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
| Propellants | Fuel: 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. |
| Dimensions | Length: 168 in. Diameter: 96 in. Weight: 7,775 lb. Area Ratio: 69:1 |
Media Gallery
RS-25 Engine Testing
The first RS-25 powerhead produced by L3Harris in over a decade shipped from the Los Angeles site and arrived at its facility at NASA’s Stennis Space Center near Bay St. Louis, Mississippi, on Oct. 25. The powerhead serves as the structural backbone to the RS-25.
The first RS-25 powerhead produced by L3Harris in over a decade shipped from the Los Angeles site and arrived at its facility at NASA’s Stennis Space Center near Bay St. Louis, Mississippi, on Oct. 25. The powerhead serves as the structural backbone to the RS-25.
August 2015 - RS-25 engine inspection inside the engine assembly room at our Stennis Space Center facility.
August 2015 - RS-25 development engine 0525 in the A-1 test stand at NASA's Stennis Space Center in Mississippi.
August 2015 - Technicians inspect the RS-25 controller, which provides communication between the SLS vehicle and the engine, relays commands to the engine, transmits data back to the SLS vehicle to regulate thrust, fuel mixture ratio and monitor the engine's health and status.
June 28, 2019 - Aerojet Rocketdyne, prior to being acquired by L3Harris delivered four RS-25 engines for integration with NASA’s Space Launch System core stage from its facility at NASA’s Stennis Space Center to NASA’s Michoud Assembly Facility.
June 28, 2019 - Aerojet Rocketdyne, prior to being acquired by L3Harris, delivered four RS-25 engines for integration with NASA’s Space Launch System core stage from its facility at NASA’s Stennis Space Center to NASA’s Michoud Assembly Facility.
Jan.16, 2021 - NASA conducts a hot fire test of the core stage for the agency’s Space Launch System rocket on the B-2 Test Stand at Stennis Space Center near Bay St. Louis. (Credit: NASA)
Jan. 16, 2021 - NASA conducts a hot fire test of the core stage for the agency’s Space Launch System rocket on the B-2 Test Stand at Stennis Space Center near Bay St. Louis. Credit: NASA
Jan. 16, 2021 - The core stage for the first flight of NASA’s SLS rocket is seen in the B-2 Test Stand during a scheduled eight minute duration hot fire test at NASA’s Stennis Space Center near Bay St. Louis, Mississippi. (Credit: NASA)
Assembled and flight certified after the completion of the Space Shuttle program, RS-25 engine 2063 is slated to launch on Artemis II, the second flight of NASA’s Space Launch System (SLS). Four RS-25 engines power each SLS launch.
L3Harris' RS-25 engine 2048 is an Artemis III engine, which means is it slated for the third flight of NASA’s Space Launch System.
An engineer at NASA’s Stennis Space Center examines RS-25 engine, 2057, which is slated for the Artemis III, the third flight of NASA’s Space Launch System.
An engineer examines RS-25 engine, 2057, which is slated for the Artemis III, the third flight of NASA’s Space Launch System.
An engineer examines RS-25 engine, 2057, which is slated for the Artemis III, the third flight of NASA’s Space Launch System.
RS-25 engine, 2057, is slated for the Artemis III, the third flight of NASA’s Space Launch System.
RS-25 engines, 2054 and 2057, are slated for Artemis III, the third flight of NASA’s Space Launch System (SLS). Four RS-25 engines power each SLS launch.
RS-25 engines, 2054 and 2057, are slated for Artemis III, the third flight of NASA’s Space Launch System.
Related News
Editorial | 06. 30. 2025
Artemis II Mission Advances with Successful RS-25 Engine Checkout Tests
NASA’s Artemis II mission is a step closer to the launch pad with the successful completion of RS-25 engine checkout tests at Kennedy Space Center, a critical milestone in the Space Launch System Program Specific Engineering Test series, ensuring seamless communication and proper functioning of the engines for the first crewed mission around the moon in more than 50 years.
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