Vv. Vidyakin et Ig. Popova, Expansion of the force function for the mutual gravitation of two rigid bodies of arbitrary shape in a series of spherical harmonic functions, ASTRON REP, 43(6), 1999, pp. 412-416
A series expansion of the force function for the mutual gravitation of two
arbitrarily shaped rigid bodies is considered. The constants C-nk and S-nk
are used as coefficients of the series. The first five terms of the series
are presented in explicit form.