NASA’s moon base plans, conceptualized just a few months ago, are rolling out in earnest as the space agency maps out plans to deliver landers, rovers, buggies and other assets to the lunar surface.

On Tuesday, NASA said it will pay at least half a billion dollars to three companies — Astrobotic, Firefly and Intuitive Machines — for four missions to deliver science instruments and other cargo to the moon. Astrobotic was the only vendor to be awarded two missions.

The agency also floated the possibility of repurposing a Mars rover, nicknamed Promise, for use on the moon.

It’s part of a broader effort to use robotic vehicles to build up infrastructure on the moon that can be used by future human explorers.

The deals announced Tuesday are part of what Carlos García-Galán, NASA’s program executive for the moon base, called “Phase 1” of a plan to build out a permanent lunar settlement where astronauts will live and work. This initial phase is expected to last through 2028 and cost about $10 billion.