STS-75 Day 16 Highlights

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On Friday, March 8, 1996, 9 a.m. CST, STS-75 MCC Status Report # 29 reports:

Shuttle managers today elected to wait for better weather in Florida on Saturday due to unpredictable cloud cover this morning at Kennedy Space Center. The weather forecast indicates improved conditions Saturday.

Today's landing opportunities slipped by one by one as the flight control team saw some improvement in cloud cover at the KSC landing site, only to be faced with a prediction of bands of low clouds moving over the runway area at the scheduled landing time. Weather was generally good at Edwards Air Force Base, the alternate site, but with some hope of better weather in Florida Saturday, managers decided to keep Columbia in orbit one additional day.

Early Friday, Columbia's astronauts prepared the vehicle for entry, packing up gear aboard the shuttle and closing the payload bay doors. They will now reopen the doors to provide necessary cooling and go through the deorbit preparations again Saturday morning.

The first opportunity Saturday for a KSC landing comes on orbit 250 with a deorbit burn at 5:23 a.m. CST and a landing at 6:24 a.m. CST. The second KSC opportunity is at 7:59 a.m. CST and the final opportunity in Florida comes at 9:35 a.m. Edwards landing opportunities Saturday morning are at 7:51, 9:26 and 11:01 CST.

On Friday, March 8, 1996, 9 a.m. CST, STS-75 Payload Status Report # 21 reports: (14/18:42 MET)

With over 14 days of research in space accomplished, the STS-75 Space Shuttle mission of Columbia has produced a vast array of scientific information for diverse applications -- from using electrically conducting tethers in space to improving ground-based materials processing.

The combination of real-time data already collected and samples on their way back into the hands of experimenters will stoke the fires of scientific investigation throughout the weeks and months ahead. Researchers for both the Tethered Satellite System Reflight (TSS-1R) and the third United States Microgravity Payload (USMP-3) mission phases are already hard at work to learn what these data mean.

"The Italian tethered satellite was built about 100 miles from the birthplace of Christopher Columbus. Today, he is remembered not for what he set out to find, but what he actually discovered." That is how NASA Mission Scientist Dr. Nobie Stone characterized the importance of the tethered satellite experiment. The mission demonstrated that electrical current-collection and power-generating capabilities of the system can be several times the predicted levels. This knowledge will help researchers assess and shape the future of tethered satellites in space, said Stone and Dr. Carlo Bonifazi, principal investigator from the Italian Space Agency. Promising fields for applications range from spacecraft power production to placing scientific platforms in unexplored regions of Earth's atmosphere and changing a spacecraft's orbit.

Despite the unexpected break in the tether on which the satellite was being unreeled from Columbia, TSS scientists collected data that has helped them meet several key science goals, according to Stone and Bonifazi. Early results, in fact, go beyond existing models of plasma and space physics phenomena. Stone predicted that contemporary texts that treat these subjects will address the surprising findings already gained from the deployment phase. The TSS mission also included several "firsts."

A primary goal was to study the relationship between voltage and current in a tethered satellite system. Currents measured during the deployment phase were at least three times greater than predicted by analytical modeling. When planning to use tether-produced energy as a power system, or as an electrical generator in space, the amount of power that can be generated is directly proportional to the current. This means that it may be possible for a tether system to generate two or three times more power than originally thought. Conversely, another application is to reverse current flow and use the tether in an electric-motor mode to create thrust for boosting spacecraft in orbit. Again, the force generated is directly proportional to current and was well in excess of predictions.

Another successful study was how gas from the satellite's thrusters, moving rapidly through Earth orbit, interacts with the ionosphere, the electrically charged region of the upper atmosphere. The environments around the orbiter and satellite were substantially modified by neutral gas emissions, and ionization of the gas at the satellite greatly enhanced the current capacity of the system. For the first time, measurements were made of the high-voltage plasma sheath, or ionized shock wave, around a satellite. Although essentially impossible to study in the laboratory and difficult to mathematically model, this phenomenon affects satellites, including those in much higher orbits, such as communications satellites. Also, the TSS deployment created the world's longest antenna in space. Scientists hope to analyze emissions from the TSS that may have been picked up by receivers at a ground site.

Although satellites have been flying in space for 40 years, aspects of the interaction of a moving body as it cuts through the plasma environment are still unclear. Another first is the collection of a rich data set on these plasma wakes, which are somewhat similar to the wake made by a boat moving through water. TSS has given researchers a unique opportunity to study this very fundamental interaction. This knowledge is important to understanding many types of measurements made by spacecraft and also applies to celestial bodies, such as the interaction of the moon with the solar wind -- a stream of electrons and charged hydrogen atoms that flows past the Earth at speeds over 180 miles per second (300 kilometers per second).

Meanwhile, the scientific harvest for the third United States Microgravity Payload (USMP-3) research team topped the 100-percent mark, thanks to a bonus day in space for their experiments. USMP-3 researchers, who had already won their "game," scored extra points by gathering additional data with which to better understand materials processing and fire-related phenomena in space. The ultimate benefit of USMP-3 research will be improvements in products manufactured on Earth. "I couldn't be happier. The science we've obtained is fundamental to a lot of processes that are very important to all of us," concluded USMP-3 Mission Scientist Dr. Peter Curreri.

During the eight and one-half day dedicated microgravity science phase of STS-75, USMP-3 researchers used an effective combination of remote control, or "telescience," for materials processing and thermodynamic experiments, and hands-on work with combustion studies performed in the Middeck Glovebox. Telescience will be increasingly important for long-term research in space, such as aboard the International Space Station.

The MEPHISTO science team, led by Dr. Jean-Jacques Favier of France's Center for Nuclear Study, used flight-proven equipment to learn how the chemical composition of molten material changes, and can be controlled, as they solidify. Such knowledge applies to ground-based materials processing and chemical engineering. For the first time, the changes in the microgravity environment caused by carefully planned Shuttle thruster firings were correlated with fluid flows in a crystal sample. With the help of data from the Space Acceleration Measurement System on board Columbia, research showed that in one direction of movement, a large effect was noted, whereas in another direction, there was little impact. Such information is important in future designs and experiment planning for similar facilities aboard the International Space Station. Also, the MEPHISTO team successfully monitored the point at which their sample's crystal edge underwent a key change -- from flat to grooved -- as it solidified.

During each cycle, the MEPHISTO experiment's high-temperature furnace melted and re-solidified a tin-bismuth mixture representative of alloys found in airplane turbine blades, electronic materials and many other products. The ability to remotely command the MEPHISTO experiment let the science team use a new strategy to improve data on the stability of their sample's shape. This involved tracking small changes in the speed of sample growth during several furnace operating cycles. After finishing its final run on Thursday, one sample was flash-cooled to preserve it for microscopic analysis. Measurements from the MEPHISTO facility -- one in a series of cooperative investigations between NASA, the French Space Agency and the French Atomic Energy Commission -- will now be analyzed, along with the final metallic samples, in order to increase understanding of subtle changes that occurred during the samples' cooling and solidification.

The Advanced Automated Directional Solidification Furnace (AADSF) team, led by Dr. Archie Fripp of NASA's Langley Research Center, completed more science than they had hoped to accomplish. In the AADSF, three lead-tin-telluride crystals were grown while Columbia orbited in three different attitudes, to determine how these orientations affect crystal growth. This knowledge is expected to help researchers develop processes and semiconductor materials that perform better and cost less to produce. It is also likely to lead to future furnace experiments aboard the Space Station, where crystal growth directions are subject to change. In addition to planned experiments, they got the added bonus of new data at their crystal's freezing point and an unintended, but interesting, marker in the growth of their first crystal caused by an unscheduled Shuttle thruster firing.

A team from Rensselaer Polytechnic Institute (RPI) and NASA's Lewis Research Center, designed the Isothermal Dendritic Growth Experiment (IDGE) to provide high-quality data on the solidification of a material that imitates the characteristics of common metals and alloys. The team collected twice the data they needed, which will significantly improve statistical analysis. Knowledge gained from this experiment will help improve Earth-based processes such as metal casting, welding and production of aluminum, steel and copper. The ability to perform real-time materials science in space has already shown IDGE investigators that variations in Columbia's microgravity environment did not affect variations in the speed of dendrite growth. This finding will allow materials scientists to refine theories of how tiny, pine-tree-shaped crystals, called dendrites, form as metals solidify.

The IDGE team also participated in an important technology demonstration by commanding a microgravity space instrument from a remote site located at RPI. This first-ever remote commanding to the Shuttle from a U.S. university campus foreshadows operations aboard the International Space Station. "This was an important operational experiment, as well as a significant science experiment," emphasized Principal Investigator Dr. Martin Glicksman.

Investigators for the Critical Fluid Light Scattering Experiment, or Zeno, led by Dr. Robert Gammon of the University of Maryland, were successful in observing, with unprecedented clarity, xenon's critical point behavior -- the precise temperature and pressure at which it exists as both a gas and a liquid. On Thursday, the experiment which measures changes in laser light scattering due to variations in the xenon sample's density, completed the long, methodical approach to the critical point. After nearly 14 days of stepping through a series of tiny decreases in temperature, the team reached the peak of "Mount Zeno." The transparent xenon sample displayed the unusual critical point condition, with maximum light scattering followed by a sudden increase in cloudiness. This effect was much more distinctive than observed during the USMP-2 mission (STS-62) and happened at a lower temperature than previously thought.

"We've been to the top, did our flyover of Mount ZENO, and have actually seen the highest count rates from this sample that we've ever seen anywhere," emphasized Dr. Gammon. "There's no other system that lets you approach this kind of intensity of thermal fluctuation -- you just can't do this on the ground." Dr. Gammon further compared the critical point to the violent reactions in the Sun's core and at the beginning of the universe when condensed matter expanded to the states observed today. Knowledge from this experiment will prove valuable for applications from liquid crystals to superconductors.

While USMP-3 remote commanding was in progress in Columbia's cargo bay, crew member work in conducting Middeck Glovebox investigations went so smoothly that all combustion samples on board were processed, both primary and spares. This, combined with the combustion researchers' ability to monitor and change procedures in progress, enabled the combustion team to obtain more than 125 percent of their planned science. A further bonus came with crew support for performing some post-experimentation Glovebox evaluation procedures. Valuable engineering information that was gathered will be used to verify Glovebox performance in low-gravity with what had been seen on the ground. The versatile Glovebox and the Forced Flow Flamespreading Test experiment are slated for flight aboard the Russian space station Mir later this year. The Glovebox is also one of the facilities planned for the International Space Station.

The Forced Flow Flamespreading Test (FFFT), conducted by Kurt Sacksteder of NASA's Lewis Research Center, processed 16 paper samples, both flat and cylinder-shaped. Video of the cylinder-shaped samples showed significant differences in flame size, growth rate and color with variations in air flow speed and fuel temperature. In post-flight analysis, the flame behavior will be compared with that of ground simulations to aid in better control and prevention of fires.

The Comparative Soot Diagnostics (CSD) investigation led by Dr. David Urban, also of the Lewis Center, completed 25 combustion experiment runs, 10 more than originally planned. The CSD team obtained excellent results, testing the effectiveness of two different smoke-sensing techniques, for detecting fires in microgravity aboard the Shuttle and the International Space Station. Both detectors responded to smoke from all the burning samples. Post-flight analysis involves examination of smoke particles with an electron microscope to obtain a more complete comparison of the two detectors' performance.

The Radiative Ignition and Transition to Spread Investigation (RITSI) team, led by Dr. Takashi Kashiwagi of the National Institute for Standards and Testing, reported observing new combustion phenomena, such as "tunneling" flames which move along a narrow path instead of fanning out from the burn site. Also, for the first time, these investigators studied the effects of sample edges and corners on fire spreading in microgravity. The RITSI group likewise successfully conducted 15 planned and 10 extra sample burns. Data obtained will be compared with computed predictions as part of efforts to further reduce the dangers posed by the possibility of fires aboard spacecraft.

On Friday, March 8, 1996, 5 p.m. CST, STS-75 MCC Status Report # 30 reports:

Space Shuttle Columbia's astronauts were scheduled to awaken about 10:30 p.m. Friday night to begin preparations for a Saturday landing, concluding over two weeks of science operations in space. Shuttle managers earlier today elected to pass up landing at the Edwards Air Force Base in California Friday in the hope that improving weather at Kennedy Space Center in Florida would allow for a landing there Saturday.

Early Saturday, Columbia's astronauts will prepare the vehicle for entry, packing up gear aboard the shuttle, closing the payload bay doors and getting into their launch/entry suits.

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