Next-Generation Maneuvering System with Control-Moment Gyroscopes for Extravehicular Activities Near Low-Gravity Objects

Abstract

Looking ahead to the human exploration of Mars, NASA is planning for exploration of near-Earth asteroids and the Martian moons. Performing tasks near the surface of such lowgravity objects will likely require the use of an updated version of the Manned Maneuvering Unit (MMU) since the surface gravity is not high enough to allow astronauts to walk, or have sufficient resistance to counter reaction forces and torques during movements. The extravehicular activity (EVA) Jetpack device currently under development is based on the Simplified Aid for EVA Rescue (SAFER) unit and has maneuvering capabilities to assist EVA astronauts with their tasks. This maneuvering unit has gas thrusters for attitude control and translation. When EVA astronauts are performing tasks that require fine motor control such as sample collection and equipment placement, the current control system will fire thrusters to compensate for the resulting changes in center-of-mass location and moments of inertia, adversely affecting task performance. The proposed design of a next-generation maneuvering and stability system incorporates control concepts optimized to support astronaut tasks and adds control-moment gyroscopes (CMGs) to the current Jetpack system. This design aims to reduce fuel consumption, as well as improve task performance for astronauts by providing a stiffer work platform. The high-level control architecture for an EVA maneuvering system using both thrusters and CMGs considers an initial assessment of tasks to be performed by an astronaut and an evaluation of the corresponding human-system dynamics. For a scenario in which the astronaut orbits an asteroid, simulation results from the current EVA maneuvering system are compared to those from a simulation of the same system augmented with CMGs, demonstrating that the forces and torques on an astronaut can be significantly reduced with the new control system actuation while conserving onboard fuel.

Real-time virtual reality environment for MAJIC attitude control system development and implementation

“…Each thruster is capable of producing 3.56 N of thrust and traditionally for translation commands four thrusters will fire and for rotation commands two thrusters will fire. The current SAFER system utilizes a table look-up operation to calculate jet on-times for given inputs; however, in order to minimize fuel consumption for both thrusters and CMGs, a simplex algorithm [4] is implemented to minimize the fuel consumption at each time step. …”