Single-Axis Pointing of an Underactuated Spacecraft Equipped with Two Reaction Wheels

A smooth time-invariant wheel rate command is defined, based on angular momentum balance considerations, which causes the spacecraft to rotate approximately about the admissible rotation axis, which is lying on the plane identified by the two RW axes, implementing the kinematic planning scheme at a dynamic level. Convergence toward the prescribed alignment under the action of the proposed control law is proven using a Lyapunov approach, exploiting the cascade nature of system dynamics. Asymptotic convergence in a finite region around the desired final condition is proven first.