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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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