Wsf3 An Orbiting Semiconductor Factory

The Wake Shield Facility was essentially a disk-shaped experimental 'space factory', measuring 3.6 m wide and made from stainless steel, with the purpose of producing ultra-pure thin films of semiconducting materials that might one day be used as the basis for advanced electronic components. Designed and built by Alex Ignatiev's team at the NASA-funded Space Vacuum Epitaxy Center (SVEC) at the University of Houston, in conjunction with Space Industries Inc., it was making its third journey into space with Columbia's astronauts.

On its maiden mission in February 1994, the facility experienced hardware problems which prevented Discovery's crew from deploying it; nonetheless, a significant amount of valuable data was gathered and one semiconductor film was grown as it drifted through space on the end of the RMS. When it flew again, on Endeavour in September 1995, it was successfully deployed and retrieved and made two significant breakthroughs. ''It produced a vacuum nearly 100 times better than operating vacuum levels achievable in terrestrial vacuum chambers,'' said Ignatiev, ''and also yielded the purest gallium arsenide and aluminium gallium arsenide thin films ever made.''

Essentially, the wake shield exploited the 'moderate' natural vacuum of low-Earth orbit and improved it further by creating an 'ultra-vacuum' behind an object moving boat-like through the ionosphere. As it flew, it pushed residual gas atoms in low-Earth orbit out of its way, leaving few - if any - in its wake. This yielded results on the first two missions of thin films between 100 and 1,000 times purer than any obtained in terrestrial vacuum laboratories, and Ignatiev's team hoped to create not only the next generation of semiconducting films, but also the next generation of devices they will make possible.

''The quality of the materials will surpass what can be done on the ground,'' Ignatiev said before Columbia lifted off, ''so we should be quite competitive.'' Yet the concept itself dated back to the 1970s, when NASA engineers published papers arguing that a satellite sailing through space would leave an 'ultra-vacuum' in its wake in the same way that a motorboat left a short-lived channel in the water behind it. Unfortunately, in the absence of practical applications, the idea was left

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