Development of a target marker for landing on asteroids

The proposed asteroid sample return mission MUSES-C calls for a spacecraft to approach an asteroid, touch down on its surface, and collect samples tha t will be returned to Earth. During the touchdown and sampling phase, the s pacecraft will navigate relative to the asteroid surface using optical targ et markers placed on the asteroid surface before the final approach. By usi ng the target marker as a reference point, navigation during the landing ph ase will be much more reliable and precise. Because of the microgravity env ironment on the asteroid surface, the settling time and dynamics of the tar get markers are items of interest. Thus, it is important to design the targ et marker with as small a coefficient of restitution as possible to minimiz e the settling time, which in turn minimizes the time the spacecraft must h over above the asteroid surface. To achieve this small coefficient of resti tution, the target marker will be constructed out of a bag with balls store d internally. On impact, the balls will dissipate energy relative to each o ther and, hence, will dissipate the total energy of the target marker. To b etter predict the performance of such a target marker, analytical and numer ical investigations are performed that model the motion of a bouncing targe t marker across the surface of a rotating asteroid. As a result of the anal ysis, some target limits on the target marker coefficient of restitution ar e developed. A series of microgravity tests are reported that confirm the b asic design and show that the target value of coefficient of restitution ca n be reached.