RAX Attitude Determination Results

Results of the analysis of the RAX-1 and RAX-2 attitude determination system have recently been published.

John C. Springmann, James W. Cutler, Flight results of a low-cost attitude determination system, Acta Astronautica, Volume 99, June–July 2014, Pages 201-214, ISSN 0094-5765, http://dx.doi.org/10.1016/j.actaastro.2014.02.026.

Attitude determination accuracy of RAX-2
Figure 12 from the paper. Attitude determination accuracy of RAX-2 data collected on December 9, 2011 16:00:00 UT using the 6-state MEKF without an albedo model. Albedo is treated as noise in the filter. (a) 1–σ bounds and (b) approximate total accuracy.

The paper presents flight results of the attitude determination system (ADS) flown on the Radio Aurora Explorer (RAX) satellites, RAX-1 and RAX-2, which are CubeSats developed to study space weather. The ADS sensors include commercial-off-the-shelf magnetometers, coarse sun sensors (photodiodes), and a MEMs rate gyroscope. A multiplicative extended Kalman filter is used for attitude estimation. On-orbit calibration was developed and applied to compensate for sensor and alignment errors, and attitude determination accuracies of 0.5° 1–σ have been demonstrated on-orbit. The approach of using low-cost sensors in conjunction with on-orbit calibration, which mitigates the need for pre-flight calibration and high-tolerance alignment during spacecraft assembly, reduces the time and cost associated with the subsystem development, and provides a low-cost solution for modest attitude determination requirements. Although the flight results presented in this paper are from a specific mission, the methods used and lessons learned can be used to maximize the performance of the ADS of any vehicle while minimizing the pre-flight calibration and alignment requirements.