NASA has chosen umbilical extra vehicular activity (EVA) as the space walk method for its Constellation programme's Orion crew exploration vehicle.

During the Space Shuttle programme, tethered EVA space suits have had onboard all the air and power required for working in the Orbiter's payload bay or assembling the International Space Station.

Umbilical EVAs mean the space suit will draw its air and power from the astronaut's spacecraft, in future the Orion Command Module. The last NASA umbilical spacewalk was during the agency's final Skylab mission, Skylab-4, in 1974.

NASA's Constellation space suit system concept envisages a basic suit that can have elements added to it to build up its capabilities to include lunar surface sorties.

NASA is currently considering whether each suit will be integrated into the Orion's crew seats.

"[The] configuration one [spacesuit] will protect the crew in [launch, entry and abort] mission phasesand will provide 0g umbilical-based EVA capability," says NASA.

While the configuration one suit is for launch, entry and abort, configuration two is for lunar surface work.

Skylab-4's fourth and last EVA took place on 3 February 1974 at 1519h GMT and lasted 5h 19min.

This EVA was conducted by mission commander Gerald Carr and scientist pilot Edward Gibson. The third Skylab-4 crew member and pilot designate was William Pogue.