The microgravity environment: its prediction, measurement, and importance to materials processing

Abstract

One of the primary benefits of conducting scientific research in space is to take advantage of the low acceleration environment. For experimenters conducting space research in the field of materials science the quality of the science return is contingent upon the extremely low frequency acceleration environment (⪡ 1 Hz) aboard the spacecraft. Primary contributors to this low frequency acceleration environment (commonly referred to as the steady-state acceleration environment) include aerodynamic drag, gravity-gradient, and rotational effects. The space shuttle was used on the STS-75 mission as a microgravity platform for conducting a material science experiment in which a lead tin telluride alloy was melted and regrown in the Advanced Automated Directional Solidification Furnace under different steady-state acceleration environment conditions by placing the shuttle in particular fixed orientations during sample processing. The two different shuttle orientations employed during sample processing were a bay to Earth, tail into the velocity vector shuttle orientation and a tail to Earth, belly into the velocity vector shuttle orientation. Scientists have shown, through modeling techniques, the effects of various residual acceleration vector orientations to the micro-buoyant flows during the growth of compound semiconductors. The signatures imposed by these temporally dependent flows are manifested in the axial and radial segregation or composition along the crystal.