langley Research Center was responsible for the Scout launch vehicle. Italy was responsible for the assembly, checkout, and launch of the Scout on a cost-reimbursable basis. (NASA MORs 6 May 75, 15 May 75; NASA Releases 75-101, 75-121)
Canada's Anik 3 (Telesat-3) domestic communications satellite was launched by NASA at 7:35 pin EDT from Eastern Test Range on a three stage thrust-augmented Thor-Delta launch vehicle. Originally scheduled for March, the launch had been postponed because of a strike by McDonnell Douglas Corp. workers [see 10 Feb.]. The satellite was placed in the planned highly elliptical transfer orbit with a 35 945-km apogee, 231.4-km perigee, 634.3-min period, and 24.75° inclination. Ground control fired the spacecraft's apogee kick motor at 1:30 pin EDT on 10 May, circularizing the geosynchronous orbit at 38 000 km; the spacecraft was drifting toward its final operational location at approximately 104° west longitude.
Anik (Eskimo word for brother) 3 was third in a series of Canadian domestic comsats; Anik 1 (launched 9 Nov. 1972) and Anik 2 (launched 20 April 1973) were operating at 114° and 109° west longitude, providing TV and telephone service to the most remote areas of Canada. Built by Hughes Aircraft Co., Anik 3 was 1.8 m in diameter and 3.3 m high, weighing 544 kg at launch and 272 kg in orbit. With power from 23 000 solar cells and enough battery capacity to maintain full service during a solar eclipse. Anik had 13 channels that could transmit up to 10 color TV transmissions or 9600 telephone circuits or analog or digital data.
The NASA-Telesat Canada contract defined the NASA mission objective as the placement of the satellite in a synchronous transfer orbit of sufficient accuracy to allow onboard propulsion systems to place the spacecraft into a stationary orbit with enough residual station keeping propulsion to meet mission-lifetime requirements. This objective was met and the mission was adjudged successful on 20 May.
NASA would be reimbursed for launch hardware, services, and DOD range support. The project was managed by Goddard Space Flight Center under the direction of the NASA Office of Space Science. (NASA MORs, 25 April 75, 20 May 75; GSFC Wkly SSR, 1-7 May 75; NASA Releases 75-113, 75-131)
NASA, in cooperation with the Dept. of Transportation, was investigating aircraft wake vortices-turbulent air trailing from an aircraft's wingtips and swirling at velocities up to half the flight speed of the aircraft.
Safety required an aircraft to travel far enough behind a preceding airplane to permit the vortices to dissipate, adding to congestion at already busy airports. NASA's objective was to develop methods to reduce the intensity of the vortices and render them harmless 3 km behind the aircraft. This would decrease the amount of fuel wasted and the pollution produced when aircraft were subjected to holding patterns and waits to taxi to a runway, and would permit aircraft to land and take off at a faster rate.
Engineers and scientists at Ames and Flight Research Centers were investigating the vortices by flying an instrumented Learjet and a T-37 jet trainer through wakes created by larger aircraft. Data collected during these flights, checked against wind-tunnel data, suggested several possible ways of alleviating the wake-vortex problem, including tailoring the lift across the aircraft wings, modifying engine placement, and adding wing spoilers and drag devices. (NASA Release 75-136)
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