Miscalculation of moon temperature led to Chandrayaan's early termination

      A senior official at the Indian Space Research Organisation (ISRO) has candidly admitted that scientists miscalculated the temperature of the moon and that this had led to the early termination of the Chandrayaan-I mission last month. 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." In May, 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. ISRO officials said scientists and engineers used ingenious ways to restore Chandrayaan-I by using gyroscopes as a temporary step. 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 percent of the scientific goals had been accomplished. 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.

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