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Stephen Hawking spent most of his adult life in a wheelchair, but a few years ago, he was able to float "like Superman" for a few minutes.
NASA on Wednesday paid tribute to the late physicist with a video showing him without his wheelchair and floating in zero gravity during a demonstration with the space agency in 2007.
"For me, this was true freedom," Hawking said in the video. "People who know me well say that my smile was the biggest they'd ever seen. I was Superman for those few minutes."
NASA's tribute was part of an outpouring from celebrated figures across the science and entertainment worlds in the wake of Hawking's death.
Hawking spent almost his entire adult life in a wheelchair after being diagnosed with amyotrophic lateral sclerosis (ALS), a degenerative neurological disease, when he was 21.
Hawking's zero gravity experience occurred in 2007 on a modified Boeing 727 jet flying above Kennedy Space Center in Florida.
The scientist, who was 65 at the time, went through eight rounds of weightlessness as part of a demonstration to show people with disabilities were capable of participating in zero gravity flights.
Afterward, he told reporters, "It was amazing ... I could have gone on and on."
Hawking reflected on the experience in a 2014 video recorded for astronauts Rick Mastracchio and Koichi Wakata aboard the International Space Station.
"I can only imagine what it's like for you, Rick and Koichi, to fly like Superman for six months,'' he said.
In their remembrance, NASA said, "His theories unlocked a universe of possibilities that we & the world are exploring. May you keep flying like superman in microgravity ..."
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