The first flight of NASA's expensive new deep-space rocket is going to be delayed again, and it won't have any astronauts aboard, the agency announced Friday. That decision comes after NASA and White House officials pondered an alternative plan to add two astronauts to the test flight in an attempt to do something dramatic in space during the current term of President Trump.

Going without crew in that first test flight has been NASA's plan all along. The agency wanted to do a rigorous test flight of the new rocket, called the Space Launch System, and the new crew capsule, Orion, that pushed the hardware to its limits during a three-week lunar orbit. The agency had hoped to launch in 2018, with a crewed mission in 2021.

The election of Trump scrambled the picture. Soon after the inauguration, Trump political appointees showed up at NASA headquarters and met with the veteran civil servants running the agency and reviewed the human spaceflight program. Robert Lightfoot, NASA's acting administrator, soon announced that the agency would conduct a thorough review of the program to see whether it would be possible to add two astronauts to the first test flight, then scheduled for late 2018.

On Friday, Lightfoot said the staff members doing the feasibility study had concluded that NASA should stick to its original idea.

“While it's technically feasible, they really reaffirmed that the baseline plan we had in place was the best way to go,” Lightfoot said in a teleconference with reporters.

William Gerstenmaier, the top NASA official for human spaceflight, repeatedly emphasized that the agency wants a steady, sustainable program that involves building the infrastructure for decades of deep-space ventures not only for NASA but for the private sector.

“We’re essentially building a multidecadal infrastructure that allows us to move the human presence into the solar system,” Gerstenmaier said.

This is not happening quickly. NASA does not operate with the kind of budgets available during the Apollo era. The agency has had some setbacks, including a tornado that seriously damaged the Michoud Assembly Facility in New Orleans in February. This month, as first reported by the blog NASA Watch, workers at Michoud accidentally damaged beyond repair a large dome that was to be part of a liquid oxygen fuel tank. “This was a significant event for us,” Gerstenmaier said.

The first flight of the SLS was originally envisioned by Congress for 2016. On Friday, Lightfoot said that various delays in the program have pushed the first mission to 2019, with the exact timing still uncertain. Gerstenmaier said that, after the first uncrewed mission, NASA will need about 33 months to revamp a mobile launcher at the Kennedy Space Center in Cape Canaveral, Fla., to handle the second SLS mission, which will have additional hardware and stand 40 feet taller on the launchpad. That means it is unlikely NASA will launch astronauts on the SLS before 2022.

Phil Larson, the space policy adviser in the Obama White House, said of this new delay in the rocket schedule, “This is something that I think a lot of people saw coming. I don’t think too many people within NASA are shocked.”

The commercial space sector — including SpaceX, founded by Elon Musk, and Blue Origin, owned by chief executive Jeffrey P. Bezos (who also owns The Washington Post) — is racing to develop its own rockets that are comparable in scale to the SLS.

“This really isn’t about NASA versus SpaceX, or NASA versus Blue Origin, it's more about the past way of doing business versus how do we run the government more like a business,” Larson said.

The agency had considered adding two astronauts to the first SLS flight in an effort to respond to the clear desire of Trump and his aides for some kind of dramatic space mission, with astronauts, that could be achieved in the first term. Trump has made allusions to space exploration in speeches but has never spelled out exactly what he wants.

During a conversation recently with astronauts aboard the International Space Station, Trump said he wanted to send astronauts to Mars in his first term, or by the end of his second term “at worst” — but the manner of his comment suggested that he was either joking or speaking off the cuff with minimal grasp of the technical challenges of a Mars mission.

Lightfoot, asked about that comment, said of the White House, “They have not asked us to go to Mars by 2024.”

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