Gouri Radhakrishnan, The Aerospace Corporation; Paul Adams, The Aerospace Corporation; Diana Alaan, The Aerospace Corporation; Christopher Panetta, The Aeropsace Coproration
Keywords: Laser Ablation, Hypervelocity Impact, Albedo, Debris Characterization
Abstract:
A variety of processes can alter the optical surface characteristics of orbital debris fragments in low earth orbit, resulting in a change in their albedo. Orbital debris fragments albedo is a critical parameter in the derivation of their physical sizes from optical measurements. The critical processes include scattering due to micron and sub-micron particles on the surface, effects of atomic oxygen, and space radiation effects. Here we mainly focus on the formation and effects of micron and submicron particles, generated during hypervelocity collisions.
While field testing of hypervelocity impact has been conducted, there are no known hypervelocity collision ground tests that simulate the high-vacuum conditions of 10-8 Torr or less that exist in the Low Earth Orbit (LEO) environment. Pulsed laser ablation in high vacuum offers an inexpensive laboratory simulation of hypervelocity impact under low-earth orbit like conditions and allows for well-controlled investigations that can be coupled to optical albedo (reflectance) measurements. We have previously demonstrated that laser ablations in low-pressure air offer many similarities to the recent DebrisLV and DebriSat hypervelocity impact experiments, while ablations in high-vacuum provide critical distinctions.
The results on the laser ablation of some of the representative target materials used in current satellite structures, such as 6061 Al alloy, stainless steel, titanium and carbon composite are presented. Debris generated is optically characterized with UV-VIS-NIR reflectance, and corresponding particle size distributions are measured. Additionally, the ablated plume is characterized in-situ with time-resolved spectroscopic diagnostics in the sub-microsecond time regime identifying atoms and ions in the plume and plasma temperatures, allowing a correlation of the energetics of the ablated plume with resulting albedo and particle size distributions of ablated debris. In addition, comparisons are made between plumes and debris generated in high-vacuum and in controlled gaseous ambients, both reactive and inert, such as air, oxygen, and nitrogen that reveal the roles of plume chemistry and collisional cooling. These results and the significant measured differences between high-vacuum and air have relevant implications for the determination of physical sizes of orbital debris in LEO or Geosynchronous Orbit (GEO) that are based upon optical measurements that use albedo as a critical parameter.
Date of Conference: September 11-14, 2018
Track: Optical Systems Instrumentation