Illustration of US astronaut Bruce McCandless (1911-1968) using a Manned Manoeuvring Unit (MMU) during an extra-vehicular activity (EVA, spacewalk). McCandless, who helped design the MMU, was the first person to fly it, thus becoming the first human satellite in orbit around the Earth. The MMU is propelled by small nitrogen thrusters controlled by the astronaut's hands. Because no umbilical cord attaches the astronaut to the spacecraft, it gives much greater mobility than was available to earlier spacewalkers.