As a type of vehicle Orion is Multi-Purpose Crew Vehicle (MPCV) and consists of 3 modules. The crew module houses crew of 4 to 6 members. This module is supplied with auto-docking system, unlike its predecessors which required manual piloted docking. The crew has an atmosphere close to the Earth – mixture of nitrogen and oxygen in balanced proportion. The space for the crew is nearly 9 cubic m. and ensures 21 day long flight, which could be prolonged by adding more service modules. This module will be reusable and could be used for up to 10 launches.
The service module will be the place that provides electric energy and propulsion of the whole complex. It is supposed to be made of aluminum-lithium alloy in order to reduce its weight and after every mission will be discarded. The presence of folding solar panels actually rejects the need for frequently malfunctioning fuel cells. The rocket engine has thrust of 3400kg and is upgraded version of the space shuttle engines.
via:[wikipedia]