Using Doppler Tracking to Aid Trajectory Reconstruction for Atmospheric Entry, Descent, and Landing

A Doppler tracking measurement model is presented for an Iterative Extended Kalman Filter or an Iterative Unscented Kalman Filter. Doppler tracking refers to the tracking of the Doppler shift in a spacecraft's radio communications as they travel from the transmitting antenna to the receiving antenna. Radio signals experience a deterministic Doppler shift when there is a non-zero relative velocity between the transmitting antenna and receiving antenna. Measurements of the Doppler shift at a receiving antenna on Earth can therefore be used to estimate modes of the velocity of the spacecraft broadcasting those signals. The measurement model presented in this work enables the use of Doppler shift measurements in the trajectory reconstruction of an atmospheric entry vehicle. The Doppler tracking measurement model is implemented in the New Statistical Trajectory Estimation Program, which is a trajectory reconstruction software developed at NASA Langley Research Center. The measurement model's efficacy is evaluated using simulated data from a six degree-of-freedom vehicle model of the Huygens probe as well as the actual Doppler data collected by the Huygens Doppler Winds Experiment.