Kalman Filtering for Relative Spacecraft Attitude and Position Estimation: A Revisit

A study was conducted to revisit the relative position and attitude estimation problem and to design a novel navigation filter without the assumption. Two relative quaternions that mapped the chief's local vertical/local horizontal (LVLH) frame to the chief body frame and to the deputy body frame were involved. The corresponding attitude matrices were used to construct the line-of-sight (LOS) observations. An extended Kalman filter (EKF) was derived to estimate the mentioned relative quaternions, relative position, and velocity of two spacecraft, along with gyro biases. The relative attitude between two spacecraft was obtained by using these two relative quaternions. The study also estimated the attitudes of both spacecrafts relative to the LVLH frame, in which the relative orbit equations were written so that the attitude of the chief need not be known a priori. It was also important to note that the absolute attitude for each spacecraft could be estimated if the inertial position and velocity vectors for the chief spacecraft were provided.