Guidance and Control Design for Hazard Avoidance and Safe Landing on Mars

Abstract

To ensure successful future Mars landing missions, the lander must be capable of detecting hazards in the nominal landing zone and maneuvering to a new and safe site. Trajectory guidance and attitude commanding are formulated for the terminal descent phase when the lander is off the parachute. The autonomous six-degree-offreedom controls are accomplished using engines and thrusters and guided by onboard hazard-avoidance sensors. The algorithms determine the available landing zone, survey them for hazards, select the best or alternate landing site based on state estimates and available propellant, and then maneuver the lander to land safely at the selected site. Computer simulations have demonstrated the satisfactory performance of the algorithms for safe landing on Mars with assumed atmospheric environments. Nomenclature a = acceleration a t = target acceleration a v = desired vertical acceleration at landing C 0 , C 1 , C 2 = coefficients of acceleration profile g = acceleration caused by gravity (at Mars) h = height of vertical phase m = mass at start of powered descent m prop = mass of propellant for landing q = attitude quaternion r = position relative to landing site r t = target position r 0 = initial position t go = time to go until reaching target t * = time at velocity extreme point V{.} = vector part of the quaternion argument v = velocity relative to landing site v exhaust = propulsion system exhaust velocity v t = target velocity v td = desired vertical velocity at landing v 0 = initial velocity v * = velocity extreme point (minimum or maximum) y = horizontal landing coordinate position z = horizontal landing coordinate position V = ideal change in velocity V x = vertical component of ideal change in velocity V y = horizontal component of ideal change in velocity V z = horizontal component of ideal change in velocity ⊗ = quaternion multiplication operator

Review of guidance techniques for landing on small bodies

“…This profile was not optimal in the sense that no cost function was optimised, but the quadratic coefficients could be computed analytically from the terminal boundary conditions for a pre-specified descent duration. This approach was modified for the NASA's Mars Science Laboratory (MSL) Curiosity in 2011, by adding a line-search over the powered descent duration so as to minimise propellant consumption (Ploen et al, 2006;Wong et al, 2006). In addition to these simplifications and extensions, augmenting the polynomial order of an open-loop guidance law renders the computation of the coefficients under-determined and thus, this allows choosing them so as to optimise a desired cost function.…”

Guidance for Autonomous Precision Landing on Atmosphereless Bodies

“…A similar profile was also chosen for future American lunar landings and MSL. 10,13 The Apollo GNC system is described in detail in Ref. 31.…”

Mars Science Laboratory Simulations for Entry, Descent, and Landing

“…In the final 5 m, a constant velocity descent is commanded until the engines are shut off at 1 m. Further detail on the terminal descent guidance is given in Ref. 38.…”