The OMS-E (Orbital Manoeuvring System Engine) is a hypergolic engine inherited from the Space Shuttle, now used in the European Service Module to power Orion's major orbital manoeuvres on Artemis missions.Source: /t/artemis-ii-2026/3/orion-skips-burn-trajectory-is-precise

Why is Artemis using Space Shuttle engines?

The OMS-E was reused because of its proven reliability across 135 Shuttle missions. Refurbished by ESA/Airbus for the European Service Module, it reduces Artemis development risk and cost.Source: /t/artemis-ii-2026/3/orion-skips-burn-trajectory-is-precise

How many OMS-E engines are left for future Artemis missions?

The supply of flightworthy OMS-E units is finite and not publicly quantified. NASA and ESA will need a successor engine for Artemis missions beyond the first few flights.Source: /t/artemis-ii-2026/3/orion-skips-burn-trajectory-is-precise

Background

The Orbital Manoeuvring System Engine (OMS-E) is a hypergolic rocket engine inherited from the Space Shuttle programme, now integrated into the European Service Module (ESM) that propels the Orion spacecraft on Artemis missions. It burns a mixture of monomethyl hydrazine and nitrogen tetroxide, producing approximately 26.7 kN of thrust, and is used for major orbital manoeuvres including translunar injection and lunar orbit insertion and departure.

The OMS-E was carried over into Artemis because of its proven reliability across 135 Shuttle missions. The engine was refurbished and integrated by ESA and Airbus for the ESM, bridging Shuttle-era hardware with a new generation of deep-space exploration architecture. On Artemis II, the OMS-E is responsible for the burns that shape the free-return trajectory, though Orion's precise navigation allowed the first scheduled correction burn to be skipped.

Relying on heritage Shuttle hardware for a crewed lunar mission represents both a pragmatic cost decision and a dependency on ageing infrastructure. The OMS-E supply chain is finite: only a limited number of flightworthy units remain, and the engine will eventually need a successor for sustained Artemis operations beyond the first few missions.