NASA managers have ruled out putting a crew on board an Orion capsule atop the agency’s huge Space Launch System rocket for the gargantuan booster’s maiden flight in 2019, citing technical risks and higher costs, up to as much as $900 million, agency officials said Friday.

Earlier this year, the Trump administration asked NASA to look into the possibility of either adding a crew to Exploration Mission 1, EM-1 for short, or moving up the launch of EM-2, the flight NASA already earmarked for the SLS booster’s first piloted mission. That flight is targeted for launch in the 2021 timeframe.

The NASA study concluded that while it would be possible to upgrade the Orion spacecraft to accommodate a crew for the EM-1 flight equipping it with life support systems, crew displays, a validated launch abort system and other critical elements — it would have required an additional $600 million to $900 million in funding.

And there would be additional technical risk and likely delays to accelerate software development and to retrofit the EM-1 Orion capsule to support a two-person crew.

As a result, acting NASA Administrator Robert Lightfoot said agency managers and White House officials agreed it made more sense to stick with the original plan, launching an uncrewed Orion capsule atop the first SLS booster in 2019, followed by a piloted mission using an upgraded version of the rocket two years later.

“At the end of the day, we found it technically feasible to fly a crew on EM-1 as long as we had a commitment of additional resources and schedule, and recognizing the technical risks we identified still were going to need a mitigation plan,” Lightfoot told reporters Friday.

“It really reaffirmed the baseline plan we had in place was the best way for us to go,” Lightfoot said. “Leave EM-1 uncrewed.”

“It’s really consistent with our available resources, and while it still has technical risk, we have a good handle on that and how an uncrewed mission will actually help EM-2 be a safer mission when we put crew on there.”