The Rocket Engine on NASA’s Orion Moon Ship Traces Its Lineage to Vanguard I

The AJ10 rocket engine, manufactured by a company which is now called Aerojet Rocketdyne has, over the last six decades, flown in various versions using assorted hypergolic fuels, as:

The first several European Service Modules built for NASA’s Project Artemis lunar missions will actually use refurbished Space Shuttle Orbital Maneuvering System engines. After this supply has been exhausted, new-build engines will be used for subsequent flights.

All variants of the AJ10 are pressure fed, eliminating the complexity and failure modes of turbopump feed systems, and use hypergolic propellants, which require no ignition system. This makes the design inherently reliable, ideal for applications where there is no backup, such as the Apollo Service Propulsion System. If that engine failed while the spacecraft were in lunar orbit, the crew would be stranded there with no hope of rescue.