Tag Archives: Power Pack Assembly

J-2X Progress: Current Status, The End of 2012

Posted on by .

Once upon a time, not that long ago, people used to communicate by what were known as “letters.”  These were written documents.  Yes, actual hardcopy, paper items. And they were often transcribed by hand or, sometimes, generated on what was known as a “typewriter,” which was basically a manual, analog printer with no I/O port beyond direct keypad entry.  These “letters” were sent to their intended recipients using a small denomination currency with an adhesive backing that is recognized for exchange by only one quasi-governmental agency. 


I know that some of you may have doubts that people communicated with each other in primitive ways prior to email and text messages, but witness the cultural clues from the 1961 song illustrated above. 

It was always believed that the toughest letter to receive was the dreaded “Dear John” letter (as in, “Dear John, I’ve fallen in love with someone else…”).   However, I think t’at the hardest letter to write is the “it’s been awhile” letter.  This one starts, “Well, it’s been awhile since I’ve written.  Sorry.”  This blog article is just like one of those letters.  It’s been awhile since I’ve written one of these articles and I’m sorry about that.  I could give you a big long list of all the really, really serious stuff that I’ve been doing instead, but that’s just a bunch of feeble excuses so I’ll keep them to myself.  Instead, I’ll just get down to business and give you a status report on the J-2X development effort.

Engine #1 (E10001) Testing is Complete!
Over fourteen months and across the span of twenty-one tests, more than 2,700 seconds of engine run time was accumulated and recorded, including nearly 1,700 seconds of hot fire with an instrumented nozzle extension.  With this engine we achieved stable 100% power level operation by the fourth test and full mission duration by the eighth test.  While we don’t have any official statistics on the issue, most folks around here believe that we accomplished those milestones faster than has ever been done on a newly developed engine.  We learned how to calibrate the engine and the sensitivities that the engine has to different calibration settings, i.e., orifice sizes and valve positions.  We were able to estimate performance parameters for the full-configuration of the engine at vacuum conditions and the calculations suggest strongly that all requirements are met by this design and met with substantial margin.  This is significant considering that we’ve long considered our performance goals to be pretty aggressive.  Well, our little-engine-that-could showed us that it did just fine with those goals, thank you very much.

One of the truly unique and successful aspects of the E10001 testing was the testing of a nozzle extension.  This component is a key feature that allows J-2X performance to far exceed that of the J-2 engine from the Apollo Program era.  While it is true that we cannot test the full-length nozzle extension without a test stand that actively simulates altitude conditions, we did test a highly instrumented “stub” version that allowed us to characterize the thermal environments to which the nozzle is exposed during engine hot fire and it demonstrated the effectiveness and durability of the emissivity coating that was used.  This stub-nozzle configuration is actually the current baseline for the in-development Space Launch System vehicle upper stage.

Another key success for E10001 was the demonstration of both primary and secondary power levels with starts and shutdowns from each power level and with smooth in-run transitions back and forth between them.  That smoothness was thanks, in part, to demonstrating our understanding of the control of the engine.  From the very first test it was clear that we understood pretty well how to control the engine in terms of proper control orifices for the various operating conditions.  What we did not entirely understand — in other words the fine-tuning details — we successfully learned via trial-and-error throughout the E10001 test series.  All of this learning has been fed back into further anchoring our analytical tools and models so that we can move forward with J-2X development with a great deal of confidence.

Okay, so that’s a brief description of just some of the good stuff.  We had lots and lots of good stuff with the E10001 testing, far more than just that I’ve discussed here (see previous blog articles).  The somewhat unfortunate part was the way in which the E10001 test series came to an end.  On test A2J021, we had a disconnection between the intent for test and the detailed planning that led to the actual hardware configuration we ran for the test.  That disconnection led to an ill-fated situation.  Let me explain…

The J-2X gas generator has ports into which solid propellant igniters are installed.  These igniters are like really high-powered Estes® rocket motors that light off when supplied with a high-energy electrical pulse.  The flame from the igniter lights the fire of the hydrogen-oxygen mixture during the engine start sequence.  It’s essentially the kindling for the fire of mainstage operation.  The igniters perform this function at a very specific time during this sequence.  If you try to light the fire too early, then you may not have enough propellant available in a combustible mixture so you get a sputtering fire.  If you try to light too late, then you may have too much propellant built up such that rather than getting a good fire, you get an explosion instead.  But here’s a key fact: You have to plug them in or they don’t work.

Have you ever stuck bread in the toaster, pushed down the plunger, gone off to make the coffee, and come back only to find that your darn toaster is broken?  You curse a little because you’re already late for work and this is the last darn thing you need.  You would think that somebody somewhere could make a toaster that lasts more than six months or a year or whatever.  For goodness sake!  We put a man on the moon and yet we can’t … oh, wait … um … ooops, it’s not plugged in.  My bad.

In a nutshell, that’s what happened on test A2J021.  The electronic ignition system sent the necessary pulse, but because of the uniqueness of our testing configuration as opposed to our flight configuration the wires carrying the pulse weren’t hooked up to the little solid propellant igniters in the gas generator.  In the picture below you can see the external indication that something was not entirely good immediately after the test.  The internal damage was more extensive to both the gas generator and the fuel turbopump turbine.

Many years ago, I met an elderly engineer who was still on the job well into his 80’s because he loved his work.  His entire career had been dedicated to testing.  He’d actually been there, out in the desert, in the 1940’s testing our very earliest rockets as part of the Hermes Project.  One day, they had a mini disaster on the launch pad.  He told me that the rocket basically just blew up where it sat.  Boom and then a mess.  And, it was his job to assemble the test report.  Being a conscientious, ambitious, young engineer, he recorded the facts and offered a narrative abstract and extensive, annotated introduction that categorized the test as, well, a failure.  Not long after submitting his report, one of the senior German engineers in the camp came into his office, put the test report down on the desk, and said that the tone of the report was entirely wrong.  He said, “Every test report should begin with: ‘This test was a success because…'”  The purpose of testing is to gather data and learn.  If you learn something, then your test was, by definition, a success on some level.  I’ve tried very hard to remember this very important bit of wisdom.

So, A2J021 was a success because we learned that we had some deficiencies in our pre-test checkout procedures.  It was a success because it was an extraordinary stress test on the gas generator system.  No, it didn’t recover and function properly, but neither did the engine come apart.  While that might seem like a minor detail, when you’re hundred miles from the surface of the earth, you would much rather have a situation where an abort is possible than a failure that could result in collateral vehicle damage and make safe abort impossible.  We have a stout design.  Good.  Also, this test failure was due to a unique ground test configuration.  In flight, it’s not really plausible just because we would never fly in this configuration.

So, E10001 completed its test program with a bang.  Kinda, sorta literally.  But it was nearly the end of its design life anyway, so we didn’t lose too many test opportunities, and, as I said, even with test A2J021 the way it happened we learned a great deal.  Overall, the E10001 test series was an outrageous success.  Rocketdyne, the J-2X contractor, ought to be darn proud and so should the outstanding assembly and test crews at the NASA Stennis Space Center and our data analysts here at the NASA Marshall Space Flight Center.  Bravo guys!  Go J-2X!

Power-Pack Assembly 2 (PPA-2) Testing is Complete!
Over ten months and across the span of thirteen tests, nearly 6,200 seconds of engine run time was accumulated and recorded on the J-2X Power Pack Assembly 2.  That’s over 100 minutes of hot fire.  Three of the tests were over 20 minutes long (plus one that clocked in at 19 minutes) and these represent the longest tests ever conducted at the NASA Stennis Space Center A-complex.  But more than just length, it was the extraordinary complexity of the test profiles that truly sets the PPA-2 testing apart.

Because PPA-2 was not a full engine with the constraints imposed by the need to feed a stable main combustion chamber, and because we used electro-mechanical actuators on the engine-side valves and hydraulic actuators on the facility side valves, we could push the PPA-2 turbomachinery across broad ranges of operating conditions.  These ranges represented extremes in boundary conditions and extremes in engine conditions and performance.  On several occasions we intentionally searched out conditions that would result in a test cut just so that we could better understand our margins.  As the saying goes: It’s only when you go too far do you truly learn just how far you can go.  We successfully (and safely) applied that adage several times.  In short, we gathered enough information to keep the turbomachinery and rotordynamics folks blissfully buried in data for months and months to come. 

On an interesting and instructive side note, the PPA-2 testing also showed us that we needed to redesign a seal internal to the hydrogen turbopump.  In the oxygen turbopump, you have an actively purged seal between the turbine side and the pump side.  After all, during operation you have hydrogen-rich hot gas pushing through the turbine side and liquid oxygen going through the pump side.  You obviously don’t want them to mix or the result could be catastrophic.  That’s why we have a purged seal.  But for the hydrogen turbopump you don’t have such an issue.  During operation, at worst should the two sides mix you could get some leakage of hydrogen from the pump side into the turbine side that is already hydrogen rich.  In order to maintain machine efficiency, you don’t want too much leakage, but a little is not catastrophic (and can be used constructively to cool the bearings).  What could be dangerous at the vehicle level, however, is if you have too much hydrogen floating around prior to liftoff.  This is especially true for an upper-stage engine like J-2X that’s typically sitting within an enclosed space until stage separation during the mission.  You could have the engine sitting on the pad for hours chilling down and filling the cryogenic systems and you don’t want gobs and gobs of hydrogen leaking through the turbopump since any leakage ends up within the closed vehicle compartment housing the engine.  That’s just asking for an explosion and a bad day.

To avoid this, within the J-2X hydrogen turbopump we have what is called a lift-off seal.  And, as the name applies, it’s a seal that actively lifts off when we’re ready to run the engine.  When the engine is just sitting there chilling down, not running, with liquid hydrogen filling the pump end of the hydrogen turbopump, the seal is, well, sealed.  Then, when we’re ready to go, it unseals and allows the turbopump to operate nominally.

During the PPA-2 test series we found that we formed a small material failure within the actuation pieces for our lift-off seal.  Then, upon analysis of the test data and a reassessment of the design, we figured out what was most likely the cause and Rocketdyne proposed a redesign to mitigate the issue.  Again, going back to that important piece of wisdom: This testing was a success because, in part, we learned that we needed a slight redesign of the lift-off seal.  That’s the whole purpose of development testing!  Everything always looks great when it’s just in blueprints.  It’s not until you hit the test stand do you truly learn what’s good and what need to be reconsidered.  In the end, this sort of rigor and perseverance is what gives you a final product that you feel good about putting in a vehicle carrying humans in space.  And that, truly, is what it’s all about.

As with E10001, the PPA-2 test series was simply an outrageous success.  Rocketdyne should be proud and so should the outstanding assembly and test crews at the NASA Stennis Space Center and the data analysts at the NASA Marshall Space Flight Center.  Bravo guys!  Go J-2X!

Engine #2 (E10002) Assembly is Underway
Our next star on the horizon is J-2X development Engine 10002.  It is being assembled right now, as I’m typing this article.  It is slated for assembly completion in January 2013 and it will be making lots of noise and very hot steam in the test stand soon after that.  While our current plans are to first test E10002 in test stand A2, we will later be moving it to test stand A1.  This, then, will be the first engine then to see both test stands.  The more important reason for the A1 testing, however, is because that will give us the opportunity to hook up some big hydraulic actuators and gimbal the engine, i.e., make it rock and tilt as though it were being used to steer a vehicle.  Now that will be some exciting video to post to the blog!  I can’t wait.

 
Happy New Year!
So, this has been my “it’s been awhile” letter.  Hopefully this will bring everyone up to speed with where we stand with J-2X development.  In my next article, I will share with you some of what’s been keeping me from my J-2X article writing over the last several months.  And, hopefully, it won’t be several months in the making.  So, farewell for now and Happy New Year!  On to 2013 and another great year full of J-2X successes.  Go J-2X!

J-2X Progress: Two Stands Occupied

Posted on by .

It’s been awhile since I’ve had the opportunity to update what we’ve been doing for the J-2X development test campaign.  So, everyone is probably wondering where we stand.  Well, if possession is nine-tenths of the law, then J-2X IS THE LAW for the NASA Stennis Space Center A-complex!  Right now, the J-2X development effort has our PowerPack Assembly 2 in test stand A-1 and Engine 10001 has been reinstalled on test stand A-2.

Below are two pictures of the J-2X PowerPack Assembly 2 (known as PPA2) taken from different perspectives.  In the second one, you can see that several pieces are coated with ice.  That’s obviously a picture with cryogenic propellants loaded in the ducts and turbomachinery.  In other words, to use our local jargon, in the second picture PPA2 is chilled down.

Well, you saw in a previous blog article that we spun up the PPA2 and we demonstrated ignition of the gas generator.  Beyond that, however, we’ve had a few hiccups.  For the first test intended to get to mainstage operation, we didn’t get very far.  We effectively demonstrated again the spin start and ignition of the gas generator.  Immediately beyond that, just a few tenths of a second in fact, the test shut down due to an issue on the facility side.  As I’ve described before, the PPA2 is kind of an odd beast in that it’s a half-engine and half-facility test article.  In this case, a facility valve did not function the way that it was supposed to.  It was sluggish.  A subsequent investigation into the facility hydraulic system identified and fixed the issue so we were again all ready to go.

On the next test we got a little farther but just before getting to mainstage, we busted an engine-side redline limit and had to shut down early.  The reason for that early cut was actually quite analogous to the early cut we had on our first attempt at a mainstage test for Engine 10001.  We didn’t quite understand the characteristics of the engine components and so, as we powered up the system, we were headed towards an operating point different than we’d intended.  In other words, our calibration was a bit off.  The redline system identified this situation and, properly, cut off the test before anything damaging might occur.  While early cuts are sometimes a pain in the neck, we have those safety systems built in there for a reason.  There is always a substantial and meaningful difference between a nuisance and something potentially worse. 

Over the course of the next couple of PPA2 tests we once again proved that hydrogen is a pernicious rascal.  This is something that has been proven on many former occasions throughout the history of rocket engine development.  If you give hydrogen any opportunity to leak, any at all, it will.  And sometimes, it will only leak when the system is chilled down so that when you’re checking out the system before a test, when you’re searching for potential leaks, you don’t see a thing.  But then, when you are all set up and get the test going, ta-da, you suddenly have a fire.  Why a fire?  Because with a hydrogen leak around all the rest of the hot stuff going on with the test, a leak almost always becomes a fire.  And, because pooled, un-burnt hydrogen is a potential detonation hazard, we also have devices all around the vicinity of the test article designed to make sure that any leaked hydrogen gets burnt.  So, quite simply: hydrogen leak on engine test = hydrogen fire on engine test.  The fires that we saw on these two tests were not on the “engine” half of the PPA2 test article per se.  Instead, we got fires on the facility half.  The emergency systems in place for such issues include cameras and temperature probes so that there was practically no damage and our hardware is just fine.  But the fires did mean that we’ve accumulated only a limited amount of mainstage data so far.

Undaunted, we have investigated and, we believe, solved the issue and will once again be ready for testing in the near future.

On the other test stand, specifically stand A-2, the folks at the NASA Stennis Space Center have been darn busy.  If you go back a couple of months in these blog articles you’ll find a discussion about the next phase of testing for J-2X development engine 10001 (E10001 for short).  In that article, I tell you all about the test stand passive diffuser and the engine nozzle extension that we’ll be testing.  Well, the first thing that we had to do to make this next phase for E10001 possible was to modify the test stand.  In order to make the passive diffuser function properly, you have to effectively seal off the top.  

In the picture above you’ll see what’s called the clamshell.  This two-piece device rotates out of the way for access to the engine between tests but during a test wraps around the nozzle of the engine on the top side and connects to the diffuser on the bottom side.  We’ll use a rubber-ish seal in the gap between the clamshell and the nozzle to maintain the seal while accommodating movement of the nozzle during hot fire testing.  Getting this thing designed, built, and into the stand was a heck of a lot of work.  The folks who accomplished this deserve mucho kudos.

So, that’s the test stand side.  Next, there is the test article side, i.e., the engine itself.  Because the nozzle extension is not structurally beefy enough to support the rest of the engine, the installation of the test article into the stand has to be performed in two steps.  First, you install the main part of the engine and then, once that’s in place, you install the nozzle extension. 

By the way, while it sounds easy enough to simply bolt the nozzle extension into place on the end of the nozzle, it’s actually a bit more complicated.  While both pieces are designed to be exactly round, nothing is truly exactly round, especially not pieces of hardware this large.  We have to use special “rounding” tools during the mating process.  It’s sometimes amazing to think about all of the specialized tools and equipment that you need, in addition to the engine itself of course, just to make the engine work. 

So, that’s where we stand in terms of our development test campaign.  As if southern Mississippi isn’t hot enough in the summer, J-2X will soon be adding even more heat from two active test stands very, very soon and for several months to come.  Elsewhere, FYI, we’re working on various stages of fabricating and/or assembling J-2X development engines 10002 and 10003.  They will be what follows PPA2 and E10001 into the test stands.  In other words, there’s lots of excitement yet to come.

J-2X Progress: Test Stands Moving Towards Readiness

Posted on by .

In the broadest sense, stepping back from the project, the J-2X development effort has three primary branches.  First, of course, you have our prime contractor, Pratt & Whitney Rocketdyne (PWR) who is responsible for designing the engine and demonstrating that it meets the imposed requirements.  Second, you have the team here at NASA responsible for management, technical oversight and insight, and, in a handful of specific cases, mainline work in support of PWR activities.  And, third, you have the extensive efforts underway at the NASA Stennis Space Center (SSC) in southern Mississippi to provide a site for testing of the J-2X.  If you scroll down a ways through previous articles you’ll see that I wrote an overview article about SSC and the test stands there.  Here, for this article, I’m going to provide an update and show off some neato pictures of the ongoing work.

The first engine testing will take place on stand A2.  In the picture below, technicians are using a locator tool to properly position the water spray ring to where it will need to be over the diffuser.  The water spray ring is used to cool the top portions of the diffuser and is necessary since the first tests of the engine will not have any nozzle extension attached below the regeneratively-cooled nozzle.  This means that the exhaust flow will not be entirely ‘turned’ and so it will impinge on the diffuser walls. 

Next, after getting the spray ring close to the correct position using this tooling, the diffuser will be raised into position below the ring and a laser measurement system will be used to determine the exact location of the spray ring.  At that point, the support arms will be installed so as to maintain that position.

In order to check out the extensive communications between the test control center, the test stand, and the engine itself, PWR shipped to SSC the first prototype engine controller.  In the picture below what you see is the controller actually sitting on the test stand, on the same level where the engine will be during testing, talking back and forth with the stand.  Of course, once the engine arrives, it will have its own controller mounted to the engine itself.  This one is just being used for check-outs.  Getting all such things checked out and running properly prior to installing the engine is crucial if you harbor any hopes of maintaining your schedule.  This is a fine example of PWR and the crews at SSC working together towards a common goal.

When an engine is being tested, the area around it is pretty much cleared away.  Almost anything close would be swept into the exhaust, or rattled apart, or melted from the heat in the plume.  It’s truly a violent environment.  But before and after the test, you need to be able to get your hands on the engine for a whole variety of reasons.  For example: After a test, the engine needs to be dried.  Remember that the combustion product for an oxygen-hydrogen engine is hot steam.  When the engine cools after a test, that steam condenses and becomes water.  In order to prepare for the next test, we have to dry out all that residual water and we do so by blowing heated gas, dry air or nitrogen, through the engine.  So, we need access to the engine to hook up the hoses. 

In the picture above are shown the lightweight, temporary platforms that have been created to allow for engine access.  The engine will reside in the hole in the middle of the platforms.  Prior to a test, these platforms are removed and after a test they are erected back in the position shown.

Okay, now we’re going to move over to the work being done on test stand A1.  This is where we will first be testing the PowerPack Assembly (PPA).  The PPA primarily consists of the turbomachinery and the gas-generator.  It is essentially a special test bed for the propellant feed and turbine drive functions of the engine.  Because the PPA does not have to feed a carefully balanced engine system and because we will be using special test equipment electro-mechanically activated, EMA, valves to control the PPA, we will have the freedom and ability to explore many more operational conditions for the turbomachinery than are possible during actual engine testing.  This is a way to truly wring out the design with only a limited number of test articles.  We will be calling the upcoming test article PPA2 since we had previously tested a PowerPack Assembly composed of legacy J-2S and XRS-2200 components back in 2007 and 2008.  After PPA2 testing, test stand A1 will be converted back to a full engine test facility.


Just as we are using an engine controller to check out the communication systems, and just as we have special tooling for finding the right location for the spray ring on test stand A2, a special tool was developed by PWR to help the technicians at SSC properly position all of the plumbing that feeds into the engine.  The tool is called a Master Interface Tool (MIT) and it is simply a bunch of fake interfaces all in the correct geometrical locations as though they were the real interfaces for an engine and PPA2.  In the picture below, the MIT is the yellow item in the foreground.  This portion of the MIT simulates the connections for all of the ancillary lines to the engine besides the main propellant flows.

Because the MIT properly emulates the engine, once all of the piping on the test stand side meets up with the tool, the technicians have much greater assurance that when an engine shows up, it will fit into the space provided.  This is a much better approach than attempting to locate these lines in space with no solid reference point and it saves time since these lines can be installed now rather than waiting for the engine or the PPA2 to show up on the stand.

The MIT appears in the picture below as well.  It is the yellow item on the bottom and here it is being used to position the installation of the liquid hydrogen and liquid oxygen feed lines.  Thus, when we are actually up and running with an engine, it will hang right where the MIT is currently sitting.

The other yellow items in this picture, the beams that appear to extend up and into the rafters, are the structure that carries the thrust of the engine.  These four beams will transmit a total of approximately a quarter of a million pounds-force of thrust into the thrust measurement system and into the test stand itself.

The last couple of pictures that I wanted to include here is intentionally less ‘glamorous’ than some of the previous ones showing where the engine will sit when tested or big pieces of tooling, etc.  These pictures were taken in a couple of corners of the A1 test stand on the deck above where the engine will sit.  These are the piping systems that will control and measure what on the vehicle would be the tank pressurization flows coming off the engine. 

The intended point about these last two pictures is that the facilities necessary to properly test a rocket engine are quite involved and quite complex.  The environments are vicious, the tolerances are tight, and everything that goes into or comes out of the engine needs to be controlled and measured.  Indeed, the whole reason for doing engine testing is to gather data so as to better understand how well the design works.

Work continues.  The formal Facility Readiness Reviews for these stands are currently scheduled for early March for test stand A2 and late April for test stand A1.