The reduced gravity environment on board a spacecraft in low earth orbit gives materials scientists the opportunity to undertake experiments under conditions that reduce or eliminate buoyancy driven fluid convection in comparison to earth based conditions. As a consequence, the relative importance of heat and mass transport by diffusion is increased. In crystal growth this might be expected to lead to a more uniform crystal composition than would be obtained under terrestrial conditions. The process of crystal growth by the Bridgman technique is chosen as a case study. Two and three dimensional numerical models are used to examine the response of heat, mass and momentum transport to conditions characteristic of the microgravity environment. It is shown that the orientation of the experiment with respect to the steady component of the residual gravity is a crucial factor in determining the suitability of the spacecraft as a means to suppress or eliminate unwanted effects caused by buoyant fluid motion. The process is also extremely sensitive to transient disturbances. For example, a 3×10−3g impulse of one second duration acting parallel to the interface of a growing crystal produces a response in the solute field which lasts for nearly 2000 seconds. Consequently lateral and longitudinal compositional variations occur over a length of nearly 6 mm in the grown crystal.