Spacewalk 1984. The Manned Manoeuvring Unit (MMU) has small gas thrusters which enable an astronaut move around outside the Space Shuttle without a tether. This was first flown by McCandless on the Space Shuttle Challenger 41-B (STS-10) mission in February 1984 (NASA Media Archives). Buy this as a superb wall poster, a canvas print or a framed print.