Estimating asteroid mass from optically tracked radio beacons

This Paper presents the feasibility of estimating the mass of an asteroid by tracking a number of probes ejected from a host spacecraft during a flyby. The probes are designed to fly by at a much closer distance to the asteroid than the host spacecraft, which lowers the risk of endangering the overall mission. The motion of these probes is perturbed due to the target asteroid’s mass, and by tracking the probes from the host spacecraft, the change in relative separation between the probes, which is directly proportional to the asteroid’s mass, can be measured with high precision. The probes are small reflective spheres that are tracked by an imager mounted on the spacecraft; however, the addition of radio transceivers inside the probes can greatly enhance the mass-recovery performance. A hypothetical mission to a main-belt asteroid with the physical characteristics of (101955) Bennu is used as a reference, and an extensive covariance analysis is performed to determine the recoverable mass accuracy under various conditions. The result shows that, under realistic assumptions, the mass of a Bennu-like asteroid can be recovered with a 1σ accuracy better than 20% from optical tracking. In case radio transceivers are considered, the recovered asteroid mass accuracy reduces to better than 5%.