Flight rules overruled

hoped that such research would lead to the development of more resilient metallic alloys and composites for future aircraft engines and turbine blades. For its first trip into space, MEPHISTO was loaded with three identical, 15 cm-long tin-bismuth alloy samples, which were processed by one fixed and one moving furnace.

On Earth, buoyancy-induced convection and differences in hydrostatic pressure affect how materials solidify, as well as masking several of the key processes in the solidification process. During the USMP-1 mission, sensors attached to the furnace accurately measured the temperature and shape of the solid/liquid interface and determined the speed at which it moved through the tin-bismuth sample. The third experiment, SAMS, was really a sensitive accelerometer which recorded and tracked the effect and severity of Columbia's thruster firings on LPE and MEPHISTO, in order to assess the purity of the microgravity environment during the experiments.

All three were attached to a pair of Mission-Peculiar Equipment Support Structure (MPESS) carriers, which straddled the Shuttle's payload bay like a bridge and was derived from the Microgravity Science Laboratory flown on STS-7 and STS-61C. The 'front' MPESS provided electrical power, data, communications and thermal-control services to the payload, while the experiments were mounted on the 'rear' one. Managed by NASA's Marshall Space Flight Center, the USMP system was essentially autonomous and required little crew interaction, other than switching it on and off; moreover, it also provided exciting opportunities for scientists to control their experiments from the ground, via 'telescience'.

''This is an excellent use of the Shuttle to perform microgravity experiments that are primarily operated remotely from the ground,'' said USMP Project Manager David Jarrett, adding that the ability to exercise such control would provide scientists with useful experience as NASA prepared to build a permanent space station in the mid-to-late 1990s. In terms of the kind of research being conducted, USMP could be envisaged as an 'automated' version of USML-1 flown on Columbia's previous mission, since it too was designed to capitalise on the United States' lead on worldwide microgravity research.

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