Resident Space Object Characterization Using Polarized Light Curves

Light curves, or the time-history of photometric brightness, have previously been demonstrated to allow for estimation of a space object’s attitude, shape, and surface parameters. However, these methods are subject to many limitations, including the need for accurate initial estimates to initialize filters, and the inability to regularly estimate attitude and surface parameters simultaneously due to information dilution, or the increase in uncertainty of each state when more states are simultaneously estimated. Monochromatic, unpolarized light curves can also only allow for surface reflectance parameter determination, and not determination of the materials themselves. This work develops a polarized bidirectional reflectance distribution function, and demonstrates that polarized measurements increase the uniqueness of light-curve attitude solutions to allow larger tolerance to initial error while also providing surface material estimation. Polarization of reflected light can also be measured more accurately than the intensity of reflected light through the atmosphere, thereby increasing the attitude observability from the light curves. Observability of attitude and surface materials is assessed. An unscented multiple-model adaptive estimation filter is implemented to estimate attitude, angular rate, surface material, surface roughness, and size of the space object.