The 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 complexity.

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.

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.

Astronaut Leroy Chiao works on the BCAT-3 experiment on the International Space Station. Credit: NASA

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 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.

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.