GAMMA RAY TELESCOPE

The payload on this flight was a gamma ray spark chamber experiment developed by the Max-Planck-Institut für Physik und Astrophysik, from Germany to observe low gamma rays from astronomical sources.

A schematic drawing of the instrument is shown at left. It consists of a wire spark chamber vessel sourrounded by an anticoincidence dome (A) which is triggered by a coincidence between thin (~ 2 mm) plastic scintillator counters (B) and Cerenkov counters (C). The scintillator (B) is embedded in the wire spark chamber.

That portion of the chamber situated above the scintillator (B) consisted of 13 plates (12 gaps) of 0.0114 cm thick tungsten with a repat separation of 12.4 mm, while the part situated below the scintillator (B) consisted of 4 gaps and did not contain any material apart from the wires. In this way, particle tracks can be recorded inside the volume of the telescope, but these particles are not absorbed or scattered in any material, apart from the 1.4 mm of the aluminum pressure vasel. This design feature increases the sensitivity of the instrument for low-energy gamma rays.

Each of the counters (B) and (C) was subdivided into 4 quadrants that could be operated as 4 independent parallel telescopes.

Each event recorded in the spark chamber was transmitted to the ground by a PCM-telemetry system. The data sent included the time of occurrence, which was obtained with an accuracy to within 0.1 msec by an on-board quartz-stabilized clock, as well housekeeping information. Once the data was received at the ground station, the time information was checked against the mark of the WWV time signal station, for double control.

The experiment was pointed by means of an equatorial mounting on the oriented gondola. The orientation was achieved by rotating the gondola against the balloon and by a flywheel stabilization based on magnetometer attitude measurements.

Balloon launched on: 7/13/1971 at 20:16 cdt
Launch site: Columbia Scientific Balloon Facility, Palestine, Texas, US  
Balloon launched by: National Center for Atmospheric Research (NCAR)
Balloon manufacturer/size/composition: Zero Pressure Balloon Winzen 30.500.000 cuft (0.6 mil.) 2 Cap. (0.7 Mil.) Stratofilm
Balloon serial number: Serial Nº 3
Flight identification number: 624P
End of flight (L for landing time, W for last contact, otherwise termination time): 7/14/1971
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): F 4 h 35 m
Landing site: Sierra Blanca, Texas, US
Payload weight: 1270 lbs.

This was the fourth flight of the instrument. It was launched from Palestine, Texas on July 23th, 1971. The objective of the flight was to measure x-rays in the 30-200 keV region and search
for gamma-rays from the Cygnus-Xl source and the Cygnus region.

Althought the flight was considered succesful, a reduced exposure time was obtained due to a longer ascent phase of the balloon (it was a night flight), and a partial failure of the
orientation system.

• NCAR Scientific Balloon Facility Annual Report, 1971 National Center for Atmospheric Research, February 1972
• Review of Recent Performance of Large Balloons and Balloons with Payloads in Excess of 3000 Pounds Proceedings, Seventh AFCRL Scientific Balloon Symposium, 1973