Spacecraft Stabilization and Control for Capture of Non-Cooperative Space Objects

Abstract This paper addresses stabilization and control issues in autonomous capture andmanipulation of non-cooperative space objects such as asteroids, space debris, andorbital spacecraft in need of servicing. Such objects are characterized by unknownmass-inertia properties, unknown rotational motion, and irregular shapes, whichmakes it a challenging control problem. The problem is further compounded bythe presence of inherent nonlinearities, signi cant elastic modes with low damping,and parameter uncertainties in the spacecraft. Robust dissipativity-based controllaws are presented and are shown to provide global asymptotic stability in spite ofmodel uncertainties and nonlinearities. It is shown that robust stabilization can beaccomplished via model-independent dissipativity-based controllers using thrustersalone, while stabilization with attitude and position control can be accomplishedusing thrusters and torque actuators. 1 Introduction The proposed NASA asteroid redirect mission has created considerable excitementand interest in the public as well as in the worldwide science and engineering com-munities. A study by the Keck Institute [1] has concluded that it is feasible toautonomously capture and return an entire 7-m diameter, 500,000-kg near-Earthasteroid to a high lunar orbit. An alternate approach, consisting of picking a bouldero of a larger asteroid, is also being studied. Investigations are in progress at NASAand other organizations to conceive and develop alternative approaches and methodsfor capture, manipulation, and transport of asteroids.Another important challenge that is technically similar to asteroid capture isorbital debris mitigation. The near-Earth as well as geostationary orbital debrispopulation is continuously growing and its growth is expected to continue in thefuture due to ongoing space activities. On-orbit satellite explosions and collisions(accidental or intentional) create even larger numbers of debris items. Space debrisposes a serious threat both to human-occupied vehicles and to commercial satellites.Some suggested approaches for orbital debris mitigation would involve docking acapture spacecraft with the debris or making a physical impact. This is a techno-logically challenging task as most debris are non-cooperative and possibly tumblingwith unknown spin, precession, nutation, amplitude changes etc.A third technically similar challenge is autonomous on-orbit capture and servic-ing of defunct or functioning satellites. For example, on-orbit refuelling or repairscan extend a satellite’s life at a fraction of the cost of constructing and launching anew satellite. Also, with the rapid ongoing advancement of micro-component tech-nologies, it may be desirable to replace components of older functioning satelliteswith advanced components and signi cantly increase the capabilities. (For refuellingor refurbishment of functioning satellites, the capture and manipulation should besomewhat simpler since they would likely be cooperative objects). A related problem is asteroid strike threat mitigation, which would involve chang-ing an asteroid’s trajectory to avoid collision with Earth.1