Tag Archives: engine E10001

J-2X Progress: A New Star on Our Horizon

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J-2X Progress:  A New Star on Our Horizon

For weeks and weeks (or months and months really), we’ve been going on and on about the star of our J-2X project, development engine E10001.  And there is every reason to focus much of our attention on this first example of our new engine.  It has really put on one a heck of a show, generating oodles of data, and we’re far from being finished with it.  


 
So, E10001 is unquestionably a star.  Beyond this, however, we have other potential stars waiting in the wings.  I would liken this situation to “American Idol” except that I’ve never actually seen that show and, further, all of our test articles are not in competition with each other.  Indeed, the whole point of a coordinated and integrated development plan is for all of the test plans and test articles to complement each other.  One big star that will soon be making an important contribution is called “PowerPack Assembly 2” (or “PPA2”).  Okay, you’re saying to yourself:  I know what an engine is, but what is a “powerpack assembly”?  And, why is this number two?  Good questions.  We’ll start with the first one…

A powerpack assembly — or simply a “powerpack” — is a subset of the total engine.  Specifically, it is the engine minus the thrust chamber assembly (i.e., the main injector, main combustion chamber, and nozzle/nozzle extension).  About a year ago, I wrote an article here in the J-2X development blog talking about what a gas-generator cycle rocket engine looks like.  The schematic of that cycle is shown below for reference and comparison:


Where:
MCC = Main Combustion Chamber
GG = Gas Generator
MFV = Main Fuel Valve
MOV = Main Oxidizer Valve
GGFV = Gas Generator Fuel Valve
GGOV = Gas Generator Oxidizer Valve
OTBV = Oxidizer Turbine Bypass Valve

The lines and arrows in red denote fuel (hydrogen) flow; the green lines and arrows denote oxidizer (oxygen) flow; and the gray lines and arrows denote the flow of combustion products.  Using the same abbreviations and same color schemes, here is the schematic for a gas-generator cycle powerpack:


See?  As I said, you simply pull off the whole thrust chamber assembly and there you go: powerpack.  If you think of the thrust chamber assembly as what you use to make thrust, then the powerpack portion of the engine is what you use to feed the thrust chamber assembly.  In other words, to be particular, it’s the gas generator, the turbopumps, and the full set of major control valves…plus, of course, the lines and ducts that connect everything together.

What this configuration allows you to do, far more so than the complete engine configuration, is “play games” with turbomachinery conditions and operations.  And here’s why.  On the full engine configuration, you have to feed the thrust chamber assembly a pretty steady diet of fuel and oxidizer.  If you deviate too far, things get too hot or too cold or you get too much pressure in the chamber or too little.  The thrust chamber assembly is a wonderful piece of equipment, astonishingly robust when functioning in their normal regimes, but it’s basically static and, to be honest, a bit persnickety when it comes to significantly off-nominal operations. 

So, you first get rid of the persnickety thrust chamber assembly to give yourself more flexibility and then, taking the next step, you get creative with the valves.  On the complete engine configuration for flight, the J-2X engine has pneumatically actuated valves.  As we’ve discussed in the past, this means that they have two positions to which they are actuated: open and close.  We can’t partially open or close them and hold them in intermediate positions thereby altering or directly controlling the propellant flows through the engine.  But for powerpack, we’re not so constrained.  For powerpack, we will use electro-mechanical valve actuators for the two gas generator valves (the GGFV and the GGOV) and we will use hydraulically-actuated facility valves to simulate the two main valves (the MFV and the MOV).  All four of these valves will then no longer be simply open/close.  They can be held as partially open or closed and, using these as control tools, we can vary temperatures, pressures, and flowrates throughout the powerpack.  We can vary the power with which we drive the turbines.  We can vary the downstream resistances seen by the pumps thereby altering the flows and pressure-rise profiles through the pumps.  The OTBV — the valve that we normally use to alter engine mixture ratio by applying differential power levels to the two turbines — will not be actively actuated for the powerpack testing, but it will be configured such that we can alter its fixed, incremental position from test to test.  In that manner, we can use the OTBV position variations to explore inlet mixture ratio deviations on powerpack that the full engine configuration simply couldn’t tolerate.

Thus, the powerpack assembly configuration is first and foremost (though not exclusively) a test bed for the turbomachinery.  Just as with the “bomb test” philosophy discussed in the previous article, we already know that the J-2X engine works, but now we need to further explore the detailed implications of the design.  We need to anchor and validate our analytical models, demonstrate operations across the spectrum of boundary conditions and environments, better characterize our margins, and exercise the full slate of design features and operational capabilities.  The powerpack assembly test series is one very important means for doing this.

Okay, so it’s a useful test article, but where does the actual Powerpack Assembly 2 stand?  Well, while we’ve all been heavily (and appropriately) focused on the testing of J-2X development engine E10001, our contractor, Pratt & Whitney Rocketdyne, has been also quietly assembling Powerpack Assembly 2 back in the engine assembly area.  Here is a picture of the complete Powerpack Assembly 2.


It kind of looks like an engine, almost, doesn’t it?  Well, that’s because we assembled it kind of like an engine but used a “dummy” thrust chamber assembly.  You should recognize the yellow thing that looks like a cage.  That’s the nozzle simulator that we used early on in the assembly of E10001.  Sitting on top of the nozzle simulator is a simulated main combustion chamber and a simulated main injector.  By making it look so much like a regular J-2X engine, it allows us to install the PowerPack Assembly 2 into the test stand much like we do a regular engine.  The only special adaptations are lines to catch the propellants coming out from the pumps and the discharge coming from the turbines.  In a regular, full configuration engine all of these flows get routed through the thrust chamber assembly to produce thrust.  For PowerPack Assembly 2 testing, these fluid streams are collected and disposed of off of the test stand.

Next is a picture of the PowerPack Assembly 2 being carefully loaded onto the truck to transport it out to the test stand.  Road trip!


PowerPack Assembly 2 will be tested on test stand A-1, which is the sister test stand to A-2 where E10001 is currently being tested.  Here, below, are a couple of pictures of PowerPack Assembly 2 being lifted onto and then sitting on “the porch” of A-1.  In the background you can see a portion of the canals that weave in and around the big test stands at the NASA Stennis Space Center.  Nowadays, these canals are mostly used just to transport barges full of propellants.  But back in the Apollo era, these canals were used to transport whole rocket stages in and out of the test facilities since they were too big for trucking.


And here, is Power Pack Assembly 2 installed into the test position on stand A-1.  Many kudos should be extended to our diligent contractor Pratt & Whitney Rocketdyne and our faithful partners at the NASA Stennis Space Center for making this milestone possible.  Great work guys!


Now, getting back to that other question regarding the “2” part of “PowerPack Assembly 2.”  That denotation is simply there because this is the second powerpack assembly we’ve tested as part of the J-2X development effort.  PowerPack Assembly 1 testing was conducted about four years ago using residual hardware from the XRS-2200 (linear aerospike) development project.  While that first PowerPack Assembly did not use any true J-2X hardware since that hardware was not yet designed or built, it did help inform the J-2X turbomachinery designs.  It used what were essentially J-2S turbopumps to explore J-2X-like operating regimes.  The J-2X turbopump designs then began with the J-2S designs and made the changes necessary to fulfill the J-2X mission.  Another way of looking at this is that PowerPack Assembly 1 was used to inform the design and PowerPack Assembly 2 will be used to validate and characterize the design.  To me, this sounds like a very nice pair of bookends on either side of the J-2X turbomachinery development effort.


J-2X Progress: Mission-Duration Test

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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!


 

 

Inside The J-2X Doghouse: A2J006 &Turbopump Thrust Balance

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Okay, before I even get to the subject of thrust balance, I want to report that J-2X development engine E10001 got back into the stand and that the next test, A2J006, was conducted.  The test went the full planned duration of 40 seconds and the issues that caused us to remove the engine after the previous test all appear to be fixed.  In other words, it was a complete success.  Here’s a video for your viewing pleasure:

 

https://www.nasa.gov/multimedia/videogallery/index.html?media_id=113620611

 

Now, speaking of issues on E10001 that appear to be resolved, I want to talk about turbopump thrust balance.  While I hadn’t previously mentioned it, the data from the first several tests showed that there was a thrust balance issue with the oxidizer turbopump (OTP).  So, that naturally leads to the question:  What is “thrust balance?”

 

Here is a crude drawing of a turbopump for this discussion (And, please, save your cards and letters telling me that I am a terrible artist.  I will already catch plenty of grief from the turbo guys over this drawing.).  The arrows are intended to illustrate fluid flows.

 


 

I’ve drawn this in three colors because a turbopump can be thought of as having three fundamental elements.  The first element, the one in blue, is the part that spins.  This is the rotor onto which is attached the pumping stuff (i.e., the inducer and the impeller) on the pump side and the turbine stuff (i.e., the disks and blades) on the turbine side.

 

The second element, shown in green, is the part that doesn’t spin.  This is the housing.  It is the shell within which the rotor spins.

The third element, shown in red, is the bearings. 

 

Whenever you’ve got one thing spinning and another thing stationary, you’ve got to have some way of communicating between the two pieces.  Maybe the rotor just spins and slides around in some kind of restraint holding it in place.  Well that might work except that you can’t put grease into a cryogenic oxygen environment and, should too much heat build-up due to friction, then you’ve got a very combustible situation.  Mix heat with a pure oxygen environment and anything and everything will burn, including metal. 

 

What we do instead is typically use ball bearings between the rotor and the housing.  In some other pumps we use roller bearings that look like little cylinders rather than little balls, and there are other solutions as well.  These bearings do two things, they allow the rotor to spin and they hold the rotor in place.  So they need to be loose enough to spin yet tight enough to maintain control of a heavy hunk of metal spinning at over 10,000 rpm.  How much force the bearing put on the rotor to maintain control and, conversely, how much the rotor puts back on the bearings is called the bearing load. 

When you are designing a turbopump, you design it so that the bearings have a specific load, and that means more than just a value, it also means a direction as shown in the sketch above.  You design the whole bearing package assuming that you know the magnitude and direction of the forces loaded through the package.  This then allows you to do some calculations that tell you, “Yep, I’ve got the rotor properly and sufficiently controlled.”  Those calculations are part of what is often referred to as rotordynamics (and, by the way, NASA MSFC has some of the world’s best experts in that area).

 

Question: How do you get different bearing loads in a turbopump?  Answer: Pressures.

 

Here is a nifty little fact: Pressure is all around us.  We don’t feel the atmospheric pressure of 14.7 pounds-force over every square inch of your body because, well, it’s always been there.  That’s the environment within which we’ve evolved.  Now, go to the bottom of the ocean and you’ll find a whole other pressure environment, one that would crush our delicate bodies into mess.  The basic principle to remember is this: Pressure applied over an area equals force.

 

Within a turbopump, you are explicitly manipulating pressure.  That’s the whole purpose of a pump: to move fluid through the use of pressure.  So, in the pump end you have a low pressure coming in at the inlet and a very high pressure at the outlet.  On the turbine end, it’s the opposite since on that end you’re extracting energy (and therefore pressure) from the fluid.  So, on the turbine end you have high pressure at the inlet and lower pressure at the outlet.  Thus, throughout the turbopump, you’ve got pressures of all sorts and those pressures are pushing on the different pieces of the rotor.  This means that you’ve got all kinds of forces pushing on the rotor.  Some of the forces push the rotor towards the turbine end.  Some of the forces push the rotor towards the pump end.  Getting the right balance of forces is called your thrust balance.

 

 

 

So, what’s the “right” thrust balance?  It is the one to which you’ve designed your bearings.  You design your bearings to have a certain load and a big part of that load is determines by the thrust balance on the rotor.  So, if your thrust balance is off, i.e., not what you intended, then your bearing loads are off and you’re therefore not controlling the rotor the way that you wanted.  In the worst of circumstances, an out-of-control rotor represents a catastrophic situation.  In less-than-worst circumstances, operating with a thrust balance significantly different than the design intent could lead to unexpected wear on components and therefore limited operational life. 

 

The next question is this: How do you create the thrust balance that you want and need to accomplish all this? 

 

That’s a matter of designing the internal guts of the turbopump and analytically modeling all of the internal flows within these guts.  In addition to the big flows coming into and out of the pump and turbine, you’ve got internal flows around seals, between pump or turbine stage, and through the bearings (as coolant).  When operating, the whole turbopump is full of fluid.  And, everywhere you have fluid, you have a pressure; and everywhere you have pressure applied to an area, you have a force.  So you calculate pressure drops through small passages or through seals and figure out a whole detailed map of different pressures and forces throughout the whole unit and you can understand your thrust balance.  And then, as necessary, you manipulate your clearances and seals and passages designs until you achieve the thrust balance you need.

 

 

 

Getting back to the E10001 OTP, what appears to have been the issue was that we had some seals that were too tight.  The tight seals overly restricted internal flows and, basically, messed up the intended force balance on the rotor.  This could be seen in the data collected from the testing.  Remember when I said several articles ago that this engine is instrumented to the max so that we can learn all about how it is working.  Here is a case where special instrumentation identified an issue.  The interesting part is that these seals were kinda sorta fine in terms of design but the processing of the material of which they are made — it feels like hard plastic — was not quite refined enough so that when subjected to operational conditions it changes dimensions and actually tightened up. 

 
 
 

Prior to test A2J006, while we had the engine out of the stand, our contractor Pratt & Whitney Rocketdyne was able to partially disassemble the engine and the OTP just enough to change out the seals in question and then get the whole thing buttoned up and ready for test in record time.  They truly did some excellent work here.  And the success of test A2J006 is the proof!