<title>Reconstruction of a hypervelocity impact event in space</title>

Abstract

This report describes an investigation with the objective of substantiating the current hypothesis that describes the source of continually recurring space borne optical sensor readings of unknown origin received from several monitoring satellites. These unidentified optical signals have several characteristics such as long duration, short rise time, and magnitude, which do not correspond to expected signals. Up to now, the limited qualitative evidence indicates the possibility of micro-particle impact induced signals. A quantitative investigation is presented from laboratory experiments and numerical analysis which further support this hypothesis. Sources that can be definitely eliminated include signals from lightning, solar compensation, platform motion, or NUDET. Additionally, it can be concluded from several pieces of evidence that the source is local to the satellite. We can also eliminate the possibility of a hardware anomaly of a specific sensor design since data from 1988 to the present are being detected by each of the different types of optical sensors used (3 satellite platforms and 5 different optical sensor designs are involved). Therefore, it is believed that these signals are a consequence of some real, external physical phenomenon and not just a consequence of some anomalous sensor behavior. The current evidence is not a sufficient basis for a complete description of the phenomenology and needs to be studied in greater detail to verify whether or not hypervelocity particle impact is indeed the source of the optical triggers described above, and if so, to work out the phenomenology in quantifiable terms. To substantiate the hypothesis of a HV particle impact source for these signals, the physical phenomenon was reconstructed both experimentally and computationally. Detailed numerical calculations representing the interaction of a specific particle size and velocity were conducted. The intensity of the impact flash is inferred based on temperatures using a black body radiation assumption. Laboratory experiments consisted of HV impacts of iron particles onto a lens specimen and sunshade specimen using a 2 MV Van De Graaf accelerator. Results of the experimental data obtained using a photomultiplier are compared to the numerical calculations and with existing data.