Attitude Determination for Small Satellites with Modest Pointing Constraints

This monograph reports on the development of the attitude determination backbone of the Ionospheric Observation Nanosatellite Formation (ION-F). Three spacecraft with similarly modest pointing constraints comprise the ION-F constellation. Pointing requirements for the constellation are dictated by the formation flying mission objective and communication demands. To satisfy pointing requirements the attitude control system for each spacecraft will require attitude estimates with accuracies on the order of 1 degree. An investigation into sensor suites capable of satisfying this requirement within the additional monetary, mass, and power constraints imposed by the ION-F program was carried out. Ultimately, a gyroless magnetometer-based Kalman filter was chosen as the attitude determination backbone. A high fidelity simulation created specifically for ION-F spacecraft revealed the filter was capable of attitude errors below 1.6◦ (1σ) and rate errors below 0.006 deg sec . Further tests using actual telemetered data from the Danish Øersted satellite were performed with satisfactory results. Other sensors may be added to this backbone to increase accuracy and speed filter convergence. For example, the possibility of incorporating solar panel data into the filter was examined. It was concluded that under fairly general conditions solar panel data speeds initial filter convergence and may also be used to estimate magnetometer mounting misalignments. Although designed for the ION-F constellation, the attitude determination system described in this paper is generically applicable to many small spacecraft in inclined low-earth orbit. The 1-2 degree accuracy of which the system is capable lends itself well to small satellite applications such as formation flying and imaging or docking with other spacecraft.