Uncategorized – Page 5 – Liquid Rocket Engines (J-2X, RS-25, general)

J-2X Extra: Shiny Metal Pieces

Finally, it has been discovered: Proof that rocket engineers can indeed have a sense of humor. This is an exchange that actually happened in a meeting here at NASA not too long ago.

Manager #1: What are those feedlines made of?
Manager #2: Really shiny metal.

Translation: He didn’t know, but he would find out. Okay, so it’s not Saturday Night Live material, but it was funny in context. (You had to be there…really.)

The truth is that we use lots and lots of different kinds of shiny metal in all kinds of strange shapes, under all kinds of severe conditions, and with uncompromising standards against failure. We use aluminum and steel and titanium and copper alloys and nickel-based super alloys and, sometimes, rare earth metals and precious metals. We cast it, forge it, roll it, spin it, weld it, you name it. Suffice it to say that if you like or know something about metal working or machining or welding or metallurgy, then even if you haven’t got a clue about rockets, we’ve probably still got a place for you. It’s a fascinating field that ranges from enormous factory tooling necessary for large structures production all of the way down to microscopic crystal formations deep within the parts being produced.

Now, the pursuit of new technology demonstrations has never been a primary objective for the J-2X development effort. We are supposed to make it work – that’s the prime directive. However, in the course of J-2X development, we came across a situation where we were forced to consider innovative solutions and, from that consideration, identified an opportunity to pursue something really pretty cool and it has to do with shiny metal.

So let’s start at the beginning. In order to avoid combustion instabilities in the gas generator assembly, we found that we needed a very short gas generator discharge duct. What is a combustion instability? In this case, think of a pipe organ. The size of the pipe determines the pitch. Big pipes make big booming sounds. Little pipes make little whistling sounds. What we found through component testing was that the pipe connected to the gas generator was acting like a pipe from a pipe organ and the sound was so big and so loud that it had the potential of ripping the whole thing apart. To find a place where we were de-tuned from the booming loud vibrations, we had to make the pipe quite short.

Now, though, we had a problem. We had a duct so short that it basically looks like a U as pictured in the drawing above. Note, however, that the unit used on the engine is welded on one end and flanged on the other. This picture is a drawing of the test configuration. But regardless of the flanges and such on the ends, this part is basically U made out of very high-strength “shiny metal” (a nickel-based super alloy). Given the diameter of the tube, the strength of the metal, the thickness of the walls, and the fact that we can’t allow the walls to get too thin from bending, we had a devil of a manufacturing situation for what looks like, on the surface, a relatively simple component. So, we (and that’s the big “we” of both NASA and our prime contractor, “Pratt & Whitney Rocketdyne”) started looking for solutions.

Below is a picture of the baseline solution illustrated with a manufacturing demonstration unit. Rather than trying to do the whole bend in one piece, it is done in three pieces, each with a 60-degree piece of the overall 180-degree bend. Those three pieces are then welded together; the end pieces are trimmed back; and the flange is welded on the end. It works. But it is labor intensive with all that welding and with all of work that comes along with welding along the lines of inspections and re-work cycles. To give you an idea of size here, the duct is 3.5 inches in diameter so it is a healthy hunk of metal.

Now comes the really interesting part.

In addition to the baseline solution, another solution was proposed. It’s called “Direct Metal Laser Sintering” or DMLS. The company that does this is called Morris Technologies (look them up!). And, like most high-tech stuff, if I knew the nitty-gritty details I wouldn’t be able to share them, but I can tell you the basics. First, you start with a whole bunch of very fine metal powder. Next, you load into the computer your three-dimensional CAD model for the part you want to make. The CAD model is analytically cut into thousands of horizontal slices. Then, in a special, automated chamber, a thin layer of metal powder is laid out and fused by a laser into the shape of the first slice of from your CAD model. Then another layer of powder and fused slice is added, and then another, and then another. With each slice, a layer of powder is laid out and fused to the previous layer precisely duplicating your CAD model a little bit at a time. So, any shape that can be decomposed into and built up from a series of thin layers can be made. Below is a picture of a small pump impeller with a relatively complex geometry that was made by Morris Technologies using this process.

Ignoring how it works, you’ve got this: you put in your computer model; you put in the powder; come back a week later; and, your part is cooked (actually there are post-process surface finishing operations, but that’s just a minor detail). It’s almost like something from The Jetsons cartoon series.

So, we asked, can you make our U-shaped tube? The answer was: almost. The size limitations of the existing chamber dictated that we could do the whole tube part but the flanges would have to be welded on. Still, it’s a pretty good demonstration. Below, you can see a couple of pictures of the finished part.

But that’s not the end. So, we made a fancy pipe. Big deal.

Here is the big deal: making it was very cheap and very fast. Of course, cheap isn’t always helpful if the thing doesn’t work. So, we have to prove that it works. Towards that end, we are performing materials properties tests on samples made in the chamber simultaneously with the duct, we are doing non-destructive evaluations of the duct itself, and we plan to incorporate it into a component level test series of the workhorse gas generator. Below is a kind of creepy picture of the duct after it was inspected for tiny flaws using a fluorescent penetrant solution and ultra-violet light.

Because of the severe environments that this duct will see, the material properties throughout the duct have to be consistently good. There can’t be any flaws on the surface that could lead to the development of cracks. So far, the piece has come through all of the inspections with flying colors. The next step will be actual hot-fire testing. Below is a photograph of previous testing of the workhorse gas generator.

If everything goes well and post-test inspections show that the part did not sustain damage, we will have taken a huge step towards making this fabrication approach viable for not only this particular piece of the J-2X engine, but for all kinds of parts on all rocket engines in the future. There are technology issues to overcome – notably current limitations on the size of the parts to be made – but this process is potentially an order of magnitude improvement in terms of the costs for building complex, severe environment components out of that ubiquitous substance that we’ve got all over in a rocket engine, i.e., “shiny metal.”

J-2X Progress: Test Stands Moving Towards Readiness

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.

J-2X Progress: Valves, Commands into Action

Everyone seems to like analogies between the composition of a rocket engine and that of the human body. These are often colorful but not always helpful. In some cases, however, they work pretty well.

Okay, so let’s start with your body as it is. Now, imagine removing all of your bones. Guess what? You’re an immobile lump. Even if your brain is sending signals and your muscles are contracting, you’re not really moving anywhere.

This time, let’s instead start with your body as it is, but now imagine removing all of the muscles and tendons that connect the muscles to the bone. You’ve got a central nervous system and you’ve got bones, but with nothing to flex, the chain is broken and you’re stuck where you sit (assuming that you can still actually sit).

And, of course, if you instead start with your whole self and imagine removing your brain and/or your central nervous system that connects your brain to your muscles, again, you’ve achieved perfect immobility (i.e., you look like me on Saturday afternoons during college football season).

The point is that in order for you to be up and about, shoveling snow, doing laundry, playing pool, typing, whatever, you need both the command center that figures out what signals to send — your brain — and you need things that turn those signals into action — your muscles and tendons and bones. In a rocket engine, the analogue for the brain is the engine controller. It is a computer that receives instructions from the vehicle and sends out commands to the engine pieces so as to fulfill those instructions. The analogue for the muscles are the valve actuation systems. These are the things that “flex” and cause movement. And the analogue for the bones, the final effectors that make things happen, are the valves.

The controller sends out signals and then the actuation system responds by shuttling pressurized working fluid — helium for J-2X though some engines use hydraulic fluid instead — where it needs to go so that the valves move and the engine comes to life. The engine goes from being a lump of inert, shiny metal to a “living” beast of flowing propellants, spinning turbomachinery, lots of fire, and thundering, rumbling thrust.

On the J-2X, there are 42 valves. Most of this number is made up of small valves like check valves, solenoid valves, and valves in small lines like the bleed lines. There are also a handful of big valves — the primary valves — that directly control the flow of propellant and, in one case, combustion products along the plumbing of the engine. Each of these primary valves is connected to a valve actuator, i.e., the muscle. These valve actuators convert the energy of high pressure helium gas into mechanical rotation of the valve. This is accomplished by pressurizing cavities and moving pistons and, in this way, the valve is pushed opened or closed. I’ve used this schematic shown below before, but it is useful here as well since it illustrates the primary J-2X valves: Main Fuel Valve (MFV), Main Oxidizer Valve (MOV), Gas Generator Fuel Valve (GGFV), Gas Generator Oxidizer Valve (GGOV), and the Oxidizer Turbine Bypass Valve (OTBV).

The control logic for J-2X is relatively simple. The whole subject of different kinds of control logic is a good topic for a future article, but suffice it to say that for normal operation the J-2X: starts on command, can change between two power levels on command, and shuts down on command. The control system is designed to do other things as well, including monitoring the health of the engine, but these operations are the commanded functions. Start and shutdown can be simplistically thought of as: the valves open and the valves close. It’s a bit more complicated since the timing of opening and closing is extremely important, but the open/close notion is basically true. The oddball action is the one consisting of changing power levels. That is accomplished by controlling the power to the oxidizer turbine via the OTBV. This bypass valve effectively allows for limited, independent control of the two turbopumps. By altering the power to the oxidizer turbopump (OTP), you can control the engine thrust level (and, simultaneously, mixture ratio).

The OTBV for J-2X is designed and built by Pratt & Whitney Rocketdyne (PWR), the prime contractor for the whole engine. In addition to being responsible for the “oddball action” on the engine of changing power levels, it represents a challenging design due to the range of operating conditions. Unlike the other primary valves on the engine that see, essentially, one narrow range of environmental conditions, the OTBV has to function in temperatures approaching 420 degrees below zero Fahrenheit (liquid hydrogen conditions) immediately prior to start and then, suddenly, within 1 second of ignition of the gas generator, see temperatures approaching 750 degrees above zero Fahrenheit (combustion products). That broad range of operating conditions requires special design considerations and special materials. Not only do you have to worry about wear and tear under such harsh conditions, but you also have to think about simple operation under the extremes of thermal expansion.

The original, Apollo-era J-2 engine also had an OTBV, but it was used slightly differently and was designed much differently. It was a butterfly valve whereas the J-2X OTBV is a ball valve.

No, the valves shown in the picture are NOT rocket engine valves. I can’t show any internal workings of rocket engine valves. In fact, I am not even allowed to describe the general design details that make the J-2X OTBV kind of unique. However, the basic elements of rocket engine valve functionality for butterfly and ball valves are essentially the same as these water valves. The biggest difference is the replacement of the handles with pneumatically driven actuators. Back during the Apollo era it would seem that butterfly valves were most frequently used, but after many years of usage on the Space Shuttle Main Engine, ball valves are often preferred these days. They generally require less torque to move and they generate better flow characteristics and flow rate control capability.

The first OTBV unit for use on the upcoming development engine testing for J-2X is in the later phases of manufacturing at the PWR in Los Angeles. All of the individual piece parts are schedule to be complete by the beginning of February and assembly will begin the middle of February. The valve then will be integrated the actuator and shipped to the NASA Stennis Space Center to be put on the first engine.

J-2X Extra: The Faces Behind J-2X, NASA MSFC, Part 1

Years ago, I worked in support of the Space Shuttle Program, specifically on the Space Shuttle Main Engine (SSME) from the engineering side of the house. I was an analyst and sometimes Datadog. By happenstance, I learned from another relative that whenever a launch occurred my mother, back home in Pennsylvania, would routinely tell folks at work or at church or wherever that her son was responsible for that Shuttle launch. I said, “Mom, don’t tell people that. I’m just one of hundreds or, really, thousands of people behind the whole thing.” She replied, with biased motherly wisdom, “Yes, but you’re all responsible for doing a good job so that the whole thing works, right?”

Lesson learned #1: Don’t argue with Mom.

Lesson learned #2: She was right. Any venture as big and complex as Shuttle, or even as big and complex as the development effort for J-2X really does require that everyone does their job well. In that way, we’re all responsible.

So, I’m going to introduce you now to just a few of the people (out of hundreds) responsible for making J-2X a reality. Right now I’ll focus on the top leaders Upper Stage Engine Element office here at NASA Marshall Space Flight Center. In another posting, I’ll tell you all about the subsystem managers. And perhaps, later if I’m lucky, I’ll sneak some pictures of the good people out at Pratt & Whitney Rocketdyne as well.

So, here we go…

First, we have our Element Manager, Mike Kynard. He is a graduate of the University of Alabama [Roll Tide!], grew up not far from Tuscaloosa, and, to put it mildly, is a devoted fan of Crimson Tide football. He started working at NASA MSFC as a co-op in college back and accepted a full-time job in 1985. He spent a good spell supporting SSME from the resident office at NASA Stennis Space Center in Mississippi in the 1990s and eventually rose to become the deputy project manager for SSME back in 2004. He has two beautiful little girls and, in addition to everything else, somehow finds the time to play on a team with me in a billiards league. Sometimes, on rare occasions such as a blue moon, he even manages to beat me in a game of 8-ball.

Mike’s deputy is Tom Byrd. He is a graduate of Memphis State University who, once upon a time long, long ago was a competitive bicyclist. He started working here at NASA MSFC in 1983 in the area of valves and actuators, specifically supporting SSME (yes, you’ll see SSME as a recurring theme both here and when later tell you about the subsystem managers). Along the way since then, he was a subsystem manager for the Fastrac engine development effort (a NASA MSFC in-house project), was the NASA chief engineer for COBRA engine development effort, and he supported the Shuttle program in the area of systems engineering and integration. Plus, back in 1994, representing the NASA engineering community, he spent a total of four weeks in Russia studying their space transportation technologies. Tom has one young son who, given the uncanny resemblance, we suspect might be the product of a direct cloning experiment … but we don’t talk about that too much.

Our Chief Engineer is Eric Tepool. His job is to function as the balance point between technical and programmatic aspects of engine development. He also indirectly functions as a balance in another way, relative to our element manager’s tendencies, in that he is a graduate of Auburn University [War Eagle!]. After making his mark as a star high school athlete, just as his father was a star high school and collegiate athlete, Eric turned down athletic scholarship offers to settle into the pursuit of engineering. He started at NASA in 1990 in the turbomachinery branch, supported development and certification of the two new turbopumps for the Block 2 SSME configuration, moved on to be a subsystem manager for the COBRA engine development effort, resident manager for the Fastrac project, and the NASA-side lead systems engineer for the Integrated Powerhead Demonstrator project. He has two kids currently in college (one at Alabama, one at Auburn … yikes!) and one soon to be on her way to college.

The other “technical balance point,” in accordance with the NASA governance model, is our Chief Safety Officer Phil Boswell. He’s been working here at NASA MSFC since 1985. He started right after graduating from the University of Alabama at Birmingham (UAB). While he started in the Safety and Mission Assurance Directorate, and he’s back there now, in the interim he spent many years working within the Engineering Directorate on such projects as microgravity experiments for Shuttle and the MIR space station, the Orbital Space Plane program, and just about every propulsion element of the Shuttle itself including engines, tanks, and boosters. Phil played on the college tennis team, plays tennis still, and is an excellent golfer. His son, who will be attending UAB starting in the autumn (pre-med) follows in his father’s footsteps and is also an excellent golfer. Little known fact about Phil: he loves swing dancing and even took a year of lessons with his wife.

So, that’s the top leadership group for the J-2X development effort. Good guys, hardworking engineers and managers, all around.

J-2X Progress: The Main Combustion Chamber — the Heart of the Fire

My background is analytical modeling. There are all kinds of modeling in use today, including some extraordinary computational fluid dynamics and structural dynamics work that is amazing, but back when I did more hands on work I did zero/one-dimensional, system-level modeling of fluid systems, thermodynamics, and heat transfer. Rather than looking at the micro-level, my work was usually a step back at the macro-level.

I’ve told you all that because, over the years I found that one of things that I found most challenging and most enjoyable to model is combustion devices. Take the main combustion chamber (MCC) as the prime example. Its job is to contain the combustion, squeeze the combustion products to sonic velocity, and then direct them towards the nozzle. It’s just a big, hourglass-shaped tube. It all sounds simple until you realize that those combustion products are at about 6,000 degrees Fahrenheit and, for the J-2X, at a pressure of over 1,300 pounds per square inch. How it is that the MCC doesn’t melt or burst – or both – is amazing.

So, let me tell you a little about MCCs.

The only way to build one where the walls don’t melt during operation of a large liquid hydrogen / liquid oxygen engine is to actively cool them. This means flowing cold hydrogen inside the walls. On one side of the wall you have combustion 6,000 degrees and on the other side, you have hydrogen that is typically entering at less than 100 degrees above absolute zero. Now you see why this is a delight for someone who enjoys modeling thermodynamics, fluid flow, and heat transfer.

How do you make walls that allow for active cooling? Well, years ago, back during the era of the Apollo Program the walls were made of tubes. They took a whole bunch of tubes, bent them into the profile shape of an MCC, stacked them up into a circular pattern, lay in or pack in binder metal, and then brazed them together. Brazing is essentially a welding process where you stick the whole thing into an oven, make it really hot, and the thing melts together (as someone who enjoys cooking, I tend to think of it kind of like a stiff metal stew). In this case what melts together is binder metal stuck between the tubes so that when you take it out of the oven, you’ve turned several hundred tubes into a single piece. Note that the regeneratively-cooled portion of the J-2X nozzle is made in this manner using tubes, but when doing this with an MCC where the pressures are higher and the temperatures are hotter: we’ve advanced a long way since the 1960’s.

First of all, in order to make the tube-wall MCC structurally sound, you were kind of forced to use steel tubes (steel of some sort at least). What you’d really like to use is something like a copper alloy that has higher thermal conductivity properties. Copper tubes might be possible, but you would have to put behind them a steel support structure, a jacket of some sort. That, however, introduces potential issues of hot stuff or high-pressure stuff seeping behind the tubes and causing all kinds of problems including catastrophic failure of the engine. The hourglass geometry required for the combustion products flow path complicates nearly all of the structural issues.

Then, along came the development effort for the Space Shuttle Main Engine (SSME). Here you’re dealing with MCC pressures over 3,000 pounds per square inch so you needed a whole new approach since tubes just weren’t going to cut it. What they came up with, conceptually, is the same thing used by J-2X and most other large rocket engines, although the means for fabrication vary. They used a liner and jacket concept. The liner replaced the hundreds of tubes. It is a single piece with the hourglass shape within which the combustion takes place. Around the liner is fitted a structural jacket. Thus, the liner can be made of something like a copper alloy to deal with the heat transfer issues and the liner can be made of some steel or nickel alloy to deal with the structural issues. Where before the tubes provided the coolant flow path, here groove are cut into the backside of the liner so that when the liner and the jacket are fit together, these grooves become channels. Ta-da!

The first step in manufacturing an MCC involves hot spin-forming a copper-alloy forging. The resulting piece is then machined to a precise contour. The liner is then slotted, meaning that the grooves for the coolant flow passages are cut into the backside away from where the combustion products will flow past.

The really tricky part about this kind of MCC is making the whole thing fit together and stay together given the different metals being used. The different metals have different properties and different structures at the micro level so a variety of methods including electro-plating and brazing and welding methods are used to make a single unit. It is these details that are proprietary and export-controlled technologies that cannot be revealed but that make the whole thing possible. Luckily, this humble analyst knows little about metallurgy so there is almost no danger of me exposing something useful-but-sensitive to the world at large. In the past, developments for methods of producing a robust bond between the liner and the structural jacket resulted in cheaper, more reliable, yet heavier design. The J-2X design, however, has allowed for significant weight decreases by optimizing the design for post-bond machining.

Another recent innovation in MCC fabrication, and one being pursued for the J-2X MCC design, is the use of castings for the manifolds that distribute the coolant to the flow passages and collects the coolant at the end of the passages. These pieces of hardware see very high fluid pressures due to their function as manifolds but also are used by a number of other components for structural mounting into the engine system. Thus, they are heavy and complex pieces. In the past, the typical practice was to machine these parts out of wrought forgings. The J-2X cast manifolds offer a significantly more cost efficient way to produce these parts.

The MCC for the first J-2X development engine is currently planned to complete fabrication in early February 2011. All of the major parts for the second MCC are already in work including the manifolds, the liner, and the jacket. It is slated for completion in July. So now, analytical modelers, like me, will just have to sit back and wait for the testing to commence in a couple of months. Then the process of reconciling models to test results, understanding the clash of approximations and standard correlations and actual, particular physics, starts in earnest. That’s the truly fun part!

J-2X Progress: Turbomachinery: One More Pic

The previous article for this blog, the one down below regarding progress with the J-2X turbomachinery, was written about 2 weeks ago. There is an inherent lag in the process for big articles. That’s just the way things are. So, that being said, I am tossing a supplemental entry on here to provide an update: The turbopumps for Engine 10001 are assembled!

Below is a picture of the Pratt & Whitney Rocketdyne team responsible for assembling the Fuel Turbopump standing around the completed unit. Way to go guys!

Inside The J-2X Doghouse: The Gas-Generator Cycle Engine

Welcome back to the J-2X Doghouse. The last time that we met here, we discussed the fundamentals of what exactly makes something a rocket. As I explained, on the conceptual level, rockets aren’t really “rocket science.” You get the propellants together, light them on fire, and eject them out the back end of the vehicle. Simple enough.

Okay, but how do you move that much propellant and make that much smoke and fire, enough to propel something as big as, say, the Saturn V that was over 300 feet tall and weighed millions of pounds? That’s where things get interesting and technically difficult. As I said before it is all a matter of power. And to get power you use an engine.

What makes a rocket engine an engine is the fact that it contains more than just a combustion chamber where the propellants mix. It is an arrangement of machinery that, once started, feeds and powers itself. During operation, a rocket engine uses some cycle – some circuit of piping and thermodynamics and combustion and valves and control system and rotating machinery – to keep itself up and running and generating thrust.

Think about your car engine. You turn the key, the engine gets up and going, and then it can sit there for hours idling, running happily all by itself, converting gasoline and air into mechanical energy, with no additional input from you. You don’t have to manually pump the gas into the injectors (or the carburetor). You don’t have to plug it into an outlet to feed it more electrical energy. It’s self-sufficient until you turn it off or until you run out of gas. That’s what truly makes it an engine. It’s similar with a rocket engine except that the product is not mechanical energy; the product is very fast moving gases generating lots of thrust.

For rocket engine conceptual design, in terms of making it an engine, the goal is always, “How do you keep the pumps pumping?” These are extremely powerful pumps moving lots and lots of fluid, so you need some powerful energy source to drive them. The answer is to use what you’ve already got in the engine: the propellants. There are different ways to do this and thus you have different engine “cycles,” i.e., component arrangements. The most common rocket engine cycles are the gas-generator cycle (examples include J-2X, J-2, F-1, RS-68, and Vulcain 2 – see pictures above), the expander cycle (examples include RL10 and Vinci), and the staged-combustion cycle (examples include Space Shuttle Main Engine and RS-170/180). In addition to these, there are many other cycles and variations as well. Each different cycle has advantages and disadvantages and, usually, constraints linked to physics. Choosing the right cycle to fit the mission application is generally the first decision that an engine designer has to make. Because this is a blog dedicated to J-2X, I will focus on the gas-generator cycle engine.

Ideally, what you would want to do with a rocket engine is use all of your propellants in as efficient manner as possible meaning that you would want to use all them in the production of thrust. In a gas-generator engine, however, you concede right up front to a loss of some efficiency to achieve greater engine simplicity. You use a certain amount of the propellants brought into the engine almost entirely to keep the engine running rather than for generating thrust. In practice what this means is that you have a separate, small combustion chamber within the engine that does nothing but produce gases to drive the turbines connected to the propellant pumps. As compared to the large quantities of propellants being pumped through the whole engine, the amount going to the gas generator is small (less than 3% for J-2X), but once used to drive the turbomachinery, the exhaust is drained of much of its thrust-generating energy.

Below is a simplified schematic of a gas-generator cycle rocket engine like the J-2X. The propellants, liquid hydrogen (fuel) and liquid oxygen (oxidizer), enter the engine and go immediately into the pumps: the fuel turbopump (FTP) and the oxidizer turbopump (OTP). There, the mechanical energy of the spinning pumps is turned into high pressures in the liquid propellants.

After exiting the pumps, a small amount of each propellant is tapped off to supply the gas generator (GG). The GG is, in essence, a small rocket engine embedded within the larger rocket engine. It makes hot, high-pressure combustion products, steam and gaseous hydrogen, that are used to drive first the turbine connected to the fuel pump and then the turbine connected to the oxidizer pump. After driving the two turbines, this still-warm gas is used first to warm the helium flowing through the heat exchanger (HEX) that is used to pressurize the oxygen tank of the stage and is then dumped along the walls of the nozzle extension to keep that relatively cool. The video below is a component test of the J-2X GG performed at NASA MSFC. Even with the relatively small amount of propellant that the GG burns, an enormous amount of energy is released to drive the turbopumps.

The rest of the liquid oxygen coming out of the oxidizer pump, meaning that which is not going to the GG, is directed through the main injector and into the main combustion chamber (MCC). The main injector is analogous to a fuel injector in a car engine except that here it injects two propellants through hundreds of injector elements. The effectiveness of this injection and the mixing of the propellants are crucial for overall engine performance.

The hydrogen circuit after the fuel pump is more complicated. This is because the hydrogen is used to cool the nozzle and combustion chamber walls. The walls of these two components are essentially hollow. They contain hundreds of passages for the hydrogen to flow thereby keeping the walls from melting due to the extreme high temperatures of the contained combustion zone. After doing its job as coolant, the hydrogen is then directed through the main injector and into the MCC. Not shown on the diagram is the fact that a very small amount of the warm hydrogen gas is tapped off prior to entering the main injector and is routed back to the stage to pressurize the hydrogen tank (like the helium through the HEX on the oxygen side).

It is in the MCC where the mixed hydrogen and oxygen combust to make steam and residual hydrogen gas. The temperature of that combustion is approximately 6,000 degrees Fahrenheit and in the J-2X the pressure is approximately 1,300 pounds per square inch. These combustion products are then accelerated to sonic velocity at the converging throat of the MCC and then to supersonic velocities down the diverging nozzle and nozzle extension. As discussed previously, it is the high-velocity expulsion of these hot gases that produces thrust.

Note that the turbine exhaust gases dumped along the nozzle extension still generate some thrust, but not as effectively as the combustion products that are accelerated through the nozzle throat. This loss of effectiveness is the price that you pay for this relatively simple engine cycle. As a comparison to a more complex engine cycle, do a web search for the schematic for Space Shuttle Main Engine (SSME).

FYI, the other items denoted on that GG-cycle schematic above are the control valves: the main fuel valve (MFV), the main oxidizer valve (MOV), the gas-generator fuel valve (GGFV), and the gas-generator oxidizer valve (GGOV). These primary valves, along with several other minor ones, are used to control the engine during the start and shutdown of the engine.

So that’s how a gas-generator cycle engine like the J-2X works. As this blog continues and as we head towards testing next year, I will continue to report on the progress of the components that make up the engine.

J-2X Progress: Turbomachinery — The Rotating Components

It was once pointed out to me that most of a rocket engine really isn’t a whole lot more than a jumbled bunch of specialized plumbing. Notable exceptions to that general rule are the engine controller — the brain of the engine — and the rotating components, i.e., the turbomachinery. Of course, the person who was telling me this was a turbomachinery person, which means that I cannot entirely concede the point lest I yield my traditional posture of giving them a hard time. But there is no denying that rocket engine turbopumps are truly remarkable pieces of machinery.

What is a rocket engine turbopump? Typically, and this is true for J-2X, a turbopump consists of two parts: a turbine and a pump (hence the name). Pump portion is what draws in the propellants into the engine the pushes that fluid through all of the “plumbing” that leads, ultimately, to its fiery, thrust-generating expulsion. The turbine portion is what provides power to drive the pump. The turbine converts the power of hot gases into the power of rotational machinery. The pump converts the power of rotational machinery into fluid power otherwise known as pressure (thousands of pounds-force per square inch) within the propellant being pumped. For J-2X, there are two turbopumps: one for pumping liquid hydrogen (fuel) and one for pumping liquid oxygen (oxidizer, or often called “LOX”).

Soon, I will be writing an article for this blog that further explains the system-level workings of a gas-generator-cycle rocket engine like J-2X. So, stay tuned.

Recently, the Pratt & Whitney Rocketdyne (PWR) / NASA turbomachinery team has made significant progress toward completing the final assemblies of the hydrogen and oxygen turbopumps for the first J-2X development engine (E10001). The first two images show two major milestones for the liquid oxygen turbopump. In the first picture, the turbine-end manifold (top of the photo) is shown being mated to the pump-end volute that is secured in the build dolly.

J-2X Liquid Oxygen Turbopump after Successful Turbine Manifold Installation

The second picture shows that the oxygen turbopump has now been flipped over with the pump end now near the top of the image and the turbine manifold below. It is sitting in an oven where it underwent a drying operation after successful insertion of the first-stage turbine disk and the turbopump shaft.

J-2X Liquid Oxygen Turbopump Following First Stage Turbine Disk and Shaft Installation

The hydrogen turbopump has also made good progress by completing all pump-end assembly operations and the turbine manifold installation. The first picture of the fuel turbopump below was taken after the successful assembly of the impeller into the bearing support, and subsequently that bearing support assembly being installed into the pump end volute, which has been chilled in cryogenic liquid nitrogen. The nitrogen was used to create the proper fit for the volute and the bearing support to prevent hydrogen leakage under engine operating conditions.

J-2X Liquid Hydrogen Turbopump After Successful Mating of Volute and Turbine Bearing Support

The process of (1) chilling one metal piece so cold that it shrinks, (2) heating another metal piece so warm that it expands, and (3) then fitting the two pieces together in those states is a process used throughout engine assembly on many different components. It is a means for accomplishing an “interference fit” (also called a “compression fit” or a “press fit”), which means that the two parts, machined to their appropriate tight tolerances, would otherwise not quite fit together — almost but not quite. At room temperature, the pieces would interfere with each other if you tried to push them together. The chill/heat process during assembly allows them to fit together very, very tightly.

The second fuel turbopump picture below shows the successful installation of the turbine manifold onto the turbine bearing support representing a major milestone in the assembly process.

J-2X Liquid Hydrogen Turbopump Turbine Manifold Installed Onto Bearing Support

In the beginning of this article, I told you that rocket engine turbopumps are remarkable pieces of machinery. Yet, what I have shown you in the pictures are mostly images of shiny-metal external pieces, big hulking manifolds and volutes. For reasons largely having to do with export control considerations (Rule #1: blog author does not go to prison!), I cannot show you pictures or detailed schematics of the inner workings. I can describe them by saying that on the pump side you have an inducer, which looks like a fluid screw, and that feeds an impeller for a typical centrifugal pump. On the turbine side, I can tell you that there are two rotating disks of turbine blades and, effectively, two rows of stationary blades called stators or nozzles. And in between the pump ends and the turbine ends are a series of seals that separate the two ends. Ideally, the only contact between the pump and turbine ends would be the mechanical power of the rotating shaft.

To give you a better appreciation of the “remarkable” aspects of these units, let’s consider these machines in terms of their output. In terms of horsepower, the table below compares various machines with which you are likely familiar. At only 30 inches long and 20 inches in diameter, the J-2X hydrogen turbopump produces an incredible 16,000 horsepower. This power level is equivalent to more than 120 automobiles, or 90 light aircraft, or even 5 diesel-electric locomotives. In terms of energy generated in a small package, the J-2X fuel pump provides almost as much power as a large aircraft engine on the Boeing 747.

The two turbopumps for the first J-2X development engine are currently on track to complete assembly in December. These units will then be boxed up, shipped to NASA Stennis Space Center, and await engine assembly. So, the first development engine coming soon! And then, it’s on to testing!

Note that thanks are due to Jeff Thornburg, Upper Stage Engine Element Deputy Turbomachinery Subsystem Manager, for providing the largest portion of the technical updates and pictures that informed this article.

J-2X Extras: Rebuilding the Past

Several years ago, I was determined and ready to buy a new vehicle. I happened to be at my grandparents place at the time in upstate New York and my grandfather saw me perusing the local paper for dealerships making good deals. I told him that I was interested in getting a new pickup truck, something that I could use to go back and forth to grad school and carry all my stuff.

“Well, I’ll tell you what,” he said, “the best darn vehicle I ever had was a 1937 Ford Pickup. That thing just ran forever, it seems to me.” Then he winked, smiled, and added, “And, even better, I met your grandmother while I was driving that thing.”

So I went on down to the local Ford dealership and announced to the salesman wearing a plaid jacket and striped tie that I wanted to buy a pickup truck. My new best friend smiled a huge smile, shook my hand, and led me over to the part of the showroom dedicated to their latest line of beautiful F-150s.

“No, no,” I said, “I want to buy a 1937 pickup.”

“But we don’t sell used cars here, son, and certainly not classics like that.”

“I don’t want a used 1937 pickup,” I replied. “I want a new 1937 pickup.”

“There is no such thing,” he said, in an obvious state of confusion or maybe annoyance.

I scratched my head. “I don’t understand. I mean, you guys still have the drawings and such, right? And if you can build these big, shiny new things, then you can certainly go back and build something more simple, right? My granddad told me not to get suckered in. He said that I don’t need all these new-fangled bells and whistles.”

For the next hour, the salesman, named Pete by way (Pistol Pete, he chuckled to himself), tried to talk me into buying one of the current year models. He showed me everything, explaining with fast-talking expertise the dramatic advantages that his trucks had over the competition and even, he tossed in for me, far older models. But I was not totally convinced. Pistol Pete just shrugged and gave me his business card with a scribbled phone number for someone at their corporate headquarters who might be better able to help me. I left thinking that might have just lost the best friend I’d had for the last ninety minutes.

The next day, I called the corporate headquarters and tried to make clear what I wanted. I got bumped from department to department several times until I finally got someone named George seemingly willing to indulge me.

I told George what I wanted, but I also told him that I was impressed with what Pistol Pete the salesman had shown me. I said, “I’d really like to get that 1937 pickup with an automatic transmission, with overdrive, and cruise control. I would really like more speed and better handling. Better gas mileage too. Also, I’m thinking that I need more safety stuff, so I’d like that pickup to have air bags, modern crushable bumpers, and the latest auto glass. Plus, I’d like a bit more life and reliability, so building in that self-diagnostic system and computer would be good. And I read that some new body materials are less prone to corrosion, so build it out of new stuff.”

“So,” said George, who sounded perpetually half asleep when he spoke, “you want a 1937 pickup truck, with all modern features, built to all modern standards, with more performance, with better reliability, and with greater safety. Do I have that right?”

“Finally,” I said, “someone who understands! You’ve got it! That’s exactly what I want!”

“Right, then we will have to design you a new vehicle from scratch. That will take about two years of design effort, building a few prototypes, and then another couple of years of road testing and then certification from the federal highway authorities — which, by the way, will result in a bunch more changes unless you only want to drive it on Sundays and holidays like an antique car. Overall then I’m projecting that we’re talking, maybe, forty or fifty millions dollars as a starting point.”

“Huh? What are you talking about? That’s outrageous,” I yelled into the phone in dismay. “You built this thing 50 years ago, didn’t you? It didn’t cost that much then for goodness sake, even with inflation. Surely you’ve got the drawings just lying around somewhere, right?”

“No, actually we don’t,” said George in his tired monotone. “And even if we did and we had to build exactly a 1937 pickup, as it was built back then, it would be a project. To start, we would have to rebuild all of the tooling, recreate the materials we used back then, and reconstitute suppliers who have long since gone out of business. Add to that all of your new requirements and, well, you’ve got a whole new vehicle, right? So, basically, we’ll just have to start from scratch.”

I hung up the phone in an utter daze. Several weeks later, I bought a little Toyota pickup. I drove it for lots of years. I plan to someday tell my grandson that it was the greatest thing ever on four wheels and see where that leads…

One of the first questions that I got when I started this blog was why we didn’t just dust off the drawings of the old J-2 used for the Apollo Program and use that rather that launching into the J-2X development effort. Hopefully this little story provides a bit of insight by way of analogy. As we go along, I will tell you about the actual changes between the Apollo-era J-2 and the J-2X of today.

J-2X Progress: The J-2X Test Stands

Okay, so now you’ve got a great big rocket engine. What are you going to do with it? Well, fire it, of course. Make great big and noisy smoke and fire. There’s really not much that is more thrilling than an engine test…although, I guess, launches qualify (says the old engine guy reluctantly).

Engine Test at NASA Marshall Space Flight Center

But where are you going to do this? It’s not like you can do it in your garage. You’d blow away your entire neighborhood in the matter of a few seconds and the authorities tend to frown on such antics. Take a look (and listen) again at the video clip from the “What is a Rocket?” blog article to get an idea of what I’m talking about. Also, it’s not even like you can simply hire a company that specializes in testing stuff and there are many fine companies that do just that for all kinds of products big and small. No, rocket engine testing is an endeavor that requires its own dedicated facilities and infrastructure.

Over the past fifty years, NASA has developed a number of rocket engine test facilities, but by far the single largest and dedicated site is in southern Mississippi, Hancock County to be exact, today called the NASA Stennis Space Center (SSC). This facility is just about an hour from New Orleans. It is in a very secluded, woody bayou area far from any population centers. And that was the point when it was established. Given the size of the place needed to test rocket engines and rocket stages and given the noise that such testing makes, having no neighbors is basically a requirement.

Testing for the J-2X engine is currently planned in the “A-Complex” test area. That area is composed of three test stands. There are stands A1, A2, and A3 (no, it’s not an especially colorful naming scheme, I admit).

Stands A1 and A2 were designed to look like and function like the large test stand here at the NASA Marshall Space Flight Center. They were built in the 1960’s and were originally stage test facilities to accommodate testing of the S-II stage, the second stage of the Saturn V launch vehicle that took humans to the moon. The S-II stage was, of course, powered by the original J-2 rocket engine. Then in the early 1970’s, these two stands were converted into single-engine test stands to facilitate the development of the Space Shuttle Main Engine (SSME). Test stand A2 remained dedicated to SSME up until last year. Test stand A1 over the last thirty-five years was used primarily for SSME, but it was also used in the late 1990’s for the XRS-2200 linear aerospike engine development (which used a number of heritage J-2 and J-2S component designs) intended to support the X-33 vehicle.

Test Stand A2 Under Construction, Early 1960’s

S-II Stage being Hoisted into A2 in 1967 and the First SSME Test on A1 in May 1975

Test Stand A2 Today

Test stand A3 is a new facility currently being built specifically to accommodate development of the J-2X engine. It is unique in that it simulates the atmospheric pressures at high altitudes. Because the J-2X is being designed for maximum performance and for engine start at high altitudes, it is only within such a test facility as A3 that the complete configuration of the J-2X engine can be tested. The altitude simulation capability is produced by encapsulating the entire engine within a test chamber and using a system of steam ejectors to “suck down” the chamber using the Bernoulli effect familiar to students of fluid dynamics. Basically, what you have on A3 is a series of rocket engines, powered by liquid oxygen and alcohol, used to make a huge amount of high-velocity steam that creates a low-pressure environment into which the J-2X fires (itself also making a huge amount of steam). When A3 is up and running, the J-2X testing conducted there is going to be even more impressive than the usual engine tests.

Test Stand A3 Under Construction Today

The J-2X puts out approximately 300,000 pounds-force of thrust when fully configured and operating in space. As currently rigged, each of these three test stands can handle 600,000 pounds-force of thrust and, with some modifications, significantly more (the current thrust measurement systems being the limiting factor). Back when they were testing the S-II stages on A1 and A2, those stands were seeing nearly one million pounds-force of thrust with five J-2 engines firing simultaneously.

Within the last month, I had the opportunity to tour NASA SSC and see the progress of the work being done on these test stands to support the J-2X test campaign. Below are a series of photos with some accompanying commentary.

Above is a picture looking up and into the flame bucket on Stand A2. To give you an idea about dimensions, notice the person in the blue jacket and orange hardhat down on the right-hand wide. During an engine test, this entire area is deluged with water for the purposes of cooling and sound suppression. The flame bucket diverts the rocket exhaust from shooting downwards to shooting outwards and away from the stand. The long tube-like structure in the middle is a feature unique to Stand A2. It is a passive diffuser that creates simulated high-altitude conditions while the engine is running. The difference between this passive diffuser and the active diffuser on A3 is the fact that A3 can simulate higher altitudes and can do so even when the engine is not firing.

This is a shot taken near the top of stand A3. They have not yet built in the elevator so I know firsthand that the walk to the top is just about 23 flight of stairs, give or take a couple. I’ve marked stand A2 and also stand B1, which is currently used for RS-68 engine testing that supports the Delta IV launch vehicle. Stand A1 is off to the left, out of the frame of this picture. The low white building in the middle of the picture is the control room from where they conduct engine tests on A1 and A2. The control room for A3 will be in a different building.

Above is a picture of Jason Turpin (Liquid Engine Systems Branch, ER21, NASA MSFC) and Rick Ballard (Upper Stage Engine Element Systems Engineering and Integration Manager) standing on the Level 5 deck of stand A1 with the A3 construction site in the background. The water that you see behind them is part of a canal system that runs throughout the test area. On these canals they bring in barges filled with the propellants used for the testing. Back in the day, these canals were used to float in the assembled Saturn stages. This is not, however, necessary for engine testing since a single engine can be loaded onto a truck.

Overall, this tour of the facilities showed that NASA SSC is making tremendous progress in getting the test stands ready for the J-2X development test series campaign. In only a few months, we will be making smoke and fire (mostly steam!) and rumbling the acres of swampy woodlands that surround the site. I can hardly wait!