John Young, America's "most experienced astronaut" who walked on the Moon during the Apollo programme and commanded the first space shuttle mission, has passed away, NASA said on Saturday.Young died on Friday night following complications from pneumonia, Xinhua quoted the US space agency as saying. He was 87 years old."Today, NASA and the world have lost a pioneer," acting NASA Administrator Robert Lightfoot was quoted as saying.Young is the only US astronaut to go into space as part of the Gemini, Apollo and space shuttle programmes and the first to fly into space six times, said NASA.Young made his first flight as an astronaut in 1965, joining astronaut Gus Grissom on Gemini 3, the first manned flight of the early NASA human spaceflight programme that helped the agency get ready for the Apollo moon landings.Then, in 1966, he flew as Commander on Gemini 10, the first mission to rendezvous with two separate spacecrafts on the course of a single flight.He also orbited the Moon in Apollo 10 in 1969 and landed there in 1972 as Commander of the Apollo 16 mission.In 1981, he served as Commander of STS-1, the first space shuttle mission, which some have called "the boldest test flight in history."Two years later, on STS-9, his final spaceflight, Young landed the space shuttle with a fire in the back end, according to NASA.He retired from NASA in 2004."Astronaut John Young's storied career spanned three generations of spaceflight," Lightfoot said, adding, "He was in every way the 'astronaut's astronaut. We will miss him."