OPALE - GAMMA RAY TELESCOPE

OPALE was a balloon-borne gamma-ray telescope designed to study low-energy gamma-ray emission sources, as well as to measure the diffuse component of cosmic radiation from the Galaxy's diffuse emission in the 60 keV-10 MeV energy range. The instrument was developed in 1973 at the Centre d'Etudes Spatiale des Rayonnements (CESR) of Toulouse, France and was a sophisticated instrument for its time, emphasizing active shielding, thermal stability, and a robust control system.

In the image at left we can see a picture of OPALE before a flight (click for more details of the detector).

The main detector consisted of a CsI(Tl) crystal, 10 cm in diameter and 2.5 cm thick, coupled with an NE 102 scintillator of the same diameter but 1 cm thick. The assembly was enclosed in a 0.02 cm thick aluminum housing with anti-magnetic shielding made of Netic and Conetic materials. A Radiotechnique RTC2030 photomultiplier processed the detector signals while pulse shape discrimination circuits separated signals from plastic scintillation and CsI scintillation.

For the active shielding OPALE employed a NaI(Tl) structure to reduce atmospheric gamma-ray background. The shielding was an annular ring, 5 cm thick and 8.5 cm high, with additional plates (discs) closing the ends. It also included a lead disk for extra protection and a thin plastic scintillator to detect charged particles via anti-coincidence signals. A shutter mechanism with two half-cylinders alternately blocked and exposed the detector to sources, enabling background and source measurements in 10-minute cycles.

OPALE used layers of aluminized Mylar and polyurethane foam for insulation. Aditionally, a 105 W heating resistor maintained a stable operating temperature (20-22°C) during the flight in the stratosphere. The electronics processed detector data, providing anti-coincidence signals, digitized pulse heights, and housekeeping metrics (e.g., temperatures, voltages). Also was included a telemetry and command system for transmitting data and commands between the gondola and the ground station.

The telescope was mounted on an equatorial platform stabilized using the Earth's magnetic field. Pointing was refined by a solar tracking system for precise alignment with celestial sources.

Balloon launched on: 2/9/1977 at 6:09 UTC
Launch site: Guaratinguetá Air Base, Sao Paulo, Brazil  
Balloon launched by: Centre National d'Etudes Spatiales (CNES)
Balloon manufacturer/size/composition: Zero Pressure Balloon model 350sf Zodiac - 350.000 m3
End of flight (L for landing time, W for last contact, otherwise termination time): 2/9/1977 at ~ 11:00 UTC
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 5 h
Landing site: In Paraguacu Paulista, Sao Paulo, Brazil

• A infraestrutura do INPE para lancar balao cientifico Elisete Rinke dos Santos, editorial Transtec, 1993