Capability Development for Space
Inclusive Dates: 01/08/01 - 05/08/01
Background - During the past five years, SwRI has established a major basic research effort in the study of the origin of the solar system, and, in particular, the process of planetary formation. Numerous lines of evidence derived from physical characteristics of our own planetary system and from astrophysical observations have demonstrated that the planets were formed through the accretion of material in the original solar nebula. After the collapse of the solar nebula from an interstellar cloud of dust and gas, the terrestrial (i.e., Earth-like) planets formed via a process involving the accretion of progressively larger particles striking each other in random collisions that would often stick together. Laboratory studies to identify and study this accretion process have not been successful due to the difficulties of simulating the environment of the early solar nebula (e.g., microgravity conditions with low gas pressures and the possible dominance of tribo-electrostatic forces between particles). Hence, important parameters that determine if particles stick to each other or bounce apart after a low-speed collision have not been measured successfully in a laboratory environment.
Approach - The purpose of this quick-look internal research project was to investigate and develop an experimental technique to simulate the collisions of small particles in a microgravity environment that could be proposed as a more extensive experiment for the International Space Station (ISS) or the space shuttle. A microgravity experiment called OASIS (for Orbital Accretion Science In Space) was designed to conduct collision studies of fluffy dust aggregate particles aboard the ISS or the space shuttle. OASIS was designed to conduct the following tasks: 1) prepare dust aggregates for use as projectile and target samples; 2) provide a means to propel a projectile sample into the target sample at velocities from 1 to 100 centimeters per second; and 3) provide a means of recording both the projectile motion and collision with the target using a high-time cadence [30 frames per second] stereo-imaging camera system. This experiment would allow a study of the dynamics of collisions as a function of material composition, collision velocity, and angle within a vacuum enclosure. To test this experimental approach in microgravity conditions, a prototype OASIS experiment was designed and built for test flights aboard the NASA KC-135 Zero-G aircraft.
Accomplishments - A detailed design of OASIS was performed followed by the development and fabrication of an OASIS prototype experiment that made two successful flights aboard the NASA KC-135 Reduced Gravity aircraft, nicknamed "Weightless Wonder V." During these two flights, 80 zero-g parabolas were performed, while experimental runs were conducted with the OASIS prototype to test the following experiment functions: 1) the sample-preparation technique using various dust samples [fine silica sand, small plastic chips, and small styrofoam balls]; 2) the structure of the dust bunnies and their fragility in microgravity; 3) the effects of launch forces on each of the sample types; and 4) the effects of the target collisions with the dust samples. The main findings of these experimental runs were the following: 1) the sample preparation, load, and launch techniques worked extremely well in the microgravity environment; 2) The dust aggregates created using silica sand were found to be extremely fragile and prone to breaking apart easily (or not forming at all with the larger 500-micrometer sand) under the microgravity conditions that NASA aircraft can provide; 3) The plastic and styrofoam samples formed into aggregates more easily and were more robust during preparation and launch; 4) Extreme care is required to keep the samples (especially the silica sand samples) dry during all phases of the experiment to maintain a high tribo-charge on the particles. From these "lessons learned," further refinement of the OASIS experimental design techniques are now possible for a future microgravity experiment proposal to NASA in 2002.