Speaker
Mr
Stefaan Van wal
(University of Colorado Boulder)
Description
Recent missions to the small bodies of our Solar system have established a core understanding of the origins, characteristics, and dynamics of these pristine bodies. Furthermore, the feasibility and benefit of including lander platforms capable of performing in-situ (sub-)surface measurements was demonstrated most notably by Rosetta’s Philae lander. The inclusion of such landers on small body mission motivates the need for capability to generate high-fidelity simulations of the landers’ trajectories. In this work, we discuss and demonstrate the SAL tool, which provides that capability.
Our tool models small body environments at three distinct scales: at the large scale, the coarse shape and gravity field of the target body are represented using a constant-density polyhedron. The intermediate scale consists of rocks and boulders on its surface, which are recreated following statistics observed on asteroid Itokawa. Finally, at the small scale, interactions between the target body surface and a lander are captured using a contact dynamics model based on the normal, friction, and rolling resistance forces and torques.
The major challenge in simulating this environment results from the high resolution of the applied models. The computational load of detecting collisions between a lander and a small body shape model with hundreds of thousands of facets is reduced through the use of bounding boxes and the subdivision of the target body shape into local worlds. By constructing simplified gravity models from the high-resolution shape model, we reduce the cost of gravity field evaluations in exchange for only a small reduction in the gravity field accuracy. Generating the full distribution of millions of surface rocks is computationally unfeasible; instead we apply a procedural generation strategy that creates these surface features “on the go,” and only on the active local world when the bounding-box collision module detects an impending collision. This provides a reproducible, low-cost technique for creating rock distributions. Finally, regional variations in the properties of the small body surface are captured by locally varying the coefficients of restitution, friction, and rolling resistance, which govern the energy dissipation during contact interactions.
Using this tool, we may carry out sets of Monte Carlo deployment simulations in which the release conditions, rock field parameters, and surface interaction coefficients are varied. The resulting trajectories allow mission designers to analyze the feasibility of a given deployment strategy, and establish related hardware requirements, such as the on-board battery capacity, which follows from the expected time-to-land. The trajectories’ geographical spread provides information on the illumination, thermal, and scientific characteristics of the expected landing site. Finally, our tool may also be used to simulate surface mobility operations, in which a lander uses mobility devices such as reaction wheels to generate impulses, which allow it to travel on and over the small body surface in a series of “hops,” enabling a single lander to obtain scientific measurements at multiple sites.
| Applicant type | First author |
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Primary author
Mr
Stefaan Van wal
(University of Colorado Boulder)
Co-authors
Prof.
Daniel Scheeres
(University of Colorado Boulder)
Dr
Simon Tardivel
(Jet Propulsion Laboratory (California Institute of Technology))
