RS-25
Reusable Space Shuttle main engine repurposed for SLS; four fly on each Artemis core stage.
Last refreshed: 17 April 2026 · Appears in 1 active topic
Why is NASA using 40-year-old Space Shuttle engines on its new Moon rocket?
Timeline for RS-25
Scheduled to ship from Stennis to KSC by July 2026
Artemis II Moon Mission: Artemis III core stage ships MondayMentioned in: Artemis III capsule powered up at KSC
Artemis II Moon Mission- Why does NASA still use the Space Shuttle engine on the new Moon rocket?
- NASA repurposed proven RS-25 Shuttle engines for SLS to avoid new development costs and risk. The existing fleet had already flown 135 Shuttle missions. On SLS they are expendable rather than reused.Source: briefing
- How many RS-25 engines are on the SLS?
- Four RS-25 engines power the SLS core stage. The four Artemis III engines are at Stennis Space Center and scheduled to ship to Kennedy Space Center by July 2026.Source: briefing
- Are RS-25 engines reusable on SLS?
- No. Unlike on the Space Shuttle, RS-25 engines on SLS are expendable. They are discarded with the core stage after each launch.Source: briefing
Background
Four RS-25 core-stage engines are processed at Stennis Space Center and scheduled to ship to Kennedy Space Center no later than July 2026 for integration with the Artemis III SLS core stage arriving by Pegasus barge. They will produce a combined 1.6 million pounds of thrust at sea level alongside the twin solid rocket boosters during the Artemis III ascent.
The RS-25, originally the Space Shuttle Main Engine (SSME), was developed by Rocketdyne (now Aerojet Rocketdyne) in the 1970s and flew on all 135 Space Shuttle missions. NASA repurposed the existing Shuttle fleet of engines for SLS Block 1 missions rather than developing a new engine, on the basis that the heritage hardware was proven. For SLS, the RS-25 is expendable: it Burns up or splashes into the ocean with the core stage after each launch.
NASA is under budget pressure that may affect whether enough RS-25 engines exist for the full Artemis manifest. Each engine costs significantly more in expendable configuration than it did as a reusable Shuttle asset. The FY2027 NASA budget proposal included cuts that Senator Jerry Moran has called a mistake, and the Artemis engine supply chain is one of the items dependent on sustained appropriations.
