November 25, 1997
United States Microgravity Payload-4 - Flight
Day 6
Science experiments aboard the U.S. Microgravity Payload (USMP-4) have stayed on schedule and are returning striking results as the mission nears its midpoint.
"We're right on the timeline," said mission scientist Dr. Peter Curreri at the Payload Control Center at NASA's Marshall Space Flight Center.
USMP-4 comprises four large experiment
facilities in Space Shuttle Columbia's payload bay plus four experiments
conducted in the Middeck Glovebox inside Columbia's crew cabin. Several
additional payloads are aboard Columbia, including the Spartan 201 solar
observatory.
The microgravity experiments were scheduled with this week's Spartan and spacewalk activities in mind. Curreri explained that because the USMP-4 payload is designed for telescience - remote-controlled operations with minimal crew involvement - so scientists quickly saw when a change in thruster firings affected their experiments. Each primary thruster firing gave the shuttle a push of 0.01 g every three minutes or so to keep it pointed in the right direction. That seems small enough except that it's 100 times stronger than the 0.0001 g vernier thrusters for which the experiments were designed.
"We were able to make a good case very fast," Curreri said of the USMP-4 science team. "The orbiter [team at Johnson Space Center] realized that we could loose the majority of our science and they gave us a gentler ride all the way to the spacewalk."
A summary of the experiments so far:
MEPHISTO "is showing new information on how faceted, multigrain
crystals grow in microgravity," he said. MEPHISTO moves a furnace across
three identical samples. An electrical current passed through one measures
measure how the liquid/solid interface is moving through the sample (the
Seebeck effect). The furnace has made 12 of 13 Seebeck measurements planned
to this point, and is providing highly detailed data.
"The Advanced Automated Directional Solidification Furnace has performed flawlessly," Curreri said. The first of three samples has been processed and the furnace is being cooled in preparation for inserting the second sample on Wednesday. This specimen will need at least 70 hours of smooth sailing.
"Confined Helium Experiment has been an extraordinary success," he said. CHeX is growing extended regions of superfluid helium inside ordinary liquid helium. When these regions grow until they fill the gap between silicon wafers, they act as if they were two-dimensional. Forces on one atom are felt across the entire superfluid region. In this way, it simulates some aspects of electricity passing through ultrasmall circuits. CHeX has made more than 21 high-resolution scans showing this "finite size" effect. Some scans have been at temperature differences of less than a tenth of a billionth of a degree.
"Isothermal Dendritic Growth Experiment is operating as well as expected," Curreri said. "The real-time video [showing crystals growing and dissolving inside the chamber] has proved to be extremely valuable." With it, scientists will be able to make more detailed analyses of how crystals grow as metals cool. IDGE has made more than 40 growth cycles with the solution cooled to 0.39 deg. below the normal freezing point. Another cycle now starts at 0.45 deg. undercooling. This repetition will help define the detailed shape of the dendrites.
Wetting Characteristics of Immiscibles (left) "has already seen wetting of one composition
that's not seen on the ground," Curreri said. One liquid in the model
mixture stuck to the walls of the container in a manner not seen on the
ground. This may be the same phenomenon that has caused problems with some
space experiments where droplets did not disperse as fine as planned.
Particle Engulfment and Pushing was started Tuesday night.
Enclosed Flame Experiment is scheduled for Saturday evening.
Space Acceleration Measurement System (SAMS) and the Orbiter Acceleration Research Experiment (OARE) have each been in demand by the science teams during the shuttle's maneuvers. Each has provided more than 120 hours of highly detailed measurements.
Check
out the daily
Mission Status Reports prepared by Marshall's Public Affairs Office.
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Author: Dave
Dooling
Curator: Linda Porter
NASA Official: Gregory S.
Wilson
