— This year's U.S. Astronaut Hall of Fame induction ceremony was also a reunion of sorts, as the two honorees took to the stage under the spacecraft on which they once crossed paths.

NASA's Kennedy Space Center Visitor Complex in Florida hosted the ceremony under its display of the retired space shuttle Atlantis on Saturday (June 1). A full house of former astronauts, space program officials and the public were there to see David Hilmers and Marsha Ivins be added to the hall's ranks.

"We're here to honor two distinguished space explorers, who each have outstanding careers and have made incredibly significant contributions to NASA and the world," said John Zarella, a former CNN space correspondent who served as the master of ceremonies. "Together they comprise the 25th class of astronauts to be inducted into the Hall of Fame, bringing the total number of astronauts in this prestigious society to 109."

Although they did not fly together — Hilmers and Ivins were chosen four years apart to become astronauts — they were both at NASA when the agency's fourth winged orbiter made its maiden flight.

"It's particularly gratifying that I'm so honored below Atlantis. I was on board Atlantis when it blasted into the sky for the very first time on a beautiful October day in 1985," said Hilmers, who made the first of his four flights as an STS-51J mission specialist. "When we got out to the [launch] pad, the "Cape Crusaders" and Marsha was there and she helped strap us in and get into our survival vests, and get into our seats."

"It is a privilege, really, to share a stage with someone I consider one of the finest human beings on or off the planet," said Ivins, addressing Hilmers before turning her attention to Atlantis and the audience seated beneath it. "If you haven't, please look up and acknowledge this piece of of human history that you are sitting under."

Hilmers also paid tribute to Atlantis in his remarks.

"Although she's retired, she continues to be on duty, giving many thousands of visitors the opportunity to see what it was like to be on board," he said. "Like Atlantis, I too retired from active duty with NASA and started a new mission. My path took me down in an entirely different direction and this is actually the first time I've returned to the Kennedy Space Center for over three decades."

Welcoming Hilmers and Ivins into the Hall of Fame were one of their crewmates: Norm Thagard, who flew with Hilmers on STS-42 in 1992 and was inducted into the Hall of Fame in 2004, and John Grunsfeld, who launched with Ivins on STS-81 in 1997 and was enshrined in 2015.

"My original thought was this is going to be one of the most difficult things I ever did because Colonel, Dr. David C. Hilmers is a pretty incredible individual," said Thagard. "My concern was no matter how convincing I might try to be, those of you who don't know Dave would say 'you're exaggerating.' The easy part is I don't have to exaggerate because what I'm going to tell you is pretty incredible in its own right."

Half of Hilmers' missions were flown in service to the Department of Defense. Both STS-51J and STS-36, the latter in 1990, launched on Atlantis with payloads that remain classified to this day. Hilmers' other two flights were on shuttle Discovery, including STS-26 in 1988, NASA's "return to flight" after the Challenger tragedy in 1986; and STS-42, which was focused on the effects of microgravity on a variety of types of life.

After leaving NASA in 1992, Hilmers received his Doctor of Medicine (M.D.) degree and a second Master's degree in public health. He is is currently a professor of internal medicine and pediatrics at Baylor College of Medicine and, in addition to his volunteer work in disaster relief and low-resource countries, Hilmers has been helping NASA determine what the requirements for medical expertise will be on missions to the moon and Mars.

Ivins left an equally impressive mark on NASA, said Grunsfeld, though she might be the last to acknowledge it.

"Marsha is not an attention seeker. In fact, when [the call came] to announce that she was selected into the Astronaut Hall of Fame, I think she had some reticence about this whole event," Grunsfeld said. "[Yet] Marsha, not wanting to be in in the limelight, still helped push NASA forward."

"All of us who flew on the space shuttle owe her a debt of gratitude for work that she did," he said.

Ivins' first flight into space was the first of her two on space shuttle Columbia. On STS-32 in 1990, she and her crewmates retrieved the Long Duration Exposure Facility (LDEF), a school bus-sized free-floating materials science platform. Four years later on STS-62, she and her four crewmates continued to study the effects of microgravity on materials sciences and spaceflight technologies.

Ivins' three other missions were aboard Atlantis, making her one of the orbiter's three most frequent fliers. On STS-46 in 1992, she helped with the first attempted deploy of the Tethered Satellite System. On STS-81 in 1997, Ivins visited Mir on the fifth shuttle mission to dock with the Russian space station. Finally, on STS-98 in 2001, Ivins helped to install the U.S. "Destiny" laboratory for the International Space Station and brought supplies for the orbiting complex's first resident crew.

Since leaving the agency, Ivins served as a consultant on "A Beautiful Planet," the last IMAX documentary to be shot in space, and supported proposal work on a human lunar landing vehicle. Today she is the director of human systems integration at Sophic Synergistics, a Houston-based design consulting firm, which supports human space exploration endeavors.

As with past inductee classes, Hilmers and Ivins were selected by a committee of Astronaut Hall of Fame members, former NASA officials, historians and journalists. The process is administered by the Astronaut Scholarship Foundation.

To be eligible for nomination, an astronaut must have made his or her first flight at least 15 years before the induction. Candidates must be US citizens and either a NASA trained space shuttle commander pilot, mission specialist, or an International Space Station commander or flight engineer who has orbited Earth at least once and whose last day eligible for a flight assignment as a NASA astronaut was at least five years ago.

Saturday's ceremony came to a close with the reveal of the glass-etchings that will represent Hilmers and Ivins.

The plaques, which bear Hilmers' and Ivins' likenesses, as well as mission patches from their respective spaceflights, will be displayed in the U.S. Astronaut Hall of Fame, which since 2016 has been part of the Heroes & Legends attraction at the Kennedy Space Center Visitor Complex.