Donald Trump has renominated billionaire investor Jared Isaacman to run Nasa, five months after withdrawing his first nomination.

The 42-year-old entrepreneur, who has ties to SpaceX founder Elon Musk, had looked set to lead the space agency when Trump abruptly pulled his nomination in late May, following what the president said was a "thorough review of prior associations."

While the White House did not specify what those associations were, it was during Trump's high-profile feud with Musk.

Isaacman, who is worth an estimated $1.9bn (£1.46bn), is an amateur jet pilot and also became the first non-professional astronaut to walk in space last year, on a mission with SpaceX that he bankrolled.

Why Trump has suddenly changed his mind is unclear, and the president made no mention of the past when he wrote on his Truth Social platform that he was "pleased to nominate" Isaacman for the role.

"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," the president wrote.

The Nasa administrator role will be Isaacman's first job in politics, representing a departure from the last two men appointed to the job.

It requires confirmation by the Senate, where the Republican Party holds a 53-47 majority. Even though the US government has been shut down since early October, the Senate is still able to confirm presidential nominees.

Thanking the president, Isaacman wrote on X that "it will be an honor" to serve in the role.

"The support from the space-loving community has been overwhelming," he wrote in a long post, that also acknowledged Nasa scientists and innovators.

"I am not sure how I earned the trust of so many, but I will do everything I can to live up to those expectations."

Sean Duffy, the head of the transport department, has been interim Nasa chief since July.

Isaacman's initial nomination withdrawal came just days after Elon Musk left the Trump administration, following a tumultuous drive to shrink the size of government departments with his Doge initiative, leading to thousands of job cuts.

Concerns were voiced over Isaacman's ties to Musk and his SpaceX company, where Isaacman has reportedly spent hundreds of millions of dollars. He has also made donations to the Democrats in past elections.

His nomination has encountered scepticism, and at his initial confirmation hearing in April, members of both parties questioned Isaacman about possible conflicts of interest, budget cuts and his desire to send astronauts to Mars.

They expressed fears he would sacrifice the long-planned Moon mission to focus on Mars, but Isaacman said both can be possible.

"We don't have to make a binary decision of Moon versus Mars, or Moon has to come first versus Mars," he later added.

The billionaire - who was a high-school dropout - made his fortune from payment processing company Shift4 Payments, which he founded in 1999 in his parents' basement when he was 16.

Isaacman has a longstanding interest in flying - having first taken pilot lessons in 2004 and later setting a world record for the fastest circumnavigation of the world in a light jet.