It operated for 4 times longer than expected and returned a stunning array of data, but on November 2nd 2006, the Mars Global Surveyor spacecraft made its last call home to Earth. The Jet Propulsion Laboratory in Pasadena, California, has now released the preliminary conclusions of a report by an internal review board, and it appears the reason for the failure may have its origins in a computer mistake made 5 months previously. A routine update in September 2005 sent to onboard computers caused inconsistencies in the spacecraft's memory. When engineers tried to fix the problem they compounded the error by sending further incorrect software commands, and then did not catch these new mistakes because the existing procedures to do so were inadequate. The spacecraft continued to function, but on November 2nd, the spacecraft was ordered to perform a routine adjustment of its solar panels which triggered a series of alarms. Though it then reported that the situation had stabilised, the spacecraft re-orientated to an angle that exposed one of two batteries carried on the spacecraft to direct sunlight. This caused the battery to overheat and in turn caused the 2nd battery to degrade. By now the spacecrafts antenna were unaligned with Earth and so the spacecraft could not report its plight to ground controllers, which sealed its fate.
The report points no specific finger of blame as the team followed procedures correctly, (which were themselves flawed), and JPL rightly emphasises the successes of Mars Global Surveyor. The mission was undoubtedly a spectacular success, with the highlight been a series of before and after images of gullies on Mars which appeared to show strong evidence that water had run on the surface in just the last few years. Other discoveries include the identification of the remnants of a magnetic field which would have shielded Mars from deadly cosmic rays and Laser altimeter measurements that produced an incredibly detailed topographic map of the planet.
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