Purpose of the flight and payload description
The aim of the XGAP Experiment was to obtain simultaneous measurements of variations in the terrestrial magnetic field and the intensity of atmospheric photons (20 KeV - 10.0 MeV) in the South Atlantic Magnetic Anomaly. Three flights were performed in 1978 during periods with little magnetic activity in combination with passages of artificial satellites electron detectors on board above the Anomaly. The project was carried out by the Department of Astrophysics of the Instituto Nacional de Pesquisas Espaciais (INPE) from Brazil.
The payload consisted of two omnidirectional detection systems located in the same gondola, one for x-ray and the other for gamma rays, with their associated electronics, on-board telemetry, and precision and temperature sensors. X-ray and gamma detectors used 3" x 1/2" and 4" x 4" NaI(T1) scintillator crystals. The 4" x 4" NaI(T1) crystal worked in anti-coincidence with a 2 cm thick plastic scintillator shield. The detectors were calibrated to measure X and gamma radiation in the ranges 20-400 KeV and 0.3-10.0 MeV respectively. The accepted events were pulse height analyzed by a 256 channel encoder. The data along with other scientific parameters (pressure, temperature etc.) were transmitted to ground via FM/FM telemetry. The data received through telemetry were recorded on magnetic tapes and on paper using a multichannel printer for subsequent analysis.
All the equipment was installed in an aluminum gondola, cylindrical in shape, 1.5 meters high and 0.5 m radius. A 10 cm thick styrofoam outer box, coated with 1 mm thick aluminum foil, guaranteed thermal protection for the equipment during flight.
Details of the balloon flight
Balloon launched on: 12/15/1978 at 7:43 utc
Launch site: National Institute of Space Research, Sao Jose dos Campos, Sao Paulo, Brazil
Balloon launched by: Instituto Nacional de Pesquisas Espaciais (INPE)
Balloon manufacturer/size/composition: Zero Pressure Balloon model 7PRP25 87.000 m3
End of flight (L for landing time, W for last contact, otherwise termination time): 12/15/1978 at 16:00 utc
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 8 h
Landing site: Separation mechanism failure. Payload lost.
Payload weight: 122 kgs
The balloon was lauched at 7.43 UTC and reached a ceiling of 5.4 g/cm2 at 09:32 UTC. The flight was terminated by a mechanical device at about 16:00 UTC. The electronics functioned well during all the flight. The pressure sensors showed that the float altitude remained constant at about 5.2 g/cm2 till about 15:00 UTC. The latitude variation of the flight was smooth and very small, being between -22.9º and 23.1º degrees.