* Mission Overview

The spin stabilized satellite Radsat was launched by the US Air Force on 2 October 1972 into a noon-midnight, Sun-synchronous orbit. The satellite is sometimes referred to as 1972-076B (its international launch number) or P72-1. The inclination was 98.4 degrees; the apogee and perigee were 761 and 736 km, respectively. The cylindrical spacecraft was 2.13 m long and 1.37 m in diameter. Antenna booms extended 2.74 m from each end, coincident with the spin axis. The orbital period was 99.5 minutes, and the spin period was 5 s. The satellite carried 5 instruments: a gamma-ray spectrometer, an extreme ultraviolet detector, 2 low-altitude particle detectors, and a thermocontrol coating test instrument. The satellite is not expected to decay into the atmosphere until the year 2012. The gamma-ray instrument, however, ceased function after ~7 months.

* Instrumentation

The gamma-ray detector was a 50 cubic-cm Ge(Li) spectrometer with an active area of 15 sq-cm. It was cooled by solid CO2. The detector was surrounded by a W collimator and a stainless steel tungsten rear shield, which was in turn surrounded by a 4-pi anticoincidence plastic scintillator. The detector covered the energy range 40 keV - 2.8 MeV, with 4096 channels. The maximum resolution was ~ 4 keV (FWHM) at all energies. However, this resolution was short-lived, and during most of the lifetime of the experiment the resolution was between 10 - 50 keV. Data were accumulated in 1-ms time bins during a burst. This instrument represented the first high-resolution germanium spectrometer flown on a satellite.

diagram of Radsat's instrument

* Science

Several gamma-ray bursts which were also seen by the Vela satellites were seen by Radsat. A ~60-ms microburst was seen prior to the Vela trigger time for the 18 December 1972 event. Furthermore, the spectrum was seen to soften in this event at later times.

*Other information

  • Imhof et al, 1974, Ap J Lett, 191, L7-L10.
  • Imhof et al., 1975, Ap J, 198, pp. 717-725.
  • E.L. Chupp, Gamma-Ray Astronomy, pp. 238-242.
  • The RAE Table of Earth Satellites 1957-1982.

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