Purpose of the flight and payload description
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
Details of the balloon flight