Small body in-situ Multi-probe Mass Estimation Experiment (SIMMEE)

This research describes a method and hardware prototype for resolving the mass of asteroids and comets during flybys or orbital phases. In this concept, called OpGrav, a host spacecraft releases a group of small white spheres, which it then tracks using an on-board telescope. The spheres, which act as test-masses and are called probes, are deployed such that they pass very near to the small body and their trajectories are measurably perturbed. A spacecraft-mounted camera determines the relative measurements of the probes, including right ascension and declination angles. These measurements are then processed on the ground and used to estimate the body's mass. The relative measurements have the advantage of being high signal-to-noise and high resolution, owing to the short distance between the host spacecraft to the probes and the probes to the small-body. They are also numerous, since multiple probes can be deployed from a single spacecraft, possibly to different relative geometries. These benefits enable the accurate determination of mass for bodies that are too small to study using typical ground-based radiometric tracking. The concept is evaluated in a modeling and simulation environment, which includes high-fidelity acceleration models for the small body's gravity, planetary gravity, and solar radiation pressure. The simulation results show relevant performance during a typical flyby (many kilometers per second) for asteroids as small as 1 kilometer in diameter, which represents a meaningful improvement over current methods. For most encounters, 1-3 well placed probes can be very effective, with marginal improvement for additional probes. This research focuses on the key implementation challenges, including the design and testing of an instrument hardware implementation called Small-body In-situ Multi-probe Mass Estimation Experiment (SIMMEE). This instrument consists of the probes, their dispenser, and a means of measuring the ejection conditions. The probes are stored as thin “pucks” but are dispensed as 150 mm diameter spheres, which can be tracked for 1000's of kilometers with existing optical instruments. A primary driving requirement is that the hardware must operate accurately after a 5+ year duration in space. This hardware is being fabricated and will undergo a series of test activities to determine its deployment accuracy and its suitability for space.