The rocket engineers were giddy Thursday, cheering through their face masks. Applauding, virtually high-fiving and wishing they could hug each other to celebrate when NASA’s massive Space Launch System rocket finally successfully completed a key test of its main engines.

It was a moment of triumph for the space agency, which over the past year successfully restored human spaceflight from United States soil, collected a sample from an asteroid 200 million miles away and whose Perseverance rover made a pinpoint landing on Mars.

On Friday, the Biden administration officially announced its intent to nominate former Democratic Sen. Bill Nelson of Florida to lead the agency as its next administrator. If confirmed, he would take over an agency that’s rolling, and attracting public attention in a way not seen in years.

But, if confirmed, Nelson will face a host of serious challenges that could change the course of the agency for years. It will be up to him to oversee one of the most ambitious human exploration efforts since the Apollo era — NASA’s Artemis program, which aims to return astronauts to the moon for the first time since 1972.

NASA is also in the early stages of flying its astronauts to the International Space Station with SpaceX and Boeing, a program that poses significant risks and has had a series of stumbles. And the agency plans to fly the James Webb telescope this year, after a series of delays and setbacks to a signature science program.

In a statement Friday, Nelson said he was “honored to be nominated by Joe Biden and, if confirmed, to help lead NASA into an exciting future of possibilities.”

Achieving that future, though, will be no easy task. One of the biggest tests will be shepherding the Artemis program from concept to reality.

The return-to-the-moon program started as one of former president Trump’s signature initiatives, but the burden of the execution will fall squarely on Nelson’s shoulders.

One of the keys will be the SLS rocket, which as a senator from Florida, Nelson championed. Now he would need to make sure it flies.

Despite its successful engine test Thursday, the program has suffered years of setbacks, delays and significant cost overruns. NASA’s Inspector General recently estimated the rocket would cost $27.3 billion through fiscal year 2025. It has never flown, and critics have long derided it as the Senate Launch System, more jobs program than exploration vehicle.

NASA was aiming to fly the rocket for the first time this year, but that timeline is very much in doubt given its many problems.

Nelson also would oversee the awarding of the next phase of the contracts for the spacecraft that would ferry astronauts to the lunar surface. Last year, Congress appropriated $850 million for the so-called “Human Landing System,” the first time money has been spent on a lunar lander since Apollo. But that was well short of the $3.3 billion NASA had requested, and now the 2024 deadline the Trump administration had imposed on NASA to land people on the moon is out of the question.

Under Nelson, the agency would have to figure out what sort of schedule is feasible.

Another challenge will be ensuring that Boeing is back on track with the Starliner capsule it is designing for NASA to fly crews to the space station. During a test flight without any astronauts on board in late 2019, the spacecraft ran into troubles almost as soon as it reached space.

NASA and Boeing decided to redo the test, which is now scheduled for this spring. That will have to go well in order for Boeing to finally fly astronauts for the first time, a mission NASA hopes to achieve by the end of the year. And something rival Space X accomplished twice last year.

It also hopes to fly the James Webb telescope, a massively ambitious project that would look back in time to the beginning of the formation of galaxies, explore galaxies and look for other signs of life in the universe.

It is scheduled to launch in October, after years of problems that pushed the program’s price tag to nearly $10 billion.

Nelson is well suited to take over the agency, his supporters say, given his long tenure in Congress, where he took a keen interest in NASA and oversaw many of its signature programs.

“In the senate he was known as the go-to senator for our nation’s space program,” the White House said in its announcement, noting that Nelson even flew on the space shuttle in 1986.

Nelson quickly received glowing praise from members of Congress and industry groups Friday.

Rep. Eddie Bernice Johnson (D-Tex.), the chair of the science, space and technology committee, said: “Through his committee leadership positions in both the House and Senate, Sen. Nelson has amassed decades of experience in dealing with NASA, Congress, and the space and aviation communities, and I know he will be able to hit the ground running when he becomes administrator.”

Sen. John Hickenlooper (D-Colo.), chair of the subcommittee on science and space said, “Senator Nelson has the experience to lead NASA to new heights.”

And former NASA administrator Jim Bridenstine, a Republican who served under Trump, praised Nelson, who tried unsuccessfully to block Bridenstine’s nomination. He said Nelson was “an excellent pick” and urged the Senate to confirm him “without delay.”