Issues of Landing on Near Earth Asteroids

Orbital and landing operations at near-Earth asteroids involve a variety of difficulties due to the irregular shape of these asteroids and their potential for non-uniform rotation. These difficulties make it common to find trajectories that evolve from stable, near-circular orbits to crashing or escaping orbits in a matter of days. Even in less dramatic situations the nature of orbital mechanics about asteroids are different than the familiar planetary orbiter cases. The understanding and control of orbits about asteroids is essential if a human or robotic presence at asteroids is to become commonplace. A complementary issue to understanding these dynamics is the modeling of the asteroid environment. Much of the difficulty in planning missions to a small body stems from ignorance of the shape, spin state and gravity field of the target prior to asteroid rendezvous. For this reason, realistic a priori physical models of the targets can dramatically reduce the cost and risk of asteroid missions. This paper defines and discusses a variety of asteroid landing scenarios, gives a simple analysis of the benefits and difficulties involved with each of them and addresses the benefits of having accurate information about the target asteroid and about asteroids in general. In conjunction with this paper some examples of orbiter and lander trajectories about asteroids will be available in a video format. These examples use shape models of asteroids 4769 Castalia and 4179 Toutatis obtained by inversion of radar images.