Measured spacecraft instrument and structural interactions

Evaluation of flight data from the Upper Atmosphere Research Satellite shows that the solar-disk tracking subsystem within the Halogen Occultation Experiment responds to and completely accommodates cyclic disturbances from the spacecraft solar-array vibration and continuous scanning motions by the High-Resolution Doppler Imager instrument. A fine sun 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 principally determined by the apparent solar motion. Power-spectral-density renderings 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 frequency. A mathematical model developed for this analysis demonstrates the factors that influence the frequency-modulated measurements. Modeling analyses verified the frequency content and allowed estimates of local relative amplitudes of the principal disturbances imparted to the spacecraft. (Author)