Orbit determination in the presence of unmodeled accelerations

In this investigation, the unmodeled accelerations acting on an orbiting space vehicle are approximated by a first-order Gauss-Markov process. An extended Kalman-Bucy filter is used to estimate the state and the unmodeled accelerations at each observation epoch. Applications of the estimation algorithm to tracking data obtained during the Apollo 10 and 11 missions indicate that a more accurate estimate of the state is obtained and that the estimated values of the unmodeled accelerations can be correlated with physical phenomena neglected by the mathematical model.