  Kipping (2017) discusses relativistic reflection from light sails. As an
extension to this work, we present a new formula for relativistic reflection of
sunlight from a light sail moving at a velocity inclined at an arbitrary angle,
using an elementary two-body analysis. The formula is shown to reduce to the
formulas of Euclid, Einstein, and Gjurchinovski in the relevant limits. This
calculation may be extended to calculate the kinetic energy gained by a
relativistic light sail inclined at an arbitrary angle.
