The MMU was first tested in orbit in February of 1984. In that same year it was used on two successful missions to retrieve satellites that were returned to earth for repair.

The MMU propellant is gaseous nitrogen which is stored under high pressure and can be recharged from the orbiter. The unit has a dual parallel system rather than a backup redundant system. In the event of a failure in one parallel system, the remaining system can be used to return the MMU to the orbiter cargo bay. The MMU weighs 310 pounds and includes a 35-mm still photo camera that is operated by the astronaut while working in space.