Purpose of the flight and payload description
The GRIS instrument consists of an array of seven coaxial n-Type germanium detectors surrounded by a thick active NaI shield/collimator. Located above this assembly is an active NaI coded-aperture mask for imaging and precise source location. The seven germanium detectors are each enclosed in individual cryostats. This design (rather than a single large multi-detector cryostat) was chosen for two principal reasons: to minimize the internally produced background and for easier replacement of individual detectors, as well as upgrades and modifications.
The instrument is mounted in a gondola offering a conventional azimuth-over-elevation pointing system with a momentum wheel for azimuth control. Coarse pointing control used the earth's magnetic field as a reference. A CID camera was used to image star fields and the sun to obtain an independent and more accurate measure of the absolute pointing direction.
Details of the balloon flight
Balloon launched on: 5/31/1990 at 13:09 utc
Launch site: Scientific Flight Balloon Facility, Fort Sumner, (NM), US
Balloon launched by: National Scientific Balloon Facility (NSBF)
Balloon manufacturer/size/composition: Zero Pressure Balloon SF3-480.10-080-NSCHR-04
Balloon serial number: W39.96-3-02
Flight identification number: 289N
End of flight (L for landing time, W for last contact, otherwise termination time): 6/1/1990 at 15:54 utc
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 21 h
Landing site: 5 miles NE of Show Low, Arizona, US
Observations of SCO X-1, NGC 4151 and the Crab Nebula.