Adds details, background throughout

By Kanishka Singh and Steve Gorman

WASHINGTON, Nov 4 (Reuters) - U.S. President Donald Trump said on Tuesday he was re-nominating Jared Isaacman, the private astronaut and ally of fellow billionaire and SpaceX founder Elon Musk, for the post of NASA administrator, five months after Isaacman's original nomination was withdrawn.

Isaacman, an e-commerce mogul who flew to orbit twice on all-private astronaut missions as a customer and collaborator with SpaceX, was removed from consideration to lead the space agency in May amid a high-profile falling-out between Trump and Musk. Sean Duffy, the head of the U.S. Department of Transportation, was then named acting NASA chief.

"This evening, I am pleased to nominate Jared Isaacman, an accomplished business leader, philanthropist, pilot, and astronaut, as Administrator of NASA," Trump said on social media. The role requires confirmation by the Senate, where Trump's Republican Party holds a 53-47 majority.

Last year, Trump, as president-elect, tapped Isaacman to lead NASA at the recommendation of Musk, the SpaceX chief executive officer who had been an influential adviser to the president and sought to more closely align the U.S. space program with his goal of flying missions to Mars.

Isaacman, a billionaire investor and amateur jet pilot with thousands of hours of flight time under his belt, had spent months navigating the Senate confirmation process, balancing the Musk and the Trump administration's desire to focus on Mars with NASA's multibillion-dollar strategy to return astronauts to the moon ahead of China in a geopolitical race to the lunar surface.

"Jared's passion for Space, astronaut experience, and dedication to pushing the boundaries of exploration, unlocking the mysteries of the universe, and advancing the new Space economy, make him ideally suited to lead NASA into a bold new Era," Trump wrote in his post.

Isaacman, founder and CEO of the financial transactions service Shift4 Payments FOUR.N, was the commander and chief benefactor of the first all-private space crew to reach Earth orbit in 2021. He led a four-member team of civilian rookie astronauts aboard a SpaceX rocket vessel on a three-day mission dubbed Inspiration4.

He returned to orbit in September 2024 with a follow-up commercial voyage that he again bankrolled, leading another quartet of private astronauts on a mission dubbed Polaris Dawn, in which he joined a SpaceX engineer in conducting the world's first private spacewalk.

(Reporting by Kanishka Singh in Washington; Editing by Leslie Adler and Richard Chang)

((Kanishka.Singh@thomsonreuters.com; +12024508248))