First SLS Flight Engine Roars to Life for Testing at Stennis Space Center

The first SLS flight engine roared to life for testing at Stennis Space Center on March 10, 2016. Intended for the first crewed SLS mission, EM-2, the engine last saw action powering the space shuttle Endeavor into orbit in 2011 on STS-134. Photo Credit: NASA
The first SLS flight engine roared to life for testing at Stennis Space Center on March 10, 2016. Intended for the first crewed SLS mission, EM-2, the engine last saw action powering Space Shuttle Endeavor into orbit in 2011 on STS-134. Photo Credit: NASA

The first of 14 former space shuttle main engines, now being repurposed to power NASA’s Space Launch System (SLS), roared to life at Stennis Space Center in southern Mississippi today. Under highly instrumented and controlled conditions, the most efficient rocket engine in history unleashed over a half-million pounds of thrust on the deep south during a 500-second full duration hot-fire test, marking the beginning of a new (second) series of test fires this year as engineers modify the engines to the new requirements for what will become the most powerful rocket in history.

“Every test is important, but there really is a different energy level associated with flight engines,” said Ronnie Rigney, RS-25 project manager at Stennis. “It’s hard to describe the feeling you get knowing you’re going to see that engine lift off into the sky one day soon. It’s a very exciting time for all of us here.”

RS-25 Engine Hot Fire Test on the A-1 test stand at Stennis. Photo: Aerojet Rocketdyne
RS-25 Engine Hot Fire Test on the A-1 test stand at Stennis. Photo: Aerojet Rocketdyne

The 500-second test fire, carried out by flight engine E-2059 on the historic A-1 test stand, went off without issue—something that has come to be expected of the RS-25 engine. The RS-25 was the first reusable rocket engine in history, as well as being one of the most tested large rocket engines ever made, having conducted more than 3,000 starts and over one million seconds (nearly 280 hours) of total ground test and flight firing time over the course of 30 years of NASA’s 135 space shuttle flights.

Aerojet Rocketdyne has 16 flight engines in inventory (14 former shuttle and 2 new), plus two more development test engines.

The engines proved their worth time and time again, but the RS-25 now requires several modifications to adapt to the new environment they will encounter with SLS and meet the giant 320-foot-tall rocket’s enormous thrust requirements.

Engine E-2059 last saw action on Space Shuttle Endeavor in 2011, mission STS-134, powering the baby of NASA’s shuttle fleet into orbit on its 25th and final flight.

After its test series it will fly one more time, on the second mission of the SLS, Exploration Mission 2 (EM-2), the first mission with crew onboard to go beyond low-Earth orbit in 50 years (by the time that mission flies, no sooner than 2021 and as late as 2023).

“This rocket will take humans farther and faster into the solar system than we have ever traveled and increase our capability of making exciting new discoveries by launching large astronomical observatories and other scientific missions,” said Eileen Drake, Aerojet Rocketdyne CEO and president. “Mission success is our driving factor, which is why testing each engine is critical to ensure the safety of the astronauts and cargo that will fly on SLS.”

Last year NASA and Aerojet carried out a series of seven test fires on a development engine, #0525, to provide engineers with critical data on the engine’s new state-of-the-art controller unit—the “brain” of the engine, which allows communication between the SLS and the engine itself, relaying commands to the engine and transmitting data back to the vehicle. The new controller also provides closed-loop management of the engine by regulating the thrust and fuel mixture ratio while monitoring the engine’s health and status, thanks to updated hardware and software configured to operate with the new SLS avionics architecture.

“We’ve made modifications to the RS-25 to meet SLS specifications and will analyze and test a variety of conditions during the hot fire series,” said Wofford. “The engines for SLS will encounter colder liquid oxygen temperatures than shuttle; greater inlet pressure due to the taller core stage liquid oxygen tank and higher vehicle acceleration; and more nozzle heating due to the four-engine configuration and their position in-plane with the SLS booster exhaust nozzles.”

For shuttle flights the engines pushed 491,000 pounds of thrust during launch—each—and shuttle required three to fly, but for SLS the power level was increased to 512,000 pounds of thrust per engine (more than 12 million horsepower). The SLS will require four to help launch the massive rocket and its payloads with a 70-metric-ton (77-ton) lift capacity that the initial SLS configuration promises.

“Not only does this test mark an important step towards proving our existing design for SLS’s first flight,” said Steve Wofford, engines manager at NASA’s Marshall Space Flight Center in Huntsville, Ala., where the SLS Program is managed for the agency. “But it’s also a great feeling that this engine that has carried so many astronauts into space before is being prepared to take astronauts to space once again on SLS’s first crewed flight.”

Rows of RS-25 Space Shuttle Main Engines at NASA Kennedy Space Center Space Shuttle Main Engine Processing Facility to ship to Stennis Space Center Photo Credit Alan Walters AmericaSpace
A row of Rocketdyne-built RS-25 Space Shuttle Main Engines just before being shipped to Stennis Space Center for use on the Space Launch System program. Photo Credit: Alan Walters /

With engine E-2059 having carried out its test, engineers at Stennis will swap it for another development engine and conduct at least a handful of test fires with that this summer, followed by test firings of two new engines to the inventory that have never flown (engines 2062 and 2063).

An all out test fire of the SLS core stage, with all four of its engines, will be conducted at Stennis in late 2017, prior to the inaugural EM-1 flight of SLS with Orion no earlier than late 2018.

Known as the “Ferrari of rocket engines,” the RS-25 can handle temperatures as low as minus 400 degrees (where the propellants enter the engine) and as high as 6,000 degrees as the exhaust exits the combustion chamber where the propellants are burned.

To put the power of the Aerojet Rocketdyne-built RS-25 engines into perspective, consider this:

  • The fuel turbine on the RS-25’s high-pressure fuel turbopump is so powerful that if it were spinning an electrical generator instead of a pump, it could power 11 locomotives; 1,315 Toyota Prius cars; 1,231,519 iPads; lighting for 430 Major League baseball stadiums; or 9,844 miles of residential street lights—all the street lights in Chicago, Los Angeles, or New York City.
  • Pressure within the RS-25 is equivalent to the pressure a submarine experiences three miles beneath the ocean.
  • The four RS-25 engines on the SLS launch vehicle gobble propellant at the rate of 1,500 gallons per second. That’s enough to drain an average family-sized swimming pool in 60 seconds.
  • If the RS-25 were generating electricity instead of propelling rockets, it could provide twice the power needed to move all 10 existing Nimitz-class aircraft carriers at 30 knots.

“There is nothing in the world that compares to this engine,” said Jim Paulsen, vice president, Program Execution, Advanced Space & Launch Programs at Aerojet Rocketdyne. “It is great that we are able to adapt this advanced engine for what will be the world’s most powerful rocket to usher in a new space age.”

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Missions » SLS »


  1. “‘There is nothing in the world that compares to this engine,’ said Jim Paulsen, vice president, Program Execution, Advanced Space & Launch Programs at Aerojet Rocketdyne.”

    We have long had the magnificent RS-25 and other useful rocket engines, as well as the solid rocket motors, that are quite capable of helping us build permanent resource extraction colonies on the Moon and use those Lunar resources to economically develop the other regions of cislunar space.

    “Mike Griffin. ‘Our space policy is bankrupt.'”

    “Eileen Collins. Program cancellations ‘made by bureaucracies, behind closed doors, without input by the people, are divisive, damaging, cowardly, and many times more expensive in the long run.'”

    “Policy leaders are asking astronauts to risk their lives on space journeys and it is our experience that testing in similar environments, like the moon, will minimize risk.”

    From: ‘Witnesses Support Goal of NASA Restructuring Legislation, But Not Specifics’ By Marcia S. Smith 29-Feb-2016 At:

    What we have lacked is a consistent national leadership that understands the many real reasons why cislunar space, including the Lunar surface, is important.

  2. So they are going to employ a reuseable engine once and then discard it? What a waste. Typical government thinking.

    • They already have the these engines. Why wouldn’t they use them before building more?

      It isn’t like NASA is planning on making a reusable launcher (like the space shuttle) to use them on…

        • The new engines are intended to be expendable and as such are being designed to be less expensive to manufacture and more reliable (elimination of quick disconnects, etc.).

          They are also looking at use of additive manufacturing (3D Printing) for some components.

          • What is the status on additive mfg and RS-25? I heard it was pushed out of RS-25E; quick disconnects seems like low hanging fruit. Just concerned that NASA has been talking up 3D printing for a while but could be a bait and switch in the end. I know work is being done on the research side down in Huntsville but production?

            • Believe (per the above discussion) the engines we are talking about are “standard” RS-25’s built for the NSTS program and left over. Therefore (rather than “waste” them) they are to be used in the early SLS flights.

              Mark seems to have assumed that when they were used more “reusable” engines would be built. In fact they are working (as I said) on an expendable version of the RS-25 intended to be less expensive and more reliable.

              “I heard t was pushed out of RS-25E”.

              Do not know for sure, quite a bit of work was underway the last time I heard. If 3D manufacturing were not used in the early RS-25E’s it would likely be due to technical delays and should not preclude later implementation. Not sure why it would be assumed to be a “bait and switch” which usually means a con job passing off one product for another. Unless of course you are accusing someone of potential criminal activity. If you are please be specific and provide evidence of same.

              • Well in English parlance “bait and switch” can be used more broadly than the strict illegality of not having the advertised merchandise in stock purposely and trying to up sell.


                If Stanford can extend the concept to foreign policy I can extend it to Space policy; clearly not talking criminality. Simply that the most exciting part of RS-25E was the prospect of 3D printed injector elements. Years of NASA PA talking about lowering cost and increasing reliability via 3D printing. I know a lot of work had been done at Marshall. Then the 800M dollar contract drops and the first thing to go is 3D printed parts (or deferred…with no target date). Back in the day it could be said, well the tech just isn’t ready. That may be true but harder to swollen knowing Blue has been doing this on a similar scale engine in BE-4 and SpaceX is doing this for Raptor testing as Stennis, albeit currently at sub-scale. It’s just depressing; I hope they can get it back on track.

                • Clio,

                  You can use whatever inappropriate/prejudicial words and phrases you want (just do not expect no one to notice), it will not make them truly descriptive.

                  Do not really care what SpaceX says they are doing with the Raptor (SpaceX says a lot of things), but am interested in the BE-4. It should be noted, however, that the BE-4 is not yet to the production phase. I wish Blue Origin luck, just as I do the SLS Team.

                  Have a nice weekend.

      • When reusable 1st stages are proven to be an ECONOMICAL and RISK REDUCING feature, then the SLS’s core with the four valuable RS-25s could be MODIFIED to be reusable.

        Also, note that the CASINGS for the Space Shuttle’s powerful SRBs were reused. Reusable boosters for the SLS could also become an OPTION.

        • I’m sure that will entertain a similar success as the Falcon 9 bargeings. You spacedx fans are wierd.

          • “Mark
            March 11, 2016 at 8:10 am · Reply

            Looks lke reples cannot contan the letter ‘I’ n lower case.”

            Yep! Use CAPITAL letters on words WITH an I.

            March 11, 2016 at 7:48 pm
            ‘You spacedx fans are werd.'”

            I’M not a SpaceX or Facon 9 fan.

            Mr. Musk’s ‘GRABBING onto’ a monopoly control of Launchpad 39A that’s needed for “Dual SLS” and “SLS Launch on Need” MISSIONS appears to be SIMPLY another IGNORANT and POLITICAL attempt to ‘stab IN the back’ the SLS and ITS HIGHLY EFFICIENT and RELIABLE RS-25.

            By SpaceX and ITS BILIONAIRE owners ‘GRABBING onto’ and MONOPOLIZING the taxpayer PAID for, extremely useful, huge, and HISTORIC Launchpad 39A, Mr. Musk, HIS SpaceX owning FRIENDS, and the PRESIDENT have apparently done THEIR INFANTILE best to damage NASA and the SLS and RS-25, WHILE also TRYING to INCREASE both the costs and RISKS for the future human Lunar MISSIONS that NASA IS REQUIRED by law to do.


            Of course, we now understand that our laws are not really relevant for the PRESIDENT or HIS ‘wonderful’ BILIONAIRE POLITICAL FRIENDS that own SpaceX and CONTINUALLY DIP THEIR hands deep INTO the pockets of the AMERICAN taxpayers.

            I am a LONG-TIME RS-25 and SLS fan and strongly APPRECIATE THEIR COMBINED CAPABILITIES to enable NASA’S legally REQUIRED future Lunar MISSIONS.

            • So you’re going to crash sls into a carrier like your hero is showing you with barges? It’s ok to copy the people you worship, just don’t expect us to applaud you crony campaign contributing exsample, The carriers don’t need your damage

              • Make the SLS fully reusable and we would decrease the SLS’s LEO payload by about half. That’s not useful or wise.

                I would rather strongly suggest that we should just follow PUBLIC LAW 111–267 (the “NATIONAL AERONAUTICS AND SPACE ADMINISTRATION AUTHORIZATION ACT OF 2010.} and use all of the SLS’s expected payload to get humans to the Lunar surface and back to Earth.

                NASA has already had decades of harsh reusable LEO launcher test exposure through launches of the reusable Space Shuttles.

                Leave the agenda of reusable launcher tests for other folks to pursue.

                NASA’s legal ORION/SLS goal, one that Congress has repeatedly supported and funded, can be seen from Earth. Yep, the Moon’s where ORION and SLS are legally headed to.

                And after January 2017, I would tell ‘poor SpaceX the squatter’ to pronto vacate SLS’s Launchpad 39A.

          • And you Dinospace fanboys can’t help yourselves with the insults. It’s all you lot have left these days. Musk is changing the space industry for the better, thank God!

            And get a new keyboard!

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        • Even If falcon 9 1st stages are proven to be economIcal to reuse, It may not be sImple to modlfy the SLS booster.

          And lt also doesn’t prove the SLS booster would be economIcal to reuse. If spacex is to be believed, they put a slgnlflcant amount of effort lnto making the falcon 9 1st stage reusable from the start.

          • “If spacex s to be beleved, they put a slgnlflcant amount of effort into making the falcon 9 1st stage reusable from the start.”

            That is a big if, otherwise they would have put some effort into making the Merlin engine have more of a throttling capability.

            For what it is worth, I doubt trying to use the complete SLS first stage would be economical. The evaluations of the Side Mount configuration SDHLV (SLS Block I is essentially an in-line variant) did look into recovering the engine pod down range by parachute (similar to what ULA is considering for their new Vulcan booster) but even that would have required a launch rate in excess of 8 – 10 flights/year to conceivably be economically practical.

            • I was simply making the assertion that just because one rocket’s 1st stage can be economically landed/reused, doesn’t mean that it would be economical to modify an existing (and very different) rocket’s 1st stage to add that capability.

              “That’s a big if” I agree. They could have made landing much easier if the merlins had a better throttling capability. I believe they initially intended to recover using parachutes (thus rendering lower throttling capability moot). If so, it may have been (and/or may still be) cost prohibitive to re-design with the lower throttling capability. Also, adding that capability may make the engines heavier, which would hurt that T/W ratio their so proud of…

              • Agreed.

                Am actually familiar with an early presentation of SpaceX Falcon 9 plans. At that time they were talking about down range/parachute recovery of the first stage not for reuse but for examination in hopes of learning things to make the stage more reliable/cheaper to manufacture. Seemed like a good idea.

                Per Jim Hillhouse’s history that later morphed into down range/parachute recovery for reuse. Then when that did not work out (for whatever reason) they changed to powered landing.

                The whole thing has the feel of a program where they began trying to build a “work horse” expendable rocket and then step by step changed it in to an attempted reusable vehicle.

                Trouble is they may have very well taken their “work horse” and turned it into a “show horse”, capable of occasionally performing an impressive trick but not doing it reliably.

                • Indeed. Time will tell if the newest version of the Falcon 9 ever launches on time and without failures…

                  The cold LOX, the on-time part doesn’t seem likely at this point.

            • wrt 8-10 flights a year for the SLS,

              (note idle musings ahead)

              For all that I’m not overly enthusiastic about the SLS, if it were to fly 8 – 10 times a year that would be fantastic. With that much payload to orbit, we could get some real science/exploration done.

              (end idle musings)

              You seem knowledgeable about the SLS. What are your thoughts about the following:
              My biggest issues with the SLS come from a couple issues
              1) It costs ALOT of money to build and (will cost a lot) to launch.
              -That money could go to funding actual missions on our current launchers (Delta IV Heavy launches may be expensive, but their cheap comparied to developing the SLS)
              -The smaller payload capacity of the Delta IV Heavy/Atlas compared to the SLS would mean that more on-orbit assembly/fueling would be required but again the SLS is REALLY expensive…

              2) The SLS was required to use certain shuttle components.
              -The only issue here is that it limits the flexibility in design and thus may produce a sub-optimal design. If shuttle components were the best option they should be selected through design studies, not mandated for political reasons.

              And the biggest issue from my point of view:
              3) Even when the SLS is flying, it isn’t supposed to fly often (due to cost) and the missions NASA is looking at seem useless.
              -ARM to get a little rock and send astronauts to it. Why are astronauts involved? Just so we can say “look we sent astronauts to an asteroid first!”
              -Mars missions 20+ years in the future. Why are we even pretending these will happen like we say, it seems entirely implausible that NASAs goals would stay the same long enough for these to happen. Also, We are going to spend billions of dollars to send some astronauts to mars to get some samples and plant a flag?!?

              -With just a few launches of a rocket like the SLS we can finally get started on having a permanent cis-lunar presence. Why don’t we talk about that. It’s achievable in the near future, it wouldn’t cost as much as Mars missions, and it could actually provide lasting benefits if we set up a Lunar ISRU process. Even if we are only extracting oxygen or water (if enough is present) or for that matter just rock/dust for shielding.
              -The proposed missions don’t seem to make much sense to me.


              • Just a bit of background:

                (1) I am a payload and operations guy, not propulsion.
                (2) I have never been involved in SLS development and have no inside information.
                (3) In past jobs as was involved with Shuttle Operations and Constellation Systems hardware development. It was in those positions that I worked with the Propulsion Folks who taught me what I know.

                They were specifically involved with development of the Side Mount configuration SDHLV. Anything I say is based on what I know about that configuration and is extrapolated to the SLS (I think this is fair as the SLS is essentially an In-Line version of the Side Mount).

                Based on that I will note a few things as to your questions/statements:

                (1) It does not automatically cost “ALOT” of money to build and operate an SDHLV. Just as an example the budget estimates for the Side Mount’s use would have allowed for simultaneously developing the Orion and Lunar Lander as well as the lunar robotic precursor missions originally intended to help select a site for a Lunar Outpost. Before it was passed over for the Ares I/Ares V the target date for the first Human Lunar Return was 2015 (that’s correct last year).
                (2) The SLS flight rate limit and it’s cost of operation are interrelated. Like any other transportation system it has a fixed cost and a per flight cost. As an example prior to the Colombia accident the total yearly cost of shuttle operations was about $3B/year. The vast majority of that cost was fixed the actual cost/flight was lost in rounding error. We used to get a kick out of newspaper stories that one year would say the shuttle cost/flight was $750M (if it flew 4 times) and $500M (if it flew 6 times). They were simply dividing the reported total cost/number of flights in any particular year. Interestingly any time the cost/flight “went up” it would be reported that the shuttle cost were going up, but when the cost/flight “went down” the program was never given credit for saving money.
                (3) The limit to 2 flights/year for SLS is real but imposed. For some reason (best known to the Administration’s Office of Science and Technology Policy) they replaced the still functional manufacturing equipment (at considerable expense) with new equipment less capable than that it replaced. They also gave away one of the 2 launch pads (and then told Congress they could not support a dual launch scenario because they only have one launch pad).
                (4) As far as ARM and Mars Mission, they do not make any sense to me either. I am in favor of a Human Lunar Return.

  3. Deep Space Rocket? More like a Deep Ocean Rocket. Such a waste to throw these motors away. No wait. Why not burn and turn em? Better than wasting away in a museum.

  4. I see the SLS bashers are at their old tricks again.

    I don’t know of very many engines not thrown away.

    • Yep!

      Even the BILLIONAIRES that own SpaceX have had the tendency to throw away rocket ENGINES.

      Maybe sometimes THROWING away rocket ENGINES ISN’T a completely bad IDEA.

  5. Such a monumental waste. The only part of SLS being recovered is the Orion capsule, everything else is being chucked into the sea. It would seem NASA could do with some help from SpaceX on how to run a competent space program.

    • Nice spin. But Zimmerman is as hostile to the SLS as you (and about as straight forward).

      The article headline reads (note the question mark):

      Second SLS flight delayed until 2023?

      If you go to the link of the source article, the possible delay is caused by a congressional mandate to use the SLS to launch the Europa Clipper Probe (and the attendant upper stage work, not anything to do with the core SLS Block I). Fair enough (whether it is a good decision or not) if that is what congress and the president decide.

      In the meantime the first launch of the Falcon Heavy (with no congressional interference) has been delayed from 2014, to 2015, to April 2016, to September 2016, to no earlier than November 2016 (2017 anyone?).

      So what is your point?

    • On a subject unrelated to the RS-25 Engines (or any of their variants)which is the subject of the article and the other comments.

    • …uh, did I miss something because I totally dig Polysics!Otherwise I can relate with this review… I’ve had couple of friends think its not that great but I similarly felt that this was the step in the right direction.

    • Do you think the bulk of the media is unbiased? Most claims of media bias come from an analysis of what stories get run, the tone, the types of words used, etc. Subjectivity must be accounted for, but the concern is that the MSM is sculpting public opinion deliberately, not giving us data from which we can make our own decisions.Do not invoke Fox. I want to know how you account for the bias found within CNN, ABC, NBC, CBS, MSNBC, HuffPo, WashPo, NYT . . . you know, 85% of the media?Reply

  6. JOE WROTE: “In the meantme the frst launch of the Falcon Heavy (wth no congressonal nterference) has been delayed from 2014, to 2015, to Aprl 2016, to September 2016, to no earler than November 2016 (2017 anyone?).”


    • Exactly the same amount as a potential future delay (which has not happened) in the second SLS flight has cost.

    • Not nearly as much as the F-35. Christ, if the military was under the same scrutiny you’re putting the space program under, you’d have a heart attack a day.

  7. You twerps would bitch about anything. Maybe you should vote for congressmen that actually support the space program instead of more conservative fops that only care about cutting taxes.

  8. “To put the power of the Aerojet Rocketdyne-built RS-25 engines into perspective, consider this:

    •The fuel turbine on the RS-25’s high-pressure fuel turbopump is so powerful that if it were spinning an electrical generator instead of a pump, it could power 11 locomotives; 1,315 Toyota Prius cars; 1,231,519 iPads; lighting for 430 Major League baseball stadiums; or 9,844 miles of residential street lights—all the street lights in Chicago, Los Angeles, or New York City.”

    Does anyone know what does one of these Bad Boys Cost?…And how do we make it cheaper?

    • I’ve read north of 60M apiece at the slooow production rate of 3/4 an engine a year toward the end of shuttle era. Should be easy to beat that just by marginally increases the production rate but we’ll see what the “poor pride” can do.

  9. Look at it this way.

    Launch SLS minus a payload to have something like ATLAS SCORE–stage and a half style.
    Move the core to CERES–fill hydrogen and LOX from the Brines.

    Launch SLS from CERES–with huge amount of material to earth.

    The SLS core block is now a tug.

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