A setback to ISRO

The loss of INSAT-2D will slow down the communication revolution that was brought about by the first and second generation INSATs.

T.S. SUBRAMANIAN

THE loss on October 4 of INSAT-2D (INSAT is an acronym for Indian National Satellite), the indigenously built communication spacecraft, has come as an unexpected blow to the Indian Space Research Organisation (ISRO). The loss of INSAT-2D will slow down the communication revolution that was brought about in India by the deployment of the first and second generation INSATs - the INSAT-1 and INSAT-2 series, which comprised eight spacecraft.

INSAT-2D is the third INSAT that has had to be abandoned. INSAT-2D, weighing about 2,500 kg, was built and launched at a cost of Rs. 300 crores. The recent setback to ISRO comes at a time when its engineers have succeeded in raising the perigee of the Indian Remote-sensing Satellite (IRS-1D) that was injected into a lower elliptical orbit (instead of the planned circular orbit) by the Polar Satellite Launch Vehicle (PSLV-C1) on September 29.

INSAT-2D had been in space for exactly four months before it was abandoned. It was built by the ISRO Satellite Centre (ISAC), Bangalore. It was launched on June 4 by the Ariane rocket of Arianespace organisation from Kourou island in French Guyana and deployed in a geosynchronous orbit at a height of about 36,000 km above the earth. At that altitude, satellites move at the same speed as the earth's rotation. Because of this, they appear to be stationary over the same place above the earth and for that reason are called geostationary satellites. These satellites help beam television and radio programmes, transmit telephone calls and take weather pictures. They also function as navigational aids for ships and aircraft.

INSAT-2D had 23 transponders that were meant to be used to relay telephone calls and beam radio and television signals. Of these, only seven had been switched on when the mishap occurred on October 1. At 10 p.m. on October 1, INSAT-2D lost the earth lock because of a short circuit in one of its two power lines (or power "buses"). These lines supply electricity from the solar panels and batteries to the satellite systems. If the satellite's antenna does not point towards the earth, it is not possible to use its transponders for communication. The satellite then loses its earth lock.

After INSAT-2D lost the earth lock, scientists at ISRO's Master Control Facility (MCF) at Hassan in Karnataka switched off its transponders. One of the scientists said that the cause of the short circuit in the power line was not known and had to be investigated.

Scientists' hopes rose when the satellite regained the earth lock on October 2. Three transponders were switched on. However, ISRO personnel were fully aware of the gravity of the problem. One of the scientists said that it was a "fairly serious problem" even though three transponders had been switched on. The scientists were to have watched the behaviour of the satellite over the next few days and then taken a decision on whether any more transponders can be switched on. However, on October 4, the satellite lost the earth lock again and became inoperable.

With the loss of INSAT-2D, trading in the National Stock Exchange (NSE) has been seriously affected. The NSE declared a closure from October 3. The NSE depends heavily on the Very Small Aperture Terminals (VSATs) - very small antennae that transmit information via INSAT-2D. The NSE has 1,600 VSAT networks all over the country. Of these, 779 were hooked to INSAT-2D. After the loss of INSAT-2D, the NSE set about shifting the 779 VSATs to INSAT-2A.

According to ISRO officials, the loss of INSAT-2D will not affect the functioning of Doordarshan, All India Radio and the Railways, since they had not yet started using INSAT-2D transponders. ISRO scientists pointed out that only seven transponders had been switched on when the mishap occurred. INSAT-2D did not have a meteorological payload, that is, it was not transmitting weather pictures. (While INSAT-2A and 2B had meteorological payloads, INSAT-2C and 2D did not.) INSAT-2E, to be launched by the Ariane rocket in June 1998 from Kourou, will have a meteorological payload. (Under a commercial agreement, ISRO has agreed to lease out 10 transponders from INSAT-2E to INTELSAT, a consortium of 120 countries that operates 22 satellites.)

To offset the loss of INSAT-2D, ISRO is exploring the possibility of leasing transponders from other communication satellites. Some of the load is being transferred to INSAT-2A, 2B and 2C that are in orbit.

The first generation of INSATs - 1A, 1B, 1C and 1D - were built by Ford Aerospace of the U.S. They were either launched by the Delta rocket of the McDonnel Douglas Corporation of the U.S., the space shuttle or the Ariane vehicle. APPLE (Ariane Passenger Payload Experiment) was the first experimental telecommunication satellite built by ISAC, Bangalore. The second generation of INSATs - 2A, 2B, 2C and 2D - were all built by the ISAC. They were, however, launched by the Ariane vehicle from Kourou because India did not have a launch vehicle that was powerful enough to put a 2,500-kg communication satellite into orbit. (ISRO will acquire this capability towards the end of next year when its Geosynchronous Satellite Launch Vehicle (GSLV) will lift off from Sriharikota to orbit the G-SAT, a 2,500-kg multi-purpose satellite.)

INSAT-1A and 1C were also abandoned. INSAT-1A was launched by the Delta vehicle from the U.S. on April 10, 1982. Its solar sail did not deploy and it was affected by a power shortage. Its C-band antenna, the vital instrument for its telecommunication segment, did not deploy. The C-band antenna deployed 12 days after the launch, after a considerable amount of on-board fuel was spent. After that, the solar panel did not open out, resulting in the over-heating of the S-band transponder which affected television and radio broadcasting. The non-deployment of the solar sail also affected the meteorological payload, the Very High Resolution Radiometer, and the VHRR stopped sending weather pictures from August 13, 1982. The satellite lost the earth lock because of an "unanticipated moon interference" on September 4 and was finally deactivated on September 6. The Satellite Tracking and Ranging Station (STARS) at Kavalur, Tamil Nadu, was, however, asked to hunt up the satellite.

INSAT-1C was affected by a short-circuit in one of its power buses after it was launched in July 1988. The satellite was abandoned on November 1988 when it went out of control.