  In asteroid rendezvous missions, the dynamical environment near the
asteroid's surface should be made clear prior to the mission launch. However,
most of the asteroids have irregular shapes, which lower the efficiency of
calculating their gravitational field by adopting the traditional polyhedral
method. In this work, we propose a method to partition the space near the
asteroid adaptively along three spherical coordinates and use Chebyshev
polynomials interpolation to represent the gravitational acceleration in each
cell. Moreover, we compare four different interpolation schemes to obtain the
best precision with the identical initial parameters. An error-adaptive octree
division is combined to improve the interpolation precision near the surface.
As an example, we take the typical irregular-shaped near-Earth asteroid 4179
Toutatis to show the advantage of this method, as a result, we show that the
efficiency can be increased by hundreds to thousands times with our method. In
a word, this method can be applicable to other irregular-shaped asteroids and
can greatly improve the evaluation efficiency.
