Online attitude determination of a passively magnetically stabilized spacecraft

Abstract

An online attitude determination filter is developed for a nano satellite that has no onboard attitude sensors or gyros. Specifically, the attitude of NASA Ames Research Center's O/OREOS, a passively magnetically stabilized 3U CubeSat, is determined using only an estimate of the solar vector obtained from solar panel currents. The filter is based upon the existing multiplicative extended Kalman filter (MEKF) but instead of relying on gyros to drive the motion model, the filter instead incorporates a model of the spacecraft's attitude dynamics in the motion model. An attitude determination accuracy of five degrees is demonstrated, a performance verified using flight data from the University of Michigan's RAX-1. Although the filter was designed for the specific problem of a satellite without gyros or attitude determination it could also be used to provide smoothing of noisy gyro signals or to provide a backup in the event of gyro failures.

Optimal geometry and materials for nanospacecraft magnetic damping systems

“…Due to the large demagnetizing effect of the dissipating array, the magnetic hysteresis loops measured on the overall system show a pseudolinear behavior. This allows one to use a simplified semianalytical model for the magnetization of the strips, which is useful for the dynamical simulation of the spacecraft attitude motion, as suggested in [14,24]. Numerical simulations confirm the superior performance of the amorphous alloys and the proposed geometrical arrangement with respect to the Ni-Fe alloys.…”

“…Unexpected performance in orbit was observed also in the Delfi-C3 mission [12], in which PERMENORM 5000H2 (Ni-Fe alloy) permeable rods were used [13]. The O/OREOS mission in-orbit measurements revealed a much longer settling time of the attitude motion, with respect to numerical simulations, as reported in [14].…”

“…A simplified model has been proposed in [24] and successfully applied for example in [17,18,29,30]. This model has been recently elaborated further, leading to an analytical solution for the hysteresis curves, given an initial condition [14]. Taking advantage of the increased accuracy and related savings in computational burden, this solution was used in setting up the numerical simulations for the study cases analyzed in this section.…”

“…Due to the particular implementation of nanosatellite dispensers in multiple spacecraft launches performed by CubeSats, the satellite motion after separation from the launcher assumes an unpredictable initial attitude and angular velocity [31,32]. Typically, a quite large initial angular rate, as high as 30 deg/s can be expected [14], with no preferential direction. The motion typically observed in passive magnetic attitude stabilization systems is a fast motion of the magnet axis with respect to the magnetic field, with large energy dissipation in the bars.…”

“…Actually, a range of values for the magnetization level reached in satellite damping systems is given in the literature. Depending on the rod geometry, material, and treatment, magnetization levels of the order of 0.1 T, 0.7 T, 0.015 T, 0.14 T, 0.07 T, and 0.15 T are reported in [1,3,14,17,18,19], respectively. This shows that the "optimal" material choice, clearly related to the overall geometry of the system, is ill defined and needs further investigation.…”