Divert Architectures and Guidance, Navigation, and Control to Enable Pinpoint Landing for Planetary Exploration

Future robotic and human missions to Mars require improved landed precision and increased payload mass. Two architectures that seek to meet these requirements using supersonic propulsive diverts are proposed in this paper: one utilizing a high-altitude propulsive divert and another with thrust vectoring during supersonic retropropulsion. Low ballistic coefficient entry vehicles decelerate high in the thin Mars atmosphere and may be used to deliver higher-mass payloads to the surface. A high-altitude supersonic propulsive divert maneuver is proposed as a means of precision landing for low ballistic coefficient entry vehicles that decelerate to supersonic speeds at altitudes of 20-60 km. This divert maneuver compares favorably to traditional precision landing architectures with up to 100% improvement in range capability while saving over 30% in propellant mass. Architectures which utilize hypersonic vehicles with ballistic coefficients of 10 kg/m2 were found to land within 500 m of a target with this maneuver alone. This high-altitude divert range capability is sensitive to altitude and flight-path angle variations at maneuver initiation and relatively insensitive to velocity at initiation. Propellant mass fraction is relatively invariant to the initial conditions and correlates directly with the divert distance. Supersonic retropropulsion has also been proposed as a means to deliver higher-mass payloads to the surface, and thrust vectoring during supersonic retropropulsion can save a substantial amount of fuel in a precision landing scenario. Propellant mass savings greater than 30% are possible if thrust vectoring is unconstrained during the supersonic phase of flight. Propellant mass fraction is found to be sensitive to the divert direction and also the altitude and flight-path angle, favoring low altitudes and shallow flight-path angles.