SPACE — NASA is planning to build a station for astronauts orbiting the moon, a project known as the Lunar Orbital Platform Gateway.

According to an ESA press release, the Gateway space station will follow a near-rectilinear halo orbit, or NRHO. Gateway will pass 3,000 kilometers from the lunar surface ant its closest, and 70,000 kilometers at its furthest. One revolution around the moon takes approximately seven days.

The ESA reports that a halo orbit is possible due to the gravitational interplay between the Earth and the Moon, which creates a small area of stability or near-stability known as libration or Lagrange points.

But as an NRHO isn't entirely stable, the Gateway will require periodic maneuvering to keep it from drifting off-course.

The space station is slated for completion in the mid-2020s. NASA calls for launching the power and propulsion module into space in 2022. Two additional launches by 2025 will add habitation, logistics, and airlock functions.

According to the ESA, Gateway will serve as a staging post where astronauts can dock and leave their spacecraft, then travel to the lunar surface in a lander.

It will also provide them shelter, a place to stock up on fuel and supplies and relay communications, and a base to dispatch crew and robots to the moon.