STS-75 Day 8 Highlights

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On Thursday, February 29, 1996, 9 a.m. CST, STS-75 MCC Status Report # 15 reports:

Columbia's crew continues its work with the United States Microgravity Payload experiments supporting a variety of investigations including crystal growth, materials solidification and fluid dynamics. Meanwhile, payload controllers continue to obtain snapshots of data from the tethered satellite as it passes within range of available groundstations around the world.

As TSS battery power diminishes, plans are in work to turn on science instruments, Earth sensors and stabilizing gyros in anticipation of the closest approach of TSS to Columbia at about 11 p.m. central time today (approximately 07/08:50 mission elapsed time). At that point, the orbiter should pass within about 50 miles of the satellite possibly allowing payload bay instruments a chance to gather data on the satellite as well.

Because of the instability of the satellite and its varying gravitational drag, the distance between the two spacecraft and the time of closest approach likely will change. In any case, there is no concern about Columbia passing too close to the satellite. Whether or not the crew can visually observe the satellite during the fly-by will depend on lighting conditions at that time.

The Tethered Satellite is currently about 3,000 nautical miles ahead of Columbia with the distance between the two spacecraft closing at the rate of 340 nm with every revolution of the Earth.

On Thursday, February 29, 1996, 6 a.m. CST, STS-75 Payload Status Report # 13 reports: (6/15:42 MET)

The third United States Microgravity Payload (USMP-3) completed another night of successful operations aboard the Space Shuttle Columbia, with the four experiments that make up the payload processing good data in the microgravity environment of Earth's orbit. The smooth ride aboard Columbia, in free fall around Earth, was made even smoother yesterday as crew members restricted their movements in "quiescent" periods. This allowed USMP-3 researchers with the MEPHISTO experiment to gather baseline data about the effects of movement on their delicate semiconductor material samples by comparing them to times of no activity.

The scientific activities of the MEPHISTO experiment, led by Dr. Jean-Jacques Favier of the French Atomic Energy Commission, included a study of "g-jitter," or microgravity disturbance effects such as those caused by crew activities and orbiter thruster firings. As expected, the first 25-second thruster firing, or "burn," produced accelerations of more than 10,000 micro-g's, a force equal to one- hundredth of Earth's gravity, and provided a significant response in the experiment's real-time data transmission. Another 15- second firing also produced a marked change in this signal. The science team observed that the measurements continued to increase for a few minutes after each of these burns before slowly decreasing. Before and after each thruster firing, the crew remained in a relatively still mode to allow scientists to perform real-time correlations of MEPHISTO's data with information collected from the Space Acceleration Measurement System (SAMS) aboard the Shuttle.

The understanding gained from the MEPHISTO experiment may ultimately lead to improvements in materials preparation and processing on Earth. MEPHISTO uses very selective methods to study the role of gravity-driven fluid flows in the solidification of materials. Microgravity reduces fluid flows caused by sinking and rising, allowing researchers to explore effects normally hidden by gravity.

This morning, the Marshall Space Flight Center's Advanced Automated Directional Solidification Furnace (AADSF) began its first experiment operations, melting a lead-tin-telluride sample to test theories about gravity's effects on growing semiconductor materials. Today, the instrument's science team, led by Principal Investigator Dr. Archie Fripp, will continue melting and positioning all three samples, then actually start growing crystals by seeding and re-solidifying the lead-tin-telluride alloy.

Yesterday afternoon, Pilot Scott Horowitz and Mission Specialist Claude Nicollier performed runs of the Lewis Research Center-managed Forced Flow Flamespreading Test (FFFT) experiment in the Middeck Glovebox Facility. They burned flat paper samples to help the science team, led by Glovebox Investigator Kurt Sacksteder, study how air motion affects flame spreading in microgravity.

Scientists who study combustion want to know the details of how air motion affects flame spreading and how to better control fires that may occur on orbit. On Earth, gravity causes hot air to rise and cool air to fall. Because of the complexity of the physical and chemical processes involved, the theoretical understanding of flame spreading in space is still a relatively new science. The microgravity environment available in the self-contained Glovebox aboard the Space Shuttle is an important tool for scientists and engineers to study this important phenomenon.

The Isothermal Dendritic Growth Experiment (IDGE), developed by the Rensselaer Polytechnic Institute, has completed 15 dendrite growth cycles during its primary science phase. Images of free-floating dendrites, acquired during melting after a growth cycle, show no detectable motion compared with images of dendrites attached to the experiment's container. Analysis of such post-melting images help researchers define the mobility limits of the free-floating, pine tree-shaped dendrite crystals in the microgravity environment.

The ZENO Critical Fluid Light Scattering Experiment's sample cell temperature continues to approach the critical temperature and pressure at which xenon exists simultaneously in both the liquid and vapor phases. ZENO uses precise light-scattering measurements as an unintrusive way of seeing changes in a xenon sample as it fluctuates rapidly between two states of matter.

In addition to continued sample processing by the four USMP-3 investigations, the next 12-hours will begin with the first in a series of Comparative Soot Diagnostics combustion experiment runs in the Middeck Glovebox.

On Thursday, February 29, 1996, 5 p.m. CST, STS-75 MCC Status Report # 16 reports:

Columbia and the Tethered Satellite will pass within about 51 nautical miles of each other at 11:17 p.m. central time today (approximately 7/08:59 MET), providing the astronauts a chance to glimpse the errant spacecraft since it separated from the orbiter Sunday night.

Tonight's encounter with TSS marks the point of closest approach for the two spacecraft before they begin to separate once again. Currently, the orbiter trails TSS by a distance of about 1900 nautical miles, with Columbia closing on the satellite at the rate of 340 nm with each revolution of the Earth. Whether or not the crew will be able to see the satellite during the fly-by will depend on lighting conditions and orbiter position.

This afternoon, crewmembers discussed the progress of the flight during an in-flight interview with two Philadelphia television stations. A second interview, at 6:08 p.m., is with the United States Information Agency's Worldnet program.

Columbia is functioning normally, with no problems being tracked by the flight control team as the Shuttle orbits the Earth every 90 minutes at an altitude of 180 statute miles.

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