Long-term vibration monitoring onboard Mars Express mission

This work describes mechanical vibration monitoring onboard the ESA Mars Express orbiter, in a period of eight years since the spacecraft commissioning. The vibrations are measured using the planetary Fourier spectrometer, an infrared spectrometer based on a modified Michelson interferometer, which is part of the mission payload. The instrument is very sensitive to thermomechanical inputs, and the mechanical vibrations are a source of disturbance for its scientific measurements. However, the instrument sensitivity to mechanical disturbances and the exploitation of a diagnostic mode provide a chance to monitor the vibration environment onboard the spacecraft. It has been assessed that the main vibration contributions derive from the reaction wheels and the laser ring gyroscopes that implement harmonic dithering. Spacecraft acceleration levels at the instrument mounting interface are provided with the aim of defining reference figures for engineers and scientists who have to cope with a usually unknown in-orbit vibration environment. Moreover, the vibration levels evolution along the mission lifetime is analyzed to highlight the effect of the spacecraft aging in that respect.