On-Orbit Spacecraft Inertia and Rate Sensor Scale Factor Estimation for Microsatellites

A key challenge in testing and operating small satellites is the determination of the moment of inertia. Attitude control systems engineers use the moment of inertia to develop closed loop pointing controllers as well as accurate feed-forward pointing commands that predict the satellite’s motion. Traditionally, engineers measure the satellite moment of inertia using a mass properties table. However, for small, relatively lightweight satellites, this process is error-prone and costly regardless of the satellite size. This paper presents a novel on-orbit inertia-estimation technique. The algorithm is based on standard non-linear function solvers that can be run on the ground and requires only a rudimentary initial inertia estimate as a starting point (such an estimate can be obtained from structural modeling software). In addition to estimating the satellite inertia matrix, the estimator can also provide rate sensor scale-factor corrections. This paper demonstrates the inertia and scale factor estimator using the MOST spacecraft (now in its fifth year of operations)