space agency's explanation that Chandrayaan's orbit around the Moon had been raised from 100km to 200km in May this year for a better view of the Moon's surface, it is now known that this was because of a miscalculation of the Moon's temperature that had led to faulty thermal protection.
Admitting this, Dr T K Alex, director, ISRO Satellite Centre, Bangalore, said, “We assumed that the temperature at 100km above the Moon's surface would be around 75 degrees Celsius. However, it was more than 75 degrees and problems started to surface. We had to raise the orbit to 200km."
On May 19, however, ISRO said it had raised Chandrayaan's orbit to "enable further studies on orbit perturbations, gravitational field variation of the Moon and also enable imaging of the lunar surface with a wider swath".
It now transpires that heating problems on the craft had begun as early as November 25, 2008, forcing ISRO to deactivate some of the payloads — there were 11 in all.
As a result, some of the experiments could not be carried out which raised questions on whether the pre-launch thermal vacuum test done on the spacecraft at the ISRO Satellite Centre in Bangalore was adequate.
In early 2009, the situation improved and Chandrayaan-1 started operating normally. However, the snags resurfaced. This time with the two star sensors of Chandrayaan because of high temperature. The sensors are crucial in determining the orientation of the craft in space.
The first star sensor packed up on April 26, and even the back-up sensor failed during the second week of May.
An official requesting anonymity acknowledged: "This was purely a temporary step. It was like a broken car's steering wheel being repaired with scotch tapes. We could not predict how long this arrangement would last," he admitted.
The official said much before the official announcement of the project's end on August 30, it had become clear that the two-year mission would be cut short since 95% of the scientific goals had been accomplished.
Despite the failure of the star sensors, Chandrayaan-1 transmitted excellent images including that of the solar eclipse on July 22. Also at 12.30am on August 21, it flew along with Nasa's Lunar Reconnaissance Orbiter (LRO) for four minutes to detect water ice in the north pole of the moon.
But worse was to follow. At 1.30am on August 29, communication with the spacecraft snapped all of a sudden. ISRO chairman Madhavan Nair has been quoted as saying that due to unforeseen radiation problems the two computers in the spacecraft controlling communication got affected resulting in the breakdown of communications. He has admitted that many of the heat-related problems were not anticipated at all, and it was definitely a learning experience.
"Keeping this in mind, Chandrayaan-2's thermal design will be strengthened to withstand more than 100 degrees Celsius," Alex told TOI on the sidelines of the recently concluded eighth international conference on low cost planetary mission conducted by the International Academy of Astronautics in Goa.
BARC is collaborating with ISRO to strengthen the radiation shield of Chandrayaan-2, slated for lift off in 2013 from Sriharikota. The average day temperature on the Moon's surface is 107 degrees Celsius, while the mean night temperature is -153 degree Celsius.
Although, ISRO claims that 95% of its planned experiments have been completed, it remains to be known whether payloads designed to operate at a 100-km orbit completed their missions. The issue has triggered a fierce debate on whether ISRO should have declared it a one-year mission right at the beginning rather than an ambitious two-year programme.
Among the experiments to be conducted from a 100km orbit were observations in the visible, near-infrared and soft and hard X-rays. Further, the Lunar Laser Ranging Instrument's objective was to provide ranging data for determining the height difference between the spacecraft and the lunar surface. Scientists admit that at an altitude of 200km, the return signal could be too weak for the purpose.
Chandrayaan's objectives also included orbiting around the Moon at a height of 100km for chemical, mineralogical and photo-geologic mapping of the surface and its X-ray spectrometer was to use X-rays to map the surface composition of the Moon and help scientists understand its origin and evolution, as well as quantifying the mineral resources that exist there.
The spacecraft's 11 scientific instruments were built in India, USA, UK, Germany, Sweden and Bulgaria. The mission was formally called off on August 30 by ISRO, which said that a failure analysis committee will probe into the matter. ISRO chairperson G Madhavan Nair also said US and European space agencies who had also taken part in the Indian space mission "were satisfied" with the results.
(Source:TNN)
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