Close proximity dynamics and control about asteroids

Small solar system bodies such as asteroids and comets are of significant interest for scientific, robotic, and human exploration missions. However, their dynamical environments are among the most extreme found in the solar system. Uncontrolled orbital trajectories in the vicinity of an asteroid are highly unstable in general and may either impact or escape in timespans of hours to days. Even with active control, the chaotic nature of motion about these bodies can effectively randomize a trajectory within a short time period, creating fundamental difficulties for the navigation of spacecraft in these environments. Dealing with these navigation issues through the estimation and control of asteroid-relative motion and models is a burgeoning area of research that has become higher profile with the recently announced NASA Asteroid Retrieval Mission. The goals of that mission will require significant extensions of capability beyond previously flown asteroid rendezvous missions. Despite this, there has been significant prior research and application of estimation and control techniques for spacecraft in these small body environments that can directly inform and motivate the necessary direction of future research. This tutorial paper will review previous research and applications for asteroid relative proximity operations and indicate areas where additional future research is needed.