Description of the payload

Is an instrument developed for mapping of the far-infrared emission from the Galaxy and external galaxies with the same spatial resolution as that of the IRAS (Infrared Astronomical Satellite) launched on 1983.

It has a telescope with an off-axis parabola glass mirror of 50 cm diameter and a focal length of 1200 mm. The instrument is mounted on the direct focus of this mirror. There is no other un-cooled optics. In order to reduce the instrumental infrared radiation noise from the periphery of the mirror, a ring-shape reflector is attached to the mirror.

Also was developed a far-infrared array camera dedicated for FIRBE. The array has 4 x 8 pixels, and the pixel pitch is 1.5 arcmin. The array uses stressed Ge:Ga photoconductor elements and is installed in a helium cryostat together with a cold reimaging optics.

The gondola on wich the instrument is mounted combines several aluminum pipes and angles, so FIRBE could be lighten the weight of the main frame less than about 100 kg, which also leads to reduce the total weight.

The telescope is deriven by an alt-azimuthal mounting system, the attitude stability is less than 30 arcsec. The attitude during the flight is determined with the data of three-axes fiber-optic gyro assisted by the CCD star camera and derived by a reaction wheel in azimuth and by a drive mechanism of a geared motor in elevation.

Details of the balloon flight and scientific outcome

Launch site: Sanriku Balloon Center, Iwate, Japan  
Balloon launched by: Institute of Space and Astronautical Science (ISAS)
Balloon manufacturer/size/composition: Zero Pressure Balloon model B120 120.000 m3
Flight identification number: B120-3
Payload weight: 560 kgs

The balloon was launched from the Sanriku Balloon Center by vertical launch method on September 6th in 1998.

The launch smoothly advanced and the balloon reached without trouble the level-flight altitude near 37 km.

After a flight of 3 hours the balloon was terminated and the payload landed in the sea, from were was recovered.

The objective of this first technological flight was to test the instrument behavior. All operations necessary for remote control the balloon-borne telescope such as data transmission, command decoding, acquisition the observational data, and attitude control were executed.

However, since after a while a failure occurred in the power supply for the readout circuit of the detector, the flight was terminated.

External references and bibliographical sources