STS-75 Day 12 Highlights
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- On Monday, March 4, 1996, 8 a.m. CST, STS-75 MCC Status Report # 21
- 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
- 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
- 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
- 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
- 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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