Advanced Momentum Management and Propellantless Control Technologies for Solar Sail Spacecraft

Solar sail propulsion leverages solar radiation pressure (SRP) acting on large, lightweight reflective membranes to provide continuous, propellant-less thrust. This capability enables long-duration missions, non-Keplerian orbits, solar polar trajectories, and other mission architectures aligned with NASA's heliophysics, astrophysics, and deep-space exploration goals. However, the same continuous SRP forces that enable propulsion also generate persistent disturbance torques. Small offsets between the sail's center of pressure and center of mass, combined with structural flexibility and environmental disturbances, result in steady angular momentum accumulation. Over time, this can lead to reaction wheel saturation, degraded pointing performance, and increased mission risk. Conventional spacecraft use propellant-based thrusters to unload stored angular momentum. For solar sail systems, reliance on consumables diminishes mission lifetime, increases mass, and erodes the fundamental advantages of propellant-less propulsion. As sail architectures scale to larger areas with lighter, more flexible structures, the magnitude and complexity of momentum management challenges increase. There is a critical need for flight-viable, propellant-less momentum management methods that can be implemented through hardware, structural features, or integrated sail mechanisms to support sustained solar sail operations. NASA seeks innovative, propellant-less momentum management methods that enable reliable attitude control and angular momentum regulation for solar sail spacecraft. Of particular interest are methods that modify the shape of the sail. These methods could be static (e.g, a fixed fin on a single boom), or dynamic (e.g., the capability to actively deform the booms or membrane). The following definitions are to be used for this solicitation. The angle between the normal axis of the solar sail and the sun is defined as the Sun Incidence Angle or SIA. The following specific concepts are suggested: 1. A fixed fin on one boom (out of a presumed four sail booms) to be used specifically for momentum management about the normal axis of the sail. This method will only work at non-zero SIAs (Sun Incidence Angles) 2. A method of deforming or articulating the booms to change the shape of the sail. 3. For the quadrant sail design (four roughly triangular quadrants segmented by booms), the capability to gimbal the individual panels. The proposals will be evaluated based on which best can trim the SRP torque to manage momentum. For reference, the follow maximum torques should be addressed: Torque Results (No Center of Mass offset) Max Moment in X Direction: 0.0018533 Nm Max Moment in Y Direction: 0.0018571 Nm Max Moment in Z Direction: 6.7941e-05 Nm Max Moment in Sail Plan: 0.0026236 Nm The mass of any additional system added to manage the momentum will ideally be limited to less than 5 kg. Masses up to 10 kg may be considered with sufficient justification.