STS-75 press kit

Edited by Richard W. Orloff, 01/2001/Page 23
Critical Fluid Light Scattering Experiment (Zeno)
Principal Investigator: Dr. Robert Gammon, Institute for Physical Science and Technology,
University of Maryland, College Park, MD
Objective. The Zeno investigation, named for the Greek philosopher, will explore an unusual state of
matter by measuring the density of the element xenon at its critical point, a unique set of conditions when it
is literally on the edge of simultaneously being in a gaseous phase and a liquid phase. More precisely, the
material rapidly changes back and forth from one state to the other so that one is unable to determine the
state of a given volume of material.
Scientists are interested in what happens at the critical point because these phase change phenomena are
common to many different materials. Understanding how matter behaves at the critical point can provide
insight into a variety of physics problems, ranging from state changes in fluids (gas to liquid) to alterations
in the magnetic properties of solids. This knowledge will be valuable in a wide variety of fields, including
liquid crystals, superconductors and even matter fluctuations in the early formation of the universe.
Procedure. Aboard the Shuttle, Zeno will measure properties of xenon a hundred times closer to its critical
point than is possible on Earth. USMP-3 will use a refined procedure for approaching the critical point
temperature more slowly, gradually scanning from one temperature to the next, taking advantage of the
Zeno instrument's sensitivity to minute variations in fluid density that arise in microgravity. This will be
done by shining laser light on a xenon sample and analyzing the resulting light scattering. At controlled
temperatures extremely near the critical temperature, the fluid will be a billion times more compressible
than water but will have similar density. It will change from a vapor clear as glass to a milky white fluid
with a large capacity for absorbing heat, but will transport heat very slowly. Accurate measurements of a
fluid's physical properties when very close to the critical point cannot be made on Earth because gravity
causes the fluid to layer, with respect to density, (vapor on top, liquid below) severely at the temperatures
of most significance. The orbital environment will permit measurements to be made within a few
millionths of a degree of the critical temperature.
The Zeno instrument is contained within two flight modules to isolate electrical noise sources and thermal
loads from the most sensitive optical and electronic subsystems in the light-scattering instrument. A
precision, high-pressure sample cell will hold the xenon sample with a 100-micron- thick fluid layer for the
light-scattering experiment. This cell and a compact, high-performance thermostat are the key elements in
making precision measurements. The main components of the light-scattering system are housed on an
optics bench.
Isothermal Dendritic Growth Experiment (IDGE)
Principal Investigator: Dr. Martin Glicksman,
Rennselaer Polytechnic Institute, Troy, NY
Objective. Metals manufacturing for many industrial and consumer products involves the process of
solidification. Industrial materials research traditionally has tried many different things instead of
developing a clear understanding of the fundamental processes involved. Microgravity research such as
this will lead to manufacturing improvements in metals and alloys that display dendrite formation.
As most molten materials solidify, they form tiny pine tree-shaped crystals called dendrites, from the
ancient Greek for "tree." The size, shape and direction of these crystals dictate the final properties of the
resulting solid material, such as its hardness, its ability to bend without breaking and its electrical
properties. On USMP-2, dendrite researchers were able to observe dendrites in the absence of convection
at extremely small temperature differences below the freezing point, a phenomenon never seen on Earth.
During USMP-3, the experiment will continue to build upon that foundation.