BBC News image captionArtwork: The service module will push the Orion capsule through space Europe will be building a further three service modules for the US space agency's (Nasa) Orion crew capsule. The module is the "back end" of the American astronaut vehicle, and provides propulsion and electrical power, as well as life-supporting supplies of water and oxygen. Europe had already committed to build three service modules. Tuesday's contract between the European Space Agency (Esa) and Airbus takes the total number now to six. All the European Service Modules (ESMs) will be used on Nasa's Artemis missions. Artemis is the follow-up to Apollo and will see astronauts once again walk on the surface of the Moon, as well as operating a station in lunar orbit called the Gateway.