2016 is well underway. Another year over, another year begun.
For the SLS program, it means we’re even further past the halfway point toward launch readiness. It’s been only four years since the program officially began in September 2011, and we’re working toward being ready in less than three years for our first launch.
The day this is a photograph instead of an artist’s concept will be a good day.
The bulk of the first four years was focused on completing the design. To be sure, there was smoke and fire and bending metal as we tested boosters and engines and began building the barrels for the core stage of the rocket. Building on the foundation of the Space Shuttle Program allowed us to move quickly into testing of the engines and boosters, and the design work on the core stage progressed rapidly enough to allow us to begin early manufacturing, and all of that was preparation for what would come when we completed the critical design review of the plans.
RS-25 Engine 2059 is currently in the stand for testing at Stennis Space Center. A few years ago, it powered Atlantis’ longest mission, and a few years from now, it will loft SLS’ first crew into space.
With the design work all but done, the push toward the pad is well underway, and there’s a lot of work that entails.
For the rocket to roll out to the pad for launch, each element of the vehicle has to arrive at the Vehicle Assembly Building at Kennedy Space Center to be stacked together with the Orion crew vehicle. And each part has its own road to get there.
For the upper stage portion of the vehicle, which will push Orion out of Earth orbit and into deep space, to be ready to fly, test articles will be built of the adapters that connect the upper stage to the rest of the rocket and to Orion, along with a test article of the upper stage itself. These three test articles will be placed in a stand together, and subjected to stresses and strains to make sure they’re ready for launch. Based on the results of that test, the actual flight articles of the upper stage and adapters will be completed and transported from Marshall Space Flight Center in Huntsville, Ala., to Kennedy Space Center.
For the solid rocket boosters to be ready to fly, qualification motor tests will take place at Orbital ATK in Utah. The results of those tests will pave the way for processing, fueling and completion of the flight boosters, using hardware already at Kennedy Space Center. The boosters will be the first piece of SLS to be stacked in the VAB at Kennedy.
For the 200-foot-tall core stage, which its large fuel tanks and RS-25 engines to be ready to fly, the engines and the stage itself must each undergo individual preparation, and then be integrated together. Tests will be conducted at Stennis Space Center in Mississippi of individual engines, to make sure the RS-25 is ready for the environment it will encounter during launch. Test articles will be built of the large pieces that make up the core stage, and will be transported from Michoud Assembly Facility outside New Orleans to Marshall, where they’ll be placed in large test stands – which have to be built for this purpose – to undergo structural testing. Using the results of those tests, the actual first flight core stage will be completed. Engines will be transported from Stennis to Michoud to be integrated into the core stage, which will then be transported back to Stennis for the largest rocket test firing since the Apollo era. Once it has been tested, the stage will then be shipped down to Kennedy for stacking.
And that’s just the big pieces. In the meantime, work must be done on things like making sure the software that controls the rocket is ready to go.
At Marshall Space Flight Center, work is taking place now on the stands that will be used for the test versions of core stage components.
We’ve already made a good start on this “building” phase of the program. In March of last year, we conducted the first qualification test of the solid rocket boosters, and we’re currently preparing for the next, which will take place later this year. At the same time, we’ve started working on the flight hardware for the boosters for SLS’s first launch.
We’ve completed the first series of individual engine tests, using an unflown development engine, and are about to start the second early this year, using an engine that has flown on shuttle missions and will fly again on the second flight of SLS.
We’re almost finished with the upper-stage element test articles, and will use them to conduct structural tests over the course of this year. At the same time, work has already begun on the actual upper stage that will be used to push Orion beyond the moon on SLS’s first flight.
We’re well underway building the pieces that will be used to finish the core stage test articles and the stands on which they’ll be tested. Very soon, we’ll be welding together test articles of the rocket’s liquid hydrogen and liquid oxygen tanks, as well as other core stage components. Those, in turn, will be followed by the flight articles for the first core stage.
It’s an exciting time, and making it more exciting is the fact that this work is taking place in the modern era of digital media, giving you an unprecedented look at the process. As we continue to grow closer, one step at a time, to launch, you’ll be able to follow us every step of the way.
Next Time: May The Forces Be With You
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Way back in 2011, when the world’s attention was on the end of the space shuttle program, a small group of engineers was tasked with planning what would come next. NASA revealed the answer on Sept. 14 of that year in the form of Space Launch System (SLS) – which would be the most powerful rocket in history and would allow astronauts to travel beyond Earth orbit for the first time since Apollo.
In the four years since, we’ve made substantial progress, going from an early concept into manufacturing, testing, and even flying our first hardware on Orion’s Exploration Flight Test-1 in December 2014.
In honor of the fourth anniversary of that announcement, here are four things we’ve learned in four years. (With a big thanks to former SLS Program Manager and now Marshall Space Flight Center Deputy Director Todd May, who helped with this list.)
Atlantis’ final landing four years ago marked the ending of one era. It also marked a beginning of the next.
1) Change Is Hard. It’s Also Necessary.
The space shuttle was pretty amazing. A lot of people were sorry to see it go, myself included. I was born a week after the last Apollo capsule landed, so I grew up with the shuttle. I played with space shuttle toys as a little kid. It was “my” spaceship. I was sorry to see it go. I know an engineer who not only worked on the first shuttle flight, he was the last person to go inside its external tank before launch. He worked every shuttle mission from first to last. He also was sorry to see it go.
Change is hard. It’s also necessary. The space shuttle allowed NASA to do some amazing things in Earth orbit, but we were limited on how far we could go. To get to Mars and beyond, we needed something new, and the shuttle program was complex enough that we couldn’t do both at the same time for very long. With the International Space Station, and the work our commercial partners are doing with cargo and crew transportation, we can still do amazing things in Earth orbit without the shuttle.
Which doesn’t mean that there aren’t days I don’t fondly recall the past. I’m just more excited about the future.
And that’s been good to remember as we move forward. Even within the program, there’s been change. Leaders and coworkers have moved into new positions, some of them outside the program. They’re missed, but we keep moving forward. As we’ve matured the design of the vehicle, we’ve made changes, which sometimes means details we are attached to give way to something better. The only constant is change.
If there were such thing as a “more cowbell” philosophy or rocketry, this would be it. Everything that made the space shuttle so powerful and reliable, but more.
2) There’s the Baby, and the Bathwater. You Have to Know the Difference
When we stopped flying the shuttle, we understood the capability gap we would have to send our own astronauts into space, which was far from ideal. Moving forward, we will look to avoid these kinds of gaps so as to not lose critical workforce skills and capabilities. Sometimes, gaps like these are necessary, and in our case, it was necessary to strengthen the future of our space program. As we work toward sending humans back into deep space, we don’t have to reinvent the wheel.
At least, not entirely.
As I talked about back in the Designing A Rocket In Six Easy Steps post, when we were choosing the design of SLS, we realized that there were advantages to using hardware from the shuttle program to give us a head start in developing a new rocket. And not purely because they were already available, but because they were the result of extensive, hard work. The shuttle solid rocket boosters were the most powerful ever flown. The RS-25 engines are paragons of reliability and efficiency. If we’d started from scratch designing a new engine to replace them, not only would it have taken us longer and cost us more, but at the end of the process, we would most likely have come out with something very much like the RS-25. Since NASA already invented the RS-25 once, it doesn’t make sense to invent it again.
But that doesn’t mean that we can’t reinvent it – take what’s already been done and innovate to make it better. Another thing we’ve learned over the course of this program is that while using “heritage hardware” can be easier than starting over, it can also be harder. SLS is not the shuttle. They have enough similarity that they can both use the RS-25 – to wit, they’re both really big things that use large quantities of hydrogen fuel to make large quantities of fire in order to go up. The similarities stop there. SLS is taller, which means the fuel goes into the engine at a higher pressure. SLS has more engines and they’re closer to the boosters than on shuttle, which means the outside of the engines gets hotter. SLS is designed for deep space, which means we have to get more power out of the engines and boosters. All of those things, and more, mean that we even if we can fly the same engines on SLS that we did on shuttle, we can’t fly them the same way.
And so, even more than we anticipated, we’re having to take some of these systems and modify them and upgrade them and test them.
Still worth it? Totally.
Look how gracefully SLS soars through the clouds in this awesome picture. In reality, it’s not as easy as it looks.
3) You Can’t Cheat Gravity, but You Can Beat It
When talking about space flight, people will sometimes talk about “cheating gravity.” They see a rocket gracefully and majestically rising off a pad and through the sky and into space, and talk like somehow gravity no longer applies to it.
There are some laws you can’t break and some rules you can’t cheat, and gravity is pretty high on that list. We don’t cheat gravity; we beat gravity.
Every second of a launch, gravity is still acting on a rocket just as surely as it’s holding you to the planet’s surface right now; the biggest difference being that the rocket weighs millions of pounds more than you do. In order to rise into space, the rocket has to create and sustain a force greater than gravity, and not tear itself apart in the process.
Getting off the planet is the opposite of entropy. Entropy is the easy way out for all things; left to their own devices, things will fall apart. We are doing just the opposite — we are putting things together and bending them to our will using chemistry, physics, math and engineering.
It’s been said a fair bit recently that space is hard. Well, space is hard. John F. Kennedy told the nation as much more than half a century ago – “We choose to go to the moon in this decade, and do the other things, not because they are easy, but because they are hard.”
Make a list of what we’ve learned over the past four years, and even those who have been in this industry for years will say that this is hard. And because it’s hard, we work hard. It’s a challenge, and one we have to be steadfast every day in rising to meet.
See all that? Those are missions managed by NASA’s Goddard Space Flight
4) NASA Is Alive and Well
In the wake of the retirement of the space shuttle, there seemed to be a perception in the public that not only was the space shuttle going away, but human space flight was going away, that NASA was going away.
So, technically, we knew this wasn’t true. Again, while the public was watching the shuttle stop flying, we were planning a Mars rocket, which, really, is pretty not dead. But as we would go out into public to talk to people about what we were doing, particularly in those early years, we would hear it a lot – “I thought NASA was dead.” And hearing that reminded us just how true it isn’t.
Hearing it became a reminder of the resiliency, dedication and talent of our workforce. They had heard the same thing about NASA. They have faced numerous challenges along the way. And yet they have poured themselves into this new program, and have done incredible work. Many of these people worked on shuttle, some of them even worked on Saturn. And yet they come to work every day to ensure that this current project is their masterpiece.
Hearing it also became a reminder of the fact that we are living at the cusp of a golden age of space. The idea that NASA is out of the human spaceflight business misses one of our most amazing accomplishments – most school students today don’t remember a time when there was not an American astronaut in orbit. For every second of every day of the last 15 years, NASA astronauts and our partners from other nations have been living and working in orbit about the International Space Station. Not only does the work they do pave the way for future exploration of deep space, teaching us more about how the human body adapts to long-term exposure to microgravity, but those same lessons, and many others gained aboard the space station, also improve life here on Earth. The International Space Station is not only NASA’s outpost on the space frontier, it’s a research laboratory available for the nation’s use, and at any time numerous experiments are being conducted in a variety of fields. NASA’s support of the International Space Station is also paving the way for commercial development of Earth orbit, making space ever more accessible.
And NASA is doing far more than that; our reach literally extends from one end of the solar system to the other, and beyond. Since this program started, NASA’s reach has spanned the solar system, from MESSENGER at Mercury to New Horizons at Pluto. We’ve landed Curiosity on Mars, and InSight is about to head that way. Juno is speeding toward Jupiter. We’re revealing the mysteries of Ceres. The Voyager probes launched 40 years ago still send back signals from a region of space where the influence of our sun is overpowered by the collective strength of other stars. Hubble continues to reveal the beauty and secrets of far reaches of space while Kepler discovers new planets around distant stars, and work is well underway on the large next-generation James Webb Space Telescope that will unveil the first luminous glows of the beginnings of the universe. Satellites orbiting our home planet help with crop growth around the world. Closer to home, we’re working to make air transportation safer and more efficient. Work we’re doing today means that in the next three years, three different new American crew vehicles are scheduled to be flying from Kennedy Space Center.
And those are just some highlights of what we’re doing.
NASA’s not dead. We’re just getting started.
Early this month, nine crew members, from five countries, were aboard the International Space Station at the same time, including NASA astronaut Scott Kelly and Roscosmos cosmonaut Mikhail Kornienko, who just passed the halfway point of a year-long stay in space.
Next Time: Throwing Martians
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David Hitt works in the strategic communications office of NASA’s Space Launch System Program. He began working in NASA Education at Marshall Space Flight Center in 2002, and is the author of two books on spaceflight history.
NASA’s Journey to Mars is not simply a human exploration mission; it will bring together much of the best of what NASA does.
How do you get to Mars? You build a rocket, and go.
OK, it’s actually a bit more complex than that. A lot more complex, really. But that’s still a vitally important step. We’ll come back to why in a minute.
First, let’s talk about that “complex” part.
Mars is hard. Really hard.
To start with, Mars is far, far away. At its closest, it can come within 34 million miles of Earth, but that’s a once-in-millennia approach. Usually, if the distance gets within the low 50s, that’s really close. At farthest, Mars is about 250 million miles away. Distance means it takes time to get there.
As you travel that distance, there’s a giant ball of gas in the center of the solar system that really wants to kill you. Once you leave Earth, you’re being constantly bombarded with radiation from our own sun and distant stars.
Then there’s the fact that, if you wanted to design a planet that would be hard for humans to land on, Mars would be a good start. The atmosphere is thick enough to combine with the gravity to make an Apollo-style powered descent difficult, but it’s too thin to make a Shuttle-style glide or Orion-like parachutes easy.
Once you make it past the distance, through the radiation, and to the surface, Mars is still inhospitable. Back in 1972, following a detailed survey of planetary conditions, noted Mars expert Elton John summarized that it ain’t the kind of place to raise your kids, and for the moment that’s not a bad assessment.
All of these challenges are substantial. All of these challenges can be overcome.
Not only is NASA’s Journey to Mars the most ambitious mission the agency has undertaken, it will consist of a series of stepping stones that will also be some of the most ambitious missions we’ve ever flown.
NASA’s Journey to Mars is a holistic approach to solving those challenges, to landing humans on Mars, and to answering key scientific questions about Mars, its environment, its history and its habitability.
This Journey is not something NASA is planning to do; it’s something we are doing, right now, in numerous ways, combining the best of our experiences and abilities in a variety of fields.
Robotic explorers are today orbiting the planet and driving across its surface, teaching us more about the conditions there in order to answer those scientific questions and help us prepare for human exploration.
Astronauts aboard the International Space Station are conducting research regarding living in space for the long durations a Mars mission will require, learning more about how to maintain both equipment and the human body during the journey.
Scientists and engineers are working to mature the advanced technologies that will be needed to solve the complex challenges like radiation protection and entry through the Martian atmosphere.
We are also building the robust systems that we need to carry out the trip. The Exploration Flight Test-1 of the Orion crew vehicle in December 2014 was a major milestone, and the first flight of Space Launch System will be another. Later will come in-space propulsion systems, deep-space habitats, and more.
An important thing to keep in mind when talking about Mars exploration is that we’re already there. This “footprint” photo was captured by the Spirit rover of a track left by one of its wheels, and is a good reminder that our robot explorers are already taking “first steps” on the Journey to Mars.
We’re still in the early phases of the Journey, when our human spaceflight is still “Earth-Dependent,” relying on the supply line and other benefits that come from proximity to our home planet.
Soon, we will begin a series of increasingly ambitious “Proving Ground” missions, traveling farther into space and testing new systems and capabilities.
Finally, when we’ve demonstrated we can be “Earth-Independent,” we’ll be Mars-ready. It will be time to take the next giant leap – possibly first into Mars orbit or the Martian moons, and ultimately to take our first steps on the surface of another planet.
Which brings us back to how you get to Mars – You build a rocket, and go.
All of those challenges will ultimately be solved with hardware – habitats to live in on the long journey, shielding to protect from radiation, supersonic decelerators to descend through the Martian atmosphere, advanced life support for living on the surface, and much more. There will be a lot of that hardware, and some of it will be truly massive. And none of it does any good sitting on the surface of the Earth. If you want to get to Mars, you have to be able to put all of that into space. And that’s where Space Launch System comes in. You have to build a rocket. A big one.
A mission to one of Mars’ moons could potentially provide an opportunity for meaningful scientific work while the final Mars entry, descent and landing systems are still being completed.
And none of it matters unless you do it. Wernher von Braun went on Walt Disney’s Tomorrowland television program in the 1950s to talk about going to Mars, and much time has been spent talking about going to Mars in the decades since, by NASA, other countries, technical societies, industry, and others. You have to talk about Mars, you have to plan, before you can go, but talking and planning alone won’t get you there. You have to do something.
Today NASA is doing something in a way that neither we nor anyone have before. NASA’s Journey to Mars is unique in that it is the first and so far only time that any organization has actually begun building systems designed for human exploration of Mars. We have a long way to go, but we’re taking the first steps.
How do you get to Mars?
You build a rocket.
And go.
Next Time: Four Lessons In Four Years
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David Hitt works in the strategic communications office of NASA’s Space Launch System Program. He began working in NASA Education at Marshall Space Flight Center in 2002, and is the author of two books on spaceflight history.
Comparing space to football is a grand tradition that may well have been started by John F. Kennedy himself, who compared going to the moon with Rice playing Texas in his ‘We Choose to Go to the Moon’ speech. If it’s good enough for JFK, it’s good enough for me.
Ah, September. That wonderful time of year when the air becomes cooler, leaves begin to turn color, and every discussion is required by law to include football metaphors. You certainly won’t see me intentionally grounding such a great opportunity, so let’s talk about what it means to “go long” in human spaceflight.
The first launch of SLS will send the Orion spacecraft into a large lunar orbit beyond the moon. But, really, how does that compare to previous human spaceflight missions? Let’s use a comparison to a football field to find out.
In real life, a football field, from the back end of one end zone to the other, is just slightly longer than the 322-feet-tall SLS. But for the sake of this metaphor, we’re going to scale the distance Orion will reach at its farthest point on Exploration Mission-1 to the length of that field. Imagine you’re standing at the very end of the end zone of an American football field. In the distance, at the far end of the other end zone, 120 yards away, is the farthest point Orion will reach on EM-1. Are you imagining it? Good.
First play, we’re tossing from the back edge of our end zone to the International Space Station. Complete! We’re well on our way! Well, sort of. This doesn’t quite get you out of your own end zone. In fact, at about 230 miles — roughly the driving distance between New York and Washington, DC — you’ve only gained about three and a half inches on our field.
The vast majority of time Americans have spent in space has been around the altitude of the International Space Station, but it’s just the beginning of this journey.
For second down, we’re going to be a bit more aggressive. Back in 1966, almost 50 years ago, two astronauts, Pete Conrad and Dick Gordon, set an Earth orbit altitude record of 854 miles on the Gemini 11 mission – the farthest humans have been without heading to the moon. But even when Gordon takes the ball, you’ve only covered a total of one foot.
Third down, aiming farther still. The altitude record reached on Gemini 11 is less than a third of the altitude Orion reached on its first spaceflight, Exploration Flight Test-1, in December 2014. Using that altitude, 3,600 miles, for our next play, we’ll be just over one percent of the way to our goal, at a total of four feet and eight inches from where we started.
It’s now fourth down, and we’re still at the back of our own end zone. For an even longer distance, we’ll use the distance the International Space Station travels during one orbit of the Earth – 26,250 miles. This play gives us our first down, and also put us out of the end zone by almost four feet.
Technically, orbital mechanics means that the physics of two Robonauts both in the same orbit around the Earth throwing a football any substantial distance between them wouldn’t actually be possible. (Besides, wouldn’t it have been easier to throw it the other direction?)
Sticking with Earth orbit distances is getting us nowhere. We’ve got to be even more aggressive. A long Hail Mary throw sends the ball to the far end of the field, where it’s caught … by Neil Armstrong on the moon! The crowd goes wild! TOUCHD… Wait… What? That’s still only at the other eight-yard line? Oh, well. Let’s keep going.
For the record, that picture’s not really Neil Armstrong. Also, the football wasn’t really in this picture.
You look toward the end zone, and there’s astronaut Jim Lovell of Apollo 13! He’s open, and you make the pass. On their emergency free-return trajectory around the moon on Apollo 13, Lovell, Fred Haise and Jack Swigert traveled farther from Earth than anyone has ever been, almost 249,000 miles out. But although Lovell went around the moon on two different Apollo missions, he was never able to touch down, and, unfortunately, he doesn’t now, either. Even the human distance record from Earth is short of the end zone, by three and a half yards.
Back in formation, the quarterback steps back, fires to Orion, caught in the very back of the end zone for a 23 and a half yard gain from where Lovell had it! TOUCHDOWN! On EM-1, Orion will travel about 10 percent farther into space than Apollo ever did. Not bad for a first test flight.
TOUCHDOWN ORION!
And, from there it gets interesting. Since this was just the first possession, you’d better not let that arm get tired – on our field, the trip to Mars will be about a 77,000 yard pass. Now, THAT is going long.
Next Time: The Journey to Mars
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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?
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 standsand 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.
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.
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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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.
To be fair, the Indy car probably handles better in the turns.
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.
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.
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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