Updated Jan 23, 2025 3:59 PM EST NASA Administrator Bill Nelson stepped down Monday, January 20, after serving nearly four years under former President Joe Biden. [Courtesy: NASA] Share this story NASA Administrator Bill Nelson stepped down on Monday after President Donald Trump was inaugurated, and the departing space agency chief had some words of advice for his replacement. In a letter addressed to the next NASA administrator—who, if Trump’s nomination is confirmed, will be Shift4 CEO and SpaceX ally Jared Isaacman—Nelson highlighted the space agency’s work during his tenure and urged continuity. He emphasized NASA’s responsibility to return Americans to the moon and land them on Mars for the first time. “I am rooting for you. Your success is NASA’s success, and NASA’s success is the nation’s success,” Nelson wrote. “I am at your service to help in any way that I can.” In particular, Nelson lauded NASA’s Artemis program—a series of planned missions to the moon and eventually Mars that took shape during Trump’s first term. During Nelson’s tenure, the agency launched Artemis I, the uncrewed inaugural mission of the campaign. Nelson also laid a foundation for future Artemis missions—including a return to the moon scheduled for mid-2027—by commissioning new lunar landers, rovers, and spacesuits. In his view, it only makes sense to build on that foundation. “We are merely temporary stewards of this extraordinary space agency,” Nelson wrote. “The work we do, the missions we launch, they transcend the length of a single administration and a single administrator.” Not everything has gone the way Nelson has wanted. Artemis III, for example, has slipped from 2025 to mid-2027 due to a litany of issues. The program is also estimated to be billions of dollars over budget, which could be significant given Isaacman’s comments that NASA’s Space Launch System (SLS), the launch vehicle for Artemis missions, is “outrageously expensive.” Nelson encouraged Isaacman—who after purchasing four orbital missions from SpaceX and flying on two is arguably the company’s largest private customer—to continue leaning on commercial partnerships to get the job done. “Powered by these commercial and international partnerships, NASA will continue to propel American leadership and American values forward—on Earth, in the skies, and in the stars,” the outgoing administrator wrote. Nelson was appointed by former President Joe Biden in May 2021 after spending 18 years in the U.S. Senate and 12 in the House, serving as chairman of both chambers’ subcommittees on science and space. Previously, he flew aboard the space shuttle Columbia on the STS-61C mission in 1986. In addition to making progress on Artemis, Nelson’s term saw the launch of eight commercial crews to the International Space Station (ISS) on SpaceX Dragon capsules. His administration launched the largest spacecraft ever developed for a planetary mission, Europa Clipper, to study Jupiter’s icy moon; the James Webb Space Telescope, the most massive, powerful, and complex telescope ever launched; and the first three Commercial Lunar Payload Services (CLPS) missions to the moon, one of which achieved the first lunar landing by a commercially built vehicle. Nelson was in charge as NASA collected samples on Mars with its Perseverance rover and on asteroids through the OSIRIS-REx mission, and he oversaw the first controlled flight on another planet with the Ingenuity Mars helicopter. Under his watch, NASA revealed the design of the X-59 supersonic aircraft and began work on the X-66: a unique airframe being developed by Boeing that is expected to reduce fuel consumption and emissions. Like this story? We think you'll also like the Future of FLYING newsletter sent every Thursday afternoon. Sign up now. Share this story