The two Advanced Star Compass instruments onboard of CHAMP are used to determine the attitude of the satellite body and the satellite boom. The highly precise determinations are based on pictures, taken by special designed electronic cameras. Each ASC unit operates two of these so called Camera Head Units. The Camera Head Units look into space while a connected data processing unit compares all luminous objects on the digital pictures with stored star-patterns. This enables the instrument to determine the attitudes in relation to the identified (fixed) star positions.
Some pictures are routinely inspected by GFZ and DTU in order to check the CHU sensor chips for a possible degradation from e.g. radiation. The picture above is one of these snapshots, taken on the 31st of January 2002. The Field Of View is 18.4 � x 13.8 �, showing parts of the Lion star constellation. Please notice that the moon is only as small as about 0.5 �, appearing much bigger due to ring-shaped reflections from the CHU lens system. Although these bright reflections cover some areas, the CHU is still able to detect a couple of stars and sun reflections from a satellite passing through the FOV. You will have to zoom in to pinpoint particular objects.
GFZ, CHAMP Back