More than thirty years ago, two lucky astronauts, Bruce McCandless and Bob Stewart took the ride of their lives.
In 1984, McCandless and Stewart were the first to travel untethered, 300 feet away from their space shuttle and tested out the Manned Maneuvering Unit (MMU), a jet-powered backpack.
“I knew the laws of physics hadn’t been repealed recently,” said McCandless, who was confident in the MMU despite the uncertainty of the test drive.
“I decided that this was the easiest thing I had ever flown,” Steward added. “The only way it could’ve been easier was to directly connect it to the brain.”
McCandless, along with Charles “Ed” Whitsett, had an important role in the development of the MMU. Whitsett began researching the idea for the maneuvering unit in 1960, and eventually produced a test version of it with the help of McCandless in the late 1960s. This prototype was tested out in 1973 at the Skylab space station. In 1974, improvements to the design were later made using the test results when Whitsett arrived at NASA.
The final version of MMU was produced by Martin Marietta Aerospace. This version contained 24 small compressed nitrogen powered thrusters; it was less of a backpack and more like a refrigerator, weighing 300 pounds. Designed to be operable even with very little training, the MMU was never flown faster than a crawl, due to safety and fuel concerns.
In April 1984, a couple of months after the MMU’s first drive, astronauts put it to work and mounted it on a rescue mission to repair a malfunction on the satellite, Solar Max. George “Pinky” Nelson was the astronaut assigned to snare Solar Max. He trained in a simulator to catch and tether the satellite and his crewmembers would use the shuttle’s robotic arm to place the satellite in the cargo bay and later repair it.
That was the plan, anyway. It proved unsuccessful because the capture device would not grab on. In the end, the mission did succeed but without need of the MMU. Instead, the satellite was slowed down enough by ground controllers then grabbed by the shuttle’s robotic arm. Despite this mission, Nelson still only has praise for the MMU.
Although the MMU didn’t prove itself as a satellite rescue tool on its first mission, in November 1985 it was used to retrieve a pair of errant communications satellites by astronauts Joe Allen and Dale Gardner. Eventually NASA re-evaluated the space shuttle missions and deemed the MMU unnecessary in 1986 and thus becoming, as Nelson explained, “a really cool piece of technology that didn’t quite have a purpose.”
[Sources: Smithsonian; NASA]