where [ A ( t ) ] = [ cos ⁡ ⁡ ( θ θ ( t ) ) − − sin ⁡ ⁡ ( θ θ ( t ) ) sin ⁡ ⁡ ( θ θ ( t ) ) cos ⁡ ⁡ ( θ θ ( t ) ) ] , is the rotation matrix that defines the angular position of M relative to F as a function of time.