In order to simulate physically plausible surfaces that represent geologically evolved surfaces, demonstrating demanding surface-relative guidance navigation and control (GN&C) actions, such surfaces must be made to mimic the geological processes themselves. A report describes how, using software and algorithms to model body surfaces as a series of digital terrain maps, a series of processes was put in place that evolve the surface from some assumed nominal starting condition.
The physical processes modeled in this algorithmic technique include fractal regolith substrate texturing, fractally textured rocks (of empirically derived size and distribution power laws), cratering, and regolith migration under potential energy gradient. Starting with a global model that may be determined observationally or created ad hoc, the surface evolution is begun. First, material of some assumed strength is layered on the global model in a fractally random pattern. Then, rocks are distributed according to power laws measured on the Moon. Cratering then takes place in a temporal fashion, including modeling of ejecta blankets and taking into account the gravity of the object (which determines how much of the ejecta blanket falls back to the surface), and causing the observed phenomena of older craters being progressively buried by the ejecta of earlier impacts. Finally, regolith migration occurs which stratifies finer materials from coarser, as the fine material progressively migrates to regions of lower potential energy.
This work was done by Joseph E. Riedel and Nickolaos Mastrodemos of Caltech and Robert W. Gaskell of the Planetary Science Institute for NASA’s Jet Propulsion Laboratory. NPO-47233
This Brief includes a Technical Support Package (TSP).
Surface Modeling to Support Small-Body Spacecraft Exploration and Proximity Operations
(reference NPO-47233) is currently available for download from the TSP library.
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Overview
The document from the Jet Propulsion Laboratory (JPL) outlines the development of realistic surface models for small-body rendezvous and sample return missions, particularly focusing on autonomous landing capabilities. It discusses the creation of detailed models for asteroids and comet nuclei, which are essential for validating the AutoGNC (Autonomous Guidance, Navigation, and Control) system used in these missions.
The modeling process begins with constructing a gross shape of the target body, informed by visual observations and physical characteristics of similar bodies. This initial model is then refined through a detailing process that incorporates fractal texturing, crater distributions, and rock formations, ensuring that the surfaces are physically plausible and representative of actual celestial bodies. The document emphasizes the importance of simulating realistic surface conditions to enhance the effectiveness of navigation algorithms and image processing systems during missions.
The paper describes two comprehensive simulations of sample return missions using a "Touch and Go (TAG)" methodology, which involves landing on the surface, collecting samples, and returning them to Earth. The models developed serve as a basis for creating images that the AutoGNC system will use to navigate and land on these small bodies. The document highlights the challenges faced in modeling, such as the appearance of previously "invisible" rocks at higher resolutions, which can impact the performance of sampling mechanisms.
Results from the modeling efforts demonstrate the viability of TAG methodologies for sample return missions, providing high confidence in the proposed missions to visit these bodies. The document concludes by acknowledging the collaborative efforts at JPL and the funding from NASA's internal Research and Technology Development program.
Overall, this document serves as a technical support package that details the innovative approaches taken to create realistic surface models for small-body exploration, showcasing the advancements in technology that will facilitate future space missions. It underscores the significance of accurate modeling in ensuring the success of autonomous landing operations on asteroids and comets.
