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A numerical algorithm to estimate an achievability limit for crewed planetary landing

Crewed planetary landing is a particularly difficult mission phase that involves astronauts collaborating with automated systems to identify a suitable landing point that is free of hazards. The landing vehicle needs to be capable of making final maneuvers to a suitable landing point with a highly constrained amount of fuel. To assist with this process, the concept of providing “achievability limit” information to the astronaut pilot has been proposed. However, an approach to accurately estimate the achievability limit in a complex three-dimensional planetary landing task has yet to be developed. Here, we present an algorithm to estimate the achievability limit. This algorithm consists of three components: 1) vehicle and environmental dynamics, 2) guidance algorithms which define a reference trajectory from current vehicle position to any potential landing point on the planetary surface, and 3) a standard “crossover” pilot model to predict the pilot's joystick inputs likely made in an effort to track this reference trajectory. By combining these components, we can numerically simulate any flown trajectory and predict the fuel required to reach any potential landing point. The algorithm performs many simulations to identify the landing points that are predicted to require exactly all of the vehicle's remaining fuel (i.e., the achievability limit). Our preliminary human subject experiment suggests the algorithm very accurately predicts the limits of achievability in a range of scenarios. An accurate prediction, of this achievability limit, is necessary to provide this information to the astronaut pilots and assist with landing point selection.