J-2X Progress: Mission-Duration Test

Five hundred seconds is exactly eight minutes and twenty seconds.  Nope, that’s not rocket science.  But that was what I had to keep in mind as I watched the stopwatch application on my smart phone during the last J-2X test.  Eight minutes and twenty seconds.  That seems like a really long time when you’re counting every second.

Let me set the scene.

At the NASA Stennis Space center you have collected the directors from seven of the ten NASA field centers around the country.  You have representatives from the NASA headquarters in Washington, DC.  You have a live feed being picked up by NASA TV and broadcast into the living rooms of thousands or millions of dedicated NASA TV junkies.  You have dignitaries in suits and technicians and test conductors in jeans and Hawaiian shirts (test-day tradition), reporters with notepads and cameras from every paper and television station in the greater New Orleans and southern Mississippi area, and, sitting in his ceremonial throne, the Grand High Exalted Mystic Ruler of the International Order of Friendly Sons of the Raccoons.

Well, okay, that last part about the Exalted Mystic Ruler is just fictional (bonus points to anyone who gets the 20th-century cultural allusion without Google help), but that’s the way that it felt.  This was test A2J008, the seventh planned hot-fire test of the very first development engine and it was time to play show-and-tell.

Does everyone remember show-and-tell in elementary school?  You bring in something that you think is neato or special and, by getting up in front of class and talking about it you reveal something about yourself and you accidentally practice public speaking and presentation.  Once, when I was seven years old, I brought in my new baby brother, or, well, my mother did so at my behest.  I wish that I could remember what I said about him.  I imagine it was something like, “He’s short, cranky, and smells funny.”  Today, at least he can say, he’s taller than me.

J-2X is our new baby brother — of a sort to carry forward the analogy — and we’re showing him off to the world.  Through the first six hot fire tests of engine E10001, we accumulated a total of 225 seconds of test time.  For test A2J008, on November 9th, our show-and-tell for the world, we scheduled a test lasting 500 seconds, which is the mission duration requirement for the engine.  Here is what I saw during the test, while holding the stopwatch, standing out in the field in front of the test control center:

Can’t see anything?  Okay, I’ll expand the picture in pieces starting on the left.

This is the hydrogen burn stack.  All of the excess hydrogen coming from the facility or from the engine before, during, and after the test needs to be burned off.  This is all bleed flows and waste flows that you cannot avoid when dealing with a cryogenic propellant.  If you let hydrogen accumulate anywhere around the facility, then “BOOM” you’re eventually going to have an explosion.  Talk to the guys who work out in the test areas and they’ll tell you plenty of tales of such things.  What is amazing as you’re standing out in that field to watch the test is the radiation heat coming off that thing.  It was a chilly day and yet you almost feel like you’re going to end up with a sun-tanned face.  It feels like the sun while you’re on the beach except that as warm is it makes your front side, your back side is still chilly from the blustery November breeze.  Kind of an odd sensation being both overheated and chilly at the same time.

In the middle of the picture is a sign for anyone who was born without that instinctual reflex for self-preservation.  While it would seem obvious to me to not walk in front of a roaring rocket engine throwing out a plume reaching hundreds of feet in the air, the fact that they have a sign like this suggests to me that for someone, somewhere, at some time, this was not so obvious.  An unfortunate thought…

And, on the right-hand side of the picture, in the distance, is test stand A-2 with the engine firing.  In the middle of the picture below, there is a tiny, very white spot in the middle of the test stand.  That’s the flame coming directly out of the engine nozzle.  In the bottom right corner of the picture below you can just see the edge of one of the liquid hydrogen barges.  For both liquid oxygen and liquid hydrogen, for extended duration tests, the propellant tanks on the test stand are not quite big enough to hold all of the necessary propellant.  So, during the test you actually transfer propellants from these barges into the test stand tanks.  So, the engine is draining the test stand tanks while you are simultaneously re-filling them from the barges.  With all of this going on, you start to appreciate the coordination necessary to pull off one of these tests.


When you’re standing there being halfway cooked by the burn stack, several hundred feet away, the roar from the engine is nearly deafening.  Many people wear hearing protection.  Others of us are aging rock-n-roll fans.  I honestly don’t think that anyone gets a complete sense of how powerful these machines are until they see, hear, and feel one of these tests.  All of the performance numbers in the world simply do not have the same visceral impact as when the engine lights and the initial sound wave runs over, around, and through you and you watch the flame bucket fill with billowing, thick, white steam.  Even twenty years after having seen my first test in person, I still cannot help but stand there like a bedazzled goof and say to myself, “Wow.”

Here, below, is a picture of the test from the other side of the stand.  Why is this important (other than the sign on the fence clearly advertising what you’re looking at)?  Because this is the side from which all of the non-NASA folks, some of the NASA dignitaries as well – including an astronaut representative – and the local press corps watched the test.  

So as to not keep you in any more suspense, the test came off perfectly.  The full, planned duration of 500 seconds was achieved thereby effectively tripling out test experience to date.  The coverage on NASA TV was good.  The bigwigs clapped and cheered with infectious excitement right along the rest of us.  And the press corps wore out their thesauruses trying to capture just a slice of the actual experience.  It was a complete success on all fronts.

Congratulations to the Pratt & Whitney Rocketdyne J-2X development team, the NASA SSC test crew, and the NASA Marshall Space Flight Center project management team.  While I had every bit of confidence that we’d be successful, with so many people watching our show-and-tell exercise, those 500 seconds — eight minutes and twenty seconds — ticking away on my stopwatch seemed like a whole lot longer.  Whew! and Yahoo!



J-2X Extras: Here Comes the Bride — Vehicle Integration

I just got back into the office a few days ago after a long weekend in Philadelphia. My wife’s niece got married. It was a beautiful venue and a moving service and good food, fabulous band, great party, and celebratory beverages flowed freely. Our niece looked gorgeous and her new husband was suitably handsome. A good time was had by all! Congratulations Ashley and Carmello!

And in the midst of all these festivities, an analogy came to mind regarding J-2X (well okay, perhaps not truly in the midst of the festivities, but certainly as part of the next-day hangover).  It’s not a perfect analogy, but it kind of works on a couple of levels.  I am referring to engine-to-vehicle integration.  Here, follow my thinking…

The wedding itself is a great big project.  Everything needs to be figured out, from the biggest stuff (Where?  When?  Who to invite?) to the finest details (What food is to be served at the cocktail hour?  What are the different lighting schemes for the service and for the dinner?).  So too is the development and launch of a great big launch vehicle.  When the engine and the stage come together and the mission comes off as planned, it’s beautiful.  Launch day is just like a well planned, well coordinated wedding.

Also, beyond just the singular event of the wedding day, there it the issue of everything that follows, i.e., the marriage.  And that is a matter of compatibility.  The most spectacular venue for the service and the best food for dinner and the grooviest band for the reception doesn’t guarantee happily ever after.  Things have to work together on many levels in order for success to be found in a match, whether that’s two people married or the engine and the stage coming together and successfully fulfilling a mission.

(Okay, so how’s that analogy working for me?  Not bad, huh?)

So what’s “vehicle integration”?  Well, it’s lots of stuff.  On the one hand, it’s the basic engine requirements.  After all, who says that J-2X ought to generate 294,000 pounds-force thrust at vacuum conditions?  It’s not as if us engine folks get to randomly pick a power level requirement out of thin air.  It comes from an integrated, comprehensive mission analysis of the vehicle.  While we like to think that the engine folks run the world, the truth is that without a vehicle and a mission to dictate requirements, we’d be nothing more than an expensive science project.

But beyond this, how do we interact with the stage?  I would suggest that there are four essential categories of interaction:
• Integrated analysis
• Boundary conditions
• Induced environments
• Operations

The first area, I’ve already discussed in part.  Integrated vehicle/mission analysis is used to establish the basic requirements for the engine.  Beyond that, though, you have other analyses such as contingency and hazards analyses that examine what happens if something goes wrong.  How should the vehicle respond if there is an issue with the engine or the stage or with how the engine and stage interact with each other?  So, in addition to defining upfront what the pieces should do, integrated analysis looks at how the actual, designed parts will interact under different circumstance.  Note that an output of integrated analysis often leads to the category of induced environments discussed below.

Next, you have boundary conditions and these are the most straightforward consideration.  In order to figure out what you need here, all you have to do is draw a box around the engine and see what stuff has to go into or out of the box to make the engine-vehicle combination work.  In fact, that’s basically how we started in creating the Interface Control Document (ICD) for J-2X.  That’s where you capture all of the agreements between the engine and the stage.  Here’s a piece of that “what’s crossing the box” diagram:

This diagram shows the fluids (liquids, gases) that cross the interface with the stage.  You have, of course, the propellant flows of liquid hydrogen and liquid oxygen, but then you also have the propellant tank pressurization flows that are used by the stage to keep the tanks pressurized during flight.  There are also gases used for pneumatic control of the valves and to perform purges through different phases of the flight.  There is a dedicated line that handles high-pressure helium for spin-starting the engine.  And then there are drain flows back to the stage for disposal of excess hydrogen and oxygen.  This latter category is necessary for safety reasons since, for an upper stage engine, it’s usually enclosed within the vehicle for much of the mission and you don’t want to build up an explosive mixture of fuel and oxidizer in the intertank area.

For each of these interfaces, we have to define throughout the different phases of the mission acceptable pressure ranges, temperature ranges, flowrates, and fluid qualities (purity, particulate contamination, etc.).  Both sides have to agree that these values at this interface will happen during the mission or else someone might make an erroneous assumption and either the engine or the stage could fail to perform.  Sometimes, we need to specify even more detail to ensure mission success such as the two-dimensional velocity profile of the propellants as they enter the engine.  Something like this can drive significant design effort on one side or the other (or both) so such details are rarely trivial. 

Now, add to this one set of interface just for fluids additional interfaces for electrical power, control and data transmissions, and then the actual physical connections (including not just the forces and moments applied to these connections but the actual physical designs themselves in terms of dimensions and materials, bolt-hole patterns, and seal configurations).  After you’ve done all that — fully negotiated and agreed to by both sides — you then have an ICD, one of the bedrock documents in the life of any engine.  It’s like a really, really detailed marriage license that goes on and on between the engine and the stage: who cuts the grass, who does the laundry, who sleeps on what side of the bed, who cleans the litter boxes, who opens the pickle jars, who has the remote control come football season…

The next area of consideration with regards to vehicle integration is induced loads.  In truth, these are really just another boundary condition, but we often break them out separately for convenience of tracking and documentation.  What we’re talking about here are loads: structural dynamics, acoustics, and thermal loads.  Rocket engines and launch vehicles make lots of rumbling, roaring noise and lots of smoke and fire.  That’s part of what makes them kinda cool (right?!).  But it’s also the kind of stuff that can cause damage if not properly accounted for in the design. 

Above is the output from an integrated analysis looking at thermal conditions of the engine during a stage separation event.  In this case, depending upon the design of the stage separation system, there were situations where the engine was getting exposed to damaging thermal loads.  In other words, the stage was imposing a load on the engine that jeopardized mission success, so the stage design was altered.  All of the elements of the vehicle have to live with the environments created by everyone else.  So, this is not too much unlike figuring out how to live together after getting married.  You learn, for example, that the combined environment of stogie smoke, an overgrown lawn, and blaring NASCAR on television apparently do not constitute the most congenial, constructive induced environment at home…

The last category in my simplified breakdown of vehicle integration is that of operations.  This comes down to who does what, when, and how.  Bringing together a whole vehicle requires quite a detailed set of instructions.  It’s a lot more than “Insert tab A into slot B.”  And the pieces that you’re assembling come from several different project office and different contractors located all over the country.  So, on the one side of the issue is the technical matter of how you do the whole thing, but on the other side, just as importantly, you have the issue of who is responsible for performing the tasks.  With tasks come manpower, roles and responsibilities for facilities and tooling and, before you know it, meaningful expenses.  Thus, (ta-da!) you’ve got more negotiations and agreements and documentation.

So, engine-to-vehicle integration is, in the end, like a long, complex, heavily negotiated, analyzed, and documented marriage.  Perhaps then, other than the documentation part, it’s probably like most successful marriages over the long haul.