Landing on Mars: probabilistic modeling enables quantifying the last "six minutes of terror"

© 2020 The last three phases of landing of a spacecraft on Mars, the parachuting phase (PP), the retro-rocket phase (RRP) and the freefall phase (FFP), are of major importance, as far as the spacecraft's safe landing is concerned. The characteristics of these phases are addressed considering inevitable uncertainties that affect their times, altitudes and landing velocities. A probabilistic predictive model, using physically meaningful Rayleigh distribution, is developed. The general concepts are illustrated by numerical examples. It is concluded that it might be impossible to assure a low enough probability that an acceptable landing velocity is exceeded and, because of that, cocooning the spacecraft in airbags to cushion the blow might be inevitable. In any event, landing on Mars will still remain a risky business for years to come.