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.
To include astronauts in the first launch, the Orion capsule would require life support and a fully working launch abort system, which is created to help the crew capsule escape a failure.
While NASA has been working toward a launch date in 2018 for EM-1, the agency now admits that it won't be able to hit that deadline.
"After evaluating cost, risk, and technical factors in a project of this magnitude, it is hard to accommodate changes needed for a crewed EM-1 mission at this time", NASA's acting administrator, Robert Lightfoot, sent in an email to agency employees that was obtained by The Verge.More news: Prince Philip, 95, keeps calm but won't carry on royal duty
"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.
"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". Lightfoot was effusive in his praise of the Trump White House for giving NASA the opportunity to look at the possibility of adding crew to EM-1, as well as its support of NASA's programs overall.
The SLS program is the centerpiece of NASA's effort to send humans deeper into the solar system, starting with the first manned mission beyond Earth orbit in a half century. Pegasus is transporting test articles for the largest rocket stage in the world, the Space Launch System, from the Michoud Assembly Facility in New Orleans to Marshall Space Flight Center in Alabama for testing.
The agency's current schedule calls for the initial, unmanned SLS-Orion flight in 2019. Unlike the EM-1 rocket, the Block 1B version of the SLS would feature a more powerful, human-rated "exploration upper stage", or EUS.More news: Kerber advances to 3rd round in Madrid, secures No 1 ranking
While this delay means that the next-generation NASA rocket won't fly with humans until the next decade, it does not mean there will be no crewed launches from USA facilities before then. However, President Trump could still decide he wants to do this and ask Congress for the money.
The delay would push back the rocket's second flight beyond 2021, said NASA Associate Administrator William Gerstenmaier. Just getting EM-1 off the ground will be hard enough.
Rockets in the early years of space flight were unreliable in test phases and sometimes blew up on the pad or shortly after liftoff.
Putting a crew aboard would have driven that cost even higher.More news: Aric Almirola wins Xfinity Series race at Talladega
We are building both systems and supporting infrastructure to ensure a sustained cadence of missions beginning with EM-1 and continuing thereafter. "So we knew those had to get added in".