NASA acting administrator Robert M. Lightfoot Jr. at the Marshall Space Flight Center in February. (Bill Ingalls/NASA/AP)

Robert M. Lightfoot Jr., who has served as acting administrator at NASA for more than a year, said Monday that he will retire from his position in April. No immediate announcement was made on who will follow him.

In an agencywide memo, Lightfoot wrote that he had “bittersweet feelings” about the decision. He also said he will “work with the White House on a smooth transition to the new administrator.”

NASA has been without a permanent administrator since Charles Bolden, a former astronaut and retired Marine Corps aviator, resigned the day that President Trump took office last year. The second-in-command, deputy administrator Dava Newman, also left the agency as Trump was inaugurated. In stepped Lightfoot, who had held NASA's highest-ranking non-appointee position.

In September, Trump nominated Jim Bridenstine, a Republican congressman who represents Oklahoma in the House, to be NASA administrator. Bridenstine previously worked as the director of the Tulsa Air and Space Museum. He supports an increased role of private industry in spaceflight.

Bridenstine's confirmation process has not gone smoothly. At a hearing in November, Sen. Bill Nelson (D-Fla.) argued that Bridenstine lacked the ability to be “a leader who has the ability to unite scientists, engineers, commercial space interests, policymakers and the public on a shared vision for future space exploration.” Senate Democrats have been joined by Sen. Marco Rubio (R-Fla.) in opposition to Bridenstine, putting the nominee's future in jeopardy.

In an email late Monday, a NASA representative wrote that “the White House may direct anyone who qualifies under the Vacancies Reform Act to serve as acting NASA Administrator.” The agency also has no chief of staff or deputy director.

Of the seats normally filled by scientists or engineers in Washington, many remain empty. The White House does not have a science adviser, and other positions in the Office of Science and Technology Policy remain vacant. Trump also has yet to appoint members to the President's Council of Advisors on Science and Technology.

Below is a copy of Lightfoot's memo:

NASA team,

 It is with bittersweet feelings that I am announcing I will be retiring from the agency on April, 30, 2018.  I will work with the White House on a smooth transition to the new administrator.

 I cannot express enough my gratitude to the entire NASA team for the support during my career and especially the last 14 months as your acting administrator.  The grit and determination you all demonstrate every day in achieving our missions of discovery and exploration are simply awe inspiring.  I leave NASA blessed with a career full of memories of stunning missions, cherished friendships, and an incredible hope for what is yet to come.

 When I look back on my time at NASA, I can’t help but think about the people. From my friends in the test areas at Marshall and Stennis, to the folks that I sat with on console launching shuttles, to the Marshall team when I was the center director, and now as the acting administrator to the entire NASA team — what a privilege to work with such dedicated and passionate people every day.

 There is no way I would be where I am today without having had such amazing opportunities and such a great set of colleagues.  I’ve learned in so many ways that at NASA we make the impossible possible — whether it is with the missions we do or whether it is a small town kid who was able to lead the greatest agency in the world.

 NASA’s history has many chapters with each of us having a part.  I’ve written my part and now the pen is in your hands — each one of you.  I know you will make this nation proud as you accomplish the many missions you have in front of you. For me, I look forward to more time with my family and closest friends, and cheering the NASA team on from the outside. 

 God speed to all of you and thanks for the opportunity to be part of something truly bigger than each of us individually!  It’s been an unbelievable ride!



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