The first launch of NASA's Space Launch System (SLS) rocket, which will carry the new Orion spacecraft, could be delayed until 2020, indicates a new review report of the launch schedule.
But NASA hopes that it would be able to launch the uncrewed mission by December 2019.
This mission, known as Exploration Mission-1 (EM-1) is a critical flight test for the agency's human deep space exploration goals.
The review follows an earlier assessment where NASA evaluated the cost, risk and technical factors of adding crew to the mission, but ultimately affirmed the original plan to fly EM-1 uncrewed.
"While the review of the possible manufacturing and production schedule risks indicate a launch date of June 2020, the agency is managing to December 2019," said acting NASA Administrator Robert Lightfoot.
"Since several of the key risks identified have not been actually realized, we are able to put in place mitigation strategies for those risks to protect the December 2019 date," Lightfoot said in a statement on Thursday.
NASA said its ability to meet its agency baseline commitments to EM-1 cost, which includes SLS and ground systems, currently remains within original targets.
The Orion spacecraft is designed to take astronauts to deep space destinations,
NASA said it now plans to accelerate a test of Orion's launch abort system ahead of EM-1, and is targeting April 2019.
Known as Ascent-Abort 2, the test will validate the launch abort system's ability to get crew to safety if needed during ascent.
Moving up the test date ahead of EM-1 will reduce risk for the first flight with crew, which remains on track for 2023, NASA said.
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