Purpose of the flight and payload description

The instrument launched in this flight was the second generation of a high sensitivity Nal/Csl phoswich X-ray telescope (area 1000 cm2) composed by two banks of five detectors each, collimated to a field of view of 5° x 5° FWHM.

Each detector consists of a Nal(TI) scintillator (5mm) and a Csl (Na) scintillator (50 mm) of area 100 cm2 viewed by a single 127 mm diameter photomultiplier and equipped with a graded shield collimator.

Non-X-ray background photons are rejected by requiring that only signals characteristic of Nal (and not Csl) -as revealed by the pulse shape- are accepted. This "phoswich" technique reduces the background at ceiling altitude by a factor 10 to 20. The detectors have good efficiency in 20-150 keV range. The two banks of detectors are mounted, one on each side of central column, on a platform steerable in both the azimuth and the zenith to track the X-ray sources as they move on the sky. An Am-241 radio-active source is used to periodically calibrate each detector. Signals from each detector, the telescope aspect and the house-keeping information are telemetered to ground. The arrival time of an X-ray photon can be determined with great accuracy. This high time resolution is especially valuable in search for short (millisecond) periodicities in the X-ray sources.

Details of the balloon flight

Balloon launched on: 3/24/1990 at N
Launch site: TIFR National Balloon Facility, Hyderabad, India  
Balloon launched by: National Balloon Facility, Tata Institute of Fundamental Research
Balloon manufacturer/size/composition: Zero Pressure Balloon Winzen Stratofilm (tow+main) 242.900 m3
Flight identification number: 406
End of flight (L for landing time, W for last contact, otherwise termination time): 3/24/1990
Landing site: Control instrumentation failure. Payload lost
Payload weight: 719 kgs
Overall weight: 1.205 kgs

Control instrumentation failure.

External references

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