When a solar sailing craft is successfully getting force from solar photon pressure, that force applies a small torque to the craft because the center of pressure is never perfectly aligned with the center of mass. Therefore, solar sailing craft need an attitude control system to maintain the correct angle to the sun. This can be done using reflective control devices on the solar sail itself (like IKAROS), by translating masses around to change the center of mass, or any other means of attitude control.
However, these control devices need control inputs to function. How have previous solar sailing missions provided these control inputs? Did it come from measurements of attitude over time? Measurement of the forces on the sails? Simulated or estimated forces on sails?