The Busiest

Once inserted into a 280-km orbit, inclined at 39 degrees to the equator, which enabled the crew to maintain the normal sleep/wake circadian rhythms that they were used to on Earth, the seven astronauts set to work transforming their launch vehicle into a home and laboratory for the next 16 days. By 4:15 pm, less than one-and-a-half hours into the mission, Columbia's payload bay doors were opened and ahead of schedule the Spacelab module and its experiments were activated.

''Today'', said LMS Mission Scientist Patton Downey on the evening of 20 June, ''was the busiest first shift of activities we've ever had for Spacelab. Virtually every experiment on board either had its equipment activated or checked out.'' From their stations on Columbia's flight deck, Henricks and Kregel oriented the spacecraft in a 'gravity gradient' attitude, with its tail pointing Earthwards, so that only very few thruster firings were needed and thus did not disrupt the sensitive microgravity experiments.

One of the most important payload packages in the Spacelab module was ESA's Advanced Protein Crystallisation Facility (APCF), which housed 11 separate experiments to study three different growth methods. In total, during the course of

The busiest day 271

the mission, more than 5,000 video images were taken of protein crystals grown in the facility to track their development over time.

The APCF, which had previously been on board Columbia for the IML-2 mission in July 1994, was a relatively late arrival in the LMS payload. It only arrived at KSC from its home base in Europe on 13 June and was installed on board the Spacelab module, in a vertical orientation, the day before launch. It was switched on six hours into the mission and the crew typically provided daily reports of the status of its front-panel displays, as the facility had no space-to-ground telemetry capability of its own.

Also provided by ESA was the Advanced Gradient Heating Furnace (AGHF), which was flying for the first time on STS-78 and successfully processed no fewer than 13 samples for one semiconductor and five metallurgical experiments. The furnace was switched on by Favier late on 20 June and operated near-continuously for 16 days, performing better than in ground-based tests. Its objective was to solidify alloys and crystals in a number of experiments designed to understand the conditions in which the structures of freezing materials change in the solidification process.

It was ultimately hoped that AGHF research would increase scientists' knowledge of the physical processes involved in solidification and lead to improvements in ground-based materials research. The first actual experimental run with the furnace got underway when Susan Helms inserted a sample cartridge to examine the transition in solidifying metal mixtures from ordered, column-like grains to unordered, round ones. Processing of AGHF samples was sequential and required the exchange of experiment cartridges and the activation and deactivation by a crew member.

On 22 June, a sample of pure aluminium, reinforced with zirconia particles, was placed into the furnace as part of Doru Stefanescu's investigation into the physics of liquid metals containing ceramic particles as they solidified. The experiment ''may lead to more inexpensive ways to make mixtures of metals and ceramics -particularly for the metal casting industry'', said Stefanescu, a researcher from the University of Alabama at Tuscaloosa. ''We hope to find ways to help manufacturers make composite products with superior quality.''

Other experiments included a polycrystalline sample used to gather information on how to combine liquid metal alloy components into precise, well-ordered solid structures. It was anticipated that knowledge from melting and resolidifying such compounds could help manufacturers make higher-quality metal alloys and semiconductors. Later, an aluminium-copper mixture was solidified as part of an investigation designed by Denis Camel of the French Atomic Energy Commission in Grenoble. One sample was solidified at near-constant temperatures, a second at a high-temperature gradient; both were then compared to theoretical models as part of efforts to understand the influence of fluid flows on metal-alloy processing.

Brady and Helms also ran an experiment which sought to control the internal structures of aluminium and indium alloys during solidification, which was expected to have terrestrial benefits in producing new materials for engineering, chemical and electronics applications. On the whole, the facility performed exceptionally well, although on 2 July - after the insertion of a mix of pure aluminium and aluminiumnickel alloy - Marshall Space Flight Center investigators discovered it was not providing data readouts. The problem was quickly resolved, however, when Helms switched off and reset the facility. In total, six individual experiments, many with separate runs, were performed.

Was this article helpful?

0 0

Post a comment