DOUBLE FAR-INFRARED TELESCOPE

The payload was composed by two 20 cm off-axis parabolic reflective telescopes feeding two photometers. The photometers consisted of multiple reststrahlen reflection filters operating at pumped liquid helium temperature, followed by Gallium doped Germanium bolometers. Two filter-detector combinations were located at the bottom plate of a helium dewar. At left we can see a bottom view of the two reflection filter photometers.

Both telescopes were mounted vertically in a balloon gondola looking outward via a rocking flat. A ten degrees rocking motion of the flat mirror around a horizontal axis allowed to scan the sky in elevation, while the gondola was magnetically oriented in the southern direction. The sidereal motion leaded to a series of drifts scans at different elevations. A command system allowed for an offset of the magnetic sensor in both directions, thus allowing repeated observations of the same celestial area during a single flight. The telescopes were field stopped to approximately 0º.2 by diaphragms at pumped liquid helium temperatures. The optical design was such that at only some 15 cm effective diameter of each of the telescopes was used to avoid contribution to background radiation arising from high emissivity mounting surfaces.

The gondola was stabilized by applying a torque on the suspension cord. A fluxgate magnetometer was used as the primary sensor

Balloon launched on: 6/10/1971
Launch site: Aérodrome de Gap-Tallard, Haute Alpes, France  
Balloon launched by: Centre National d'Etudes Spatiales (CNES)
Balloon manufacturer/size/composition: Zero Pressure Balloon  
End of flight (L for landing time, W for last contact, otherwise termination time): ??/??/1971

Althought the paper mentions that the balloon was launched in France by CNES, the information regarding the exact launch site is incomplete. Our best guess based on the time of the year of the mission is that it was launched from the Gap-Tallard aerodrome, in the Alps, which was the alternative site used during the summer months.

• Far infrared observations of the galactic center region Les spectres des astres dans l'infrarouge et les microondes, p. 597