Magnetometer-based attitude and rate estimation for spacecraft with wire booms

A magnetometer-based filter and smoother are presented for estimating attitude, rate, and boom orientations for a spinning spacecraft that has wire booms. These estimates are needed to analyze science data from the subpayloads of a recent sounding rocket mission. The estimator is initialized with the measured angular rate of each subpayload at ejection and thereafter relies solely on three-axis magnetometer data. The estimation process is complicated by the flexible wire booms whose full parameterization for even the simplest pendulous modes would require 16 state elements. Several simplifying assumptions about the motion of the booms reduce the problem's complexity. A magnetometer-based attitude and rate estimator is developed that is suited to the time-varying model errors resulting from these assumptions. The estimator uses inertial angular momentum in place of angular rate in its state vector, and it explicitly includes an error model for its approximate relationship between angular rate and angular momentum. The estimator, a filter/smoother, is applied to synthetic data from a truth-model simulator and then to actual telemetry from the mission subpayloads. Accuracies are on the order of several degrees. The estimator is applicable whenever Euler-type equations must be used to propagate rate estimates in the presence of significant dynamics modeling errors.