Quality requirements for microgravity experiments

The conduct of scientific experiments under zero-gravity conditions entails that fluid static pressure be held constant, that there be no free convection, and that buoyancy vanishes. The achievement of reduced gravity rather than zero-gravity calls for the effects of the residual pressure differences, the free convection, and particle movements on the quality of the data to be obtained, and this requires fluid-dynamic modeling in which several dimensionless numbers encompassing gravity must be small. The resonances of liquid volumes must be carefully avoided. Attention is given to the motion of spherical fluid or solid particles in a fluid matrix.