(Georgia Institute of Technology, 2021-05-01)
Gundamraj, Athreya
The Space Weather Atmospheric Reconfigurable Multiscale Experiment (SWARM-EX)
mission is a three 3U CubeSat mission which will collect plasma and atomic oxygen data in the
upper atmosphere at unprecedented resolutions. The design and simulation of guidance laws
and representative control algorithms for the major sub-modes within the science phases was
conducted. While a baseline, radial-tangential-normal (RTN) tracking attitude profile meets
the pointing requirements, poor solar energy absorption and downlink throughput resulted in
a need for optimal attitude states which utilize the available margins on each requirement. A
numerical optimization framework was developed which computes the optimal attitude by solv ing a constrained minimization problem. The results demonstrate a significant improvement
when the pointing requirement margins are considered. To develop a flight software imple mentation, a constrained guidance law was devised which computes a commanded direction
for one body frame vector such that a secondary body vector is maximizing alignment. The
constrained guidance solution was integrated with the XACT-15 commanding architecture to
create pseudocode for the complete ADC guidance software. Simulations in STK verified the
ability of the ADC guidance software to output commands which satisfy the pointing require ments, and a reaction wheel controller was simulated to model spacecraft slews as the guidance
software outputs commands. A representative desaturation controller was developed which
enables near-complete wheel desaturation within one orbit period. These analyses resulted in
a robust set of analysis tools and models that not only characterize the performance of the ADC
system, but also will continue to mature as the spacecraft and mission design progress.