Autonomous controls for active space debris removal

Abstract

Space debris poses a major threat to the long-term endeavors of humanity. A build-up and consequential cascade of debris collisions may very well render space travel nearly to completely impossible. The economic, scientific, and militaristic ramifications to the congestion of orbital planes around the Earth are very real. At the date of writing, several space agencies have acknowledged that active debris removal (ADR) is the only viable method to keep our near Earth orbits clear. Proposed here are two algorithms that will be on-board a 3U CubeSat, OSCaR (Obsolete Spacecraft Capture and Removal), that will track and de-orbit pieces of debris on orbit. The first algorithm is an improvement on standard linear quadratic regulator (LQR) attitude controls for CubeSats. Instead of a single linearization of the non-linear dynamics with corresponding LQR gains, OSCaR will relinearize and calculate the newly corresponding gains. This allows for a faster pointing time when near low angular velocities. In addition, OSCaR will also account for the dynamics of the reaction wheels--a consideration rarely taken into account on-board CubeSats. The second algorithm proposed is an inverse kinematics based impulse method to bring OSCaR to a near-rendezvous. OSCaR must pass by the debris with a defined separation. It need not stop, but rather pass close enough to launch a net with an electromagnetic tether attached. Current literature either utilizes inefficient continuous controls to rendezvous or ignore the error accumulated by the linearization of the non-linear equations of motion. However, this impulsive method will subtract out predicted error at the start of the intercept maneuver to produce a highly accurate interception.