In 1984, NASA sent astronaut Bruce McCandless floating farther from the safety of a spacecraft than anyone had ever been, or has since been. It was a test of the Manned Maneuvering Unit, a system designed to allow astronauts to float freely in space. The MMU didn't last long; NASA realized that it was safer and easier to take advantage of the space shuttle orbiters’ own maneuvering capability. But for a brief moment in its history, astronauts got to fly in space with an actual jetpack.
From Science Fiction to Science Fact
The idea of maneuvering in space with a personal propulsion system predates the space age. As early as the 1920s and 1930s, science fiction stories featuring jet pack-wearing heroes brought this futuristic idea to the public.
But jetpacks didn’t start the transition from science fiction to science fact until the space age had properly begun. After the Soviet Union launched Sputnik and the United States launched Explorer I, it was clear that both nations would begin launching men into orbit before long. In anticipation of Americans living and working in space, the US Air Force began researching ways these men might maneuver around in the vacuum of space.
Hand Held Units
The very first astronaut propulsion systems were hand-held units that used compressed air. They were far from perfect. Test subjects routinely found it was nearly impossible to line up the gun’s directive propulsion with their own centre of gravity; every time they fired the gun, they spun as much as they moved forwards or backwards. Though troublesome in testing, the hand-held compressed air gun was the first personal propulsion unit NASA used in space. Completing agency’s first spacewalk was among the goals for the Gemini 4 mission, the second flight of America’s second manned space fight program.
The mission launched on June 3, 1965, with commander Jim McDivitt and pilot Ed White on board. It was White who stepped outside armed with the compressed-oxygen gun that used two one-pound tractor jets and one two-pound pusher jet to move the astronaut around. He was also tethered to the spacecraft by a thick cable that provided him with oxygen and communications. The gun wasn’t a great tool in space, and White expended the gun’s available gas just a few minutes into his 20-minute spacewalk. He was left with only the bulky tether as a tool to pull himself back into the spacecraft, a process that was both difficult and exhausting for the astronaut.
Ed White on America's first spacewalk in 1965, holding a compressed air gun.
The First Backpack Jetpack
Even before Ed White’s test with the hand-held gun in late 1963, the USAF’s Aero Propulsion Laboratory began studying a backpack-like system that NASA astronauts could wear for increased mobility during spacewalks. The system was completed in April of 1966, and it was a far cry from the hand-held gun. Called the Astronaut Maneuvering Unit (AMU), it consisted of a 165 pound backpack that was 31 inches high, 22 inches wide, and about 19 inches deep. This pack had self-contained life-support, communications, telemetry, and propulsion, as well as manual and automatic stabilization systems. A form-fitting seat and 148-foot long nylon safety tether turned the AMU into a comfortable personal spacecraft for a single astronaut. Far too big to store inside the small spacecraft, the AMU was housed outside in the Gemini’s rear adapter section, meaning a spacewalking astronaut had to make his way back to the AMU before using it on a mission.
Recovering the AMU was far easier said than done. The first unit flew aboard Gemini 9, which launched on June 3, 1966, and it fell to the mission’s pilot Gene Cernan to test the unit in in space. But he never achieved this goal. Once outside, Cernan found that the tether and handlebars fixed to the spacecraft were little use as he fought to move to the rear of the spacecraft. The spacewalk took considerably more physical effort than it had in training, and before long Cernan was drenched in sweat and his visor was fogged up reducing his visibility to nothing. Concern for the astronaut’s safety ultimately won over the need to test the AMU. The EVA was cut short and the backpack was never tested.
A technician tests the AMU designed for the Gemini 9 mission.
Real Maneuverability in Space
The spacewalks done during the Gemini program were designed to support the Apollo program. They were a way for NASA to test the technologies it would need to keep astronauts alive on the way to, and on the surface of, the Moon. These early maneuvering units were designed as experimental systems to test technology. But with the space shuttle program, NASA had a new need for mobility in orbit. Mobility was poised to become an asset on a flight, not just an experiment. Among the goals for the shuttle program were building a space station as well as servicing orbiting satellites. The idea was to give astronauts personal propulsion systems so they could float over to a satellite during an EVA. Donning a jet pack would turn the astronaut into a workman, stepping out to make a repair before returning home for lunch.
The system designed with future mission goals in mind was the NASA Manned Maneuvering Unit (MMU). Approved for development in 1975, two units were delivered to NASA in 1983. Each was valued at $10 million. Like the AMU before it, the MMU was marked improvement over previous systems. It was far more responsive, featuring finger-tip controls for translational changes (left, right, up, and down) with the left hand, and rotational controls with the right. Electrical power was provided by two silver-zinc batteries, and propulsion came by firing nitrogen gas through two dozen thrusters; two tanks each fed twelve of the small jets. It was painted white to help with temperature control; even with unfiltered sunlight beating down on it it was kept below 150º Fahrenheit, and in the shake, electrical heaters kept key components just warm enough to work.
The full system, stored inside the shuttle’s cargo bay where it could be charged between uses, had a mass of 340 pounds, an operational lifetime of six hours, and a range of 450 feet from the shuttle. Astronaut Joe Allen likened the MMU to the shuttle’s dinghy, describing it as an overstuffed rocket chair with armrests.
The MMU in Flight
NASA sent two MMUs into orbit on three space shuttle missions in 1984, the tenth, eleventh, and fourteenth flights of the program: 41-B in February, 41-C in April, and 51-A in November. Over these three missions, six astronauts took the MMUs out for test flights on a total of nine sorties lasting a total of ten hours and 22 minutes.
The most notable MMU spacewalk was done by Bruce McCandless. On February 7, 1984, he became the first person to fly untethered away from the safety of his spacecraft, and he set a distance record in the process: he floated more than 300 feet from the orbiter Challenger. Crewmate Robert Gibson snapped the now iconic picture of McCandless, a human satellite floating far in the distance high above the planet.
Bruce McCandless during his record setting MMU flight in 1984.
From Orbit to Storage
The MMU never flew again after 1984, though not because of flaws with the system. NASA ultimately determined that all its EVA activities could be done as easily and with less risk to its astronauts using the shuttle’s own maneuverability to fly close to satellites. Tethers and handlebars would be a safer way for astronauts to make repairs, keeping them close to the spacecraft.
Another factor in the death of the MMU was the Challenger disaster in January of 1986. The post-accident investigation ended with a slew of new safety rules and regulations, many of which affected the MMU. The adjustments to the system that were deemed necessary for safety were both complicated and expensive, and ultimately not worth the time and money to make. By the early 1990s, NASA’s attention focused on building the International Space Station, and there was no longer a need for the MMU.
Though it was short lived, the MMU was a brilliant system recognized for its sophistication. In 1984, the Collier Trophy was awarded to Bruce McCandless, Charles Whitsett from NASA, and Martin Marietta's Walter Bollendonk for their roles in developing the innovative unit.