Astronaut John Young -- the first man to make six trips to space and the ninth to walk the moon -- died Friday night from complications from pneumonia. He was 87.

Young was one of the nation's longest-serving astronauts, spending 47 years leading missions in the Gemini, Apollo and space shuttle programs.

"Today, NASA and the world have lost a pioneer," NASA Administrator Robert Lightfoot said. "Astronaut John Young's storied career spanned three generations of spaceflight; we will stand on his shoulders as we look toward the next human frontier."

Young's bravery and commitment "sparked our nation's first great achievements in space. But, not content with that, his hands-on contributions continued long after the last of his six spaceflights -- a world record at the time of his retirement from the cockpit," Lightfoot said in a prepared statement.

He served in the U.S. Navy for 25 years, retiring as a captain in 1976. The pilot joined NASA in 1962 in the second astronaut class, known as the "New Nine." Young was inspired to join NASA by President John F. Kennedy's 1961 call to land a man on the moon.

"I thought returning safely to Earth sounded like a good idea," said Young, according to a NASA statement.

Lightfoot noted that Young commanded the Gemini 10, the first mission to rendezvous with two separate spacecraft; orbited the moon in Apollo 10; landed on the moon as commander of the Apollo 16 mission; and, on his final mission, landed the STS-9 with a fire in the back end.

In early 1973, Young became chief of the Space Shuttle Branch of the Astronaut Office at Johnson Space Center. The following year, he was named chief of the Astronaut Office, a post he held until May 1987.

During his decades, he received a Congressional Space Medal of Honor, three NASA Distinguished Service Medals, the NASA Outstanding Leadership Medal, two Navy Distinguished Service Medal and dozens of other awards, including four honorary doctorate degrees.

He was inducted into the National Aviation Hall of Fame in 1988.

Young, who lived in El Lago near Clear Lake, retired in 2004 after logging 835 hours in space.

"I've been very lucky, I think," Young said at his retirement from NASA in 2004. As to which moment was most memorable, he says simply, "I liked them all."

Around his retirement, Young recounted his first trip to the moon on Apollo 10 with the Houston Chronicle. "The impressive thing about the back side of the moon is how many darn craters it has," he said. "If the back side of the moon was facing us, I think human beings would be far more adaptive, far more educated, about (asteroid or comet) impacts on planet Earth."

Former President George H. W. Bush mourned the loss of the astronaut in a statement Saturday, saying that Young was a good friend and also "a fearless patriot whose courage and commitment to duty helped our Nation push back the horizon of discovery at a critical time."

Bush went on to say that Young, "represented the best in the American spirit — always looking forward, always reaching higher" and "leaves a tremendous legacy of accomplishment, in addition to his wonderful family."

Former NASA astronaut Terry Virts shared his sadness about Young's death, tweeting on Saturday: "You were one of my heroes as an astronaut and explorer and your passion for space will be missed."

Retired NASA astronaut Scott Kelly, who spent 340 days on a mission to the International Space Station, called Young "a true legend" and "the astronauts' astronaut," in a statement posted to Facebook Saturday.

"Fair winds and following seas, Captain," he wrote.

John Watts Young