Physics-Based Simulator for NEO Exploration Analysis & Modeling

As part of the Space Exploration Analysis and Simulation (SEAS) task, the National Aeronautics and Space Administration (NASA) is using physics-based simulations at NASAs Jet Propulsion Laboratory (JPL) to explore potential surface and near-surface mission operations at Near Earth Objects (NEOs). The simulator is under development at JPL and can be used to provide detailed analysis of various surface and near-surface NEO robotic and human exploration concepts. In this paper we describe the SEAS simulator and provide examples of recent mission systems and operations concepts investigated using the simulation. We also present related analysis work and tools developed for both the SEAS task as well as general modeling, analysis and simulation capabilities for asteroid/small-body objects. The SEAS simulator incorporates high-delity models of the NEO environment including its irregular geometry, the gravity eld, and the eect of perturbing forces such as other body gravity elds and solar pressure. A local regolith model consisting of many individual irregular particles interacting through friction and cohesive forces can be used to model the details of contact events at or below the NEO surface. The NEO orbit is propagated from planetary ephemerides data and the option is available to model its rotation using either a kinematic or dynamics model. The spacecraft trajectory is propagated in the low-gravity eld of the NEO and the simulation is capable of providing collision and line-of-sight information between the spacecraft, NEO and other objects. Representative NEO models based upon the Itokawa and Eros NEOs are currently in use within the simulation and a Phobos model is also under development. Spacecraft and surface assets at the NEO are modeled with full multi-body dynamics and include models for spacecraft devices such as thrusters, reaction wheels, Inertial Measurement Units (IMUs), star-trackers, tethers and anchors. Illumination from the sun is modeled to allow synthesis of images from surface viewing navigation cameras. Standard spacecraft Guidance, Navigation and Control (GNC) functions are incorporated into the simulation to provide attitude and position control. This NEO simulation is based upon the DSENDS spacecraft modeling tool available at JPL that has been previously used on such missions as the Mars Phoenix Lander. Studies being conducted with this simulator in the NEO context include spacecraft-mounted arms performing contact and surface sampling activitites, a surface hopping robots landing interactions with the surface, iterative guidance laws for surface hopping mobility, regular and irregular orbits, station-keeping at various distances and periods, visualization of the surface and near-surface gravity elds, approach guidance simulation, tethered free-ying operations, evolution of dust plume/ejecta arising from surface operations, and anchoring of surface assets.