Tuesday, September 8, 2009
India's Lunar Honeymoon Over
By Ameer Alam
The Indian Space and Research Organization (ISRO) terminated the Chandrayaan-1 mission 18 hours after losing contact with the spacecraft on Aug 29, 09. The spacecraft completed less than half (10 months) of its two year mission life.
The initial inkling of something amiss came of May 19, 09 when the satellite was suddenly raised from a lunar orbit of 100 km to 200 km orbit. ISRO did not disclose the nature of the problems at that time, instead it claimed that "the higher altitude would enable further studies on gravity anomalies and imaging a wider swath of lunar surface". Later it was revealed that both the primary and secondary star trackers (sensor units), had failed on orbit. Star tracker is a part of the spacecraft attitude control system, which accurately orients the spacecraft and helps keep the cameras and other instruments properly aimed at the lunar surface. The ISRO controllers then switched to a less accurate option of a combination of gyroscopes, antenna-pointing data and lunar landmarks to determine spacecraft orientation.
To make matters worse the Chandrayaan-1 had earlier lost power supply to the satellite primary bus management unit due to overheating. The bus management unit is an on-board computer that performs real-time data, navigation and control processing for the satellite. After the secondary unit lost power the ground controllers stopped receiving telemetry data, radio contact was lost and the mission was abandoned.
Earlier on Aug 20, NASA and ISRO performed joint observations with their lunar orbiters to determine evidence of water/ice at the moon’s North Pole Erlanger Crater, using the US built Mini-SAR/Mini-RF devices. The hope was that bistatic imaging data will reveal whether the radars were actually seeing ice or just surface material with same characteristics. Later on Sep 3, 09 it was announced that the experiment failed because of the pointing problems (gyro drift of 0.8 deg/hr) with Indian spacecraft. Ground controllers managed to get data back from both spacecraft, but it turned out to be unusable. Further experiments were cancelled due to the loss of Indian spacecraft.
These failures are indicative of a lack of understanding of space environment; as a result erroneous thermal profiling caused cascading failures of the spacecraft equipment. Compared to Chandrayaan-1 the Chinese Chang’e-1 and the Japanese Selene lunar missions have performed beyond their expected mission life. The Chinese indigenous space programs continue to thrive despite the technological restrictions imposed by the West.
Nevertheless, Chandrayaan-1 completed 312 days in lunar orbit, circling the moon more than 3,400 times and providing a large volume of data from its suite of sensors which included the Terrain Mapping Camera, Hyper Spectral Imager and Moon Mineralogy Mapper. High-resolution cameras relayed over 70,000 digital images of the lunar surface, providing breathtaking views of mountains and craters, including those in the permanently shadowed area of the moon's polar region. The ISRO Chairman G. Madhavan Nair declared that the mission was a success with 95% of the objectives achieved.
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Editor's Note: Ameer Alam believes that ISRO is not coming clean with actually what happened to the spacecraft. His view is that it is a great set back to India's space program. Ameer thinks that they are busy analyzing the data and will put out a report in six months (available only to the top govt officials).
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