USML-2 Public Affairs Status Report #11
6:00 p.m. CDT, Oct. 26, 1995
6/09:07 MET
Spacelab Mission Operations Control
Marshall Space Flight Center

Payload Commander Kathy Thornton and Payload Specialist Al Sacco had a
busy day conducting a wide variety of experiments in the microgravity
environment aboard the Shuttle Columbia in the second United State
Microgravity Laboratory (USML-2).

The Colloidal Order-Disorder Transition experiment, an investigation
into the solidification process in crystal growth, revealed unexpected
results today.  In studying electronic still photographs provided by
Sacco this morning, researchers saw that crystals of varying sizes
were formed in the samples.  This is something they haven't seen on
Earth.

Sacco told researchers on the ground that particles in the 15 sample
vials were randomly spaced, and ranged in size from 10 to 150 microns
(millionth of a meter).  Scientists are interested in what happens at
the boundaries between solid and liquid states during crystallization
of a colloid, allowing them to see how atoms and molecules move and
arrange themselves when they form a crystal.  This may help improve
materials processing methods on Earth, as well as in microgravity.
 
A crystal of the semiconductor material gallium arsenide has grown
about 1 inch (2-1/2 centimeters) since it was placed in the Crystal
Growth Furnace last night.  The temperature in the Crystal Growth
Furnace is the hottest it has been during this mission' between 22 and
23 hundred degrees Fahrenheit . The crystal is growing at a rate of
1.8 millimeters per hour.  Although this is a slow growth period,
gallium arsenide crystals have the potential to make computers,
satellites and other electronics work much faster than with silicon
chips.  Chips made of gallium arsenide are now too expensive for
widespread use - current processing techniques yielding only one good
chip out of every ten that are made.

   Thornton this morning began deploying liquid drops in the Drop
Physics Module in tests to help the science team finalize a procedure
to slow down the rotation of the drops.  Later, the USML-2 crew will
add a small amount of chemical, called a surfactant, to the drop in an
experiment known as Science and Technology of Surface Controlled
Phenomena, managed by Principal Investigator Dr. Robert E. Apfel, of
Yale University.  Scientists are comparing characteristics of drops
containing surfactants to drops of pure water.  Surfactants are
substances which alter the surface properties of a liquid, aiding or
inhibiting the way it adheres to or mixes with other substances.
Applications of this research apply to many industrial processes,
among them the production of cosmetics and improvement of oil
recovery.

    University of California's Riverside's Dr. Alex McPherson is 
principal investigator for the handheld diffusion test cells 
experiment.  The experiment is growing proteins by liquid-
liquid diffusion, a process in which fluids diffuse into each 
other by random motion of molecules, rather than being mixed 
together.  This method is difficult on Earth because gravity 
causes solutions with different densities to mix.  The 
experiment is a precursor for long-duration crystallization 
experiments aboard the International Space Station and Mir.

  The Three-Dimensional Microgravity Accelerometer experiment ground
support team continues to troubleshoot the cause and resolution of a
data downlink problem.  This has not impacted science since all data
is recorded onboard the Shuttle.  This experiment measures
accelerations and vibrations that could affect investigations in the
Spacelab.

  Thornton spent the afternoon working with the Surface Tension Driven
Convection Experiment.  Researchers on the ground relayed instructions
for Thornton to raise the temperature of the silicon oil surface in
order to study the change from steady thermocapillary fluid flows to
oscillatory (or unsteady) flows.  This investigation could one day
lead to better, stronger high-tech crystals, metals, alloys and
ceramics.

  Sacco spent the last part of his shift working in the Glovebox
activating new protein crystal growth experiments, based on his
observations of results from previous experiments.  An advantage of a
longer mission like USML-2 is that it allows science teams on the
ground to perform several experiment runs, analyze their data, and
have the crew devise a new set of experiments.  This allows
investigators to quickly capitalize on their observations in real
time.


Status reports are issued from Johnson Space Center's Mission
Control at 8 a.m. and 5 p.m.; and from Marshall Space Flight
Center's Spacelab Mission Operations Control at 6 a.m. and 6
p.m. weekdays, 6 a.m. on weekends.  For additional information, see
the Internet USML-2 payload homepage,
http://liftoff.msfc.nasa.gov/spacelab/usml2/welcome.html and the
STS-73 Shuttle homepage, http://shuttle.nasa.gov