Apollo vs FNPEG Entry Terminal Point Guidance Comparisons For a Mars EDL Mission

The Apollo Entry Terminal Point Guidance algorithm has flown onboard Mars lander missions but requires significant parameter tuning. For future human to Mars missions, an operationally simpler yet robust guidance is desired, motivating evaluation of the Fully Numeric Predictor Corrector Entry Guidance (FNPEG) algorithm. For a representative Mars low L/D entry, descent and landing mission, Apollo and FNPEG were compared within an established 6 degree-of-freedom simulation. FNPEG improved terminal point precision, reducing downrange ellipse spread by about half, but also decreased terminal altitude by ~2 km, raising parachute deployment load concerns. A mid-point bank energy term may further refine FNPEG and recover altitude performance, similar to Apollo’s bi-level reference trajectory approach.