Mars Science Laboratory entry guidance improvements study for the Mars 2018 mission

Finite-time super-twisting sliding mode control for Mars entry trajectory tracking

“…Complex atmosphere environment requires the control system to be robust enough against parameter perturbations and external disturbances. The most efficient way to improve the landing precision at the parachute deployment point is to steer the vehicle trajectory during the entry phase [2,5,7]. To this end, how to design a robust controller to precisely track the entry trajectory under complex atmosphere environment is the core of Mars mission navigation [7,8].…”

“…During the entry phase, the angle-of-attack α is kept to be the trimmed attack angle, that is, the vehicle will not rotate and its motion can be deemed as a manner of mass motion [7,14]. The forces acting on the vehicle during entry phase are shown by Fig.…”

“…The Mars vehicle mission usually utilizes an offset of mass center to create a nominal angle-of-attack which is used to reduce the landing error [7]. During the entry phase, the angle-of-attack α is kept to be the trimmed attack angle, that is, the vehicle will not rotate and its motion can be deemed as a manner of mass motion [7,14].…”

“…The vital mission of Mars entry is to guide the entry vehicle to a prescribed parachute deployment point [7]. Generally speaking, in order to make the entry vehicle land on Mars safely and precisely, the prescribed parachute point should satisfy the following conditions [3,7]: 1) the altitude should be more than 7 km, 2) the velocity should be less than 400 m/s, and 3) the downrange error should be less than 10km (taking MSL as a reference).…”

“…As such, the landing precision at the parachute deployment point has a vital influence on pin-point Mars landing. In general, Mars entry phase is confronted with many system engineering challenges such as high entry speed, thin atmosphere and complex atmosphere environment [1,7]. The high velocity (as high as 20 Mach) and thin air density (only one percent of that on earth) will inevitably lead to the problem of actuator constraint especially in the entry phase [1][2][3].…”