Measurement errors of star positions due to detector spatial non uniformities and star centroid computation
NOTE 1 Because of their ‘spatial’ nature - these errors vary with the position of stars on the detector - they are well captured by metrics working in the angular domain. The pixel spatial errors are then well defined as the errors on the measured attitude (respectively the measured star positions) due to star measurement errors with spatial period of TBD angular value. Several classes of spatial periods can be considered.
NOTE 2 These errors can be converted to time domain using sensor angular rate. Then, from temporal frequency point of view, they range from bias to high frequency errors depending on the motion of stars on the detector. They lead to bias error in the case of inertial pointing, while they contribute to random noise for high angular rate missions.
NOTE 3 The detailed contributors to the pixel spatial error are given in clause 5.5.
NOTE 4 Spatial non uniformities include PRNU, DSNU, dark current spikes and FPN.
NOTE 5 Inter-pixel crosstalk.
NOTE 6 Star centroid computation is also called interpolation error.