Spaceflight Insider

RS-25 engine testing completed at NASA’s Stennis Space Center

RS-25 test-fire at SSC on 2015-08-27.

The RS-25 engine fires up for a 535-second test on Aug. 27, 2015, at NASA’s Stennis Space Center near Bay St. Louis, Mississippi. (Click to enlarge.) Photo Credit: NASA

This past Thursday, Aug. 27, Aerojet Rocketdyne and NASA successfully carried out another RS-25 hot-fire engine test at the space agency’s John C. Stennis Space Center in south Mississippi.

The RS-25, formerly known as the Space Shuttle Main Engine (SSME), helped power the Shuttle to orbit for 30 years and is now being upgraded and tested for use on the agency’s new Space Launch System (SLS).

RS-25 rocket engines at Kennedy Space Center in Florida. Photo Credit: Jason Rhian SpaceFlight Insider

Aerojet Rocketdyne’s RS-25 engines at NASA’s Kennedy Space Center in Florida. (Click to enlarge.) Photo Credit: Jason Rhian / SpaceFlight Insider

During Thursday’s test, RS-25 Engine No. 0525 (an unflown developmental engine) burned its liquid hydrogen (LH2) and liquid oxygen (LOX) for approximately 535 seconds (the expected flight duration) and generated some 1,859 kN (418,000 lbf) of thrust. The test, once again, took place at Stennis’ A-1 test stand, which was originally built to test the Saturn V second (S-II) stage and its five J-2 engines.

This latest test was the last in a planned series of seven that were used to assess engine performance with a new (J-2X derived) controller, and also under the colder LOX temperatures, higher LOX inlet pressure, and greater nozzle heating conditions expected with the SLS.

The first test took place on Jan. 9 and was the first hot-fire test of an RS-25 since 2009. During this test, Engine 0525 fired for approximately 500 seconds and provided engineers with critical data relating to the performance of the new controller and the higher inlet pressure.

After the initial test, there was a pause to allow for scheduled upgrades to the high-pressure water system that provides the thousands of gallons of water needed to cool the test stands during engine firings.

Following the water system upgrades, the second test of Engine 0525 took place on May 28 with a firing of 450 seconds which further evaluated the new controller to assure that the engine and the controller were in sync and that the engine could deliver the performance required for the SLS.

The testing then continued on June 11, with the third test of Engine 0525.

SpaceFlight Insider speaks with Aerojet Rocketdyne's Jim Paulsen. Photo Credit: Aerojet Rocketdyne

SpaceFlight Insider speaks with Rocketdyne’s Jim Paulsen prior to the Aug. 13 test. Photo Credit: Aerojet Rocketdyne

By all accounts, this test went as planned and Steve Wofford, manager of the SLS Liquid Engines Office at NASA’s Marshall Space Flight Center (MSFC) in Huntsville, Alabama, explained that “[w]hile we are using proven space shuttle hardware with these engines, SLS will have different performance requirements. That’s why we are testing them again. This is a whole new ballgame – we need way more power for these engines to be able to go farther than ever before when it comes to human exploration. And we believe the modifications we’ve made to these engines can do just that.”

The fourth test of Engine 0525 took place on June 25 and was the longest test firing yet of an SLS RS-25 engine – some 650 seconds. This test expanded on the performance objectives of the prior firings – allowing engineers to thoroughly analyze the engine under a range of operating conditions.

Next, on July 17, the fifth test of Engine 0525 took place with a 535-second firing where operators ran the engine through a series of power levels, including a period of firing at 109 percent of the engine’s rated power. During this test, data was collected on the performance of the engine under various conditions, along with data on the performance of the new controller.

The sixth test of Engine 0525 took place on Aug. 13 with another 535-second firing that continued to collect performance data in furtherance of the qualification of the new controller and to put the upgraded SSME through the rigorous temperature and pressure conditions it’s expected to experience during the SLS flight.

According to NASA, more than 1,200 people, including elected officials, community leaders, media (including SpaceFlight Insider), social media, NASA employees, contractor employees, and employee family members witnessed the Aug. 13 test.

SLS RS-25 flight engine mission assignments. Photo Credit: Aerojet Rocketdyne

SLS RS-25 flight engine mission assignments. Photo Credit: Aerojet Rocketdyne

Lastly, as detailed above, the seventh test of Engine 0525 took place on Thursday, Aug. 27 – signaling the completion of the first developmental test series on the engine that’s expected to power the SLS on crewed missions deeper into space than ever before.

Wofford explained: “The completion of this test series is an important step in getting SLS ready for the journey to Mars.”

“What a great time to be at Stennis,” Center Director Rick Gilbrech stated. “When it comes to powering the future of the deep space exploration program for this country, this is the front lines, where we enable those missions to fly.”

The next round of RS-25 testing at Stennis is scheduled to begin in the next few months, with the firing of Engine 2059 – currently planned for flight on Exploration Mission 2 (EM-2), the first crewed flight of the SLS in 2021.


Scott earned both a Bachelor's Degree in public administration, and a law degree, from Samford University in Birmingham, Alabama. He currently practices law in the Birmingham suburb of Homewood. Scott first remembers visiting Marshall Space Flight Center in 1978 to get an up-close look at the first orbiter, Enterprise, which had been transported to Huntsville for dynamic testing. More recently, in 2006, he participated in an effort at the United States Space and Rocket Center (USSRC) to restore the long-neglected Skylab 1-G Trainer. This led to a volunteer position, with the USSRC curator, where he worked for several years maintaining exhibits and archival material, including flown space hardware. Scott attended the STS - 110, 116 and 135 shuttle launches, along with Ares I-X, Atlas V MSL and Delta IV NROL-15 launches. More recently, he covered the Atlas V SBIRS GEO-2 and MAVEN launches, along with the Antares ORB-1, SpaceX CRS-3, and Orion EFT-1 launches.

Reader Comments

So, how long until NASA exhausts its supply of ex-SSMEs turned RS-25? How is the progress going on creating an expendable replacement for the RS-25? How much is that costing?

Hi Jeff,
Per Aerojet Rocktdyne:

1) 4 missions can be accomplished with our inventory of 16 engines. Graphic of configuration here:
2) NASA is looking into restarting production of the RS-25 engines to support future missions.
3) You’ll have to get $$ from NASA. Contract not awarded yet.

Sincerely, Jason Rhian – Editor, SpaceFlight Insider

Building the RS-25 in the same way that the SSMEs were built will be terribly expensive. So, I take it the “expendable” RS-25 NASA had talked about in the past isn’t being funded either?

Hi Jeff,
Per what Aerojet Rocketdyne has said, I’d imagine that contract hasn’t been issued/awarded.
Jason Rhian – Editor, SpaceFlight Insider

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