Augmented Apollo Powered Descent Guidance

The Apollo powered descent guidance (APDG) paradigm, developed over 50 years ago for the Apollo Lunar Module, is beautifully simple and elegant. Still, the limitations of APDG have become increasingly apparent and restraining as more diverse applications are considered. This paper presents a methodology, dubbed Augmented Apollo Powered Descent Guidance (A2 PDG), to significantly enhance APDG. In A2 PDG, the user can choose from a family of tunable guidance laws of APDG variants by selecting a gain. This approach unifies the two versions of APDG guidance laws in the literature as they are shown to be special cases of the tunable guidance laws. Furthermore, the guidance law offers the flexibility to balance the competing considerations among fuel usage, trajectory shaping, and guidance command variations. Another prominent feature of A2 PDG is the onboard determination of an appropriate condition to start the powered descent phase and corresponding flight time, which helps yield near-minimum fuel consumption, ensure accurate landing, and preserve sufficient guidance margins for dispersions. Extensive end-to-end closed-loop Monte Carlo simulations for a human Mars mission are used to demonstrate the working of A2 PDG and its advantages.