On This Day

Bruce McCandless, untethered spacewalk, jet pack
Bruce McCandless floats above Earth
during his untethered spacewalk.

On This Day: NASA Astronauts Make First Untethered Spacewalk

February 07, 2012 05:00 AM
by findingDulcinea Staff
On Feb. 7, 1984, NASA astronauts Bruce McCandless and Robert L. Stewart performed the first spacewalk without being tethered to the spacecraft.

“Human Triumph Over Gravity”

Prior to 1984, every spacewalk, or extra-vehicular activity (EVA), had been performed using a long cable that connected the astronaut to his spacecraft. The untethered spacewalk was made possible by NASA’s development of the manned maneuvering unit (MMU), a 300-pound nitrogen-propelled backpack that allowed the astronaut to guide himself through space.

NASA’s STS-41B mission was the first to test this technology in outer space. Astronauts Capt. Bruce McCandless II and Col. Robert L. Stewart were given the responsibility of using the MMUs to simulate the task of repairing a malfunctioning satellite in preparation for a future mission.

On Feb. 7, 1984, four days into the mission aboard the space shuttle Challenger, McCandless and Stewart performed their first EVA. Stewart worked on a mechanical arm of the shuttle while McCandless traveled as far as 320 feet away.

“He was orbiting the earth at the same velocity as the shuttle, 17,500 miles an hour,” wrote The New York Times. “In the virtual vacuum of space, however, he sensed nothing of his speed. The only sensation of motion he had came when he looked down at the rotating earth, which was going by at four miles a second.”

Stewart joined McCandless later during the EVA, which lasted five hours and 55 minutes. The two men would make a second untethered spacewalk on Feb. 9, this one lasting six hours, 17 minutes. “Free of any lifeline and propelled into the dark void by tiny jets, they became, in effect, the first human satellites,” said the Times.

A photo of McCandless floating above Earth has become one of the most famous images in the history of NASA. McCandless said it is “an icon for human triumph over gravity or triumph over nature.”

Further Untethered Spacewalks

In April 1984, STS-41C astronauts George D. Nelson and James D.A. Van Hoften performed untethered spacewalks while carrying out the repairs of the Solar Maximum Mission satellite that McCandless and Stewart had simulated. In November, STS-51A astronauts Dale A. Gardner and Joseph P. Allen used their MMUs to retrieve two malfunctioning communications satellites, the Westar VI and Palapa B2.

After 1984, NASA ended its used of MMUs and decided to perform only tethered spacewalks for safety reasons. In 1994, NASA unveiled a new backpack called Simplified Aid for EVA Rescue (SAFER) and tested it with an untethered spacewalk, the fourth and thus far last untethered EVA it has performed. Every astronaut at the International Space Station wears SAFER, which is smaller and lighter than the MMU, for use during an emergency.

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