Capillary Flow Experiments (CFEs) are a suite of fluid physics
flight experiments designed to investigate large length scale
capillary flows and phenomena in low gravity. The CFE data to
be obtained will be crucial to the Space Exploration Initiative,
particularly as it pertains to fluids management systems such
as fuels and cryogen storage systems, water collection and recycling,
thermal control systems, and materials processing in the liquid
state. NASA’s current plans for exploration missions
assume the use of larger liquid propellant masses than have ever
flown on interplanetary missions. Under low-gravity conditions,
capillary forces can be exploited to control fluid orientation
so that such large mission-critical systems perform more reliably.
CFE is a simple fundamental scientific study that can yield quantitative results
from safe, low-cost, short time-to-flight, handheld fluids experiments. The experiments
aim to provide results of critical interest to the capillary flow community that
cannot be achieved in ground-based tests such as tests to probe dynamic effects
associated with a movingcontact boundary condition, capillary-driven flows in
interior corner networks, and critical wetting phenomena in complex geometries.
Specific applications of the results center on particular fluids challenges concerning
propellant tanks. The knowledge gained will help spacecraft fluid systems designers
increase system reliability, decrease system mass, and reduce overall system
CFE encompasses three experiments with two unique experimental units per experiment.
There are multiple tests per experiment. Each of the experiments employs parametric
ranges and test cell dimensions that cannot be achieved in groundbased experiments.
All units use similar fluid injection hardware, have simple and similarly sized
test chambers, and rely solely on video for highly quantitative data. Silicone
oil will be used for these tests. Differences between units are primarily fluid
properties, wetting conditions, and test cell geometry. The experiment procedures
are simple and intuitive.
Binary Colloidal Alloy Test-3 (BCAT-3)
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.
Astronaut Leroy Chiao works on the
BCAT-3 experiment on the International Space Station. Credit:
Binary Colloidal Alloy Test-4 (BCAT-4)
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.
Binary Colloidal Alloy Test-5 (BCAT-5)
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
Binary Colloidal Alloy Test-6 (BCAT-6)
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.