The Manned Maneuvering Unit (MMU) built by the Martin Marietta Company is a self-contained, propulsive backpack that provides space-suited astronauts with six degree-of-freedom precision maneuvering capability to at least 150 meters (500 feet) from the Shuttle Orbiter. Astronauts are trained to fly the MMU in the Space Operations Simulator (SOS) Laboratory located at Martin Marietta Denver Aerospace facilities in Denver, Colorado. MMU simulations in the SOS use two major devices. The first is a six-degree-of-freedom Moving Base Carriage (MBC) that allows the trainee to fly the MMU in a large room and to maneuver around and dock with full-scale targets. The second device is a large-screen television display that provides the trainee with accurate views of tumbling targets from any point in a surrounding sphere up to 300 meters (1000 feet) in diameter. Astronauts used the SOS to train for the mission to retrieve and repair the Solar Maximum satellite in April 1984 and the mission to recover two H-376 communications satellites in November 1984. Subjective comparisons by astronauts of on-orbit MMU performance to simulated MMU performance in the SOS indicate that the simulations are very realistic. Data from the Solar Maximum mission resulted in two software upgrades that increased SOS fidelity for the H-376 recovery mission: a model of contact dynamics between the MMU and a target spacecraft, and a model of forces imparted to the target by MMU thruster plumes impinging on the target during docking. Success of both satellite retrieval missions demonstrates the value of MMU space operations simulations.

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