When astronaut Bruce McCandless II drifted away from the safety of the Space Shuttle in 1984, it was terrifying. Not just for the astronaut himself, but also for NASA, scientists, and everyone following the mission. This was the first untethered spacewalk in history.

For 6 hours and 17 minutes, McCandless became a speck in the vastness of space; flying around with no cables to hold him from going loose. Yet as terrifying as this feat was, it was a turning point for NASA. His mission was a triumph of human engineering and courage, but the sight of him floating freely—completely untethered—was both awe-inspiring and terrifying. For the first time in human history, someone experienced total isolation in the ultimate void, relying only on a backpack to survive.

Before McCandless’ groundbreaking mission, every astronaut performing a spacewalk remained tethered to a spacecraft. This umbilical connection was their lifeline, providing oxygen and preventing them from floating away into the abyss. But the limitations of being tied down became apparent as space missions grew more complex.

By the 1980s, NASA faced mounting challenges. Tasks like repairing satellites, retrieving malfunctioning spacecraft, or constructing a future space station required astronauts to venture farther from their ships. A tether system would be impractical for such operations, often creating more hazards than it solved. An untethered spacewalk would have bypassed these issues.

The solution was bold: a self-contained propulsion unit strapped to an astronaut’s back. Known as the Manned Maneuvering Unit (MMU), this device would allow astronauts to move freely in space, without the constraints of cables or ropes. It represented technological innovation at its peak, this was still the 1980s, and the implications were chilling. What if something went wrong? What if the astronaut drifted out of range, helpless and unreachable?

NASA had few options to avoid disaster; and yet, they did it.

An astronaut’s courage

When McCandless climbed into the MMU for the first untethered spacewalk on February 7, 1984, he knew the risks. A single failure could mean drifting endlessly into space, beyond the reach of rescue. The training prepared him for every scenario, but the reality of stepping away from the shuttle would test both the astronaut and the technology.

Granted, NASA took as many precautions as they could.

The MMU was designed to be the astronaut’s guardian angel. Developed over more than a decade, it used small nitrogen gas thrusters to allow precise movements in the weightlessness of space. A joystick controlled these thrusters, letting the astronaut push forward, backward, or sideways with ease. The unit had built-in redundancies to prevent malfunctions, including backup systems for propulsion and navigation. There was no realistic scenario in which the MMU didn’t work — in theory.

NASA engineers had to test the MMU extensively on Earth, but simulating the vacuum of space and zero gravity presented challenges. The technology showed promise during trials, yet there were no guarantees when it came to the real thing. As McCandless left the safety of the shuttle’s airlock and engaged the MMU, he famously crackled: “It may have been one small step for Neil, but it’s a heck of a big leap for me.”

The iconic photos

This first untethered flight took place during the STS-41-B mission, the fourth flight of the Space Shuttle Challenger.

The sight was surreal. Earth spun beneath him, a vivid blue and white orb framed by infinite darkness. He floated 320 feet from the shuttle—a distance that might as well have been a million miles to the human eye. With each movement, he demonstrated the MMU’s reliability, expertly maneuvering himself in the void.

“Hoot” Gibson, the flight’s pilot, didn’t have much to do as McCandless made his way into space, so he picked up a camera and started documenting the process. It was a stunning shot, with an untethered McCandless diligently operating. Gibson meticulously calculated the light readings and the perfect camera focus, tilting the camera to align with the Earth’s horizon.

He took several photos which became some of NASA’s most cherished images of all time.

An important mission

The untethered spacewalk wasn’t just a stunt. It had clear, practical purposes. As space missions expanded, astronauts needed tools that allowed them to work freely in the harshest conditions, and the tether was an obstacle. The MMU enabled tasks like repairing satellites, retrieving damaged spacecraft, and eventually assisting in the construction of space stations.

The 1984 mission proved the MMU’s effectiveness. Using the unit, astronauts retrieved two malfunctioning satellites during subsequent missions. These successes cemented the MMU’s place in the history of space exploration, even though it was eventually retired in favor of tethered systems that were deemed safer for routine use.

*This article was first published in 2013 and has been credited to include more information.