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SAS-2
SAS-2 (also refered to as SAS-B and Explorer 48) was launched on 19 November
1972. To minimize the background flux from cosmic-rays, SAS-2 was placed in a
low Earth equatorial orbit having a 2 degree orbital inclination. Its apogee
and perigee were 610 km and 440 km respectively, with an orbital period of
about 95 minutes.
During the ~6 months of the mission, 27 pointed observations (typically a week
in duration) were made, resulting in about 55 percent of the sky being
observed, including most of the galactic plane.
On 1973 June 8, a failure of the low-voltage power supply ended the collection
of data.
The SAS-2 satellite carried a single instrument: a gamma-ray telescope that
used a 32-level wire spark-chamber. The telescope covered the energy range
20 MeV - 1 GeV. The instrument was the work of Fichtel et. al. at
NASA-GSFC. During the short lifetime of the mission, there was some noticeable
decrease in sensitivity due to deterioration of the spark-chamber gas.
An extensive calibration program was carried out on the gamma-ray telescope
before SAS-2 was launched. The National Bureau of Standards (NBS) Synchrotron
accelerator in Gaithersburg, Maryland was used to study the performance of the
telescope in the 20 - 114 MeV range. The performance between 200 - 1000 MeV
was studied at the Deutsches Elektronen-Synchrotron (DESY) accelerator in
Hamburg, West Germany.
It is generally acknowledged that SAS-2 provided the first detailed
information about the gamma-ray sky and demonstrated the ultimate promise of
gamma-ray astronomy.
SAS-2 revealed that the galactic plane gamma-radiation was strongly
correlated with galactic structural features, especially when the known
strong discrete sources of gamma-radiation were subtracted from the total
observed radiation. The SAS-2 results clearly established a high energy
(> 35 MeV) component to the diffuse celestial radiation. High-energy
gamma-ray emission was also seen from discrete sources such as the Crab and
Vela pulsars.
[SAS-2 Home]
[About SAS-2]
[Archive]
[Gallery]
[Publications]
Page authors: Lorella Angelini Jesse Allen
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Last modified: Wednesday, 08-Oct-2003 18:59:46 EDT
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