Space Environment: Measurement of the Gaseous Environment Surrounding Spacecraft

The gaseous environment surrounding spacecraft has been revealed to differ greatly from a natural gaseous environment. The former is dominated by surface outgassing effects and is strongly influenced by spacecraft activities such as maneuvering. For this study, an atomic oxygen monitor (AOM), which was intended to measure the atomic oxygen environment that a satellite encounters, was mounted on Engineering Test Satellite-VII (ETS-VII). However, the AOM was unable to monitor atomic oxygen because the pressure around the sensor was higher than expected; moreover, and the resolution was degraded by effects of outgassing. The initial pressure was of 10-4 Pa-order. Therefore, the purpose was switched, and data acquisition such as measurement of the vacuum environment of the satellite and seasonal variations were done. Results of measurements during one year and eight months showed fluctuation within 10-5-10-4 Pa during the satellite eclipse time.