BCAT Status
March 29, 2011 - BCAT-6 launched on space shuttle Discovery's STS-133 mission on Feb. 24. Currently, BCAT-6 is a reserve payload and will be run in the future when time allows. BCAT -3,-4 and -5 are presently on ISS: BCAT-3
is in storage awaiting operations with the higher resolution
12 Mp Nikon Camera, BCAT-4 has three (of ten) samples remaining
in the baseline science matrix with the 8Mp Kodak Camera. BCAT-5
launched on 2 J/A (June 13, 2009) and is awaiting approval
to operate in the JEM. The BCAT-6 investigation is structured from
a rich history of space flight experiments that explore the
fundamental physical science and application of colloids
in a microgravity environment. Colloids are a type of homogeneous
mixture in which very small particles of one substance are
distributed evenly throughout another substance. Paints,
milk, fog, butter, smoke, ink, paint are colloids. The BCAT-6
series hardware consists of the same design as that used
for BCAT-4 and BCAT-5. This effort will address fundamental
questions in colloidal engineering that impact product shelf
life and determine how concentrated systems of particles
of select sizes and shapes cause order to naturally arise
out of disorder when gravity is removed. The BCAT-5 experiment has started operations
on the International Space Station (ISS). It contains experiments
from five teams of scientists in a collaborative effort with
the Canadian Space Agency (CSA), and is the first stand-alone
experiment to be run in the Japanese Experiment Module (JEM)
on the ISS. Binary Colloidal Alloy Test-4 (BCAT-4) is a fluids experiment with two parts: BCAT-4-CP and BCAT-4-Poly. The BCAT-4-CP part of the experiment from Harvard University
(David Weitz and Peter Lu) and Simon Fraser University (Barbara
Frisken and Arthur Bailey) will measure phase separation
rates and properties of a model critical fluid system. Acquiring
this data should lead to a much better understanding of the
shelf-life of products and how to extend it. This portion
of this microgravity experiment will be accomplished by photographing
the time evolution of seven critical point (CP) samples,
which will add needed points to the phase diagram outlined
by the related critical point samples in the BCAT-3 experiment. The Binary Colloidal Alloy Test-3 (BCAT-3) hardware supported
three investigations in which ISS crews photographed samples
of colloidal particles (tiny nanoscale spheres suspended
in liquid) to document liquid/gas phase changes, growth of
binary crystals, and the formation of colloidal crystals
confined to a surface. Colloids are small enough that in
a microgravity environment without sedimentation and convection,
they behave much as atoms and so can be used to model all
sorts of phenomena because their size, shape, and interactions
can be controlled. The Binary Colloidal Alloy Test-3 is an
Exploration Systems' transition flight experiment in the
Human System Research and Technology area. BCAT-3 provides
a unique opportunity to explore fundamental physics and simultaneously
develop important future technology, including computers
operating on light, complex biomolecular pharmaceuticals,
clean sources of geothermal power, and novel rocket engines
for interplanetary travel. These studies depend entirely
on the microgravity environment provided by the International
Space Station (ISS); in all other locations accessible to
science, gravity dominates and precludes investigation of
any other effects of interest. The experiment itself is simple
and elegant, photographing samples of colloidal particles
with a digital camera onboard the ISS. Colloids are tiny
nanoscale spheres of plexiglass a thousand times smaller
than the width of a human hair (submicron radius) that are
suspended in a fluid. They are ubiquitous (e.g., milk, smoke,
and paint) and therefore interesting to study directly. Colloids
are also small enough that they behave much like atoms and
so can be used to model all sorts of phenomena because their
size, shape, and interactions can be controlled. The 10 samples
in BCAT-3 are made from the same ingredients, each a recipe
with different proportions, and are grouped into three experiments:
critical point, binary alloy, and surface crystallization. In an ordinary pot of boiling water, bubbles
of water vapor coalesce on the bottom of the pot, growing
until they detach and float to the surface where they escape
into the atmosphere. At the boiling temperature water exists
simultaneously in two distinct phases—liquid and gas—and
as the bubbles burst, those two phases are spatially separated.
But what should the mixture look like in the absence of gravity,
when the vapor no longer floats to the top? Moreover, the
behavior changes with increasing pressure: seal the pot,
as in a pressure cooker, and the boiling temperature rises.
Continuing the pressure increase, the mixture will reach
its critical point, a unique pressure and temperature value
where the properties of liquid and gas merge. Just above
is the supercritical regime where they are no longer distinct
phases, but rather a homogeneous supercritical fluid. The
BCAT-3 samples of David Weitz and Peter Lu of Harvard University
model this behavior in a colloidal system, where the phases
analogous to liquid and gas can be seen as two different
colors. Colloids are also technologically interesting
because they are the rightsize to manipulate light. Natural
opal is likely the oldest and best known of the "photonic" crystals
that direct light: shine white light on the opal and a rainbow
appears, demonstrating how colors of light are split up and
sent in different directions. The ability to better control
the movement of light is a major technological goal, not
only to build computers operating on light instead of electricity,
but also to harness the full capabilities of existing fiber-optic
networks for improving communications. Crystal structures
built from only one building block—such as the arrangement
of colloidal silica spheres in an opal—are well under-stood,
but their optical properties are limited. More useful photonic
crystals can be built from two different types of building
blocks mixed together, yielding a binary alloy. The resulting
structures and their optical properties are vast, as both
the size and proportion of the two building blocks can be
varied. How the crystallization is affected by these changes
is only beginning to be explored. Theoretical studies suggest
that desired optical properties require more complicated
crystal structures, but this has not been well explored experimentally.
Microgravity is crucial to the binary crystal experiments,
allowing the growth of crystals far larger than those created
on the surface of the Earth. The BCAT-3 binary alloy sample
of Peter Pusey and Andy Schofield of the University of Edinburgh
furthers previous investigations on binary growth in space. Crystal structures are affected not only
by constituent building blocks, but also by the geometrical
environment where they grow. The long, thin blades of ice
on the surface of a freezing puddle are far different from
both the solid blocks in a freezer ice cube tray and the
six-sided needles in a snowflake. Arjun Yodh and Jian Zhang
at the University of Pennsylvania have prepared several samples
to study the formation of colloidal crystals confined to
a surface, allowing comparison with bulk three-dimensional
crystallization, to begin teasing out how geometry affects
crystallization itself. BCAT-3 is a simple experiment with both
important technological applications and profound implications
for fundamental physics. The phenomena under investigation
require an environment where gravity plays no significant
role, and this can only be done in space. However, BCAT-3
is limited by the nature of macroscopic photography: the
camera cannot resolve individual colloidal particles. The
more sophisticated Light Microscopy Module (LMM) scheduled
to fly to the ISS in 2006 is a microscope designed to view
and locate the millions of particles in these samples one
by one, further enabling and deepening our understanding.
Understanding supercritical fluids may accelerate present
efforts to use them as propellants in advanced rocket engines.
Developing more efficient optical communications through
better photonic crystals is particularly important to onboard
computers in outer space, where electronic circuits are constantly
being degraded by high-energy cosmic rays; optical circuits
are immune to such wear. Those developments may be critical
for long, interplanetary missions.
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Project Management: Contacts at NASA Glenn Research Center |
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