This report presents a revolutionary powered descent guidance algorithm whose computational efficiency allows for real-time operation on-board a spacecraft to minimize propellant consumption and enact an accurate landing. A manned Mars mission requires supersonic retropropulsion as a decent capability to land a large-mass vehicle. During powered descent, a powered descent guidance algorithm rapidly produces thrust controls based on current navigation data where speed, automation, dependability, accuracy, and optimality are paramount to algorithm success. This report reviews previous propellant-optimal powered descent guidance approaches and generates a fully automated and closed-form solution using an indirect method of optimal control, where user-selected values do not influence the solution’s optimality. Numerical methods and function transformations are explored to improve convergence robustness. The algorithm enhances operational safety and reliability using failsafe methods to either land close to the targeted site or utilize a globally convergent tracking law before a solution degradation phenomenon occurs during the final burn stage. Monte Carlo simulations test the algorithms effectiveness and compare it to both state-of-the-art and operationally successful algorithms.