Spaceflight Insider

Aerojet Rocketdyne successfully conducts hot-fire test of SLS RS-25

Stennis Space Center RS-25 test Aerojet Rocketdyne photo credit Scott Johnson SpaceFlight Insider

Aerojet Rocketdyne and NASA conducted a test firing of an RS-25 rocket engine at the agency’s Stennis Space Center on Aug. 13, 2015. Photo Credit: Scott Johnson / SpaceFlight Insider

BAY ST. LOUIS, Miss. — On Thursday, Aug. 13, Aerojet Rocketdyne (Rocketdyne) and NASA successfully carried out a hot-fire test of one of the aerospace firm’s RS-25 engines at the space agency’s Stennis Space Center in south Mississippi. The RS-25, formerly known as the Space Shuttle Main Engine (SSME), powered 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).

During Thursday’s test, the RS-25 burned its cryogenic fuel of liquid hydrogen (LH2) and liquid oxygen (LOX) for approximately 535 seconds (expected flight duration) and generated some 1,859 kN (418,000 lbf) of thrust. The test 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.

Crowd begins to gather for RS-25 test

A crowd begins to gather for the RS-25 test. Photo Credit: Scott Johnson / SpaceFlight Insider

This latest test was the sixth, in a planned series of seven, which will be used to determine how the engines perform with higher pressure and lower temperature SLS fuel conditions.

The test series will also check out the design of a new controller that monitors the RS-25’s performance and serves as a relay between the engine and the launch vehicle while providing close-looped control of the engine by regulating thrust and fuel mixture ratio.

The RS-25 has a 1960s heritage, and its development began in the 1970s, but it’s undergone five major redesigns and is considered one of the most efficient engines ever produced.

The engine weighs in at approximately 7,700 pounds (3.49 metric tons) and is capable of delivering a specific impulse (/sp), at sea level, of 366 seconds (3.59 km/s). It’s also capable of throttling between 67 and 109 percent of its rated performance, and NASA / Rocketdyne officials are hopeful of increasing this capability to 111 percent after the first few SLS flights.

The RS-25 flew on the aft end of the Shuttle orbiters in clusters of three, but the SLS core stage will be powered by four.

Jim Paulsen, Rocketdyne’s vice president of Program Execution for Advanced Space and Launch, explained: “I’ve been with Rocketdyne 38 years. I worked on shuttle for most of my career, so this is very exciting to see that many of the [Shuttle] products move on and have a life after that.”

The SLS, as well as the Orion capsule being built to fly atop it, will allow the space agency to return crews beyond low-Earth orbit (LEO) for the first time since the early 1970s.

The first SLS mission, Exploration Mission One (EM-1), is scheduled to fly an uncrewed Orion around the Moon in 2018. After that, the agency has plans for an asteroid redirect mission (ARM) where astronauts will fly SLS / Orion to the vicinity of the Moon and rendezvous with a portion of an asteroid previously towed to lunar orbit by a robotic craft. And then, as the ultimate goal, NASA intends to send the first crews to Mars, aboard SLS / Orion, sometime in the 2030s.

August 13, 2015, RS-25 engine test at NASA's Stennis Space Center

August 13, 2015, RS-25 engine test at NASA’s Stennis Space Center. Photo Credit: NASA



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

My wife Karen and I were there. That test was one of the most awesome things I have ever seen. Congratulations, and thanks, to the SLS and RS-25 teams at SSC, MSFC, MAF and Aerojet Rocketdyne for their hospitality this past week. Go RS-25! Go SLS!

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