In-orbit measurements of short term attitude and vibrational environment on the Engineering Test Satellite VI using laser communication equipment

Angular microvibrations of platform jitter on a three-axis attitude-stabili zed satellite are measured in space using an onboard laser communication te rminal. Stable optical tracking control allows the measurement of relative angular variations from the reference line of sight of the optical link. Th e tracking accuracy in this measurement is less than 1 mu rad rms. The angu lar variation and the drift rate on the satellite are measured at a samplin g rate of 500 Hz, and these data are downlinked to a ground station via a s atellite-to-ground optical communication link. The power spectral density o f the satellite microvibration is calculated by a Fourier transform analysi s. The frequency spectrum of the gimbal mirror's angular variation is also obtained when the coarse tracking control is operational. The rms value agr ees with the residual coarse tracking error estimated before launch of the satellite. These results will be useful for the future design of a tracking control loop for optical communication systems. (C) 2001 Society of Photo- Optical Instrumentation Engineers.