J-2X Progress: Shaking up the Night

The first rocket engine test that I ever saw in person at the NASA Stennis Space Center in southern Mississippi occurred well over twenty years ago.  I’d already been doing test data analysis and power balance analysis in support of the Space Shuttle Main Engine (SSME) Project for some months.  I had made several data review presentations in front of then chief engineer (and rocket engine legend) Otto Goetz.  I could quote engine facts, statistics, and tell you all about how the SSME worked.  I’d even seen some videos of engine tests.  But it was not until I saw a test in person that I achieved the state that can only be described as awestruck.

WVBIt was late in the evening and a little chilly.  Though we’d arrived at the control center before dusk, test preparations had dragged on so that now darkness had enveloped the center.  The test stand stood out against the blackened sky like a battleship docked in the distance.  Brian, my team lead at the time with whom I’d driven down from Huntsville, and I were standing outside in the control room in the parking lot.  The radiation from the hydrogen flair stack off to our left warmed one side of our face as the breeze cooled the opposite cheek.  The wailing of the final warning sirens drifted off and all that could be heard was the burning torch of the flair stack and, in the distance, the low surging and gushing of water being pumped into the flame bucket.  We were a just a couple of hundred yards from the stand.

Then, the engine started.

Picture1First, there is the flash and then, quickly, the wave of noise swallows you where you stand.  Unless you are there, you cannot appreciate the volume of the sound.  It is not mechanical exactly.  It is certainly not musical.  It is not a howl or a screech.  It is, rather, a rumble through your chest and a shattering roar and rattle through your head.  You think instinctively to yourself that something this primal, this terrible must be tearing the night asunder; it surely must be destructive, like a savage crack of thunder that continues on and on without yielding.  You are deafened to everything else, deprived of hearing because of all that you hear.  Yet before your eyes there is the small yet piercing brightness of the engine nozzle exit that can just be seen on what you know to be deck 5 of the stand and, to the right, there are flashes of orange flame stabbing into the billowing exhaust clouds mounting to ten stories high, tinged rusty in the fluctuating shadows.  It is like a bomb exploding continuously for eight minutes and yet the amazing thing, in incongruent fact so difficult to grasp as you are trying to absorb and appreciate the sensation is that the whole event is controlled and contained.  You cannot believe that so much raw power can be expressed by what is only a distant dot within your field of vision.

This is an experience that I wish everyone could have.  There are so many extraordinary feats of engineering all around us that we can appreciate and admire, but nothing for me has ever been as visceral as seeing an engine test, especially at night, with the nozzle open to the night air (and not buried in a diffuser).  No engine schematic or listing of characteristics or series of still pictures is an adequate substitute for the majesty of that controlled power.

Since that first test, I’ve seen any number of other engine tests including SSME (what we now call RS-25), a couple of other, smaller engines, and, of course, J-2X.  But it was not until the end of June of this year that I again had the opportunity to see a nighttime test on NASA SSC test stand A1.  This was J-2X E10002.  Below is the video, and it’s really cool, but I wish that you could have been there, standing beside me in the parking lot.  Listen carefully to the end of the recording and you’ll hear people cheering.  I was amongst the appreciative, awestruck chorus.




5 thoughts on “J-2X Progress: Shaking up the Night”

  1. Thankyou very much – a very impressive description! The loudest I ever heard was the Harrier jump jet some 200m distant at the historic event when the British Royal Airforce finally left Gatow in West Berlin in 1994. It stood there some 10m above the tarmac on its two tremendous pillars of hot air and its engines made a real hell of a noise… I guess compared to the J2X it was more a kind of a whisper after all! I wish you guys full success – a lot of people all over the world watch with delight as all this wonderful machinery is being developed which will bring us eventually to Mars and beyond! All yours: Mike

  2. Very impressive work. I’m wondering if someone will design a rocket engine so as to take maximum advantage of manufacturing cost savings by using 3-D manufacturing machines to fabricate most of the parts. That might cut costs a lot, and those machines working 24/7, could crank them out like cookies. It would seem that it would be worth sacrificing some engine efficiency, if the cost of the engine could be significantly reduced by using as much automation as possible using existing commercial manufacturing machines. I suspect that is Mr. Musk’s approach.

  3. It’s a long time since I did physics, so I thank you for simple way you explain the hard bits. But a question (probably silly): Hydrogen-Oxygen engines have a higher impule, but lower thrust than the equivalent kerosene-oxygen engines due to the mass difference being shot out the nozzle. Is there any major reason (physically or mechanically) that you couldn’t boost initial thrust of a hydrogen-oxygen engine by injecting 10% kerosene for the first ten to thirty seconds? Much the same as some low-power turboprop engines used to inject water for additional turbine throughput during takeoff. I accept that it would complicate the plumbing, pumps etc, but I would have thought the additional raw thrust for the first thirty seconds of flight would allow a larger total payload. Russell

    1. Sorry for not responding more quickly. I’m still getting used to this new blog environment. Back in the older system, I used to get notifications when people posted replies and comments, but now I have to go out and check. I didn’t realize that until just recently.

      @Michael Butler: Wow, what you describe is a cool memory, historic happenings. What’s so impressive to me is that I know how big the engine is. I’ve stood next to it while it is being assembled. I’ve had my hand on piece parts in the factory. It’s not as if the thing is the size of Godzilla. It’s kind of like on the size of my little Ford Fiesta and yet, KA-POW, it kicks out so much power that it truly rattles the night. The proportions just don’t see to fit and yet, there it is, filling the sky with a new cloud.

      @Slidell Bill: We are doing exactly that exactly now. We have a whole bunch of activity going into the development of advanced manufacturing techniques including several different versions of “3-D printing” in metals. The J-2X that was tested in the video actually has one piece that was made with this manufacturing technique. We want to do more. A lot more. But the technology is still being developed. There are all kinds of issues that have to be overcome before you start cranking out the cookies, but we’re on top of it. For example, what are the material properties for these new pieces? Are they like wrought parts or like cast parts? Do we need some kind of in-situ process check or must we depend on traditional inspection techniques? How will piece part designs change with these new methods?

      In short, there is lots of work to do, but we are already off running as quickly as possible so as to have a positive impact for the SLS Program.

      @Russell N: Kerosene has the advantage of being far, far more dense than hydrogen. I’ve always said that the day that somebody invents 50 lbm/ft3 hydrogen is the day that launching to space just got easy. However, if you can live with the volume issues, there is no reason that you cannot build a behemoth LH2/LO2 engine. Google “M-1 rocket engine” and be amazed.

      With regards to your idea, one of the problems in dealing with liquid hydrogen is that it freezes everything that you can imagine except for helium. We can’t purge the fuel system of the engine with nitrogen just because conduction through the metal of the main fuel valve will result in nitrogen ice being formed on the other side. So, flushing the system through with something like kerosene would just leave lots of residual stuff for the hydrogen to freeze. Ice crystals cause clogging and clogging causes passages to not be properly cooled or maldistribution of propellant across the faceplate or, if really bad, chunks falling into spinning turbine blades. These are all bad scenarios.

      However, with all that being said, back in the 1990’s there were some thoughts given to tri-propellant engines. Typically these were LO2/LH2/CH4 (methane). If you could make one engine with more oomph off the ground and then transition to more efficiency at altitude, then you’ve got a very useful machine. I saw a number of schematics, and I think that the Russians played with one example, but it never seemed to take off completely.

      One very interesting idea that I heard of years ago was the notion of floating small crystals of methane (or propane) in the LH2. While this would chemically suppress the efficiency overall, it would effectively increase the fuel density.

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