Effect of air motion on a microgravity vibration isolation system

Many of the experiments to be performed within the various space agencies' microgravity programs are extremely sensitive to low frequency spacecraft vibration. The microgravity isolation mount (MGIM) consists of a free floating platform, accommodated within the spacecraft's experiment racks, which isolates sensitive payloads from ambient disturbances. This paper describes the main features of the MGIM and discusses some of the factors considered when deciding on a control system strategy. The emphasis of the paper is on the trade-off which occurs between the heat dissipation capacity of the thermal subsystem and the achievable microgravity level. Thermal dissipation from the platform is by means of interleaved cooling fins located on both the platform and its enclosure. Theoretical expressions are developed for the force caused by air motion in the gap between the fins and experimental results which verify these expressions are presented. It is shown, by means of computer simulation, that the attainable microgravity quality is limited by the dimensions of the cooling fins required to support a specific payload heat dissipation capacity.