Attitude Control Approach for Solar Cruiser, a Large, Deep Space Solar Sail

Solar Cruiser is a small satellite Technology Demonstration Mission (TDM) to
mature solar sail propulsion technology using a solar sail larger than 1600
square meters, demonstrating performance as a propulsion system and a stable
pointing platform for science observations in an artificial halo orbit sunward of
the Sun-Earth Lagrange Point 1 (sub-L1). For the “sailcraft” to meet mission ob-
jectives, there are several unique attitude control challenges that the Attitude De-
termination and Control System (ADCS) must overcome. Large disturbance tor-
ques, primarily due to sail deformations coupled with off-sun pointing angles,
make it more difficult to maintain adequate controls performance and manage
accumulated momentum on the control actuators. The large-amplitude, low-
frequency flexible body modes of the sail, in concert with noisy sensors and ac-
tuators, make it challenging to mitigate control-structure interactions and main-
tain fine pointing capabilities. Stability and control performance during sail de-
ployment is complicated by rapidly and widely varying inertias. The Solar
Cruiser ADCS effectively addresses these challenges using a simple, traditional
control system – including momentum management actuators that use bang-
bang control to constrain internal accumulated momentum, a low-pass controls
filter and an attitude determination Kalman Filter (KF) that blends multiple star
tracker solutions, and a reaction wheel assembly (RWA) with controller gains
tuned to specific configurations or inertias. Solar Cruiser’s attitude control ap-
proach, and lessons learned from its development, establishes a state of the art of
high value to future solar sail missions and other small spacecraft with large de-
ployable structures operating in deep space.