287 / 2023-10-09 23:07:52

Modeling the Gravitational Field of an Irregularly shaped Ore-bearing Asteroid with Inhomogeneous Density by Using a Novel CFD-based Method

space mining,gravitational field,asteroid

Asteroids are the remnants of solar system bodies, providing us opportunities to probe into the mysterious solar system history. In particular, some asteroids are rich in minerals which are rare on the Earth, making them valuable targets in future human space exploration missions. In recent years, the major international players in space showed great interests in asteroid exploration and space mining. For example, the spacecrafts Hayabusa and Hayabusa2 from Japan managed to return the Itokawa and Ryugu asteroids to Earth, respectively; the OSIRIS-Rex mission of the United States has completed the sampling of the asteroid Bennu and will return to the Earth in 2023; the sample-return mission Tianwen-2 of China is currently under development and plans to launch spacecraft to a near-Earth asteroid around 2025.

In an asteroid exploration mission, the gravitational field model plays an important role in establishing a height system, describing the asteroid’s topography and determining the prober's tracking path. Modeling the gravitational field of an ore-bearing asteroid, which usually has an irregular shape and inhomogeneous density, is a prerequisite for asteroid exploration or space mining missions. It attracts numerous deep-space scientists' attention to developing efficient and accurate algorithms to model the exterior gravitational field of ore-bearing asteroids. To date, there are two major categories of methods for gravitational field modeling: one is of numerical integration type for solving forward modeling problems (e.g., the mascon approach), and the other of analytical boundary value solution for inversion problems (e.g., spherical-harmonic-based approaches).

In our previous research, we developed a computational fluid dynamics (CFD)-based method to describe the gravitational field structure, reformulating the gravitational field in terms of a potential flow, a concept from fluid dynamics. With this idea, the gravitational vector field is mapped onto the potential-flow vector field, and the CFD technique can be introduced to solve the gravitational field modeling problem (Yin & Sneeuw, 2021). In this study, we extend the CFD-based method to model the gravitational field of an irregularly shaped and non-uniform-density asteroid. Firstly, six types of density distribution in asteroid Bennu are simulated, and then the gravitational fields are derived with the CFD-based method, and finally the results are compared to the other two solutions, derived from the mascon approach (as a benchmark solution) and polyhedron method, respectively. The result shows a superior performance of the CFD-based method on both accuracy and efficiency. For example, it costs only 268 s for the CFD-based method computing 1,650,000 exterior gravitational vectors of the asteroid, with the relative accuracy of 1.27%. In comparison, it takes the polyhedron modeling method 14,520 s, with the relative accuracy of 3.84%. The comparison shows a good algorithm performance of the CFD-based gravitational field modeling method, thereby having a good potential application in deep-space exploration or space mining missions.