The manned maneuvering unit (MMU) is a self-contained backpack with all the necessary systems to enable the extravehicular activity (EVA) astronaut to fly free in space and reach work areas remote from the supporting spacecraft. An experimental MMU tested onboard the NASA Skylab Program orbital workshop established key piloting characteristics and capability base for future MMU systems. An operational MMU now exists for the Space Shuttle Program. This versatile mobility system has been flown on nine sorties and accumulated 10 hr and 22 min of flying time during three Space Shuttle missions. These Space Shuttle flights have demonstrated a capability for free space traverses up to 98 m (320 ft), cargo transfer, and tracking, docking, stabilizing, and orienting large satellites. These and additional MMU capabilities will benefit the Space Station and its onboard payloads. First and foremost is the capability to rescue an EVA crewmember who might inadvertently separate from the Space Station. There will also be tasks at worksites inaccessible by other Space Station equipment and tasks where EVA time is critical. Many Space Station and payload assembly and inspection tasks will need MMU support. Significant Space Station mission flexibility is added by the MMU for backup and contingency roles. These Space Station roles will require a major upgrade to the Space Shuttle MMU design.