This week forty years ago, on February 7, 1984, two NASA astronauts made history by performing the first untethered spacewalk during the STS-41B mission aboard the Space Shuttle Challenger. Using the Manned Maneuvering Unit (MMU), Bruce McCandless ventured away from the Shuttle, capturing an iconic image that remains celebrated in space exploration history. The MMU, equipped with gaseous nitrogen thrusters, enabled astronauts to move freely in space without tether constraints. McCandless and Robert Stewart conducted multiple spacewalks during the mission, demonstrating procedures for satellite capture and repair. Although the MMU was only used on three missions in 1984 due to safety concerns, it paved the way for future spacewalk technologies such as robotic arms and emergency backpacks like the Simplified Aid for EVA Rescue (SAFER). View more images.