Aircraft and spacecraft pilots frequently change their level of supervisory control between full autopilot and other modes, providing varying levels of manual control. Therefore, multimodal systems must transition "gracefully," meaning without unsafe decreases in flight performance or unacceptable changes in workload or situation awareness. Thirteen subjects flew a fixed base simulation of the NASA Constellation Program Altair lunar lander that transitioned from full autopilot to one of three flight-director-guided rate-command attitude hold manual control modes. After training, each subject flew 24 approaches, half of which included a landing point redesignation at the time of the mode transition requiring the pilot to null additional guidance errors. Bedford subjective workload and two-choice embedded secondary task response times were used to quantify temporal changes in mental workload. Situation awareness transients were detected by analysis of a tertiary task, verbal callouts of altitude, fuel, and terrain hazards. Graceful transitions were particularly difficult because Altair's large inertia made the plant dynamics relatively sluggish. Transitions to manual control increased subjective and objective workloads and decreased callout accuracy in proportion to the number of flight control axes being manually commanded.

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Conceptualizing situation awareness around the metric of system state uncertainty is a valuable way for system designers to understand and predict how reallocations in the operator's visual attention during control mode transitions can produce reallocations in situation awareness of certain states.

The “Variable Vector Countermeasure Suit (V2Suit) for Space Habitation and Exploration” is a novel system concept that provides a platform for integrating sensors and actuators with daily astronaut intravehicular activities to improve health and performance, while reducing the mass and volume of the physiologic adaptation countermeasure systems, as well as the required exercise time during long-duration space exploration missions. The V2Suit system leverages wearable kinematic monitoring technology and uses inertial measurement units (IMUs) and control moment gyroscopes (CMGs) within miniaturized modules placed on body segments to provide a “viscous resistance” during movements against a specified direction of “down”—initially as a countermeasure to the sensorimotor adaptation performance decrements that manifest themselves while living and working in microgravity and during gravitational transitions during long-duration spaceflight, including post-flight recovery and rehabilitation. Several aspects of the V2Suit system concept were explored and simulated prior to developing a brassboard prototype for technology demonstration. This included a system architecture for identifying the key components and their interconnects, initial identification of key human-system integration challenges, development of a simulation architecture for CMG selection and parameter sizing, and the detailed mechanical design and fabrication of a module. The brassboard prototype demonstrates closed-loop control from “down” initialization through CMG actuation, and provides a research platform for human performance evaluations to mitigate sensorimotor adaptation, as well as a tool for determining the performance requirements when used as a musculoskeletal deconditioning countermeasure. This type of countermeasure system also has Earth benefits, particularly in gait or movement stabilization and rehabilitation.

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