IMPROVING THE ACCURACY OF LANDER DEPLOYMENT TO ASTEROIDS BY SPIN RATE CONTROL

Deploying small landers to asteroid surface is an important way to increase the scientific return of asteroid rendezvous missions with less risk. But the deployment of a lander in a weak and perturbed gravity environment is a challenging task. The lander may rebound several times before it settles down, resulting in a large deviation from its first landing site. This paper proposes a novel method to increase the accuracy of ballistic deployment by spin rate control. Based on the contact dynamics of rigid bodies, the spin rate of a spherical lander is controlled before each impact to change its after-impact velocity so that it can be driven into a bouncing trajectory that makes it come back to its originally targeted on the surface. In that case, the lander can remain in the vicinity of its original landing site, as its velocity dissipates until it finally rests on the surface. First, the contact dynamics of a spherical lander is investigated. The analytical solution of the velocity change with the initial spin rate is derived. Then, the necessary condition of bouncing trajectories is investigated based on a spherical model. The influence of bouncing velocity, the spin rate of an asteroid and latitude of the landing site is discussed. Next, deployment trajectories suit-able for the proposed deployment method are studied with different surface parameters. Finally, the feasibility and robustness of the proposed method are verified on a polyhedron model of asteroid Bennu. It is found that the proposed deployment method can enable a precise landing if the surface environment is well-known and largely reduce the landing dispersion under an uncertain environment. This paper provides a novel idea for future asteroid lander deployment and surface exploration missions.