Welcome to the J-2X Blog!

Hello!  Welcome to the J-2X Blog. 

I would say that it’s a pretty safe bet that a large (very large) majority of the American population is unaware that we stand on the brink of testing the first new, large, human-rated liquid rocket developed in this country since Gerald Ford was President.  I might even venture to suggest that a majority of the diverse and busy population supporting NASA also don’t know that this is the case. 

Back then, during the Ford administration, the new engine was called the Space Shuttle Main Engine (SSME).  Its initial development at the conceptual level began in the late 1960’s.  The Space Shuttle itself wouldn’t fly until 1981, nearly six years after the first attempted engine test.  Today, the engine is called J-2X and this blog represents an attempt to inform those who want to follow the exciting progress of this development effort as we approach full engine testing in early 2011.

As the name suggests, the J-2X has its roots in the Apollo Program with the J-2 engine used for the second and third stages of the Saturn V rocket that first took humans to the moon.  In many ways, the original J-2 was the technological predecessor of the SSME.  The J-2X design is the beneficiary of over fifty years of rocket engine experience spanning the original J-2, the SSME, the experimental J-2S, and the RS-68 engine that today powers the Delta IV commercial rocket.

The J-2X is being developed by the NASA Marshall Space Flight Center in Huntsville, Alabama, the home of the propulsion systems for the Apollo Program and the Space Shuttle Program.  Our contracted partner in this development is Pratt & Whitney Rocketdyne located in Los Angeles, California.  Appropriately, Pratt & Whitney Rocketdyne, taking into account corporate name changes over the years, was the developer of the liquid rocket engines that powered the Apollo Program and still powers today the Space Shuttle Program.  Thus, we have assembled an experienced, formidable, and knowledgeable team for J-2X.

Your humble chronicler for this journey into the exciting final stages of J-2X development is William D. Greene.  I am currently the Upper Stage Engine Element Associate Manager.  The Upper Stage Engine Element is the NASA office responsible for J-2X engine design and development.  For the first three and a half years of this project, I was the Systems Engineering and Integration Manager for this office.  I have 22 years of experience, most of which has been in support of the NASA Marshall Space Flight Center and much of which has be dedicated to liquid rocket engine analysis, development, production, and testing.  I will be charting the progress of the J-2X development effort, introducing you to the extraordinary team responsible for this effort, and sharing what I know about both this activity as well as about rocket engines in general.

This is going to be fun!  C’mon along for the ride!  For more information about the J-2X project, see the link to the video starring some of the key people engaged in this historic effort.


NASA and Pratt & Whitney Rocketdyne managers discuss the design and
development of the J-2X engine.

29 thoughts on “Welcome to the J-2X Blog!”

  1. I think USA is making a big mistake and putting our country at risk for cutting are money from going to this program. Thanks Sam

  2. Hello William,

    I would love if you could help me with these questions:
    Why is it that the “gas mileage” of a rocket engine is measured in seconds? I would think thrust time seconds over mass of propellant would be a good indicator of “mileage”. What is it that this ISP in seconds capture which is not captured by my kg-thrust*s/kg-propellant measure?
    How much has technology improved rocket engine mileage since the Ford years? Cars went from 10 mpg to 30. Does the J2-X get three time as much mileage (ISP increased three-fold) over the old J2?
    If not, what are the difficulties with the existing technology? Shouldn’t NASA concentrate to designing a newer technology (back to cars: the hybrid traction chain could be replacing the old internal combustion engine) to substantially gain over what has been one so far?
    Thank you much.
    Patrick (from Paris, France).

  3. Looking forward to reading about this project, hope there will be lots of pictures/ videos available.

  4. Good luck! I remember reading about your testing at Marshall when I was at Space Camp back in the summers of ’08 and ’09. I hoped it would happen when I was there, so I could feel the ground shake, like people said happened at Marshall when they did the engine tests for Apollo. It didn’t work out that way, but I’ll still be rooting for you guys!

  5. Keep the faith. The J-2X plays an important role in our plans to get back to the moon and Mars. Long live CxP!

  6. Its about time americans take care of our own business,lets keep ame
    rica building. We need to stop giving jobs to other countries.By the way nice engine, keep it up nasa.

  7. Hello,
    I’m really interested in this topic. I was thinking that there was never going to be much progress on creating any new vehicles or systems to get out of earth orbit. But, I see that you and your team are moving forward with engine technology. I’ll bet that is very exciting and rewarding work! Please keep updating with new testing and developments!


  8. Thanks for providing us the opportunity to stay informed on progress of what I hope will ultimately take us out of low earth orbit.


  9. Hello,
    we’ve read the tecnical documentation on SSME and on their computer based controller available to the public (yeah).
    Could you please post some tecnical details to understand the innovations that are in the new motors?


  10. Wow, lots of comments. Thank you, everyone, for your interest. I will respond to some of these here. Some of these questions, however, deserve more thorough explanations in future articles.

    @ Patrick. I’d planned on an article in the near future dedicated to the topic of rocket engine performance calculations. The short answer, however, is that we somewhat cheat when we cite specific impulse in “seconds.” It is truly Isp = force / (mass/seconds). If you’re using pounds-force on the top and pounds-mass on the bottom, then you kinda, sorta get seconds. The “g” term then reappears within the context of the rocket equation. It’s really just a tradition/convention thing.

    @ Ski. The J-2X test campaign is currently planned to span over three years with ten different test articles. Future articles will explain more details about these plans.

    @ Ollleg. No, J-2X does not have an idle mode along the lines of what was proposed for J-2S.

    @ KaiYves. Probably what you had read about regarding testing at Marshall Space Flight Center over the past couple years were a series of component tests. If people are interested in that, I can go back and review that work in future articles. Lots of very good work has already been accomplished to get us where we are today.

    @ astrooman. J-2X was originally intended for the Ares vehicles within the Constellation Program. However, there is still likely a place for a high-thrust, upper-stage engine in the next proposed architecture for space exploration.

    @ “guest” regarding using J-2. That’s a valid question and one that I will address as a special-topic article in the future. Thank you for the posting idea.

  11. I am impressed that the new engine has reached this level of development. But with the current attitude of the US government, that war, is more important than exploration, I can’t see this machine ever being bolted to anything other than a test bed. Good on the engineers who have keep pushing on this. I know many people who have been inspired by watching the shuttles roar into the air or the sight of the space station zip across the sky. Perhaps it would help if NASA’s engineers dragged the Senate and Congress down to watch the next shuttle lunch.

  12. I wanted to thank you for this interesting post. I definitely loved every little bit of it especially the J-2X and SSME that made us readers fed with educational informations. I have you bookmarked your web site to look at the latest stuff you post…its always a pleasure to read your articles…Thank you!!!!

  13. Please!! Somebody rescue NASA from these completly illogical plans of going to an asteroid and Mars BEFORE going to back to the moon!

  14. Thank you, William, for taking the time and making the effort to chart the progress of the development of the J2X engine. It is very much appreciated.

    I, for one, will follow your blog with extreme interest.


  15. The recent Augustine Commission report on Human Space Flight recommended that NASA develop a technology roadmap to guide technology development. Does the recommended roadmap exist, and if so, is this rocket engine program an element of the roadmap?

  16. I just have to say “wow” my husband works at Pratt&Whitney, He is the one that built the model for the J-2X in Rapid Manufacturing, very excited about this site Thank You!

  17. Exciting to see the three work decks at Stennis and the yellow tubular thrust interface already in the stand.

    A mountain of hardware is on it’s way… can’t wait.

  18. Great summary of the engine and status report on the manufacture of the first development J-2X. It’s good that us retired folks can be kept up to date. Go J-2X team!

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