NASAfacts

National Aeronautics and Space Administration

Space Launch System

RS-25 Core Stage Engine

Powering America’s Exploration of Deep Space: 

The Engines Behind NASA’s Space Launch System 

NASA’s Space Launch System (SLS), the most 

powerful rocket in the world, will be powered by 

RS-25 engines that combine proven performance 

with advanced engineering and technology. The SLS 

will launch astronauts on missions to the Moon and 

eventually to Mars.

The SLS Program is taking advantage of hardware 

and cutting-edge manufacturing techniques developed 

for the Space Shuttle Program and other exploration 

programs. These are being integrated with new 

designs and new technologies, significantly reducing 

development and operations costs. SLS is designed to 

be flexible and evolvable, to meet a variety of crew and 

cargo mission needs.

The first SLS variant to fly, the Block 1, will be able 

to carry 27 t (59,525 pounds) to the Moon. It will 

use four RS-25 engines for the core stage, along 

with two solid rocket boosters.

RS-25 Core Stage Engine Evolution

The RS-25 powered the space shuttle for over 

three decades and completed 135 missions. It 

is one of the most tested large rocket engines in 

history, with more than 3,000 starts and more than 

1 million seconds of total ground test and flight 

firing time. 

During the Space Shuttle Program, the RS-25 

underwent several design updates to improve 

service life, durability, reliability, safety, and 

performance. SLS takes advantage of that 

technology investment and experience.

RS-25 engine callouts: 1-4 - Turbo Pumps, 5 - Main Combustion Chamber, 6 - Nozzle, 7 - Engine Controller
RS-25 Engine Facts

Thrust ...................................

Size .......................................

Weight ....................................

Operational Thrust ..............

Operational Time ................

Operational Temp Range ....

FS-2020-10-42-MSFC NASA Facts

National Aeronautics and Space Administration

George C. Marshall Space Flight Center

Huntsville, AL 35812

www.nasa.gov/marshall

www.nasa.gov

The SLS Program has an inventory of 16 RS-25 flight engines, 

built by Aerojet Rocketdyne of El Segundo, California, 

transferred from the Shuttle Program.

Two additional RS-25 ground test engines are being used at 

NASA’s Stennis Space Center to test fire updates to the engine, 

adapt it to SLS performance requirements and operating 

environments, certify new controllers, and support development 

of future engine components.

The RS-25 rocket engine test era for SLS began Jan. 9, 2015, 

with a 500-second – more than 8 minutes – hot fire of RS-25 

developmental engine No. 0525 on the A-1 Test Stand at 

Stennis. 

NASA tested the first SLS flight engine on March 10, 2016. 

Altogether, the agency has conducted 32 developmental and 

flight engine tests for a total of 14,754 seconds – more than four 

hours of cumulative hot fire – all on the A-1 stand at Stennis.

During the Shuttle Program, the RS-25s routinely operated in 

flight at 104.5% of their original 100% rated thrust level but were 

tested up to 111% thrust. To meet the demands of SLS flight, 

more power and performance would be required. 

Between March 2017 and April 2019, the engine test series at 

Stennis certified the engines to operate at normal SLS flight 

levels of 109%. During such tests, new and more capable 

engine controllers were tested for every engine. In the process, 

the engine was tested at thrust levels up to 113% to allow for 

operating safety margins. 

To date, two SLS flight sets of four engines each have been 

adapted for their new Artemis missions and processed for flight, 

and a third flight set is undergoing processing. All the controllers 

have been tested as well. In addition to new controllers, each 

engine received additional insulation to protect it from the hotter 

launch environment of being closer to the twin solid rocket 

boosters.

The next planned evolution of the SLS, Block 1B, would use 

a more powerful Exploration Upper Stage (EUS) to enable 

more ambitious missions, and a 38 t (83,776 lbs.) lift capacity

to the Moon. 

For more information about SLS, visit:

http://www.nasa.gov/sls 

http://www.twitter.com/NASA_SLS 

http://www.facebook.com/NASASLS

http://www.instagram.com/exploreNASA

A later evolution, Block 2, will use advanced solid or liquid 

propellant boosters, to provide up to 46 t (101,400 lbs.) lift 

capacity to deep space. In each configuration, SLS will continue 

to use the same core stage design and four RS-25 engines.

The liquid hydrogen/liquid oxygen-fueled engines are compact 

and high performance. At full throttle, each of the four engines 

will produce 512,300 pounds of vacuum thrust, generating 10 

times the equivalent thrust-to-weight power density of the largest 

commercial jet engine.

During liftoff, the Block 1 configuration of SLS will produce 8.8 

million pounds of thrust — 15 percent more than the Saturn V 

rockets that launched astronauts on journeys to the Moon.

NASA has contracted with Aerojet Rocketdyne to restart 

production of a more affordable variant of the RS-25 tested and 

certified for flight at a higher thrust level. This new engine will 

use a simplified design, new manufacturing technologies, new 

inspection technologies, and processes that reduce handling 

and support labor, hardware defects, and production time. 

One of the most promising technologies is selective laser 

melting (SLM). This technology uses a high-energy laser and 

metal powder to produce parts more quickly and at lower cost 

than is possible with conventional manufacturing methods. 

Because they are made of fewer separate parts, these SLM 

parts are more structurally sound, resulting in a safer vehicle.

512,300 lbs. (vacuum)

416,300 lbs. (sea level)

4.2m x 2.4m (14 ft x 8 ft) 

 

3.49 t (7,800 lbs.)

109 percent

approximately 8 minutes

-423 to +6000 degrees F

RS-25 rocket engine hot fire test at NASA’s Stennis Space Center