STS-75 Day 9 Highlights

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On Friday, March 1, 1996, 6 a.m. CST, STS-75 Payload Status Report # 14 reports: (7/15:42 MET)

Researchers for the third United States Microgravity Payload (USMP-3) are on an "incredible atomic journey," according to Principal Investigator Dr. Robert Gammon. He and his science team, stationed at Spacelab Mission Operations Control, are pushing the envelope of knowledge about the precise conditions under which one material can coexist in two states of matter.

This atomic journey, courtesy of the Critical Fluid Light Scattering experiment, or "Zeno," is geared toward searching for insight into the fundamental physics processes involved in this phenomenon. ZENO scientists currently are setting the stage to arrive at the point where temperature and density combine to balance two states of matter -- liquid and gas. This is known as the "critical point."

Team members are remotely commanding their small experiment cell to cool -- slowly and methodically stepping down a range of temperatures to reach a point where something quite remarkable happens. The normally clear xenon "turns milky white because it does not know whether it really wants to be like a liquid or like a vapor. It just can't decide," Dr. Gammon explains. That will be the point where the Zeno apparatus will collect the all-important data for his investigation.

Yesterday, the Advanced Automated Directional Solidification Furnace (AADSF) team members adjusted their timeline, delaying the first crystal processing run until later today, to ensure that conditions are right for their solidification techniques. AADSF team members can tell that solidification has begun in their furnace when a "seed" or solid core forms in the molten lead-tin-telluride, a sample of semiconductor material. In ground-based solidification, this seed formation would normally show up as a "spike," or sharp rise and fall, in the temperature data the team receives from the experiment.

When the seed formed more slowly than expected Thursday, appearing as a "hump" instead of a spike in the data plot, due to the low-gravity environment, the team re-melted their sample to again verify the exact time of seed formation. Having accomplished this, they decided to wait for the next period of reduced crew activity, scheduled for this evening, in order to take maximum advantage of the relatively undisturbed microgravity environment. Such "quiescent periods" are necessary to allow each of three crystal samples to develop in the best possible growth conditions.

The Isothermal Dendritic Growth Experiment (IDGE) and MEPHISTO teams are studying details of crystal growth to improve metals processing on Earth. The IDGE science team has completed data collection for their first 20-cycle phase of primary science and have begun their second phase. During each cycle, the facility studies crystal structures for clues about how to solidify liquid materials into forms with just the right characteristics for their intended purpose. Applications range from aluminum to steel products.

The MEPHISTO series of investigations explores the liquid/solid interface, or boundary, of metal alloys. Alloys are combinations of metals that reinforce or add properties not found in each constituent alone. The goal is to develop processes to distribute constituents in a precise manner to improve the final product. The MEPHISTO science team has reported previously unseen results from the effects of two scheduled Shuttle thruster firings on their molten tin and bismuth alloy sample, which finished another round of solidification last night. They noticed that the thrusters had a great impact on the sample's crystallization when fired at a perpendicular orientation, at a 90-degree angle, to the direction in which the sample grows, but no effect when fired parallel to that direction. This was the first time this effect has been demonstrated in space, and it could prove important to materials processing in similar furnaces aboard the International Space Station.

Working in the Marshall-managed Middeck Glovebox, Commander Andrew Allen successfully completed a set of Comparative Soot Diagnostics (CSD) burns ahead of schedule due to an early start. The CSD experiment team, led by Dr. David L. Urban of NASA's Lewis Research Center, received good data from the burns, which will contribute to the understanding and prevention of possible fires on spacecraft. Later in the night, Mission Specialist Claude Nicollier performed Forced Flow Flamespreading Test (FFFT) runs, burning flat and cylinder-shaped samples in the Glovebox to help FFFT investigators learn more about how flames spread in weightlessness.

Tethered Satellite System (TSS) "science of opportunity," during Columbia's final approach to within 46 nautical miles of the satellite, included firing the electron accelerators in Columbia's cargo bay. The electron guns' effects on the charged particles, electrical waves and magnetic fields around the satellite were detected by the Research on Electrodynamic Tether Effects, Research on Orbital Plasma Electrodynamics and Magnetic Field Experiment for TSS Mission's instruments mounted on the satellite. All three instrument teams reported receiving good quality data from the satellite, data which are now being analyzed by the experiment investigators.

Over the next 24 hours, in addition to AADSF's first sample crystallization, the MEPHISTO crystal-growth furnace will perform shorter and quicker melting and solidification cycles, and combustion experiments in the Glovebox will study smoldering and ignition effects as the second half of the STS-75 mission continues.

On Friday, March 1, 1996, 8 a.m. CST, STS-75 MCC Status Report # 17 reports:

Columbia's astronauts had a clear view of the Tethered Satellite as the two spacecraft passed within about 46 nautical miles overnight. The closest approach occurred at 11:17 central time last night (approximately 7/08:59 MET), and was captured on videotape as the satellite and its 12-mile tether came into view.

Meanwhile, flight controllers monitored the Tethered Satellite through ground stations as its batteries drained, but not before holding in for last night's fly-by.

About 6 a.m. today, weak signals from the satellite, indicating its battery life was waning, were observed through the Merritt Island tracking station and the Bermuda tracking station. During a second pass across the southern United States about 7:30 a.m. today (7/17:12 mission elapsed time), ground controllers confirmed there was no acquisition of signal from the satellite, effectively ending its mission.

Three in-flight special events are planned for the crew this morning and early afternoon. An Italian media interview is set for about 10 a.m.; an Italian VIP call to crewmembers Maurizio Cheli and Payload Specialist Umberto Guidoni is set for 11:50 this morning and a Swiss educational event with Mission Specialist Claude Nicollier is scheduled for 2:48 this afternoon.

Columbia is continuing to provide a stable platform for microgravity investigations as Columbia sails 180 statute miles above the Earth, circling the globe every 90 minutes.

On Friday, March 1, 1996, 4 p.m. CST, STS-75 MCC Status Report # 18 reports:

Science investigations occupied much of the crew's time on board Columbia today as the astronauts continued to support the U.S. Microgravity Payload.

Experiments into convection and the behavior of flame patterns in microgravity were the focus of activity on Columbia's middeck today. The astronauts also took time today to share their thoughts during an Italian media interview and a Swiss educational event.

Late in the afternoon, Commander Andy Allen, Mission Specialist Maurizio Cheli and Payload Specialist Umberto Guidoni accepted a congratulatory phone call from Giorgio Salvini, the Italian Minister of Universities and Scientific Research.

Columbia continues to perform in near flawless fashion as it sails 180 statute miles above the Earth, circling the globe every 90 minutes.

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