J-2X Progress: November 2013 Update

It’s been a few months since we talked about J-2X development progress.  So, let me bring you up to date.  Here’s the short version:

  • Testing for engine E10002 is complete
  • Engine E10003 has been installed in test stand A-2 and has successfully completed its first test (a 50-second calibration test on 6 November)
  • Engine E10004 is in fabrication

Okay, so that’s it.  Any questions?

Oh, alright, I’ll share more.

Engine E10002 is the first J-2X to be tested on both test stand A-2 and on A-1.  It saw altitude-simulation testing using the passive diffuser on A-2 and it saw pure sea-level testing on A-1 during which we were able to demonstrate gimballing of the engine.  Below is a cool picture from our engineering folks showing a sketch of the engine in the test position on A-2.


The clamshell shown in the sketch effectively wraps around the engine in two pieces and the diffuser comes up and attaches to the bottom of the clamshell.  This creates an enclosed space that, while the engine is running, creates the simulated altitude conditions.  I’ll show some more pictures of the clamshell when we talk about engine E10003 below.  Next is a cool picture of engine E10002, hanging right out in the open, while testing on A-1.


This next table gives a history of the engine E10002 test campaign across both test stands:


So, let’s talk about the three times that we didn’t get to full duration.

The first time, on test A2J022 we had an observer cut.  Just like that sounds, there was actually a guy watching a screen of instrumentation output and when he saw something that violated pre-decided rules, he pushed the cut button.  We use such a set-up whenever we’re doing something a little unusual.  In this case, we were making an effort to reduce the amount of cooling water that is pumped into the diffuser.  It was our general rule-of-thumb to “over cool” the diffuser.  After all, who cares?  It’s a big hunk of facility metal that we wanted to preserve for as long as possible despite the fact that it always gets a beating considering where it sits, i.e., in receiving mode for the plume from a rocket engine.  However, one of the objectives for our testing was to get a good thermal mapping of the conditions on the nozzle extension.  What we’d found with our E10001 testing was that all of the excess water that we were pumping into the diffuser was splashing up and making our thermal measurements practically pointless.  Thus, we had to take the risk of reducing the magnitude of our diffuser cooling water.  As I’ve said many times, there are only two reasons to do engine testing: collect data and impress your friends.  If our data was getting messed up, then we had to try something else.  Eventually, through the engine E10002 test series we were able to sufficiently reduce the diffuser cooling to the point where we obtained exceptionally good thermal data.  This first test on which we cut a bit early was our first cautious step in getting comfortable with that direction.

The second early cut was caused by some facility controller programming related to facility instrumentation.  Here is a little tidbit of neato information that I’ve probably not shared before about our testing: in the middle of longer runs, we transfer propellant from barges at ground level upwards and into the run tanks on the stand.  The run tanks are pretty big, but they’re not big enough to supply all of the propellants needed for really long tests.  When I’ve shown pictures of the test stands in the past, you’ve seen the waterways that surround and connect all of the stands.  These are used to move, amongst other things, barges of propellant tanks.  Liquid oxygen is transferred using pumps and liquid hydrogen, being much lighter, is transferred by pressure.  In the picture below, you can see a couple of propellant barges over to the left.  This is an older photo of a Space Shuttle Main Engine Test on stand A-2.


Thus, in addition to monitoring the engine firing during a test, you also have to watch to make sure that the propellant transfer is happening properly.  The last thing that you want to happen is have your engine run out of propellants in the middle of a hot fire test.  On test A2J025, there was an input error in the software that monitors some of the key parameters for propellant transfer.  Thus, a limit was tripped that shouldn’t have been tripped and the facility told the engine to shut down.  Other than some lost data towards the end of this test (data that was picked up on subsequent testing), no harm was done.

On test A2J027, there was something of an oddball situation.  We have redlines on the engine.  What that means is that we have specific measurements that we monitor to make sure that the engine is functioning properly.  During flight, we have a limited number of key redline measurements and these are monitored by the engine controller.  During testing we’ve got lots more redline measurements that we monitor with the facility control system.  When we’re on the ground, we tend to be a bit more conservative in terms of protecting the engine.  The reason for this is that when we’re flying, the consequences of an erroneous shutdown could mean a loss of mission.  Thus, we have different risk/benefit postures in flight versus during ground testing.  [Trust me, the realm of redline philosophy is always ripe for epic and/or sophist dissertation.  Oh my.]  Anyway, with regards to test A2J027, when doing ground testing we shutdown not only when a redline parameter shows that we may have an issue (as happened erroneously on test A2J025) but also if we somehow lose the ability to monitor a particular redline parameter.  Thus, we did not shutdown on test A2J027 because we had a problem or because we had a redline parameter indicating that we might have a problem.  Rather, we shut down because we disqualified a redline parameter.

On J-2X, wherever we have a critical measurement (meaning that it is a parameter that can control engine operation, including redline shutdown) we have a quad-redundant architecture.  In the sketch below, I attempt to illustrate what that actually means.


 Thus, we have two actual measurement ports and each port has two independent sets of associated electronics.  We are doubly redundant in order to ensure reliability.  However, does a man with two watches ever really know what time it is?  No, he doesn’t because he cannot independently validate either one.  We have a similar situation, but in our case we simply want to make sure that none of the measurement outputs that we are putting into our decision algorithms are completely wacky.  So we do channel-to-channel checks and we do port-to-port checks to make sure, at the very least, some level of reasonable consistency.  Thus, we cannot know the exact answer in terms of the parameter being measured, but we can decide if one of the measurement devices themselves is functioning improperly.  This process is called sensor qualification.  On test A2J027, our sensor qualification scheme told us that one port was measuring something significantly different than the other port, different enough that something was probably wrong with at least one of the sensors.  That resulted in disqualifying the measurements from one of the two ports.  In flight we would have kept going unless or until the remaining port measurements notified us of a true problem, but on the ground, as I discussed, we are more conservative.

When we investigated the apparent issue, what we discovered was that we should have predicted the port-to-port offset.  It turns out that due to the engine conditions that we’d dialed up for that particular test, we were running the gas generator at a mixture ratio higher than we’d yet run on the engine.  When we went back and examined some component testing that we’d done with the workhorse gas generator couple of years ago, that data suggested that yes indeed, when we head towards higher mixture ratio conditions, our two measurements tend to deviate.  This suggests, perhaps, a greater amount of localized “streaking” in the flow at these conditions.  Localized effects like this are not uncommon in gas generators or preburners.  Because of the particular configuration of the J-2X, with more mixing available downstream of the measurements, the impact due to such variations on the turbine blades is minimized.  This too was shown in the component level testing.  Thus, the sensors were fine and the engine was fine.  It was just out qualification logic that needed reexamination.  Sometimes, this is how we learn things.

So that tells you all about those handful of cases where we didn’t quite get what we intended.  Overall, however, the engine E10002 test campaign was truly a rousing success.  Here are some of the key objectives that were fulfilled:

  • Conducted 13 engine starts – 10 to primary mode, 3 to secondary mode – including examinations of interface extremes for a number of these starts.
  • Accumulated 5,201 seconds of hot-fire operation.
  • Performed six tests of 550 seconds duration or greater.
  • Conducted eight “bomb” tests to examine the engine for combustion stability characteristics.  All tests showed stable operation.
  • Characterized nozzle extension thermal environments.
  • Characterized “higher-order cavitation” in the oxidizer turbopump.
  • Demonstrated gimbal operation (multiple movement patterns, velocities, accelerations) with no issues identified.

Hot on the heels of the success of engine E10002, we have engine E10003 assembled and ready to go.  I love this picture below.  This is the engine assembly area.  We have three engine assembly bays and, on this one special occasion, we happened to have each bay filled.  Engine E10001 is all of the way on the left.  It is undergoing systematic disassembly and inspection in support of our design verification activities.  Engine E10002 had just come back from its successful testing adventure.  And engine E10003 is all bundled up and ready to travel out to the stands to begin his adventure.  [I’m not sure why this is the case, but E10003 has a male persona in my mind so the possessive pronoun “his” seems to fit best.]

e1In the picture below you see E10003 being brought into the stand on A2.  Note the water of the canals in the background.  See the concrete pilings over to the left in the background.  Those are where the docks are for the propellant barges that we discussed above.

enginelake In the pictures below, you can see E10003 installed into the test position.  The picture on the left shows half of the clamshell brought down into place.  Compare this picture to the sketch at the beginning of this article.  The picture on the right shows what the engine looks like with both halves of the clamshell brought down into position.

doubleimage So that’s where we stand.  Engine E10003 has begun testing in November 2013 and continue on into 2014.  As always, I will let you know how things are going and if anything special pops up, you can be sure that we’ll discuss it here at length.  After all, there’s not a whole lot that’s more fun than talking about rocket engines.


J-2X Progress: Two Stands Occupied

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: Engine Assembly, Volume 4

It’s been about three weeks since I last reported on the progress of J-2X Engine 10001 assembly.  What I would like to do is show you pictures of great big additions to the engine, but the truth is that for the last few weeks the engineers and technicians have been diligently plugging away at smaller stuff, at the details.

“It’s the little details that are vital. Little things make big things happen.” – John Wooden

I would hazard to guess that Coach Wooden was talking about basketball – or maybe life in general – when he spoke these words, but on a rocket engine, everything has to work so the details of the big stuff and of the little stuff are equally vital. 

So, here are some pictures and some details…

We’ll start with a picture of the overall assembly and the addition of the item in the dashed, red oval on the right-hand side of the picture.  That is the gas generator.  Yep, that little thing powers both turbopumps and therefore is the driving force behind the whole engine.  Here is a closer picture.

As I’ve mentioned before, during the whole assembly process, things either have covers attached or are wrapped in tape and other protective media so that no debris gets in the engine and so that delicate parts are not damaged.  You can see that here on the gas generator.

Note that in the image of the gas generator above, you will see the “U-duct” from an earlier blog series entry regarding Direct Metal Laser Sintering.  This, right here on the engine, is the piece for which we may have found a future innovative manufacturing method.

Next is a picture of a mounting plate.  This is not even a primary piece of the engine if you were looking at a schematic, but it’s a vital piece nonetheless.  On this mounting panel sits the two Main Injector Exciter Units (MIEUs).  An MIEU is analogous to the ignition coil in your automobile engine but with a good bit more punch.  We use two units for redundancy to further ensure overall reliability.  If, in the morning, your ignition coil goes dead in your station wagon, well you’re just stuck in your driveway.  However, if during a launch mission you can’t get the J-2X started, then you’re stuck somewhere over the Atlantic Ocean at two or three hundred thousand feet.  That’s a somewhat more treacherous situation.  So we use very highly reliable parts and we use two parallel units.

What makes this mounting plate interesting is that it has vibration isolators so that the noise and shaking of the engine don’t impact the electrical components of the units.  Those eight circles on the mounting plate are the tops of the isolators so there are four for each unit.  Kinda cool little details.

Next, more mounts.  In the picture below, you will see two rectangular items, each with eight holes.  These are mounts on which will eventually reside pressure transducers.  There are several such transducer mounts across the engine.  These particular mounts are installed on the arms that hold the oxidizer turbopump.  So, we have mounts installed on mounts and you can begin to understand the complex layering that an engine assembly represents.

One strategy that is used quite often during the assembly process is to do stuff unattached from the main assembly itself.  Over on a separate bench, you put together a bunch of smaller pieces and then take this whole subassembly over to the engine for installation.  Over the past couple of weeks, this is exactly what has been done with the ancillary line “raceway.”  Below is the completed raceway subassembly. 

All of the lines and brackets and nuts and bolts were separate pieces when the engineers and technicians began. 

Each line in that assembly is different since each line represents different fluids coming to or coming from the engine at different pressures and temperatures.  There is helium, oxygen, hydrogen, and even nitrogen.  There are pressures over 3,000 psi and less than 50 psi.  There are temperatures approaching the boiling point of water and those less than 400 degrees below zero Fahrenheit.  Thus, some of these lines shrink from the cold.  Some of them stiffen with high pressure.  Yet all of them have to be flexible to accommodate the gimballing of the engine and every one of them is vital either to the engine or to the vehicle.  In other words, it is a complex design, a complex manufacturing process, and a complex subassembly to put together.  And it all has to be correct.  Details, details, details!

Lastly, I’d like to toss in a cool picture from the test stand.  Below is a picture from test stand A-2, with the engine mass simulator installed.  This is where J-2X Engine 10001 will be tested.  The brightly painted, yellow hunk of metal is supposed to weigh the same as a J-2X and have the same dimensions.  It’s used for checkouts of various systems including the test stand.


Another thing of note in that picture from A-2 is large gray object to the right.  That is half of a water-spray system that will be used during testing when no nozzle extension is installed on the engine.  Near the top of the picture is a hinge painted bright red.  When deployed, the gray water-spray structure will have been swung down so that its two pieces (the one shown and the other one to the left and out of the picture) join at the bottom of the engine nozzle.  This is all part of the system to deal with the substantial, combustible, fast moving, and very hot exhaust from the engine during test.  This water-spray system was installed specifically for J-2X testing.

That’s where we stand.  The details of the engine assembly are coming together, with more parts arriving at the NASA Stennis Space Center every day, and with the test stand is being readied to accept installation of the engine.  This is Volume 4 of the assembly saga.  By the time Volume 5 is ready for the blog, we should be very close to having a fully assembled engine.  Wahoo!