Two-phase zero-effort-miss/zero-effort-velocity guidance for mars landing

This paper presents a new two-phase zero-effort-miss/zero-effort-velocity (ZEM/ZEV) feedback guidance strategy for Mars precision landing, which directly accommodates a variety of constraints and requirements, such as retrorocket thrust magnitude limits, obstacles over the surface of Mars, and abnormal initial conditions. For its first phase, a virtual-terminal-velocity guidance law is augmented by an online parameter searching technique for collision avoidance. For its second phase, a signed curvature concept enhances the basic ZEM/ZEV guidance law for final soft touchdown. Its robustness, fuel efficiency, and computational simplicity are demonstrated for abnormal initial conditions, especially in comparison with three other feedback guidance laws recently published in the literature.