Guidance, Navigation, and Control Technology System Trades for Mars Pinpoint Landing

Abstract

Landing site selection is a compromise between safety concerns associated with the site's terrain and scientific interest. Therefore, technologies enabling pinpoint landing (sub-100 m accuracies) on the surface of Mars are of interest to increase the number of accessible sites for in-situ research as well as allow placement of vehicles nearby prepositioned assets. A survey of various guidance, navigation, and control technologies that could allow pinpoint landing to occur at Mars has shown that negligible propellant mass fraction benefits are seen for reducing the three-sigma position dispersion at parachute deployment below approximately 3 km. Four different propulsive terminal descent guidance algorithms were analyzed with varying applicability to flight. Of these four, a near propellant optimal, analytic guidance law showed promise for the conceptual design of pinpoint landing vehicles. The existence of a propellant optimum with regards to the initiation time of the propulsive terminal descent was shown to exist for various flight conditions. In addition, subsonic guided parachutes are shown to provide marginal performance benefits due to the timeline associated with Martian entries, and a low computational-cost, yet near fuel optimal propulsive terminal descent algorithm is identified. This investigation also demonstrates that navigation is a limiting technology for Mars pinpoint landing, with overall landed performance being largely driven by navigation sensor and map tie accuracy.

Guidance for Autonomous Precision Landing on Atmosphereless Bodies

“…This was tested in Ref. 6 and found to be simple to implement and still computationally less demanding than other guidance modes. Another limitation is that it is implicitly assumed that v f = 0.…”

“…Steinfeldt et al applied a gradient-based numerical optimization-technique to the guidance problem. 6 Gradient-based techniques are essentially a computational implementation of optimal control theory. For more details, see Ref.…”

“…It is a daunting task for designers to select the most suitable guidance mode for their particular application from those available in the literature. In recent years, trades involving a selected few algorithms have been presented by Sostaric and Rea 5 and by Steinfeldt et al 6 The last broad overview of the state-of-the art in guidance modes was given by Pfeiffer,7 which is long outdated by today's standards. This paper presents a survey of most guidance algorithms for planetary landing that have been published.…”

Lossless convexification of Powered-Descent Guidance with non-convex thrust bound and pointing constraints

“…If a feasible solution exists, then interior-point methods will find the global optimal solution to an SoCP [13]. The explicit enforcement of the lower bound on thrust magnitude and the numerical efficiency and accuracy make the convex PDG algorithm a strong candidate for flight implementation [9]. Additionally, compared to heritage algorithms, the convex PDG algorithm provides a significant increase in the initial states from which pinpoint landing can be achieved [11].…”

“…Current guidance methods ensure a safe landing that avoids impact with the descending parachute/backshell after lander separation, but there is no attempt to minimize landing error. To reduce landing error, many candidate guidance algorithms have been developed [1]- [9]. These algorithms vector available thrust to maneuver the descending lander closer to the original target, thus achieving touchdown closer to a desired science location (or existing surface asset) and reducing the risk of any lengthy rover traverse.…”