Mobile robotic arm for momentum unloading and orbit control

A spacecraft system comprising:

• a spacecraft bus;
• a plurality of attachment points disposed around an exterior of the spacecraft bus, each attachment point including a mechanical interface and an electrical interface;
• a multi-joint robotic arm having a plurality of rotary joints and at least first and second end effectors, each end effector being configured to selectively latch to any of the plurality of attachment points;
• a reflective panel mounted to a distal portion of the multi-joint robotic arm;
• and
• a control system configured to:
• determine, based on sensor data and a control law, a demanded torque and/or force for at least one of momentum unloading and orbit control;
• compute, based on spacecraft attitude and orbital parameters, an external force available at the reflective panel due to at least solar radiation pressure;
• and
• command the multi-joint robotic arm to relocate the reflective panel between at least a first location and a second location on the spacecraft by alternately latching the first and second end effectors to the plurality of attachment points such that application of the external force to the reflective panel at the second location generates a torque and/or force that substantially satisfies the demanded torque and/or force while avoiding interference with at least one spacecraft structure.

A non-transitory computer-readable storage medium storing instructions which, when executed by one or more processors of a spacecraft, cause the one or more processors to perform a method for controlling a spacecraft having a multi-joint robotic arm carrying a reflective panel and a plurality of attachment points disposed on an exterior surface of the spacecraft, the method comprising:

• receiving, from an attitude and orbit control system, a demanded change in at least one of (i) stored momentum in a momentum storage device and (ii) an orbital state of the spacecraft;
• computing, based on ephemeris data, spacecraft attitude, and properties of the reflective panel, at least one external force available at the reflective panel due to at least solar radiation pressure;
• formulating an optimization problem having decision variables including (i) a discrete variable selecting an attachment point from the plurality of attachment points and (ii) continuous variables representing joint angles of the multi-joint robotic arm, an objective function related to satisfying the demanded change, and constraints including joint-angle limits and at least one keep-out region associated with a spacecraft structure;
• solving the optimization problem to obtain a target attachment point and a corresponding set of joint angles that define a target configuration of the multi-joint robotic arm and the reflective panel;
• and
• outputting commands that cause the multi-joint robotic arm to move, by alternately latching different end effectors to the plurality of attachment points, from an initial configuration to the target configuration.