The Microgravity Measurement Assembly (MMA) is a modular, centralized measurement facility for determination of disturbance accelerations aboard spacecrafts. The system is currently designed for Spacelab applications and demonstrated it's full functionality for the first time during the German Spacelab Mission D-2 in April/May 1993.
MMA has detected, during D-2 ground and on-orbit measurements, accelerations in different locations e.g. close to microgravity sensitive experiments inside Spacelab racks, as well as on other microgravity interesting positions like centrifuges, using rack mounted sensors. Also the environment inside the cabin could be measured using two mobile sensor assemblies. These mobile sensor assemblies were operated by the astronauts and could be placed at any suitable location within the Spacelab cabin.
Thus, together with the on-line connected ground station, the system was able to monitor the microgravity environment on-board D-2.
MMA uses a set of modular components which allow for different on-board configurations. The current maximum number of seven triaxial sensor packages was split for D-2 in four rack mounted assemblies, two mobile ones and completed by an impact hammer to support a transfer function experiment.
A new generation of micromechanical acceleration detectors has been used. The advantage of these accelerometers was their small size and weight allowing for installation nearly at all locations inside Spacelab racks and in the cabin. The usage of these new sensors gave MMA additionally to the main task, to measure microgravity disturbances on-board Spacelab, the character of a technology experiment. The technology aspect was increased by an impact hammer inducing defined forces on predefined locations inside the cabin. This unit was connected to MMA as mentioned above and used together with the MMA sensors in order to support determination of structural transfer functions on-ground and in-orbit.
All data were collected and formatted by the central MMA computer and sent to the ground. On ground the MMA Ground Station processed the data on-line to support other experiments and the transfer function determination.
Thus, for the first time, synchronized and comparable precise acceleration data were available in real time on ground for on-line judgement of the microgravity environment desired for experiment success, offering the possibility e.g. of experiment repetition in case of excessive g-disturbances. Furthermore MMA allows for immediate feedback to the crew concerning the microgravity effects of their own body movements with the aim to improve crew training towards lower crew induced disturbances.
The MMA on-board system and Ground Station is planned to be utilized for further Spacelab Missions and in modified configuration also for MIR.