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RS-25 Engine

Overview

Four RS-25 engines located at the bottom of the core stage power the rocket on its eight and a half minute climb to space with more than 2 million pounds of thrust.

Key Features

The RS-25 evolved from L3Harris’ Space Shuttle Main Engine (SSME) that successfully powered 135 flights of the space shuttle. The engine underwent five major upgrades during its life on the shuttle, each time incorporating the modern technologies and innovations – and each time demonstrating major improvements in safety and reliability. Between the shuttle and SLS programs, the RS-25 and SSME engines have collectively compiled more than 1.1 million seconds of firing time.

The RS-25 is a staged-combustion engine cycle powered by liquid hydrogen and liquid oxygen, making it one of highest performing engines the nation has ever produced. The SSME engines on the shuttle typically operated at 491,000 pounds of vacuum thrust (104.5-percent of rated power level). The required power level for the RS-25 engines on SLS is 512,000 pounds vacuum thrust (109 percent of rated power level). Future evolutions will have even higher thrust capabilities.

L3Harris has begun developing a new generation of RS-25 engines for when the 16 engines remaining from the space shuttle program are used. These engines are targeting a 30% cost reduction from the engines that flew on the space shuttle and will feature the latest in advanced manufacturing techniques, including 3D printing.

Engine Specifications

PropellantsFuel: Liquid hydrogen
Oxidizer: Liquid Oxygen
Mixture Ratio (O/F): 6.0
Thrust
(109% Power Level)
Vacuum: 512,300 lb.
Sea Level: 418,000 lb.
Chamber Pressure: 2,994 psia
Specific Impulse
(109% Power Level)
Vacuum: 452 sec.
Sea Level: 366 sec.
DimensionsLength: 168 in.
Diameter: 96 in.
Weight: 7,775 lb.
Area Ratio: 69:1

Resources

  • RS-25 Propulsion System Data Sheet

    RS-25 Propulsion System Data Sheet

  • Rs-25 Incredible Facts

    RS-25 Incredible Facts

Related News

NASA Stennis teams conducted a successful lift onto the Fred Haise Test Stand of RS-25 engine No. E20001, the first of 24 new production engines. Photo credit: NASA Stennis.

Editorial | 02. 18. 2025

L3Harris Completes Assembly of First RS-25 Engine for NASA’s Artemis V Mission

Designated E20001, this newly assembled RS-25 engine is one of four core stage engines that will help power the SLS rocket during the Artemis V mission.

NASA Stennis teams conducted a successful lift onto the Fred Haise Test Stand of RS-25 engine No. E20001, the first of 24 new production engines. Photo credit: NASA Stennis.

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