India Lunar Probe Copes With Sensor Failure
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By Neelam Mathews
NEW DELHI - India's first moon mission - Chandrayaan-I - has lost its star tracker, raising worries that it might not last out its two-year life span even though engineers at the Indian Space Research Organization (ISRO) have devised a functional workaround to the problem.
"With its loss we are really worried," ISRO chairman G Madhavan Nair says.
The sensor, which failed in June, helps keep the satellite oriented so its cameras and other recording equipment are properly aimed at the lunar surface. Controllers are using a combination of onboard gyroscopes, antenna-pointing data and lunar landmarks to determine spacecraft orientation, ISRO says.
"As you know, we did not have experience of this kind anytime earlier," Nair says. "This is the first time we have understood the intricacies of going around the moon and this data will help us make the subsequent missions much more reliable."
Launched in October of last year, Chandrayaan-I encountered unexpected temperatures during its first month in lunar orbit, forcing additional corrective action that included activating backup units. Without the quick response, "the entire spacecraft would have baked and would have been simply lost," Nair says.
Instead, more than 95 percent of the mission objectives have been achieved, and the U.S.-supplied synthetic aperture radar (SAR) onboard is being prepared for its second round of surface imaging.
That raises the possibility it will be able to work with the SAR on NASA's Lunar Reconnaissance Orbiter (LRO), now being checked out in lunar orbit.
The Chandrayaan-I instrument will begin imaging the lunar surface for evidence of water ice next month, and the LRO Mini-SAR already has produced imagery of the south polar region.
Working together, the similar instruments - both built in the U.S. under the leadership of the Naval Air Warfare Center - may have a better chance of collecting the signatures of ice from past comet impacts preserved by the extreme cold in the deep, dark craters at the poles.
That sort of cooperation in space was one of the items on the agenda during U.S. Secretary of State Hillary Clinton's visit to India, which produced a civil space agreement that includes broader commercial launch opportunities (See related story on p.4). Prior to India's recent election, the agreement was considered unlikely to win the necessary government support because of opposition from the left within the Congress Party coalition.
Meanwhile, Chandrayaan-I continues to send high-quality data to its ground station at Byalalu near Bengaluru (Bangalore). Detailed review of the scientific objectives and the performance results on the mission is scheduled within three months, after which further operational procedures will be worked out, ISRO says. Launched from Satish Dhawan Space Center, Sriharikota, Chandrayaan-I has made 3,000 orbits around the moon and sent back more than 70,000 images of its surface.
Chandrayaan-I photo: Indian Space Research Organization