Satellite Systems

SATELLITE SYSTEMS

Indian satellite systems fall into two categories; Remote-Sensing & Communications. The main programs being;

The Rohini series of satellites were designed and built for Indian scientific programs. Four satellite were launched in the the Rohini series; Rohini-1A, -1B, -2 and -3. The Rohini-1B was also the first Indian satellite launched by an Indian rocket.

Rohini 1B: Launched on 18 July 1980 from Sriharikota aboard the SLV-3. It's weight was 35kg and the orbit was 305x919km, 44.7°. It was India's first successful launch. This experimental satellite followed the failure of the Rohini-1A on 10 August 1979. Re-entered orbit on 20 May 1981.

Rohini 2: Launched on 31 May 1981 by SLV-3 from Sriharikota. It had a weight of 38kg and carried an imaging system. However the orbit achieved was 186x418km instead of the planned 296x834km, leading to re-entry after eight days.

Rohini 3: Launched on 17 April 1983 from Sriharikota aboard the SLV-3. It's weight was 41.5kg and its orbit was 371x861km, 46.6°. Carried two cameras and L-band beacon. This satellite returned around 5000 earth images before being de-activated on 24 September 1984. It re-entered orbit on 19 April 1990.

SROSS - Stretched Rohini Satellite Series

ISRO developed the Stretched Rohini Satellite Series (SROSS) for conducting various scientific experiments as well as for new and novel application-oriented missions. The first two satellites in the series did not make it into orbit due to launch vehicle failure. The third, SROSS-3, successfully attained an orbit on 20 May 1992. Although they decayed rapidly, the orbital parameters were initially; apogee was 430km, perigee was 255km, and the orbital inclination was 46º. The satellite spin period was 10.6 sec. The satellite carried a gamma-ray burst (GRB) experiment and a retarded potential analyzer (RPA) payload. It re-entered orbit on 14 July 1992.

Instrumentation: The gamma-ray burst experiment was operated from 25 May 1992 until re-entry on 14 July 1992. The instrument consisted of a main and a redundant CsI(Na) scintillator operating in the energy range 20-3000 keV. The crystals were 76mm (main) and 37mm (redundant) in diameter. Each had a thickness of 12.5mm. A 'burst mode' was triggered by the 100-1024 keV count rate exceeding a preset limit during a 256 or 1024 milliseconds time integration. In this mode, 65 seconds of temporal and 2 seconds of spectral data prior to the trigger are stored, as well as the subsequent 16 seconds of spectral data and 204 seconds of temporal data.

The low resolution data consists of two energy channels (20-100 keV and 100-1024 keV) from 65 seconds before the trigger to 204 seconds after the trigger in 256 milliseconds integrations. The 20-1024 keV rates are also recorded with a two milliseconds resolution for one second, prior to a one second after trigger and a 16 milliseconds resolution for one second prior to 8 second after the trigger. Energy spectra are conducted with a 124 channel PHA. Four pre-trigger spectra and 32 post-trigger spectra are recorded for every burst with a 512 milliseconds integration time.

Science: During the mission lifetime, 53 triggers occurred. Most of these, as expected, were false. There were eight candidates for real bursts. One event, on 22 of June was also seen by CGRO and is believed real. Two other events could be real, as CGRO was not recording data at the time and so could not corroborate their occurrence.