STS-73 Day 10 Highlights

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On Sunday, October 29, 1995, 9 a.m. CDT, STS-73 MCC Status Report # 19 reports:

After spending eight hours with its belly pointed toward the sun, Columbia is back in position to support the sensitive United States Microgravity Laboratory-2 experiments. For this mission, Columbia's normal attitude has its left wing pointing in the direction of travel and its tail pointed toward the Earth. This attitude, however, exposes some portions of the orbiter to the extreme cold of space for long periods of time. To keep the pressure in the tires at the levels necessary to support landing operations, the flight control team is implementing its pre-flight plan for "thermal conditioning" of the cold areas.

The maneuver, which will be conducted four times during the mission, calls for crew members to reposition Columbia so that the sun shines directly on the lower portion of the orbiter. At the conclusion of the first conditioning period, the tire pressure was measured at 334 pounds per square inch (psi), an increase from 328 psi before the period. The nominal end of mission pressure is targeted at 330 psi.

On Sunday, October 29, 1995, 6 a.m. CDT, STS-73 Payload Status Report # 15 reports: (8/21:07 MET)

Research in the unique laboratory environment of space continued at a steady pace over the last 24 hours aboard the second United States Microgravity Laboratory.

During one experiment run yesterday, the Surface Tension Driven Convection Experiment team observed a phenomenon that had never been seen before. Fluid flows were erratic, with no obvious organization or pattern, as Payload Commander Kathy Thornton increased the silicone oil surface temperature beyond the point at which flows within the fluid began to oscillate, or become unsteady. Overnight, the ground team conducted several test runs remotely from the Spacelab control center, freeing the crew for other activities. The experiment seeks to define the factors which cause subtle, surface-temperature-driven fluid flows to become oscillatory. Researchers from Case Western Reserve University in Ohio will use the extensive data gathered during USML-2 to graph the onset of oscillations under many conditions. A better understanding of how and why such fluid flows occur will be valuable for industrial applications from fuel management and storage to materials processing methods such as welding.

In a related Glovebox investigation, Payload Specialist Fred Leslie performed the mission's first run of the Oscillatory Thermocapillary Flow Experiment. Though it uses much simpler equipment, the purpose and procedure are similar to Surface Tension Driven Convection Experiment tests. The major difference is the proportions of the container. The STDCE chamber's diameter is twice its own height, while this Glovebox investigation used a very shallow chamber with a diameter four times its height. Different chamber sizes provide even more variables for determining the onset of unstable surface-temperature-driven fluid flows.

Thornton and Payload Specialist Al Sacco exchanged sample cartridges in the Crystal Growth Furnace yesterday, replacing three processed samples with three new ones. Last evening, the facility completed its shortest crystal growth cycle, depositing a thin layer of infrared-detecting mercury cadmium telluride on a base material, or substrate, in just one and a half hours.

"We're examining ways to reduce what we call crystal 'birth defects,' which are transferred from defects in the substrate material which can't be eliminated," said Principal Investigator Dr. Heribert Wiedemeier of the Rensselaer Polytechnic Institute. "In the crystal we grew on USML-1, the interface between the substrate and the first layer was much smoother than in crystals produced on the ground. This was totally new, something we had never seen before and had not expected."

On USML-2, Wiedemeier is growing much thinner layers to see how far substrate defects propagate into the first crystal layer. On the ground, the crystal material first forms separate "islands" on the base, which join to form a complete layer after about two hours of growth. Wiedemeier grew his first USML-2 crystal on Sunday for two and one-half hours to be sure a compete layer was produced. "With last night's sample, we deliberately stopped growth in less time than it takes for a layer to form on Earth. However, there is a good chance that under microgravity we may get a complete layer in the shorter time period," he said.

If this mission demonstrates that certain reduced convection conditions produce more uniform initial layers in a shorter growth time, Wiedemeier feels it could lead to crystal growth methods on Earth that are faster, require less material and energy, and therefore are less costly.

Sacco completed activating protein crystal growth experiments in the Glovebox facility yesterday afternoon. Thus far, more than 50 individual experiments have been set up using seven different proteins -- from viral disease proteins to several involved in the human immune system. USML-2 crew members will observe the samples on Thursday to monitor the growth of the crystals. Proteins play vital roles in daily life, from providing nourishment to fighting disease. Many areas of biotechnology benefit from new information on the structure of proteins, such as development of food crops with higher protein content and basic research toward more effective drugs.

Team members for the Geophysical Fluid Flow Cell Experiment slowed down the rotation of their experiment hemisphere to get additional data which relates to fluid motions in Earth's core -- motions that cause such phenomena as the forced drift of the Earth's continents. The fluid flow cell is an investigation in fluid dynamics that models fluid flows in planets, stars and oceans, using silicone oil between two rotating hemispheres. Controllers can vary electrical charges which simulate gravity, as well as fluid temperature and rotation speed of the hemispheres, to reflect conditions in different environments.

Overnight, Mission Specialist Cady Coleman patiently worked through problems with computer equipment to complete several runs of the Glovebox Colloidal Disorder-Order Transition (CDOT) investigation. CDOT uses microscopic plastic spheres suspended in a liquid to model the behavior of atoms. As planned, red shift crew members will complete the CDOT activities later today.

When he came back on duty early this morning, Payload Specialist Al Sacco began a series of experiments in the Drop Physics Module to examine how chemical additives, called surfactants, affect liquid drop behavior. The drop studies will continue throughout today's shift.

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