President-elect Donald J. Trump will nominate Jared Isaacman, a billionaire entrepreneur who led two private missions to orbit on SpaceX rockets, as the next NASA administrator.

Mr. Isaacman, the chief executive of the payment processing company Shift4 Payments, is a close associate of Elon Musk, the founder of SpaceX, and, if confirmed to the post by the Senate, would bring the perspective of an outsider to the space agency and its $25 billion budget.

“Jared will drive NASA’s mission of discovery and inspiration, paving the way for groundbreaking achievements in Space science, technology, and exploration,” Mr. Trump said in a post on his Truth Social platform.

Mr. Isaacman, 41, made his entrance to the space world in February 2021 when he announced he was financing a private mission called Inspiration4. Riding in a SpaceX Crew Dragon capsule, the mission was the first in which no one aboard was a professional astronaut.

Instead of taking some of his friends along, he opened up the other three seats to strangers. He gave two seats to St. Jude Children’s Research Hospital in Memphis, which treats young cancer patients. One went to a hospital employee; the other was raffled off to raise money for St. Jude. Mr. Isaacman personally donated $100 million to St. Jude.

The fourth Crew Dragon seat went to a winner of a “Shark Tank”-like contest run by Shift4.

The crew launched to orbit in September 2021, spending four days in space.

Mr. Isaacman followed up this year with another trip to orbit called Polaris Dawn. This mission — a collaboration with SpaceX — aimed to test out new technologies that would be needed to implement Mr. Musk’s dream of eventually sending people to Mars.

The Polaris Dawn mission included the first spacewalk by private astronauts. Mr. Isaacman has been planning to conduct two more Polaris missions, including what would be the first crewed flight of Starship, the giant new rocket currently under development by SpaceX.

Mr. Isaacman founded Shift4 in 1999 after dropping out of high school. In 2012, he founded Draken International, which owns fighter jets and provides training for pilots in the United States military. He sold that company in 2019.

Mr. Isaacman would replace the current administrator, Bill Nelson, a former Democratic senator from Florida who also traveled to orbit as part of a space shuttle mission in 1986.

In a posting on X, Mr. Musk’s social media site, Mr. Isaacman highlighted that he was born after the Apollo moon landings.

“With the support of President Trump, I can promise you this: We will never again lose our ability to journey to the stars and never settle for second place,” he said. He added, “Americans will walk on the Moon and Mars and in doing so, we will make life better here on Earth.”