Manned Maneuvering Unit

It was designed to fit over the life-support system backpack of the Space Shuttle Extravehicular Mobility Unit (EMU).

When carried into space, the MMU was stowed in a support station attached to the wall of the payload bay near the airlock hatch.

Two aluminium tanks with Kevlar wrappings contained 5.9 kilograms of nitrogen each, enough propellant for a six-hour Extravehicular activity (EVA) depending on the amount of maneuvering done.

To operate the propulsion system, the astronaut used their fingertips to manipulate hand controllers at the ends of the MMU's two arms.

Once a desired orientation was achieved, the astronaut could engage an automatic attitude-hold function that maintained the inertial attitude of the unit in flight.

In 1966, the US Air Force developed an Astronaut Maneuvering Unit (AMU), a self-contained rocket pack very similar to the MMU.

However, the test had to be cancelled because Cernan, tired and overheated, sweated so profusely that his helmet visor fogged before he could get to the AMU mounted on the back of the spacecraft.

Instead, this attempt induced higher rates and in multiple axes; the satellite was tumbling out of control and quickly losing battery life.

The ground support engineers then stabilized the satellite and nulled its rotation rates for capture with the orbiter's robotic arm, the Shuttle Remote Manipulator System (SRMS).

Astronauts Joseph P. Allen and Dale Gardner captured the two satellites and brought them into the Orbiter payload bay for stowage and return to Earth.

Although the MMU was envisioned as a natural aid for constructing the International Space Station, with its retirement, NASA developed different tethered spacewalk approaches.

This article incorporates public domain material from websites or documents of the National Aeronautics and Space Administration.