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A system to measure absolute low frequency acceleration on the International Space Station

The characterization of the microgravity environment of the International Space Station (ISS) demands acceleration measurements at various locations of the spacecraft between 0 Hz and 300 Hz. The lowest residual acceleration occurs in the quasi-static or low frequency range between 0 Hz and 0.01 Hz, where the level reaches the sub-/spl mu/g range (1 /spl mu/g=10/sup -6/ g, 1 g=9.81 m/s/sup 2/). This requires on-orbit calibration which has to be repeated from time to time to eliminate the sensor bias and its drift. The accelerometer system QSAM (quasi-steady acceleration measurement) has been developed for this purpose and was recently flown on the Space Shuttle MSL-1 mission. The combination of flipping and fixed sensors allows calibration during any operational state of the spacecraft providing a continuous set of acceleration data not interrupted by the calibration process.