STELLAR ALIGNMENT OF THE HIGH-RESOLUTION DOPPLER IMAGER

A method is described for determining the angular misalignment between the High Resolution Doppler Imager instrument and its spacecraft, the Upper Atmospheric Research Satellite, using observations of stars by the instrument. Roll, pitch, and yaw misalignments have been measured to within 0.0025 deg (1 sigma), which is an order of magnitude better than the largest tolerable alignment error. The misalignment results a re validated using observations of the nighttime 5577-Angstrom O(S-1) green line emission. In addition, the long-term behavior of the derive d alignment offsets, which shows a clear dependence of the alignment o n the solar beta angle, is presented.