Uncategorized – Page 6 – Liquid Rocket Engines (J-2X, RS-25, general)

J-2X Progress: Delivery of the Development Program HEXs!

Cain Tubular Products of St. Charles, Illinois has completed fabrication of the full set of heat exchanger (HEX) coils for the J-2X development engines. These coils have been delivered to Pratt & Whitney Rocketdyne for the next step in the fabrication process that involves integration into the hot gas ducts being assembled by Arrowhead Products in Los Alamitos, California. The very first three units are already there and in work.

Below is a photo of the Cain brothers at their facility with their handiwork on display.

The HEX is a component of the engine that contributes only indirectly to engine operation. Specifically, it is used by the rocket stage to develop pressurant gases for the liquid oxygen tank.

During flight, as the engine pulls liquid oxygen from its storage tank on the stage, and as the tank drains, you need something stuffed back into the tank to replace the liquid or it will potentially collapse. Also, due to the physics of cryogenic liquids, the pumps on the engine require a certain amount of pressure at the engine inlet in order to function effectively. From the perspective of getting payload to orbit, the most efficient stuff to put into the tank to fill the volume vacated by the liquid is warm gas. But where are you going to get warm gas while the vehicle is hurtling through space? Trying to carry it in high-pressure tanks might work, but such tanks get very heavy very fast as the vehicle design gets larger. So, the better answer is this: You make warm gas while you’re flying.

Within the engine, the HEX is placed in the discharge of the engine turbines where very hot gas is allowed to flow around the coils during operation. Dense cryogenic helium is fed into the HEX inlet, it flows within the coil tubing, that tubing is surrounded on the outside by the hot gases which makes the tubing very wary, and then, at the HEX outlet, we get very warm, much-less-dense helium. That warm helium is then fed back to the stage to pressurize the liquid oxygen tank.

While there is certainly nothing patently new or exciting about heat exchangers in general — the radiator on your automobile, for example, is a heat exchanger serving a different purpose — it should be noted that due to the extreme conditions experienced within a rocket engine, and the stringent requirements placed on this particular piece of hardware, fabrication of the J-2X engine HEXs constituted its own small development effort. Cain Tubular Products did an exemplary job in deriving a unique fabrication process for this critical part and in delivering these parts in time to support the development test program.

Inside the J-2X Doghouse: What is a Rocket?

For as long as anyone can remember here at NASA’s Marshall Space Flight Center, the collection of engineers who analyze and evaluate rocket engine test and flight data results have been called “Datadogs.” However, that time-honored moniker is a title that must be earned. It’s not automatic based upon your job assignment. It is based upon your ability to create a coherent technical narrative derived from hundreds of pieces of data spanning pre-start purge schedules, through engine start to mainstage operation, through shutdown transients and, finally, post-test inspections. With every engine firing we ask: What happened and, more importantly, why? The Datadogs provide the answers.

So, as a regular part of the J-2X Blog, I will be inviting you into the J-2X Doghouse just to ramble a bit about rockets and rocket engines in preparation for the upcoming J-2X development testing next year.

The most basic question is, of course, what is a rocket? Often, when lost in the mountain of ten thousand details of fabrication processes and assembly procedures and structural analyses and operational manuals and information of all flavors, even rocket scientists sometimes lose sight of the most basic concepts. Yet any child who has ever blown up a balloon and then let it fly across the room as it deflates has experimented in rocketry. A rocket is simply a vehicle that is self-contained and self-propelled. It takes in nothing from its external environment and it achieves motion from Newton’s principle of a reaction resulting from every action. A rocket effectively throws stuff out the back end while what remains in the rocket moves forward thereby balancing the net sum of inertia.

In technical terms, the balloon flying across the room — likely landing in your uncle’s soup thereby causing a minor family crisis — is a pressure-fed, mono-propellant rocket. The stretchy plastic of the balloon supplies the pressure and the single propellant is the breath with which the balloon was filled. The pressure from the plastic pushes the air out the back end. The air goes one way rapidly and the balloon itself goes hurtling through space in the opposite direction. Ta-da, a rocket! And now you are privy to the NASA secret that rockets, at their most basic, conceptual level, are pretty darn simple.

So, what makes a rocket engine different than a child’s balloon? Power. In order to throw thousands of pounds of a launch vehicle into the sky and accelerate it to thousands of miles per hour, you need lots and lots of power. Rather than relying on pressure to push the working fluid out the back end, a large rocket engine like J-2X uses very powerful pumps. And, rather than relying on just the velocity generated by moving the fluids, a large rocket engine taps into the chemical energy released by combustion.

For example, during every second of operation the J-2X pumps hundreds of pounds of hydrogen and oxygen into a chamber not much bigger than a large spaghetti pot. There, these fluids combust, making steam (and residual hydrogen gas) at blistering hot temperatures of thousands of degrees. That tremendous amount of energy is then directed out the back end, accelerating the hot gases down the length of the nozzle to supersonic speeds, converting thermal energy to kinetic energy all along the way.

How much steam does this make? Well, if you ever have the opportunity to see a J-2X engine test, bring an umbrella. A full duration test will make enough steam to make its own rain cloud in the sky. Below is a video of a Space Shuttle Main Engine test in stand A2 at NASA’s Stennis Space Center in Mississippi. Tests of the J-2X will look quite similar.

Thus, the tough part about rocket engines is not their basic concept. That’s simple. The tough part is building a device that can harness the power necessary to make that simple concept useful. As we go along, we’ll discuss that tough part in more detail.

Welcome to the J-2X Blog!

Hello! Welcome to the J-2X Blog.

I would say that it’s a pretty safe bet that a large (very large) majority of the American population is unaware that we stand on the brink of testing the first new, large, human-rated liquid rocket developed in this country since Gerald Ford was President. I might even venture to suggest that a majority of the diverse and busy population supporting NASA also don’t know that this is the case.

Back then, during the Ford administration, the new engine was called the Space Shuttle Main Engine (SSME). Its initial development at the conceptual level began in the late 1960’s. The Space Shuttle itself wouldn’t fly until 1981, nearly six years after the first attempted engine test. Today, the engine is called J-2X and this blog represents an attempt to inform those who want to follow the exciting progress of this development effort as we approach full engine testing in early 2011.

As the name suggests, the J-2X has its roots in the Apollo Program with the J-2 engine used for the second and third stages of the Saturn V rocket that first took humans to the moon. In many ways, the original J-2 was the technological predecessor of the SSME. The J-2X design is the beneficiary of over fifty years of rocket engine experience spanning the original J-2, the SSME, the experimental J-2S, and the RS-68 engine that today powers the Delta IV commercial rocket.

The J-2X is being developed by the NASA Marshall Space Flight Center in Huntsville, Alabama, the home of the propulsion systems for the Apollo Program and the Space Shuttle Program. Our contracted partner in this development is Pratt & Whitney Rocketdyne located in Los Angeles, California. Appropriately, Pratt & Whitney Rocketdyne, taking into account corporate name changes over the years, was the developer of the liquid rocket engines that powered the Apollo Program and still powers today the Space Shuttle Program. Thus, we have assembled an experienced, formidable, and knowledgeable team for J-2X.

Your humble chronicler for this journey into the exciting final stages of J-2X development is William D. Greene. I am currently the Upper Stage Engine Element Associate Manager. The Upper Stage Engine Element is the NASA office responsible for J-2X engine design and development. For the first three and a half years of this project, I was the Systems Engineering and Integration Manager for this office. I have 22 years of experience, most of which has been in support of the NASA Marshall Space Flight Center and much of which has be dedicated to liquid rocket engine analysis, development, production, and testing. I will be charting the progress of the J-2X development effort, introducing you to the extraordinary team responsible for this effort, and sharing what I know about both this activity as well as about rocket engines in general.

This is going to be fun! C’mon along for the ride! For more information about the J-2X project, see the link to the video starring some of the key people engaged in this historic effort.

NASA and Pratt & Whitney Rocketdyne managers discuss the design and
development of the J-2X engine.