OPTIMAL GUIDANCE FOR QUASI-PLANAR LUNAR ASCENT

The minimum-time controls (thrust pitch and thrust yaw) for the three-dimensional transfer of a constant-thrust rocket from one state to another over a flat moon are used to develop guidance laws for operation over a spherical moon. After assuming small out-of-plane motion (small yaw), three in-plane (pitch) control laws are developed. The three laws are employed in the sample and hold guidance of a lunar ascent vehicle. All three laws satisfy the final conditions and give essentially the same pitch and yaw control histories. Since the zeroth-order law can be obtained completely analytically, it merits consideration for ascent guidance.