Manned maneuvring unit space walk, 1984. Astronaut Bruce McCandless practising docking the Shuttle Pallet Satellite (SPAS) with the trunnion pin attachment device (TPAD) attached to his manned manoeuvring unit (MMU). McCandless, who helped design the MMU, became the first person to fly it earlier in this mission. The MMU is propelled by small nitrogen thrusters which are controlled by the astronaut's hands. Because no tether attaches the astronaut to the spacecraft, it gives much greater mobility than was available to earlier spacewalkers. Photographed on on 13th February 1984, during the 10th space shuttle flight (mission 41B).