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Synthetic Aperture Silhouette Imaging for Space Domain Awareness
[Technical Report, Master's Thesis]
AIR FORCE INSTITUTE OF TECHNOLOGY WRIGHT-PATTERSON AFB OH
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The increasing interest in cislunar space as a new orbital regime for artificial satellites exceeds the traditional imaging capabilities used to enable some aspects of Space Domain Awareness, an issue present even at Geostationary Equatorial Orbit GEO distances. Synthetic Aperture Silhouette Imaging SASI, which resolves a silhouette of a space object using ground based measurements of the diffraction pattern cast by the objects occultation of a distant stellar light source, provides a new method that may be used to characterize these satellites. Reverse propagation of the diffraction pattern with use of a phase retrieval algorithm leads to the reconstruction of a silhouette from only intensity diffraction distribution measurements. This research analyzes the reconstruction of satellite silhouettes using data from a scaled benchtop experiment to evaluate the distance and resolution limitations of Synthetic Aperture Silhouette Imaging at distances equal to and beyond GEO. Diffraction patterns of two scaled satellite silhouette targets are captured at various scaled distances. The laboratory data is fed to Matlab code which utilizes an iterative Gerchberg-Saxton phase retrieval algorithm to estimate the original silhouettes. The reconstructed silhouettes are compared to the original truth silhouettes to estimate the resolution at each distance. Resolutions of 36 centimeters at GEO altitude and 1.54 meters at twice GEO altitude were obtained. Refinements to further data collection and processing are analyzed and show potential for even greater resolution. These results demonstrate the value of SASI as a tool which can provide valuable information of a satellite of interest, filling in a current Space Domain Awareness imaging capability gap.
[A, Approved For Public Release]