Autonomous Low-Earth-Orbit Determination from Magnetometer and Sun Sensor Data

Abatch Ž lter has been designed to autonomouslyestimate the orbit of a spacecraft usingonly sensor data froman onboardmagnetometerand sun sensor. The goalhas been to prove the feasibility of a proposed low-cost, moderateaccuracy autonomousorbit determination system. The system uses a batch Ž lter to estimate the Keplerian orbital parameters, a drag parameter, magnetometer biases, and corrections to the Earth’s magnetic Ž eld. It does this by minimizing the square errors between measured and estimated values of two quantities, the Earth’s magnetic Ž eld magnitude and the cosine of the angle between the sun vector and the Earth’s magnetic Ž eld vector, both measured at the spacecraft. The proposed system is observable, and reasonable accuracy is obtainable. Given a magnetometer with a 10-nT 1-3⁄4 accuracy and a sun sensor with a 0.005-deg 1-3⁄4 accuracy, the system can achieve 1-3⁄4 position accuracies on the order of 500 m for inclined low Earth orbits.