Superb Scientific Success

As part of ongoing research into materials that could withstand the harsh environment of low-Earth orbit and provide potential building blocks for the space station, more than 700 samples in three identical sets were flown as part of the Limited Duration Space Candidate Materials Exposure (LDCE) experiment. Each 'set' was housed in its own container: one remained open throughout the mission, another opened only when the payload bay was facing the direction of travel (the 'ram' position) and a third opened only when the bay faced opposite the direction of travel (the 'wake' position).

This allowed station planners to better evaluate the damaging impact of atomic oxygen and nitrogen particles on delicate spacecraft surfaces in different orientations; it also took better advantage of the variety of manoeuvres performed by Columbia's crew during STS-62. In fact, the Shuttle spent its first week aloft with its payload bay facing Earthwards. Then, on the morning of 11 March, Casper and Allen moved their ship so that its tail pointed towards Earth and its payload bay faced the direction of travel in a 'ram' orientation.

Not only did these manoeuvres provide data for the LDCE samples, they also allowed MEPHISTO investigators on USMP-2 to better evaluate the effect of thruster-induced jitters on the directional solidification of their bismuth-tin rods. The IDGE team also saw some interesting changes in their data. ''We observed an 8 to 10% change in dendritic growth velocity when the Shuttle changed to a 'tail-down' attitude,'' said Project Scientist Matthew Koss. ''This indicates the exquisite sensitivity of dendritic growth - at very small temperature differences below its freezing point - and our instrument's capability to detect small differences in the microgravity environment.''

As OAST-2 operations drew to a close late on 17 March, Columbia's mission had virtually turned into a 'mini-space station' flight in its own right: not only in terms of evaluating technologies that would one day be used to build and maintain the International Space Station, but also in operating a myriad of experiments over a long period of time. Mounted in the back of the Shuttle's payload bay, for the third time, was the EDO pallet, which provided additional cryogenic oxygen and hydrogen reactant tanks to support two weeks aloft.

Also for the third time, Columbia's astronauts participated in readaptation exercises using the Lower Body Negative Pressure (LBNP) apparatus - the cylindrical device which sealed around their waists and drew bodily fluids into their legs - as part of countermeasures to better prepare them for the punishing onset of terrestrial gravity. Throughout the mission, all five STS-62 crew members undertook several 45-minute 'ramp' sessions with the sack-like unit and on 17 March Gemar wore it for four hours. This provided medical researchers with additional data by imitating the sudden return to 'normal' gravitational conditions.

Meanwhile, Casper and Allen, to whom would fall the task of guiding Columbia back through Earth's atmosphere and landing her at KSC, spent part of several of their shifts practising their piloting skills with the PILOT simulator. In recognition of the longer-than-normal nature of STS-62, each astronaut was granted two half-

days off during the course of the mission, which gave them ample opportunity to gaze out of the Shuttle's windows at Earth below. Allen also received some happy, and well-deserved, news on 12 March: the US Marine Corps Major was promoted, effective immediately, to the rank of Lieutenant-Colonel.

After a fantastic two weeks in space, a jubilant Casper told journalists during a space-to-ground news conference that the mission showed ''that we can do world-class science on the Space Shuttle''. The five astronauts then deactivated their multitude of experiments and by 9:30 am on 18 March Columbia's payload bay doors were closed for re-entry. The de-orbit burn followed at 12:16 pm and, streaking through brilliant azure-blue Floridian skies, the spacecraft swooped onto Runway 33 at KSC at 1:09:41 pm. The crew had just missed, by barely an hour, breaking the record set by STS-58 in November 1993.

''It would have been nice to get the record,'' Casper told journalists after landing, but noted ''I think we did a lot of good things.'' Columbia's landing was not, however, entirely picture-perfect, although many of the details would not be explored in depth until the spring of 2003. Infrared images of the landing showed four fragments of debris falling away from the Shuttle's underside as her nose gear was deployed. Two sources for the debris were subsequently identified: one from around the nose gear's starboard door and another from close to the door's thermal barrier.

Nine years later, during the early stages of Admiral Hal Gehman's presidential inquiry into the cause of Columbia's destruction at the end of the STS-107 mission, the loss of debris during the STS-62 landing was scrutinised in more depth. It revealed no evidence of plasma having entered the nose gear wheel well during that re-entry and determined that the thermal barrier had performed satisfactorily. Nevertheless, the STS-62 incident was serious enough for NASA to spend two days searching the KSC runway for debris. On 1 February 2003, during her 28th atmospheric re-entry, however, Columbia would not be so lucky . . .

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