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Radsat
The pin 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 gamma-ray instrument ceased function after ~7 months.
Mission Characteristics
| Lifetime | Oct 1972–May 1973 (gamma-ray instrument) |
| Special Features | First high-resolution germanium detector flown on a satellite |
Payload
| Instrument | Characteristic | Details |
|---|---|---|
| gamma-ray detector | Energy Range | 40 keV – 2.8 MeV |
| Effective Area | 15 cm2 | |
| Energy Resolution | ∼ 4 keV (FWHM) initially, 10–50 keV thereafter | |
| Time Resolution | 1 ms (burst) | |
| The gamma-ray detector was a 50 cm3 Ge(Li) spectrometer 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 4π anti-coincidence 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.
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gamma-ray detector
Science Highlights
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.
Publications
- 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 1957–1986