Snag hits moon mission

Failure of star sensor cripples performance

The Indian Space Research Organisation (ISRO) claimed the sensor’s failure had been rectified, but it has, in fact, crippled the performance of the spacecraft.

The star sensor, which is primarily used to determine the attitude of the spacecraft, was damaged due to radiation from gamma rays and X-rays emanating from the solar flares.

However, the problem was fixed in a week’s time by using the outboard gyroscopes, which do the same job but are not susceptible to radiation.

Gyroscopes are used in remote sensing satellites for orientation and were installed on Chandrayaan as a redundant measure. Briefing reporters on Friday, ISRO Chairman G Madhavan Nair said the failure had “deeply affected” the performance of the spacecraft, but dismissed rumours that the “anomaly” had affected its lifespan. “The life of the spacecraft is not affected. Life (of the spacecraft) depends on fuel and a large number of electronic packages that have to work in this environment, like telemetry, telecommand etc. If any of the vital electronics fail, then there is a problem,” he clarified. Nair also said 90-95 per cent of the scientific objectives of the mission had been completed. “We had a meeting with the scientific community a month back and they have stated that the quality of data was excellent. We have accomplished 90-95 per cent of the objectives of the mission.

What is remaining will be scheduled in the coming season which starts in two months,” he said. The three payloads — the Terrain Mapping Camera, the Hyperspectral Imager and the Moon Mineralogy Mapper — have already collected majority of the data, according to the ISRO chief.

He maintained that theoretically, it would have taken only nine months to complete the mission’s objectives, but additional time  was kept as a requirement for the design.
Nair indicated that a meeting with the scientific community would be held in August-September to review what had to be done about Chandrayaan. The gyroscopes are expected to take care of the orientation for the entire lifespan of the spacecraft.

Out of the ten payloads, the Terrain Mapping Camera will have a lower resolution as the height of Chandrayaan has been raised from 100 km from the lunar surface to 200 km.

The activities of the other instrument, High Energy X-Ray Spectrometer, has been suspended for the time being, although ISRO spokesperson S Satish said it was a temporary measure.

Chandrayaan was launched on October 22, 2008 from Sriharikota to circle the moon for a period of two years. It originally carried 11 payloads, five of them Indian and six foreign. The Moon Impact Probe, built by the Vikram Sarabhai Space Centre at Thiruvananthapuram hit the lunar surface on November 14, 2008.

What went wrong

* Radiation from a solar flare destroys the star sensor onboard on April 26

* Chandrayaan switches over to gyroscopes for orientation as back up

* ISRO raises orbit of the spacecraft from 100 km to 200 km to decrease orbit manoeuvers on May 19

* ISRO chief says failure of the sensor is a handicap, but lifespan not threatened

* 90-95 per cent of the mission objectives are claimed to have been completed

* Nair hints at early termination of the project, but cites completion of objectives as the reason