Boeing on May 1 unveiled its Gateway Demonstrator, a prototype of the deep-space outpost that is key to the United States’ plan to return astronauts to the moon’s surface within five years.

NASA contracted with Boeing and five other companies in August 2016 to design and build ground-based Gateway prototypes. The Gateway will act as a reusable moon-orbiting exploration hub, a technology test bed, and a research base for government and private organizations. It will enable crewed and robotic missions in lunar orbit, on the moon’s surface, and eventually to Mars.

Boeing built and is testing its demonstrator at NASA’s Marshall Space Flight Center in Huntsville, Ala. The demonstrator’s design is based on the International Space Station (ISS) modules that Boeing built and has supported for more than 20 years – except with 30% more habitable volume in each module.

“Our Gateway engineering is well beyond Systems Requirements Review maturity and leverages the flight-proven structural design heritage of ISS,” said Mark Ortiz, Boeing program manager for the Gateway Demonstrator.

The demonstrator includes prototypes of a habitation module (Hab) and airlock module that are designed to be launched into space on a Space Launch System rocket and assembled on orbit around the moon.

Boeing’s Gateway concept can host a crew with only the Hab module and a Power and Propulsion Element (PPE) that will able to guide the Gateway into various orbits around the moon to serve different mission needs.