Hayley Arceneaux, 29, became a physician assistant at St. Jude Children's Research Hospital nearly a year ago, almost two decades after beating pediatric cancer there herself. Now, she's set to reach new heights as the youngest American — and first with a prosthesis — to travel to space.

St. Jude announced on Monday that Arceneaux will be one of four crew members on the world's first all-civilian mission to space, which is called Inspiration4 and is tentatively set to take off at the end of 2021. The Memphis, Tenn. native, who was treated for bone cancer at the hospital as a child, called the opportunity an "incredible honor."

"When I was just 10 years old, St. Jude gave me the opportunity to grow up," she said. "Now I am fulfilling my dreams of working at the research hospital and traveling around the world. It's incredible to be a part of this mission that is not only raising crucial funds for the lifesaving work of St. Jude but also introducing new supporters to the mission and showing cancer survivors that anything is possible."

Earlier this month, trip commander Jared Isaacman — a 38-year-old tech entrepreneur, billionaire and pilot — announced that he had bought the flight from SpaceX and would donate the three other seats to members of the general public, with the goal of raising $200 million for St. Jude.

Arceneaux will occupy the mission seat representing the pillar of hope. The remaining two, representing "generosity" and "prosperity," are available through Feb. 28 and will go to one individual who donates to St. Jude and an entrepreneur who uses Isaacman's payment processing company Shift4Payments.

Arceneaux will become the youngest American in space, according to The Associated Press, edging out pioneering astronaut Sally Ride, who was 32 when she became the first American woman to launch in 1983.

She will also be the first American with a prosthesis in space, having had surgery at age 10 to replace her knee and get a titanium rod in her left thigh bone, the AP reported. She has been cleared for flight by SpaceX and will serve as the crew's medical officer.

"My battle with cancer really prepared me for space travel," Arceneaux told the AP. "It made me tough, and then also I think it really taught me to expect the unexpected and go along for the ride."

In an interview with NBC's TODAY, Arceneaux said she never thought she would be able to go to space, noting that "until this mission you really had to be physically perfect." But when the call came "out of the blue" from St. Jude, asking if she wanted to go to space, the avid traveler, roller coaster-lover and lifelong space fan said yes immediately.

She made sure to run it past her mother, as well as her brother and sister-in-law, who are both aerospace engineers and reassured her about the safety of space travel, the AP reported.

Officials involved in the two missions — launching civilians to space and fighting pediatric cancer — applauded Arceneaux's selection on Monday.

In a tweet, Isaacman called Arceneaux an inspiration not just to aspiring astronauts, but for "all people who need hope when encountering life challenges."

And Richard Shadyac Jr., president and CEO of St. Jude's fundraising and awareness organization American Lebanese Syrian Associated Charities, praised her work in the pediatric cancer community.

"It has been a personal honor to watch Hayley grow up and fulfill her dreams. As a patient, an intern at ALSAC, and then in the Pediatric Oncology Education program at St. Jude Children's Research Hospital, she was always a rising star," Shadyac said. "She will be an incredible ambassador through this mission and inspiration to children fighting cancer and survivors worldwide."

According to St. Jude, Arceneaux — who described her job as her "ultimate life dream come true" when she accepted it just under a year ago — plans to devote much of her time on the mission to interacting with hospital patients through video chats or video messages.

Arceneaux said she can't wait to talk to her patients about going to space as a cancer survivor, as her experience will show them that they "don't have to limit themselves."

"I really hope to show them that the sky's not even the limit, that they can do anything," she said.

The mission crew will undergo comprehensive training, stress testing and mission simulations provided by SpaceX, the company said. They are set to launch from NASA's Kennedy Space Center in Florida and orbit Earth every 90 minutes along a customized flight path during their multi-day journey before re-entering Earth's atmosphere for a soft water landing off the Florida coast.

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