STS-73 Day 7 Highlights

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On Thursday, October 26, 1995, 8 a.m. CDT, STS-73 MCC Status Report # 13 reports:

Research work continued on schedule overnight aboard Columbia as the crew also continued a schedule of staggered half-days off duty to relax from the around-the-clock operations.

Mission Specialist Cady Coleman and Payload Specialist Fred Leslie each had a half-day off during the night. The Red Team of crew members is now at work aboard Columbia, having begun their 12-hour shift at 6:38 a.m. CDT

Although it had no effect on the research work, a ground system problem caused two extended communications outages between Columbia and the ground during the night. The time frame for the outages was known in advance by Mission Control and the crew was informed. All data from the experiments and the shuttle itself during the communications loss was recorded aboard Columbia and has since been played back to the ground.

The communications loss was due to an equipment failure at the ground terminal for NASA's tracking and communications satellites. The failure prohibited communications using the eastern Tracking and Data Relay Satellite (TDRS-E), a satellite stationary above the Atlantic Ocean used during about the last one-third of each orbit by Columbia. On two successive orbits during the early morning hours, communications were unavailable on TDRS-E, the first time for about 36 minutes and the second time for about 27 minutes, while the ground equipment was being repaired.

Columbia is in a 169 by 165 mile orbit, completing a revolution of Earth every 90 minutes. The spacecraft remains in excellent condition, and there are no issues of concern in Mission Control regarding its performance.

On Thursday, October 26, 1995, 6 a.m. CDT, STS-73 Payload Status Report # 10 reports: (5/21:07 MET)

Crew activities were relatively quiet aboard the second United States Microgravity Laboratory overnight, as Mission Specialist Cady Coleman and Payload Specialist Fred Leslie took turns getting a few hours rest from their busy schedules. The mission's many crystal growth experiments continued uninterrupted, taking advantage of unique opportunities for discovery available only in the low-gravity environment of space.

The Crystal Growth Furnace team finished melting Dr. David Matthiesen's gallium arsenide crystal and began slowly resolidifying the semiconductor sample. At almost 2,300 degrees Fahrenheit (1,255 degrees Celsius), the furnace is operating at the highest temperature it will reach during the mission. A new Crystal Growth Furnace feature for USML-2 will periodically mark the point where the melted material is solidifying with an electric pulse. When the crystal is analyzed after landing, the marks will indicate the exact growth rate of the crystal and the location of the solid/liquid boundary at each stage of solidification.

Electronic devices using gallium arsenide semiconductors, such as high-speed digital circuits, operate at higher speeds and use less power than those using silicon crystals. Matthiesen's experiment investigates techniques for uniformly distributing a small amount of selenium within the crystal as it grows in microgravity.

"There is less than one part per million of selenium in this sample," said furnace team member Dr. Frank Szofran of Marshall Space Flight Center. "Yet it greatly alters the electrical conductivity of the semiconductor." Trace materials, called dopants, are often added to semiconductors to improve or precisely control their electronic characteristics. To produce high quality crystals, scientists need to understand the process by which dopants are distributed within a compound during crystal growth. Growing the crystals in microgravity greatly reduces uneven dopant distribution caused by gravity on Earth, allowing more subtle influences to be identified.

Leslie and Coleman spent most of their on-duty hours working with the Surface Tension Driven Convection Experiment (STDCE). Last night's runs were the first to use the experiment's largest chamber, almost 1-1/4 inches (3 centimeters) in diameter. As they have for the past five days, the science team in Huntsville and the Spacelab crew on orbit worked together to precisely adjust temperatures on the silicone oil surface. Again, they were able to pinpoint when surface-temperature-driven flows within the fluid became unsteady, or oscillatory. This was the first time oscillatory flows had ever been observed in such a relatively large container. Coleman reported seeing especially dramatic, wave-like oscillations near the center of the fluid flow during some of her experiment runs. Unwanted fluid flows affect the quality of materials solidified from a molten state on Earth. Understanding the subtle factors which control those flows gives researchers tools for eventually controlling them.

Several factors are contributing to the success of the USML-2 surface-tension experiments. A new optics system developed by Dr. H. Philip Stahl and students from Rose Hulman Institute of Technology in Terre Haute, Indiana, gives the crew and ground controllers precise pictures of oil surface shapes and flow patterns. Spacelab's new six-channel Hi-Pac Television system is simultaneously downlinking video of those images, along with a three-dimensional view of the chamber and infrared temperature readings, giving the science team a complete representation of the experiment.

STDCE team members also have been keeping a close eye on real-time data from the Three-Dimensional Microgravity Accelerometer, or 3-DMA. The low-frequency vibration detector has a sensor located in the rack next to the surface tension experiment. "3-DMA allows us to make a judgment as to whether to wait for external movements to settle down before beginning an experiment run," said Project Scientist Alex Pline.

On its first Shuttle flight, 3-DMA was developed as a low- cost commercial accelerometer system by the University of Alabama at Huntsville's Consortium for Materials Development in Space. The instrument measures both the absolute level of microgravity acceleration (the difference between zero acceleration and what is experienced during the mission) and microvibrations which could affect the investigations onboard. Principal Investigator Jan Bijvoet worked in Huntsville for the European Space Agency when it was developing the Spacelab over a decade ago. "It's good to have an experiment aboard 'my' Spacelab," he said.

The Geophysical Fluid Flow Cell Experiment team is wrapping up another six-hour solar atmosphere simulation, and growth continues in the Zeolite Crystal Growth Furnace and the many USML-2 protein crystal growth experiments.

On Thursday, October 26, 1995, 5 p.m. CDT, STS-73 MCC Status Report # 14 reports

Work on board the Space Shuttle Columbia continued to go smoothly as members of the Red Team monitored orbiter systems and conducted scientific experiments in the Spacelab.

Red Team members spent their seventh flight day working diligently in the science lab which is nestled in Columbia's cargo bay. The Red Team will wrap up its day at 5:38 p.m. CDT, a little earlier than they have the last few days. They will hand over to Blue Team members who will continue work in the Spacelab. The Red Team will return to duty at 5:38 a.m. CDT.

Friday's scheduled telelvision events include: an ABC "World News Now" interview at 8:23 a.m. with STS-73 Commander Kenneth Bowersox and Payload Commander Kathyrn Thornton; Mission Update at 11:30 a.m.; and a Mission Status Briefing at 1 p.m.

Columbia is in a 169 by 165 mile orbit, completing a revolution of Earth every 90 minutes. The spacecraft is in excellent condition and flight controllers did not have any issues they are working regarding the orbiter's performance.

On Thursday, October 26, 1995, 6 p.m. CDT, STS-73 Payload Status Report # 11 reports: (6/09:07 MET)

Payload Commander Kathy Thornton and Payload Specialist Al Sacco had a busy day conducting a wide variety of experiments in the microgravity environment aboard the Shuttle Columbia in the second United State Microgravity Laboratory (USML-2).

The Colloidal Order-Disorder Transition experiment, an investigation into the solidification process in crystal growth, revealed unexpected results today. In studying electronic still photographs provided by Sacco this morning, researchers saw that crystals of varying sizes were formed in the samples. This is something they haven't seen on Earth.

Sacco told researchers on the ground that particles in the 15 sample vials were randomly spaced, and ranged in size from 10 to 150 microns (millionth of a meter). Scientists are interested in what happens at the boundaries between solid and liquid states during crystallization of a colloid, allowing them to see how atoms and molecules move and arrange themselves when they form a crystal. This may help improve materials processing methods on Earth, as well as in microgravity.

A crystal of the semiconductor material gallium arsenide has grown about 1 inch (2-1/2 centimeters) since it was placed in the Crystal Growth Furnace last night. The temperature in the Crystal Growth Furnace is the hottest it has been during this mission' between 22 and 23 hundred degrees Fahrenheit . The crystal is growing at a rate of 1.8 millimeters per hour. Although this is a slow growth period, gallium arsenide crystals have the potential to make computers, satellites and other electronics work much faster than with silicon chips. Chips made of gallium arsenide are now too expensive for widespread use - current processing techniques yielding only one good chip out of every ten that are made.

Thornton this morning began deploying liquid drops in the Drop Physics Module in tests to help the science team finalize a procedure to slow down the rotation of the drops. Later, the USML-2 crew will add a small amount of chemical, called a surfactant, to the drop in an experiment known as Science and Technology of Surface Controlled Phenomena, managed by Principal Investigator Dr. Robert E. Apfel, of Yale University. Scientists are comparing characteristics of drops containing surfactants to drops of pure water. Surfactants are substances which alter the surface properties of a liquid, aiding or inhibiting the way it adheres to or mixes with other substances. Applications of this research apply to many industrial processes, among them the production of cosmetics and improvement of oil recovery.

University of California's Riverside's Dr. Alex McPherson is principal investigator for the handheld diffusion test cells experiment. The experiment is growing proteins by liquid- liquid diffusion, a process in which fluids diffuse into each other by random motion of molecules, rather than being mixed together. This method is difficult on Earth because gravity causes solutions with different densities to mix. The experiment is a precursor for long-duration crystallization experiments aboard the International Space Station and Mir.

The Three-Dimensional Microgravity Accelerometer experiment ground support team continues to troubleshoot the cause and resolution of a data downlink problem. This has not impacted science since all data is recorded onboard the Shuttle. This experiment measures accelerations and vibrations that could affect investigations in the Spacelab.

Thornton spent the afternoon working with the Surface Tension Driven Convection Experiment. Researchers on the ground relayed instructions for Thornton to raise the temperature of the silicon oil surface in order to study the change from steady thermocapillary fluid flows to oscillatory (or unsteady) flows. This investigation could one day lead to better, stronger high-tech crystals, metals, alloys and ceramics.

Sacco spent the last part of his shift working in the Glovebox activating new protein crystal growth experiments, based on his observations of results from previous experiments. An advantage of a longer mission like USML-2 is that it allows science teams on the ground to perform several experiment runs, analyze their data, and have the crew devise a new set of experiments. This allows investigators to quickly capitalize on their observations in real time.

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