STS-75 Day 12 Highlights

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On Monday, March 4, 1996, 8 a.m. CST, STS-75 MCC Status Report # 21 reports:

Science investigations continue aboard Columbia as mission managers on the ground contemplate extending the flight at the request of the United States Microgravity Payload customer.

Meanwhile, studies into how flame behaves in the absence of gravity continue in a controlled environment on the middeck of the orbiter. The investigations will hopefully provide additional data for improved fire-fighting techniques on Earth.

From an orbiter standpoint, Columbia is in excellent shape supporting the USMP operations. One of the three navigation units on board -- Inertial Measurement Unit number 3 -- was turned off yesterday after controllers monitored small drifts in its gyroscopes. Drifts such as these are compensated through alignments periodically and pose no problem for the flight duration since only one IMU is required for on orbit operations. The unit will be turned back on before landing day.

Columbia is in an orbit 182 by 171 statute miles above the Earth circling the globe every 90 minutes.

On Monday, March 4, 1996, 6 a.m. CST, STS-75 Payload Status Report # 17 reports: (10/15:42 MET)

The four microgravity experiments that make up the third United States Microgravity Payload (USMP-3) complement depend on the smoothest, quietest ride available on the Space Shuttle. As Columbia orbits in free-fall, it, along with everything on board, experiences the same gravitational pull; but with no resistance to the gravitational force, people and objects fall at the same speed and float within the Shuttle. Each USMP-3 investigation was precisely planned to take advantage of this valuable research tool. They also depend on the Shuttle itself, its on-board acceleration monitors, and the crew's cooperation as integral elements of their research methods.

Scientists using the NASA Marshall Space Flight Center's Advanced Automated Directional Solidification Furnace (AADSF) have finished growing their third and final sample of semiconductor material. The furnace is now in a 15-hour cooling mode in preparation for stowage. The AADSF uses a high-temperature chamber in which three samples of the material lead-tin-telluride have been processed. During the mission, the crew changed the Shuttle's orientation and reduced their activities throughout quiet, or "quiescent," periods. The result was a smooth, excellent microgravity environment in which each sample could crystallize, testing the results with different alignments of growth direction, relative to the direction of flight.

AADSF grew its first sample vertically, pointing away from Earth, with the hot end at the top and the cool end at the bottom, while the second crystal solidified in the opposite direction, with the cool end up and the hot end down. The third sample represented what would be a horizontal crystal growth on Earth. Growing the crystals in different directions will give the AADSF scientists insight on how important such orientations will be for sample processing aboard the International Space Station.

"As the Space Station structure grows, the orientation of its microgravity environment could change, and affect the direction of samples growing in an on-board furnace," explained AADSF Principal Investigator Dr. Archie Fripp. "If there's a measurable difference between the uniformity of semiconductor samples grown in different directions on this mission, then we know that this will be significant on the Space Station." The uniformity of the AADSF samples being returned for analysis will be compared with that of Earth-grown crystals to shed light on how to improve ground-based processing of such materials.

The Shuttle's attitude is also crucial for the MEPHISTO experiment, one in a series of cooperative investigations between NASA, the French Space Agency and the French Atomic Energy Commission. MEPHISTO uses a similar furnace to melt and resolidify a tin-bismuth alloy, or mixture of metals. Last night and throughout the mission, the experiment team used data gathered during firings of the Shuttle's reaction control thrusters to record the effects of orbiter accelerations on the samples. According to MEPHISTO Principal Investigator Dr. Jean-Jacques Favier, science teams at the French Space Agency's center in Toulouse and at the University of Alabama in Huntsville are getting good results by correlating this real-time data with information from Columbia's on-board Space Acceleration Measurement System.

Scientists working with the NASA Lewis Research Center's Critical Fluid Light Scattering Experiment, or ZENO, have further refined their estimate of their xenon sample's "critical point" by adjusting the experiment's heat sensors. As ZENO approaches closer and closer to this critical temperature and density, in which gas and liquid phases coexist, changes in Columbia's position become increasingly important. The ZENO science team, led by Dr. Robert Gammon of the University of Maryland, is working with mission flight controllers to control the effects these changes have on their investigation.

Early in the mission, before their primary science activities began, investigators for the Rensselaer Polytechnic Institute's Isothermal Dendritic Growth Experiment (IDGE), led by Dr. Martin Glicksman, studied the effects that a variety of orbiter attitudes had on their experiment. Using data gathered by the on-board Orbiter Acceleration Research Experiment, they compared the influence of the Shuttle's microgravity directions with the direction that their microscopic pine tree-shaped dendrite crystals grew. The IDGE team discovered that small fluid flows caused by Columbia's gradual, slow movement had no effect on the dendrites' growth rate. The shape and speed of dendrite growth ultimately determines the strength and durability of a range of metals from aluminum to steel.

The IDGE team has already completed over 90 of its planned 120 dendrite growths. This kind of space science unmasks processes that are obscured on Earth, where gravity-induced flows and other phenomena cloud the waters of understanding. Just as a jet of hot water changes the shape of an icicle, fluid flows caused by gravity on Earth distort the shape of dendrite tips. Therefore, precise determination of dendrite shapes can best be performed in the microgravity environment of space.

In the next 24 hours, more combustion studies for the Forced Flow Flamespreading Test and Radiative Ignition and Transition to Spread Investigation will continue in the Glovebox. Meanwhile, Commander Andrew Allen and Pilot Scott Horowitz will maneuver Columbia through a 360-degree roll in order to stir the MEPHISTO furnace's sample, and the IDGE team at Rensselaer Polytechnic Institute will issue the first ever remote command from a campus site to actually control an experiment aboard the Space Shuttle.

On Monday, March 4, 1996, 5 p.m. CST, STS-75 MCC Status Report # 22 reports:

Columbia's astronauts will spend an additional day in orbit after flight controllers opted to extend the flight to support ongoing scientific investigations with the United States Microgravity Payload.

Commander Andy Allen responded to the news by telling flight controllers the crew was ready to support any additional mission extensions. With the additional day, landing is now set for 6:13 a.m. CST on March 8.

Columbia's astronauts also may have an opportunity to view the Tethered Satellite once again as the two spacecraft will pass within 40-50 nautical miles of each other mid- morning Tuesday. Flight controllers will work through the night to refine the exact time of tomorrow's close approach. Currently, Columbia trails the satellite at a distance of 3,900 nautical miles, closing the gap at the rate of 314 nautical miles with every orbit of the Earth.

The seven-member crew will discuss the progress of the mission with reporters in the United States and Europe during the traditional in-flight news conference at 5:54 central time Tuesday morning.

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