MEASURED SPACECRAFT INSTRUMENT AND STRUCTURAL INTERACTIONS

Evaluation of Eight data from the Upper Atmosphere Research Satellite shows that the solar-disk tracking subsystem within the Halogen Occult ation Experiment responds to and completely accommodates cyclic distur bances from the spacecraft solar-array vibration and continuous scanni ng motions by the High-Resolution Doppler Imager instrument. A fine su n sensor within the Halogen Occultation Experiment senses the top egde of the solar disk as the primary tracking control input, Data streams from such sensing show a characteristic frequency, which is principal ly determined by the apparent solar motion. Power-spectral-density ren derings of sun sensor data streams show the disturbing frequencies as sideband peaks around a central peak at the characteristic frequency. The sidebands are analogous to frequency modulation of a carrier frequ ency. A mathematical model developed for this analysis demonstrates th e factors that influence the frequency-modulated measurements. Modelin g analyses verified the frequency content and allowed estimates of loc al relative amplitudes of the principal disturbances imparted to the s pacecraft. The model can predict mutual interactions between instrumen ts as well as the influence of structural excitations upon instruments . This analysis offers a means toward evaluating potentials for advers e interactions in cases where a spacecraft carries closed-loop instrum ents that track fixed solar or stellar targets; such interactions can become crucial if tracking requirements have small margins of error.