Tethered towing using open-loop input-shaping and discrete thrust levels

• An ADR method uses excess fuel on an upper stage rocket to tether and deorbit debris.
• An input shaped thrust maneuver reduces the post-burn motion.
• Two discrete input shaping profiles are explored: Posicast and bang-off-bang.
• Deep space input shaping reduces relative end body motion.
• On-orbit, large end body separations are achieved, avoiding collisions.

Asteroid retrieval, satellite servicing, and debris removal concepts often rely on a thrusting vehicle to redirect and steer a passive object. One effective way to tow the object is through a tether. This study employs a discretized tether model attached to six degree-of-freedom end bodies. To reduce the risk of a post-burn collision between the end bodies, discrete thrust input shaping profiles are considered including a Posicast input and a bang-off-bang thrust profile. These input shaping techniques attain desirable collision avoidance performance by inducing a tumbling or gravity gradient motion of the tethered formation. Their performance is compared to an earlier frequency notched thruster profile.