Trump tweeted on Friday criticizing NASA for its new mission to take astronauts back on the moon by 2024. He urged the space agency to focus on “much bigger” initiatives like going to Mars, undercutting his previous support for the lunar initiative.

The tweet is sent from Air Force One as Trump returned from a trip to Europe. He did not make clear whether he thinks the strategy should be entirely abandoned or whether he was more concerned about how NASA was branding the strategy.

Trump’s exact meaning was uncertain, but he may have been urging the US space agency to put more of a focus on the voyage to Mars, with the Moon serving as just a stepping stone. Vice President Mike Pence announced plans in April to return to the Moon by 2024 although some space experts doubt whether the deadline can be met.

We’re not going to leave flags and footprints and then come home to not go back for another 50 years – A tweet later Friday by NASA Administrator Jim Bridenstine

NASA plans to build a space outpost in lunar orbit that can relay astronauts to the lunar surface by 2024, part of a broader initiative to use the moon as a staging ground for future missions to Mars.