John Kielkopf, University of Louisville; Frank O. Clark, University of Louisville; Wellesley Pereira, AFRL/RV
Keywords: Remote sensing, temporal differential spectrophotometry
Abstract:
We report new ground-based observations of satellites and analysis with the goal of detecting physical activity of, or within, the satellite itself.
Alexander Graham Bell reported an optical method of detecting modulation of a surface membrane by voice at a distance (A.G. Bell) in 1880 and patented the concept. Applying this technique to resident space objects has been discussed extensively by Spurbeck, et al. 2021. Slater et al. 2021 have proposed a small satellite to do this from space. Clark (private communication) has made extensive observations of external surfaces demonstrating that light scattered from surfaces can reveal physical motion inside of the surface, including electrical motors and even structural defects. We have used the telescope described by Azari and Ehrhorn, and others, to measure these effects from Earth-orbiting satellites using several techniques guided by a goal to optimize information gathered while minimizing noise from the atmosphere, instrumentation, or intrinsic photon statistics. Spectral bands were selected from the visible to the thermal infrared, and data were acquired for focused and defocused, spatially unresolved, satellites while precisely tracked, and while allowed to drift across a field. Change in the observed flux is a consequence not only of change in the satellite, but also in its illumination, its aspect to the observer, the transmission along the line of sight, and the detection system and tracking optics. These sources of noise are well known in optical, infrared, and radio astronomy and can be modeled and moderated with techniques developed for precision part-per-thousand photometry of stellar flux variability. Noise can also be suppressed and weak signals enhanced through temporal analysis that identifies outliers, periodicities, and correlations across the multidimensional database spanning time and spectrum. These data show the possibilities and limitations of these techniques and indicate how observations may be optimized to enable extraction of a new class of information about internal dynamics and properties of resident space objects.
Date of Conference: September 27-20, 2022
Track: Non-Resolved Object Characterization