New York (CNN Business) In the face of more frustrating delays with the rocket Boeing is building for NASA, the space agency said two weeks ago that it would consider using other rockets for an upcoming Moon mission.

But NASA administrator Jim Bridenstine said in a statement Tuesday that none of its alternatives offered a way for the agency to stay "within our timeline and on budget."

Now, government officials are dialing up the pressure on Boeing to speed up development of the long-overdue rocket, called Space Launch System or SLS. The space agency contracted Boeing in 2012 to build SLS's core components.

Bridenstine's remarks came after US Vice President Mike Pence said Tuesday at a National Space Council meeting in Alabama that news of more hangups with the SLS program were a "great disappointment," and the current timeline is "just not good enough."

Pence announced that the Trump administration wants NASA to put astronauts back on the moon by 2024, which would require a drastic acceleration in SLS development.

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