The most plausible reason for the ground controllers of the Indian Space Research Organisation (ISRO) to lose radio contact with Chandrayaan-1 on Saturday was the failure of power supply to the two computers on board the spacecraft, according to T.K. Alex, Director of the ISRO Satellite Centre in Bangalore.

These two computers controlled the telemetry data flowing from the spacecraft to the ground and the telecommands given to the spacecraft from the ground. “We do not have any telemetry data. So we are not able to make out what is happening,” Dr. Alex said. Since the ISRO was not able to restore radio contact with Chandrayaan-1, “we had to abandon the mission,” he added.

Dr. Alex explained on Sunday that the spacecraft had two computers. When the power supply to the primary computer failed a few months ago, the ISRO switched over to using the redundant (that is, the back-up) computer.

But the power supply to the redundant computer also failed, resulting in loss of radio contact with the spacecraft, since these two computers controlled the telemetry and telecommand.

Asked whether Chandrayaan-1 was still in orbit, he said, “It is in orbit. But we do not have any communication with it. We cannot find out where it is.”

The spacecraft would take about 1,000 days to touch down on the moon. It was now orbiting at an altitude of 200 km above the lunar surface. “It will slowly come down. Its perigee [periselene] will go down and go up. There is dynamics for that. But we are unable to communicate with the spacecraft,” Dr. Alex said.

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