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NASA paid tribute to cosmologist Stephen Hawking following his death early Wednesday morning. SEE ALSO: The world reacts to the death of the much-loved Stephen Hawking NASA shared a video on Twitter that Stephen Hawking recorded for astronauts Rick Mastracchio and Koichi Wakata on the International Space Station in 2014. Remembering Stephen Hawking, a renowned physicist and ambassador of science. His theories unlocked a universe of possibilities that we & the world are exploring. May you keep flying like superman in microgravity, as you said to astronauts on @Space_Station in 2014 pic.twitter.com/FeR4fd2zZ5 — NASA (@NASA) March 14, 2018 In his message Hawking talks about experiencing microgravity, i.e. weightlessness. "For me, this was true freedom," said Hawking. "People who know me well say that my smile was the biggest they'd ever seen. I was superman for those few minutes. "I can only imagine what it's like for you, Rick and Koichi, to fly like Superman for six months." WATCH: How did this baby octopus suddenly change color?