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