manoeuvres were carried out between 03:30 and 04:30 UTC on 19 May 2009. The spacecraft in this higher altitude enabled further studies on orbit perturbations, gravitational field variation of the Moon and also enabled imaging lunar surface with a wider swath. It was later revealed that the true reason for the orbit change was that it was an attempt to keep the temperature of the probe down. It was "...assumed that the temperature [of the spacecraft subsystems] at 100 km 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 200 km." Attitude sensor failure The star tracker, a device used for pointing attitude determination (orientation), failed in orbit after nine months of operation. Afterward, the orientation of Chandrayaan was determined using a back-up procedure using a two-axis Sun sensor and taking a bearing from an Earth station. This was used to update three axis gyroscopes which enabled spacecraft operations. The second failure, detected on 16 May, was attributed to excessive radiation from the Sun. Radar scans On 21 August 2009 Chandrayaan-1 along with the Lunar Reconnaissance Orbiter attempted to perform a bistatic radar experiment using their Mini-SAR radars to detect the presence of water ice on the lunar surface. The attempt was a failure; it turned out the Chandrayaan-1 radar was not pointed at the Moon during the experiment. The Mini-SAR has imaged many of the permanently shadowed regions that exist at both poles of the Moon. In March 2010, it was reported that the Mini-SAR on board the Chandrayaan-1 had discovered more than 40 permanently darkened craters near the Moon's north pole which are hypothesized to contain an estimated 600 million metric tonnes of water-ice. The radar's high CPR is not uniquely diagnostic of either roughness or ice; the science team must take into account the environment of the occurrences of high CPR signal to interpret its cause. The ice must be relatively pure and at least a couple of meters thick to give this signature. The estimated amount of water ice potentially present is comparable to the quantity estimated from the previous mission of Lunar Prospector's neutron data. Although the results are consistent with recent findings of other NASA instruments onboard Chandrayaan-1 (the Moon Mineralogy Mapper (MP3) discovered water molecules in the Moon's polar regions, while water vapour