Sunday, August 19, 2012

Proba-1 is Back in Business.

ESA's Proba-1 microsat was built and launched by the ESA as a proof-of-concept for semi-autonomous Earth observation - operators can upload coordinates and the satellite will autonomously image that location. The satellite ended up turning into a heavily-used science tool, but it almost shut down in May due to star tracker degradation. 

Proba-1 captured this image of London's Olympic Park
 neighborhood.   Credit: ESA 
Many small satellites use star trackers to orient themselves. The star trackers point behind the satellite (away from the Sun and Earth) and take pictures of star fields, which they can identify and use to calculate the satellite's orientation.  The CCD camera's attached to Proba-1's star trackers had sustained severe radiation (they were 5 years older than the planned lifetime for Proba-1), and the radiation had created permanent damaged or "hot" pixels which  show up in images as white spots. The star trackers were mistaking hot pixels for stars, and sending incorrect coordinates to the main satellite computer, causing it to error out or mispoint. 

Proba-1 was saved by a software patch written specifically for the satellite, which - once loaded - allowed the star trackers to distinguish between hot pixels and real stars. The star trackers are apparently working "as good as new" now, even with degraded CCDs. The proof is in the pudding - at the right is a farewell shot of Olympic Park that the satellite shot last week.

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