The Torque Rudder: A Novel Semi-Passive Actuator for Small Spacecraft Attitude Control

The Torque Rudder: A Novel Semi-Passive Actuator for Small Spacecraft Attitude Control

This paper presents a novel concept for a semi-passive small spacecraft actuator. The proposed device consists of a set of solar cells that drive a small magnetic torquer automatically when illuminated. This device—referred to as a “torque rudder”, given its originally intended application in solar or drag sail missions—would be deployed or pre-positioned to automatically generate a magnetic disturbance torque proportional to its illumination. When the rudder is not illuminated, its residual magnetic moment would be zero, and the device would generate no torque. Thus, the proposed actuator has applications where sun-avoiding attitudes are desired in the absence of spacecraft commandability, and where permanent or bus-driven magnetic solutions are undesirable or unavailable. This paper describes the torque rudder concept, including a simple electrical and dynamic model for its use, with sample simulations derived from the CanX-7 drag sail deorbiting mission. A practical implementation is presented that enables sun-excluding modes for low-Earth orbit spacecraft with any LTAN. It is concluded that the torque rudder concept represents a novel, simple actuator when passive sun-pointing or sun-exclusion is desired, as may be the case for many small satellites.