Solar Sail Attitude Control System for the NASA Near Earth Asteroid Scout Mission Juan Orphee Ben Diedrich Brandon Stiltner Chris Becker Andy Heaton 1/19/2017 1 Introduction • Near Earth Asteroid (NEA) Scout mission uses an 86 m^2 sail for primary propulsion • The sail produces a significant solar disturbance torque • NEA Scout is a class D NASA payload in the form of a 6U cubesat • Limited volume and mass creates challenges • NEA Scout uses reaction wheels for primary attitude control • NEA Scout uses an Adjustable Mass Translator (AMT) to manage pitch and yaw momentum • NEA Scout uses a cold gas Reaction Control System (RCS) for initial de-tumble, a Trajectory Control Maneuver (TCM), roll momentum management, and safe mode • NEA Scout control software ensures all systems work smoothly together for successful mission 2 NEA Scout Spacecraft Configuration Spacecraft body axes and relative scale of sail to spacecraft 1 – BCT Star Tracker/Drive Control Electronics 1 2 2 2 – BCT Coarse Sun Sensors x 3 3 – BCT 15 milli-Nm Reaction Wheel x 4 4 3 6 4 – Sensonor MEMS IMU 5 5 – VACCO cold gas Reaction Control System (RCS) 6 – NASA in house Adjustable Mass Translator (AMT) 2 3 NEA Scout Control System Reaction wheel feedback control loop Reaction wheels are primary attitude controller Bode diagram for roll control System bandwidth is 0.067 Hz Stability margin 16 dB/67 deg 4 NEA Scout ACS Performance Meets attitude pointing requirements Meets science pointing requirement that is challenging for small sat 5 NEA Scout RCS Design VACCO cold gas RCS 6 total control jets - 4 for control - 2 dedicated to delta-V Phase plane controller 6 NEA Scout RCS Performance RCS required to de-tumble from 10 deg/sec per axis RCS meets requirement De-tumble is critical so sun pointing can occur in timely manner 7 Momentum Management Control System The reaction wheels build up momentum from the solar disturbance torque The momentum management control system uses a Proportional Integrator to manage X and Y momentum The actuator for implementing momentum management in X and Y is the Adjustable Mass Translator The AMT moves a large proportion of the spacecraft mass (~ 40%) to trim the solar torque for a given sun incidence angle 8 Momentum Management Performance Momentum management for two 90 deg slews Reaction wheels spin up and spin down twice Reaction wheel torques to initiate wheel spin Z momentum managed by RCS 9 Conclusions and Forward Work Conclusions • NEA Scout can control sailcraft despite volume and mass constraints • RCS meets requirements and manages Z momentum • X and Y Momentum is successfully managed by AMT and RCS Future Work • Verification of control software • Off-nominal control case simulations • Spacecraft integration of ACS hardware 10 Backup 11.