Engineering Seminars Test Calendar 2.10

Abstract:
There is an explosion of interest in the utilization of very low Earth orbit (VLEO, roughly 100 – 350 km altitude) for commercial and military purposes. Despite the obvious proximity advantages of VLEO, these altitudes have long been avoided because of the high density and harsh oxidizing environment of the residual atmosphere, which contains atomic oxygen (AO) and molecular nitrogen (N₂). Momentum exchange in collisions between these species and satellite surfaces results in aerodynamic drag. Aside from drag, materials on the external surfaces of VLEO satellites may react chemically with AO, resulting in oxidation, erosion, roughening, and degradation of function. Minimizing and predicting drag and maximizing AO resistance are crucial for proliferated VLEO operation. We have used molecular beams of O and O₂, traveling at orbital velocities of ~8 km s^-1, to investigate both the AO resistance and drag potential of various materials that may be used on VLEO satellites. The pulsed molecular beam, produced from a laser-driven breakdown source, was used to expose selected materials to AO fluences up to ~1 × 10²¹ O atoms cm^-2. Some of these materials were also exposed to the LEO environment on the International Space Station to similar AO fluences. Materials that exhibited significant AO resistance were used in molecular beam-surface scattering experiments, and the scattering dynamics were measured as a function of both polar (q) and azimuthal (f) scattering angles on pristine and pre-exposed sample surfaces. The velocity and angular distributions of scattered O-atoms depend strongly on the incident angle of the impinging atoms and the roughness of the surface in ways that are not a priori predictable. Based on the scattering dynamics data, a new gas-surface scattering model has been formulated, allowing for the determination of overall energy and momentum accommodation and for simulations of satellite drag. 

Bio:
Timothy K. Minton is a professor in the Ann and H.J. Smead Department of Aerospace Engineering Sciences at the University of Colorado.  He earned his B.S. in Chemistry from the Univ. of Illinois in 1980 and his Ph.D. in Chemistry from UC Berkeley in 1986.  Following two post-doctoral positions, at the Univ. of Illinois and at the Univ. of Zürich, Switzerland, he became a Member of Technical Staff at the Jet Propulsion Laboratory in Pasadena, CA in 1989.  In 1995, he joined the faculty at Montana State University, Dept. of Chemistry and Biochemistry, from which he transferred to the University of Colorado in the Summer of 2020.  He is a Fellow of the American Chemical Society, the American Physical Society, and the American Association for the Advancement of Science, and he is an Associate Fellow of the American Institute of Aeronautics and Astronautics. His research interests are in gas-phase and gas-surface energy transfer and reactions, with applications to the oxidation and decomposition of heat-shield materials on hypersonic vehicles and to the development of low-drag and durable materials for use on satellites in low Earth orbit