Europe's Lunar Powerhouse
The unglamorous-looking cylinder attached to the back of NASA's Orion crew capsule is the European Service Module (ESM), and it powers the entire Artemis program's crewed missions. Assembled here in Bremen, the ESM is a European Space Agency (ESA) contribution, making it the first time NASA has used a European-built system for a important element of a crewed American spacecraft. This module provides everything the astronauts inside the Orion capsule need to survive and for the spacecraft to maneuver in deep space.
The ESM is roughly 4 meters in diameter and 4 meters high. At launch, it weighs over 13 metric tons, with the majority of that mass—about 8.6 tons—being propellant. Inside its structure, it houses tanks carrying 240 liters of water, and 90 kilograms of oxygen and nitrogen for the crew. Its four solar arrays, each 7 meters long, unfold to a total wingspan of 19 meters. The 15,000 solar cells on these arrays generate 11.2 kilowatts of electricity, enough to power two average households, keeping the spacecraft's computers and systems running. The module's skin is a layer of Kevlar, protecting its interior of over 20,000 components and 12 kilometers of cables from impacts by micrometeorites.
A Symphony of 33 Engines
Propulsion for the Orion spacecraft is handled entirely by the ESM's 33 engines. These are divided into three distinct types. The single main engine provides the major thrust for large maneuvers, like entering orbit around the Moon or the burn to bring the crew home to Earth. This main engine is a spaceflight veteran: a refurbished AJ10-190 engine previously used for the Space Shuttle's Orbital Maneuvering System. The engine on the Artemis I mission, for example, had already flown on 19 shuttle missions. It produces 26.6 kilonewtons of thrust.
For smaller orbital corrections and as a backup to the main engine, the ESM uses eight auxiliary R-4D-11 thrusters. Finally, 24 smaller reaction control system thrusters, grouped in pods of four, provide precise attitude control, allowing Orion to orient itself in any direction. This array of engines gives the spacecraft the agility needed for complex procedures, such as docking maneuvers which will be tested on future Artemis missions. The entire system is fed by four 2000-liter propellant tanks carrying mixed oxides of nitrogen (MON) and monomethyl hydrazine (MMH). This Bremen-built module is the engine and the power station for humanity's return to the Moon.