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Design and Evaluation of Advanced Display and Control Concepts for Piloted Planetary Landing
A new generation of spacecraft are now under development to returnastronauts to the Moon. NASA has stated that manual control will continue to be provided for human-rated spacecraft. Thus, improved manual control capability and displays offer the potential for improved performance and safety during the challenging task of lunar landing. Specifically, providing real-time achievability limit information to the pilot has been proposed as a means to reduce their workload, improve situation awareness, and increase safety. Additionally, an Incremental Position Command (IPC) control system has been suggested to improve piloting handling qualities for the terminal descent portion of the trajectory. To advance these human system integration technologies for lunar landing, we develop, implement, and comprehensively evaluate their benefits in a human subject experiment within our fixed base simulator.
An algorithm was developed for an achievability limit display (ALD) that combines a behavioral model of the pilot and physical models of the vehicle and environmental dynamics to predict the propellant required to reach any potential landing site from current vehicle state. Further, we developed and implemented a blended control mode, using the Apollo standard Rate Command Attitude Hold (RCAH) when up and away, but transitioning to IPC for vertical descent.
Human subject testing was performed (21 total subjects) to validate the achievability limit algorithm, by assessing the amount of propellant remaining when piloting to landing sites which the algorithm predicted where on the edge of achievability. The results of that assessment demonstrated that the algorithm does adequately predict near-zero propellant remaining (< 5% error) and the behavioral model in the algorithm was improved by altering the model-pilot time delay.
A 40 subject study was then conducted on a ground-based flight simulator to comprehensively evaluate the impact of the ALD and IPC control mode. Subjects were assigned to one of four test conditions, 1) RCAH – baseline condition similar to Apollo and Altair lunar landers, 2) RCAH/ALD – includes achievability limit information, 3) RCAH+IPC – includes IPC mode during final descent to touchdown, and 4) RCAH+IPC/ALD – includes both achievability limit information and IPC. Subjects completed simulated lunar landing trials where they were tasked with maintaining manual control of the lander’s pitch and roll through joystick inputs. In each trial the subject was tasked to select the optimum landing site that was 1) achievable 2) minimized hazards and 3) was closest to three points of scientific interest.
Providing real-time achievability limit information, particularly in scenarios with more propellant, improved task outcomes (increase in successful landings, p = 0.004), decreased workload (p = 0.03), and improved situation awareness (p = 0.008). Subjects also reported a high level of trust in the ALD. RCAH+IPC improved task performance when subjects had multiple LS redesignations (p = 0.03), but there was only limited impact on measures of workload and situation awareness. The combination of RCAH/IPC and the ALD led to the greatest improvements to task outcomes (p = 0.002), lowest reported workload ratings, and highest SA ratings.
The factors that define LS achievability interact in a non-intuitive manner such that even experienced pilots may struggle to accurately estimate the achievable limits. The first main contribution of this research was the development and assessment of an algorithm that accurately predicts achievability limits to assist the pilot. Additionally, the studies conducted were the first comprehensive evaluations of the ALD and blended RCAH+IPC implementation. The ALD and IPC modes led to a 93% landing success rate (baseline was 67%). These two technologies and the results of this study show promising benefits to lunar landing safety and human performance.</p