Simultaneous real-time estimation of atmospheric density and ballistic coefficient

Atmospheric drag is a significant force for all spacecraft in LEO. Given the appropriate use of current best geopotential functions for gravity modeling, the most significant LEO estimation errors are due to atmospheric drag modeling. Historically, a ballistic coefficient estimate has been used to absorb atmospheric density modeling errors, as well as ballistic coefficient modeling errors. The purpose herein is to demonstrate the simultaneous real-time estimation of both atmospheric density and ballistic coefficient with simulated range data and with real range data. The approach tested is valid when the exponential half-life on ballistic coefficient errors is significantly different than that on atmospheric density errors. Though correlated, atmospheric density modeling errors and ballistic coefficient modeling errors are shown to be observable and separable. The most significant state error cross correlations are within the orbit itself. Atmospheric density modeling errors are highly correlated with those of the orbit. This suggests that if atmospheric density errors are not estimated, then they will alias into and degrade the orbit estimate. Ballistic coefficient modeling errors are negligibly correlated with the orbit. © Analytical Graphics, Inc., 2004.