August 2015 – Rocketology: NASA’s Space Launch System

The Engine Experience

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Can I make a confession? To be honest, I was a little bit jaded about going to see last week’s test firing of one of Space Launch System’s RS-25 engines.

Don’t get me wrong, when the opportunity to go came up, I took it in a heartbeat. I was even excited about it.

Let’s put this in perspective. I’ve seen shuttle launches. Not one, but three RS-25 engines, each time. Plus two solid rocket boosters. Stacked together, and heading into space atop a column of sky-splitting light and noise. If you never got to see one, they were pretty amazing.

So one RS-25? Going nowhere? Honestly?

A white cloud emerges from the A-1 engine test stand — With a history of almost 50 years, the A-1 stand was used for tests to make sure the Saturn V and space shuttle were ready for flight.

In case you missed it, in our last two blog posts, we talked about the test stand s and the engines themselves, and you can read about the 535-second test of the 12-million-horsepower engine and see video here.

But what was it like?

If some hypothetical foolish soul were to be naïve enough as to be jaded about an RS-25 test because they had seen shuttle launches, not that anyone would do that, it would be because they failed to appreciate two big differences in watching an engine test.

When you watch an engine test, you’re much closer to the action than you are for a shuttle launch. And the engine doesn’t go anywhere during the test.

The former fact means that you get a better sense of the details of what’s going on. Watching a launch, you see the shuttle rising atop a majestic plume of white. From a football field away, you see just how dynamic that white cloud is as it exits the engines, the speed and violence of the steam leaving the stand. You get a new appreciation of the power those engines are generating. You understand the volume of the engines in a new way as well. Out of curiosity, during the test, I loosened one of my earplugs ever so slightly, and quickly realized how dumb an idea that was. It’s loud. Like, really loud.

The fact that the engine doesn’t go anywhere means that you experience the entire burn. Watch a launch, and it’s ephemerally amazing and then gone. Watch an engine test, and it’s unrelenting. Power and sound washing over you for minute after long minute. More than one person commented to me about having a better sense of what was happening during a launch vehicle’s climb to orbit after witnessing the test.

David Hitt in front of RS-25 engine test — If you photograph a shuttle launch, you have your camera ready and snap as quick as you can. If you photograph a full-duration engine test, you shoot some video when it starts. Then take some pictures. Then watch for a while. Then switch cameras and take some more pictures. Then take a selfie. Then watch some more. Then get someone else to take pictures of you. Then take pictures of them. Then watch some more.

And then, at the end, a surprise I didn’t anticipate at all. In a launch, the end of an RS-25s burn comes in the silent void of space. On Earth, you hear everything. It’s hard to describe the sound that engine made as it ended the test – it reminded me of the astronaut descriptions of the shuttle I wrote about a few weeks ago. It was alive. A rolling growl of a mythic behemoth. Unearthly.

It’s been four years since I stood on a riverside in Titusville, Florida and watched the space shuttle Atlantis climb into the sky for the final time, and I still have years to wait until I watch the first SLS do the same.

To be sure, that future day seemed closer as I watched the RS-25 engine burn for a duration that would have put a spacecraft into orbit. Spaceflight is about speed, and speed is about power. The difference between being on the ground and being in orbit is less about altitude than it is velocity. Push something to 17,500 miles per hour, and it will orbit. Push it harder and faster, and it will go farther. This year, we’ve fired Space Launch System’s engines and boosters and demonstrated that right now we have the power we need to generate the speed. The next trick is completing the capability to keep those very thirsty engines fueled.

But I also came away from the test with a new appreciation for this time we’re in today, between those two launches. When I watched a shuttle launch, I didn’t have any sense of what one RS-25 engine was doing. I couldn’t distinguish it from the rest of the vehicle. Watching the test, you appreciate that engine. The power, the volume, the force of one RS-25. It’s an amazing piece of machinery. People came away with an excitement for seeing the core stage green run test in two years, when four engines will be integrated into the stage and fired together. Understanding what one engine is like, there was an eagerness to see that quadrupled.

The B-2 test stand at Stennis Space Center — Work is taking place today to prepare for an even more impressive test firing in a couple of years, when a 200-foot-tall SLS core stage will be fitted with four RS-25 engines and then placed vertically into the towering B-2 test stand and fired.

In March, we test-fired one of SLS’ solid rocket boosters, and those who were there talk about a similar experience. You didn’t get a sense watching the shuttle of what one SRB was contributing. But take it off the stack and fire it on its own? One SLS booster burns with the equivalent force of seven RS-25s, so you can imagine it’s impressive in its own right.

And it’s not just the propulsion systems. I got to stand within feet of the stage adapter that mated Orion to the Delta IV Heavy rocket used for Exploration Flight Test-1 in December 2014, a twin of which will connect Orion to SLS on our first flight. Look at a picture of SLS, and you barely notice that adapter. Stand next to the thing, and it’s a substantial piece of hardware.

This current period we’re in is about construction, but for me, I love that it has the added benefit of being about deconstruction. About taking one of the most amazing vehicles our species has created, and breaking it down to its parts. About seeing how incredible each of those parts is individually, understanding them better in their own right. About adding and understanding new parts, bigger and more advanced. And then, ultimately, taking those parts and putting them together in a new way to do a new thing.

So, yes, despite my naïve jadedness, I enjoyed watching the test firing. Immensely.

But, wow, am I looking forward to that launch.

Next Time: Exploration Football

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RS-25 Engines: Meeting the Need for Speed

Guest blogger Martin Burkey, the SLS strategic communications team’s resident expert on all things engines, returns this week as we prepare for this afternoon’s RS-25 engine testing event at Stennis Space Center – if you’re not already, follow @NASA_SLS on Twitter and our Facebook link below for more info. — David

Rocket engines are among the most amazing machines ever invented. That’s mainly because they have to do one of the most extreme jobs ever conceived – spaceflight – starting with escaping Earth’s deep gravity well. Orbital velocity, just for starters, is over 17,000 mph, and that only gets you a couple hundred miles off the surface. Going farther requires going faster. Much faster.

The RS-25 makes a modern race car or jet engine look like a wind-up toy.

It has to handle temperatures as low as minus 400 degrees where the propellants enter the engine and as high as 6,000 degrees as the exhaust exits the combustion chamber where the propellants are burned.

It has to move a lot of propellants to generate a lot of energy. At the rate the four SLS core stage engines consume propellants, they could drain a family swimming pool in 1 minute.

The most complex part of the engine is its four turbopumps which are responsible for accelerating fuel and oxidizer to those insanely high flow rates. The high pressure fuel turbopump main shaft rotates at 37,000 rpms compared to about 3,000 rpm for a car engine at 60 mph.

The bottom line is that the RS-25 produces 512,000 pounds of thrust. That’s more than 12 million horsepower. That’s enough to push 10 giant aircraft carriers around the ocean at nearly 25 mph.

If the performance requirement to turn massive amounts of fuel into massive amounts of fire wasn’t enough, an engine can’t take up a lot of mass or area in a rocket. A car engine generates about half a single horsepower to each pound of engine weight. The RS-25 high pressure fuel turbopump generates 100 horsepower for each pound of its weight.

But forget mere car engines. The RS-25 is about the same weight and size as two F-15 jet fighter engines, yet it produces 8 times more thrust. A single turbine blade the size of a quarter – and the exact number and configuration inside the pump is now considered sensitive – produces more equivalent horsepower than a Corvette ZR1 engine.

Expanded view of an RS-25 engine — And this is still only the major components of an RS-25 engine.

On the other hand, when you chug fluids that fast, a hiccup is a bad thing. In the case of a rocket engine, that hiccup is called cavitation. At the least, it robs the engine of power. At worst, it can cause catastrophic overheating and overspeeding. So rocket engineers spend a lot of time making sure fluids flow straight and smooth.

That’s also why they test rocket engines on the ground under highly instrumented and controlled conditions. It’s a lot less costly to fail on the ground than in flight with a full rocket carrying people on board and/or a one-of-a-kind multi-million- or multi-billion-dollar payload.

As rocket engines go, the RS-25 may be the most advanced, operating at higher temperatures, pressures, and speeds than most any other engine. The advantage comes down to being able to launch more useful payload into space with less devoted to the rocket structure and its propellants.

In addition to its power, another key consideration for SLS was the availability of 16 flight engines and two ground test engines from the shuttle program. It’s much harder and more expensive to develop a new engine from scratch. Using a high-performance engine that already existed gave NASA a considerable boost in developing its next rocket for space exploration.

Top of an RS-25 engine during a test firing — The RS-25 handles a wide range of temperatures – super-cold on top, super-hot at the bottom.

The remaining shuttle engine inventory will be enough for the first four SLS flights. As for the maturity part, the RS-25 design dates to the 1970s and the start of the Space Shuttle Program. But it’s undergone five major upgrades since then to improve performance, reliability, and safety. If only we could all upgrade 5 times as we age. Further, much of the knowledge and infrastructure needed to use the available engines and restart production already existed. Another hidden savings in time and money.

In its next evolution, the RS-25 design will be changed to make it a more affordable engine designed for just one flight and certify it to even higher thrust – which it is very capable of – to make SLS an even more impressive launch vehicle.

Next Time: The Engine Experience

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How Is A Test Stand Like A Space Ship?

I’d like to introduce a special guest blogger this week, Martin Burkey. Martin is the SLS strategic communication team’s resident expert on all things engines. As we prepare for next week’s RS-25 engine testing event at Stennis Space Center – if you’re not already, follow @NASA_SLS on Twitter and our Facebook link below for more info – Martin will be filling in this week and next to talk about our engines and how we test them. — David

None of the test stands at NASA’s Stennis Space Center look anything like a spaceship. But they operate a lot like a spaceship, even though none of them will ever leave the ground.

A test stand is designed to make a fire-breathing rocket engine think it’s a spaceship, while at the same time keeping it from taking off for space the way it was made to. Those two requirements account for why test stands look and operate as they do… and why they aren’t as compact, light and sleek as a rocket.

Most of the big Stennis test stands were built in the 1960s to test Saturn rocket engines. Over the years, they’ve continued to serve the nation by testing Space Shuttle Main Engines and other government and commercial rocket engines. Today, the center is buzzing with test activities in support of NASA’s Space Launch System.

The A-1 Test Stand is the focus of testing to adapt the RS-25 –formerly known as the shuttle main engine – to new SLS performance requirements and environments. It will also be used to test engines with new components for the second SLS mission. The B-2 Test Stand is being readied to support testing of the massive 200-foot SLS core stage with its four RS-25 engines.

Thousands of tons of hulking, ungainly concrete and steel hundreds of feet above and dozens of feet below the Mississippi soil keep the engine locked in place for testing under way this year. An intricate network of tanks, pipes, cables and other equipment provides the engine with all the propellants, power, pressure, vacuum, fluids, cooling, data management and other services to – safely and accurately – simulate a full rocket mission from pre-launch preparations to nearly 200 miles in space.

A worker inspects the machinery of an RS-25 engine — A test stands interface with the engine mimics the interface between the engine and an actual launch vehicle.

Why test the RS-25, an engine that flew successfully for more than 3 decades and has over a million seconds of operating time? Because the RS-25 is a complex and finely tuned piece of equipment that requires thorough understanding various component interactions and responses under different conditions. Like other rocket engines, it operates at extremes of temperature, pressure, vibration, etc. that have to be monitored. More specifically, the RS-25 needs to be adapted to SLS requirements and environments such as higher propellant inlet pressure and lower temperature and integrates technology like a new engine controller unit. The test stand environment allows controlled testing of abnormal conditions and more thorough monitoring and observation than the flight environment. Ultimately, it’s better to find problems on the ground than in flight. There’s a saying in rocket testing – “Test like you fly, and fly like you test.” In other words, make the engine do everything on the ground it’s going to have to do in flight, and don’t do anything in flight you haven’t made the engine do on the ground. Why are we testing a proven engine? Because Space Launch System is going to make its RS-25s do new things in flight, but not until every one of them has been done successfully on the ground.

The A-1 stand supporting the current test series provides the RS-25 with liquid hydrogen (LH₂) and oxygen (LOX) propellants. The stand has its own run tanks for propellants but they can also be filled from a 12-inch line running from LOX and LH barges docked near the test stand during test firing. The B test complex is also served by propellant barges, though stage testing relies on the propellant in the stage alone.

Aerial view of the test area at NASA’s Stennis Space Center.

From a safe distance, the Stennis test stands look like crude, utilitarian structures. Up close, they are intricately woven with a network of pipes, cables, and other hardware designed to exercise rocket engines and extract the important data.

The stand provides various gases such as nitrogen and helium for drying, pressurizing and preventing premature combustion in the engine, as well as breathing air for crews working in the engine nozzle before and after testing.

The stand also provides hydraulic and pneumatic pressure to operate the engine propellant valves. There’s electrical power to run the engine controller. There are data cables that carry engine performance information to and from the engine and the vehicle computers and crew. The high speed data system has 186 channels that can record various conditions at more than 100,000 times per second. Four high-speed cameras can record 250 frames per second. Low-speed video includes infrared, black and white and color cameras.

And, of course, there’s water for fire suppression on the stand and water to cool the stand’s ubiquitous “flame bucket” that directs engine exhaust exiting the nozzle at thousands of degrees away from the stand where it rapidly condenses into steam and then into rain that falls downwind. The A-1 bucket consists of 21 slanted deflector segments that make up the deflector seen in pictures. Each segment gets pressurized water, and each segment is drilled with a specific number and pattern of holes that spray water and keep the deflector cool during test firing. During tests, the stand uses 170,000 gallons of water per minute from a nearby reservoir.

The “crew” of the A-1 stand consists of about 50 people, some on the stand until 30 minutes before a test and others in the hardened Test Control Center 200 yards away from the test stand.

So while rocket engine testing may not resemble any real or fictional spaceship, it’s still very much “rocket science” and a critical part of getting NASA’s next great exploration rocket to the launch pad.

Next Time: RS-25 Engines: Meeting the Need for Speed

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