The Extravehicular Mobility Unit has protected astronauts during more than 280 spacewalks since 1981 — from Space Shuttle missions to ISS construction. Now over 40 years old, the aging EMU fleet faces water leak incidents and dwindling serviceable units while NASA searches for a replacement.
The Extravehicular Mobility Unit (EMU) is NASA's primary spacesuit for spacewalks outside the International Space Station. First used on STS-6 in April 1983, it has been the backbone of all American EVA operations for over four decades — supporting Space Shuttle missions, ISS assembly, Hubble servicing and routine station maintenance.
The EMU is a modular, two-piece suit consisting of a Hard Upper Torso (HUT), Lower Torso Assembly (LTA) and a Primary Life Support System (PLSS) backpack that provides oxygen, CO₂ removal, cooling water circulation and battery power for 6.5–8 hours. The suit pressurises at 4.3 psi (29.6 kPa) of pure oxygen, requiring astronauts to pre-breathe oxygen for several hours before an EVA to avoid decompression sickness.
The suit's 14 protective layers include a liquid cooling and ventilation garment, a urethane-coated nylon pressure bladder, Dacron restraint layer, and multiple outer layers of Mylar insulation, Kevlar and Ortho-fabric for micrometeorite and thermal protection. Despite its age, the EMU remains one of the most sophisticated pressure garments ever built.
However, the EMU fleet is in crisis. A 2017 NASA Inspector General report found only 11 fully functional flight suits remained, and subsequent water leak incidents during EVAs raised serious safety concerns. NASA's attempt to develop a replacement through Collins Aerospace was cancelled in 2024. The agency is now looking at Axiom's AxEMU and SpaceX's EVA suit as potential solutions.