J-2X Progress: Pardon Me

I’ve lived in the South for about 20 years now.  Over that time, I’ve heard and learned all kinds of quirks of regional dialect and colloquial sayings.  I’m quite sure that I’ve even picked up a few myself.  Oh well.  One particular expression shared with me by a former training partner in the gym was a compliment.  She told me that I had good “home training.”  That is a shorthand way of saying that my parents taught me to have good manner. 

With that in mind, and in consideration of what we’ve been calling the first hot-fire test of J-2X development engine E10001 (i.e., the “burp test”), I respectfully and bashfully declare:


 

In the early evening of Thursday, 14 July, E10001 generated a burst of ignition and thrust with something like a 30,000 pounds of force — enough to toss five or six crew-cab pickup trucks into the air.  That’s one heck of a burp.  Yep, we were successful.  NASA Stennis Space Center in Mississippi, coordinating with the Upper Stage Engine office at the NASA Marshall Space Flight Center and with Pratt & Whitney Rocketdyne in Los Angeles, California conducted a full-duration, 1.9-second test.  Here is a picture of what a burp that big looks like:

 


 

Here are a couple of pictures of the engine prior to the test.  These are taken from a deck inside the test stand basically looking down on the engine.  The nozzle extends through the deck to the next level below.

 



 

You’ll note that there’s some misty fog hanging around the engine in those pictures.  While it is true that most of the time you can almost see the thickly humid air of southern Mississippi in July, this is something different.  This fog is being created by the presence of cryogenic propellants in the lines.  These lines are so cold that they effectively condense water in the air around them, even at a distance, to create a fog.  Here are some close-up frosty pics of lines chilled down prior to test:

 

 

Out of one end comes smoke and fire while the other end is frosty cold.  This is a good illustration of the broad span of environments that exist within a rocket engine.

So, what’s next?

As exciting at this brief test was, what we didn’t do is light the gas generator and get the turbomachinery up to full speed.  That’s the goal for the next test.  In addition to spinning up the turbopumps with helium and lighting the propellants in the main chamber, as we did for the burp test, we’ll take the next step in the start sequence and light off the propellants in the gas generator.  This will provide the turbopumps with the power necessary to reach mainstage, steady-state operation.  And that — those initial few seconds of mainstage —  will be our first glimpse at genuine engine operation like that which will propel spacecrafts into orbit and then outwards across our solar system.

3 thoughts on “J-2X Progress: Pardon Me”

  1. I really like your blog. Very informative. I’ve a question about your big burping engine: Why is it mounted in the stand at an angle like that?

    BTW, Congratulations to all involved!

  2. @ Aaron: You’re darn tootin’ that there was clapping and hooting and hollerin’.

    @ Mark: Excellent question! I am going to give you two answers. The first one is false, but it sounds so good that it is often told to young, impressionable engineers like I was twenty-some years ago. The second story is the truth.

    Once upon a time, test stands A-1 and A-2 were built to test the S-II stage as part of the Apollo Program. Then, in preparation for the Shuttle Program, they were both converted into single-engine test stands. So far, this is all true.

    Now, the false part. In order to better simulate the position of the engines when installed on the Shuttle orbiter, the entire thrust structure of A-2 was canted. Thus, on A-2 you get to test in a position that looks much more like real life on the vehicle. This is what I was told and what I believed for years and it sounds really neato. It’s just a shame that it’s bunk

    Here is the truth. The SSME has the extraordinary functionality of being able to throttle to any power level between approximately 70% and 110%. This capability is used on Shuttle to limit the loads to which the orbiter and the crew are exposed during the mission. Another fact about the SSME is that it uses a very high expansion ratio nozzle in order to maximize engine performance (specific impulse, i.e., gas mileage analog). If you attempt to throttle down the power level of a high-expansion-ratio rocket engine at sea-level atmospheric pressure, you will eventually reach a point where the exit flow separates from the wall of the nozzle (fluid dynamics phenomenon). Severely separated flow in a nozzle is erratic, unstable, and can impose tremendous lateral forces on the nozzle, so much so that they can literally rip the thing apart.

    So, you have this necessary capability that you will need to test, but if you try to test it at normal conditions it’ll destroy the engine. What do you do? Well, what they did is they added a passive diffuser onto the test stand. This is basically a long tube that, when the rocket is running, self-pumps down to lower pressure levels thereby avoiding flow separation at lower throttle levels. Ta-da! And, in order to fit the diffuser into the stand without totally redoing the thrust bucket area, they had to cant the whole thing.

    And that’s why test stand A-2 has an angle to it. We’ve inherited the stand from SSME and so we’ve got that angle too. Now, when we go over to do testing on stand A-1, there is no diffuser (yet, we may add one later) and you’ll see that it is entirely vertical.

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