Middeck Experiments

With the Chandra deployment behind them, the five astronauts focused the last few days of their mission on a variety of scientific experiments in the middeck. One of these, tended by Hawley, was the Southwest Ultraviolet Imaging System (SWUIS), a telescope and ultraviolet-sensitive CCD device which he used to observe Mercury, Venus, Jupiter and the Moon. Its chief value was its ability to study objects much closer to the Sun than could be observed using the Hubble Space Telescope: such as a hypothetical belt of debris known as the 'Vulcanoids' inside the orbital path of Mercury.

First flown in August 1997, SWUIS had previously taken nearly half a million high-resolution images of Comet Hale-Bopp, providing important insights into its water- and dust-production rates as it receded from the Sun on its return trip to the Oort Cloud far beyond Pluto. Coupled with its unusually wide field of view, SWUIS proved useful on STS-93 by examining faint emissions from Jupiter's upper atmosphere - supporting simultaneous observations by the Galileo spacecraft, in orbit around the giant planet at the time - as well as mapping the Moon and imaging the clouds of Venus.

During typical operations, Hawley operated the telescope through the small window in the middeck access hatch, while Collins and Ashby periodically adjusted Columbia's attitude to support its observations. Elsewhere, Coleman monitored a number of protein crystal growth investigations and Tognini tended a biological cell culture experiment. Other tests included a number of OMS and RCS pulses to provide data for the military Midcourse Space Experiment (MSX) satellite, which had been placed into orbit in 1996 to collect ultraviolet, visible and infrared data from thruster firings.

After a comparatively short - for Columbia at least - five days in space, it was time for the crew to return home. ''In a way, it's going to be hard to come home, because I do like being in space so much,'' Collins told an interviewer on 26 July. ''It's a little difficult the first couple of days adjusting to zero-g and just getting used to being here again. I guess you could say it's like riding on rollerskates; it's a little bit different. But once you adapt, after three or four days, it feels almost natural to be up here.''

Weather forecasts for 28 July indicated clear skies, with a possibility of thunderstorms inside a 45-km radius of the SLF. Collins fired the OMS engines at 2:19 am to begin the descent through the atmosphere. Passing over Baja California and northwest Mexico, bisecting Texas from west to east and crossing southern Lousiana, Columbia swept into a darkened KSC an hour later with trademark double sonic booms. Little did the STS-93 crew know at the time, but what was found during post-flight inspections of the main engines would effectively ground the Shuttle fleet until the end of the year.

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