All Roads Lead to the Pad

An RS-25 engine is delivered by flatbed truck to a test stand at Stennis Space Center.
A large truck can transport a rocket component the size of one engine. But how do you transport a piece as tall as, say, the Leaning Tower of Pisa?

NASA is preparing for the first of many flights of the agency’s Space Launch System rocket and Orion spacecraft. Every day we’re making progress toward their first integrated test flight. Today, that work is taking place at numerous sites around the country, but the work of that nationwide team is firmly focused on one place – the launch pad.

Hundreds of companies across every state have been a part of SLS and the Orion crew spacecraft, many of them small businesses providing specialized components or services. That work comes together at NASA and prime contractor facilities where the “big pieces” are assembled before it all comes together on the launch pad at NASA’s Kennedy Space Center in Florida.

A crane lifts the ICPS test article out of a shipping container.
A test article of the Interim Cryogenic Propulsion Stage was delivered to Marshall Space Flight Center from United Launch Alliance in June.

1) Second Stage, From Alabama to Florida by Barge

Some of the pieces have a relatively direct route to the launch pad. At Marshall Space Flight Center in Huntsville, Alabama, where the SLS program is managed, for example, the flight unit for the Orion Stage Adapter (OSA) that will connect the SLS second stage to the crew spacecraft is being welded, and welding will begin next month on the Launch Vehicle Stage Adapter (LVSA) that will connect the core and second stages. When completed, the LVSA will travel by barge to the gigantic Vehicle Assembly Building (VAB) at Kennedy Space Center (KSC) in Florida, where final stacking of SLS and Orion will take place. The smaller OSA has the option of barge or truck, and after arriving in Florida, will make a stop at a facility where 13 CubeSats will be installed before continuing on to the VAB.

Half an hour away, the second stage of the rocket, the Interim Cryogenic Propulsion Stage (ICPS), is being completed at the United Launch Alliance facility in Decatur, Alabama. The process for the ICPS will be one step longer – after being barged from Decatur to Florida, the stage will be prepared for flight at a payload processing facility before being moved to the VAB for stacking.

Booster segments being delivered by train to Kennedy Space Center during the space shuttle era
Booster segments being delivered by train to Kennedy Space Center during the space shuttle era.

2) Boosters, From Utah to Florida by Train

Propellant is already being cast into booster segments for the first flight of SLS. The boosters will be transported by train from an Orbital ATK facility in Utah to Florida. Since the 17-story-tall boosters are far too long to be transported in one piece, the boosters will be transported in segments. They’ll arrive at a processing facility at Kennedy before being moved to the VAB where they’ll be stacked vertically and joined by the rest of the rocket.

Cutaway view of the core stage inside the Pegasus barge
NASA’s large Pegasus barge will be able to transport the SLS core stage, which will be more than 200 feet long.

3) Engines and Core Stage, From Mississippi to Louisiana to Mississippi to Florida By Barge

This one’s a little more complicated. RS-25 core stage engines are currently in inventory at Stennis Space Center in Mississippi, where engine testing is taking place. The core stage hardware for the first launch of SLS is currently being welded at Michoud Assembly Facility in New Orleans. The engines for the first flight will be transported from Stennis to Michoud, and integrated into the first core stage when it’s completed. The core stage with engines will then be transported back to Stennis, where the 212-foot-tall stage-and-engine assembly will be placed into a test stand and all four engines will be fired together in the largest liquid-engine ground test since Apollo. After the test, plans call for the stage to be shipped to Kennedy by barge, where it will be brought to the VAB for assembly with the rest of the rocket.

Artist concept of SLS and mobile launcher on the crawler transporter.
The crawler-transporter is capable of transporting 18 million pounds from the VAB to the launch complex.

4) Rocket, From VAB to Launch Pad via Crawler

Once all of the elements have arrived at the VAB, they’ll be stacked vertically and prepared for launch. The large crawler transporter will bring the mobile launcher with tower to the rocket, and will then carry rocket and launcher together to the launch pad. Which leaves only one last step:

5) Orion, From Launch Pad to Deep Space, via Rocket

NASA is on track for the first mission to launch no later than November 2018 from Florida. The first test flight of SLS and Orion will be incredible, and it will pave the way for our second exploration mission – our first with crew aboard the spacecraft. As these missions continue to come together, we’re closer to sending astronauts to Red Planet than at other point in our history. All the work we’re doing together today will continue to enable that journey in the future.

Join in the conversation: Visit our Facebook page to comment on the post about this blog. We’d love to hear your feedback!

The 83rd Thing Learned from QM-2

View from the forward end of the QM-2 booster during the test firing
During the two-minute booster test, 537 instrumentation channels provided data to meet 82 different test objectives.

They came for an awesome display of pure propulsive power.

They got a lesson in the realities of spaceflight. …Followed by an awesome display of pure propulsive power.

While engineers in Utah prepared for the second Qualification Motor (QM-2) test of a Space Launch System (SLS) solid rocket booster, another team of NASA engineers from Marshall Space Flight Center visited the U.S. Space & Rocket Center in Huntsville, Alabama to give a presentation to Space Camp trainees and museum guests explaining what would be happening during the test, how the boosters work, what the next steps are to get the boosters ready for the first launch, and how Space Launch System will play a key role in NASA’s Journey to Mars.

The museum, which is home to Space Camp, is practically in the backyard of NASA’s Marshall Space Flight Center, where SLS is managed. On the morning of the test, museum attendees and Space Camp trainees filled a theater at the museum to watch the two-minute-long firing of the 17-story solid rocket booster, the most powerful ever built for human spaceflight. The firing would provide information to answer 82 questions about how the booster performs, including how it would respond in cold-weather conditions.

What they ended up seeing that day was a huge milestone for the Space Launch System and a major step toward human exploration of deep space. The motor performed as anticipated for the burn. The inside of the motor, where the propellant had been cooled to 40 degrees Fahrenheit to simulate a cold day at the launch site, reached nearly 6,000 degrees, and the flames leaving the booster melted sand into glass. The test clears the way for qualification of the solid rocket boosters as ready to fly on the first launch of SLS in 2018.

Marshall engineer Karen Bishop gives a presentation
While the test was delayed, attendees of the viewing heard a NASA engineer explain information about the test and boosters, and their path from QM-2 to the launch pad.

In addition to the test and presentation, they also got a real-life lesson on the challenges in developing and flying space systems. As hundreds of children took their seats, the live NASA TV feed appeared on the giant theater screen, showing the booster mounted in the test stand – and the word “hold” underneath it.

A technical issue had delayed the test – a problem with a sequencing computer. When one listens to the audio feed of a rocket or shuttle launch, you can hear announcements of the steps being taken as the countdown clock nears zero – “vehicle is on internal power,” “main engines start,” etc. For a rocket to launch, numerous things have to all happen properly, and all in the correct order, one event paving the way for the next. The booster test required that same sort of preparation and precision – many things had to happen properly, and in the proper order, both before and after ignition of the booster. When the computer responsible for managing that sequence failed to function correctly, the test had to be delayed.

From a big picture view, the delay was relatively minor – after a discussion on how best to proceed, the software was changed out, the clock was reset, and the test took place just one hour after it was originally scheduled.

During the delay, the audience heard the NASA team’s presentation and got a big-screen viewing of last year’s first qualification motor test (QM-1) test. But they also got a real-world demonstration of what they’d been learning in Space Camp – the best word you can hear in the space business is “nominal,” meaning everything is proceeding as expected, but there are sometimes you don’t hear that word. You work as hard as you can to make sure that you do, and you work as hard as you can to be prepared for when you don’t. When an “off-nominal” challenge arose, the NASA and Orbital ATK team in Utah rapidly assessed the problem, identified options for moving forward, evaluated the risks and benefits, and implemented a solution that allowed the test to proceed quickly and successfully.

Museum visitors and Space Camp trainees watching the QM-2 test at the U.S. Space & Rocket Center in Huntsville, Alabama
Museum visitors and Space Camp trainees watching the QM-2 test at the U.S. Space & Rocket Center in Huntsville, Alabama.

While some of the original attendees had to leave in favor of hands-on activities like microgravity water-tank training, when the test took place, the remaining audience counted down to the firing, and cheered when the booster ignited and extinguished, the giant screen showing the close-up shots at almost life size and the sound system doing its best to do justice to the roar of the motor as it turned desert sand into glass. There was excitement over the observation that the next time a booster like this is lit, it will be powering SLS off the launch pad for its first flight.

The one QM-2 solid rocket motor, by itself, produced more thrust than it takes to lift most rockets off the ground and send them into space, and required millions of pounds of concrete in the test facility to make sure it didn’t move.

Next time, there will be nothing holding it back.


Next Time: All Roads Lead to Florida

Join in the conversation: Visit our Facebook page to comment on the post about this blog. We’d love to hear your feedback!

Three Cool Facts About QM-2

By Beverly Perry

The countdown to the last full-scale test firing of the massive Space Launch System (SLS) solid rocket boosters has begun. Mark your calendars: June 28, 8:05 a.m. MDT.

Expect two minutes of shock and awesome as the flight-like motor burns through about six tons of propellant each second during the test. With expanding gases and flames exiting the nozzle at speeds in excess of Mach 3 and temperatures reaching 3,700 degrees Fahrenheit, say goodbye to some of the sand at Orbital ATK’s test facility in the Utah desert because after the test, the sand at the aft, or rear, end of the booster motor will be glass.

NASA and Orbital ATK are rolling back the house and rocking the Utah desert for QM-2 June 28.
NASA and Orbital ATK are rolling back the house and rocking the Utah desert for QM-2 June 28.

The 154-foot long Qualification Motor 2 (QM-2) consists of the five propellant-filled segments in the middle of the booster; the aft skirt is also part of the test, but the forward assembly (nose cap, forward skirt) won’t be. (See our Boosters 101* infographic if you need a refresher on booster parts and assemblies). The test will broadcast live on NASA TV and our Facebook page. We will also live tweet from @NASA_SLS on Twitter.

For those watching at home (or work), here are three cool things that might not be so obvious on the screen, in countdown order.

3. This motor’s chill. QM-2’s been chilling — literally, down to 40 degrees — since the first week in May in Orbital ATK’s “test bay housing,” a special building on rails that moves to enclose the booster and rolls back so the motor can be test-fired. Even though SLS will launch from the normally balmy Kennedy Space Center in Florida, temperatures can vary there and engineers need to be sure the booster will perform as expected whether the propellant inside the motor is 40 degrees or 90 degrees (the temperature of the propellant during the first full-scale test, Qualification Motor 1 or QM-1).

2. This booster’s on lockdown. If you happen to be near Promontory, Utah on June 28, you can view the test for yourself in the public viewing area off State Route 83. And don’t worry, this booster’s not going anywhere — engineers have it locked down. The motor is held securely in place by Orbital ATK’s T-97 test stand.

During the test, the motor will push against a forward thrust block with more than three million pounds of force. Holding down the rocket motor is more than 13 million pounds of concrete — most of which is underground. The test stand contains a system of load cells that enable engineers to measure the thrust the motor produces and verify their predictions.

Solid rocket booster test burns so hot it turns sand to glass.
The solid rocket motor test firing will burn so hot the sand at the aft end of the motor will turn to glass.

Putting out the fire at the end of the test is the job of the quench system, which fills the motor with carbon dioxide from both ends of the test stand. A deluge system sprays water on the motor to keep the metal case from getting too hot so the hardware can be re-used. Both the quench and deluge systems had to be upgraded to handle the heat and size of the big five-segment boosters.

1. Next time, it’s for real. These solid rocket boosters are the largest and most powerful ever built for flight. They’ve been tested and retested in both full-scale and smaller subsystem-level tests. Engineers have upgraded and revamped vital parts like the nozzle, insulation and avionics control systems. They’ve analyzed loads and thrust, run models and simulations, and are nearing the end of verifying their designs will work as expected.

Most of this work was necessary because, plainly put, SLS needs bigger boosters. Bigger boosters mean bolder missions – like around the moon during the first integrated mission of SLS and Orion. So the next time we see these solid rocket motors fire, they will be propelling SLS off the launch pad at Kennedy Space Center and on its first flight with Orion. For real.

Next time: Behind the Scenes at QM-2: Getting Ready to Test the World’s Largest Solid Rocket Motor.


Join in the conversation: Visit our Facebook page to comment on the post about this blog. We’d love to hear your feedback!

We’ve Got (Rocket) Chemistry, Part 2

Editor’s note: This is the second in a two-part series on the chemical reactions at the heart of rocket propulsion. Last week, we talked about the liquid engines of the SLS core stage , this week we’ll talk about the boosters.

By Beverly Perry

To give SLS extra power to get it off the ground, twin five-segment rocket boosters, built by Orbital ATK, tower more than 17 stories tall, burn six tons of solid propellant each second and help SLS break free from the clutches of Earth’s gravity.

Solid rocket fuel is the original rocket fuel, dating back to the early fireworks developed by the Chinese centuries ago. For the SLS boosters, aluminum powder serves as the fuel and a mineral salt, ammonium perchlorate, is the oxidizer.

Artist rendition of boosters and engines of during launch
The powerful aluminum-ammonium perchlorate reaction fuels the twin SLS solid rocket boosters.

Aluminum doodleAluminum is the most abundant metal on Earth. It’s also highly reactive. Aluminum is so reactive, in fact, that it’s not found naturally in its pure form but only in combination with other minerals. It’s this ability to readily combine with other metals that makes aluminum so useful. Every day, we use products made of aluminum alloys, or mixes with other metals, for things like beverage containers, covering leftovers, or iPhones. Amazingly, it’s this same stuff that fuels solid rocket boosters.

Ammonium perchlorate, the salt of perchloric acid and ammonia, is a powerful oxidizer (read: majorly explosive). In the boosters, the aluminum powder and ammonium perchlorate are held together by a binder, polybutadiene acrylonitrile, or PBAN. The mixture, with the consistency of a rubber eraser, is then packed into a steel case.

: Interior of booster case after firing
This is what the inside of the empty booster case looked like after the first qualification motor test in March 2015. Preparations are already well underway for the second qualification test this summer.

When it burns, oxygen from the ammonium perchlorate combines with aluminum to produce aluminum oxide, aluminum chloride, water vapor and nitrogen gas – and lots of energy.

Nitrogen doodleThis reaction heats the inside of the solid rocket boosters to more than 5,000 degrees Fahrenheit, causing the water vapor and nitrogen to rapidly expand. Just like in the liquid engines, the nozzle funnels the expanding gases outward, creating thrust and lifting the rocket from the launch pad.

Compared to liquid engines, solid motors have a lower specific impulse – the measure rocket fuel efficiency that describes thrust per amount of fuel burned. However, the propellant is dense and burns quite quickly, generating a whole lot of thrust in a short time. And once they’ve burned their propellant and helped propel SLS into space, the boosters are discarded, lightening the load for the rest of the spaceflight.

So that’s it really. Make water and shoot off an enormous firecracker and you’ve got: Rocket Chemistry. On this scale though, you can’t try this at home. Watch the real show when SLS launches in 2018.


Join in the conversation: Visit our Facebook page to comment on the post about this blog. We’d love to hear your feedback!

We’ve Got (Rocket) Chemistry, Part 1

Written by Beverly Perry

What do water and aluminum have in common?

If you guessed that water and aluminum make SLS fly, give yourself a gold star!

Chemistry is at the heart of making rockets fly. Rocket propulsion follows Newton’s Third Law, which states that for every action there is an equal and opposite reaction. To get a rocket off the launch pad, create a chemical reaction that shoots gas and particles out one end of the rocket and the rocket will go the other way.

What kind of chemical reaction gets hot gases shooting out of the business end of a rocket with enough velocity to unshackle it from Earth’s gravity? Combustion.

Whether it’s your personal vehicle or a behemoth launch vehicle like SLS, the basics are the same. Combustion (burning something) releases energy, which makes things go. Start with fuel (something to burn) and an oxidizer (something to make it burn) and now you’ve got propellant. Give it a spark and energy is released, along with some byproducts.

For SLS to fly, combustion takes place in two primary areas: the main engines (four Aerojet Rocketdyne RS-25s) and the twin solid rocket boosters (built by Orbital ATK) that provide more than 75 percent of thrust at liftoff. Combustion powers both propulsion systems, but the fuels and oxidizers are different.

RS-25 engine during testing
Steam clouds, the product of the SLS main engines’ hydrogen-oxygen reaction, pour from an RS-25 engine during testing at NASA’s Stennis Space Center.

The RS-25 main engines are called “liquid engines” because the fuel is liquid hydrogen (LH2). Liquid oxygen (LOX) serves as the oxidizer. The boosters, on the other hand, use aluminum as fuel with ammonium perchlorate as the oxidizer, mixed with a binder that creates one homogenous solid propellant.

Making water makes SLS fly

Hydrogen doodleHydrogen, the fuel for the main engines, is the lightest element and normally exists as a gas. Gases – especially lightweight hydrogen – are low-density, which means a little of it takes up a lot of space. To have enough to power a large combustion reaction would require an incredibly large tank to hold it – the opposite of what’s needed for an aerodynamically designed launch vehicle.

To get around this problem, turn the hydrogen gas into a liquid, which is denser than a gas. This means cooling the hydrogen to a temperature of ‑423 degrees Fahrenheit (‑253 degrees Celsius). Seriously cold.

Oxgen doodleAlthough it’s denser than hydrogen, oxygen also needs to be compressed into a liquid to fit in a smaller, lighter tank. To transform oxygen into its liquid state, it is cooled to a temperature of ‑297 degrees Fahrenheit (‑183 degrees Celsius). While that’s balmy compared to LH2, both propellant ingredients need special handling at these temperatures. What’s more, the cryogenic LH2 and LOX evaporate quickly at ambient pressure and temperature, meaning the rocket can’t be loaded with propellant until a few hours before launch.

Once in the tanks and with the launch countdown nearing zero, the LH2 and LOX are pumped into the combustion chamber of each engine. When the propellant is ignited, the hydrogen reacts explosively with oxygen to form: water! Elementary!

2H2 + O2 = 2H2O + Energy

This “green” reaction releases massive amounts of energy along with superheated water (steam). The hydrogen-oxygen reaction generates tremendous heat, causing the water vapor to expand and exit the engine nozzles at speeds of 10,000 miles per hour! All that fast-moving steam creates the thrust that propels the rocket from Earth.

It’s all about impulse

But it’s not just the environmentally friendly water reaction that makes cryogenic LH2 a fantastic rocket fuel. It’s all about impulse – specific impulse. This measure of the efficiency of rocket fuel describes the amount of thrust per amount of fuel burned. The higher the specific impulse, the more “push off the pad” you get per each pound of fuel.

The LH2-LOX propellant has the highest specific impulse of any commonly used rocket fuel, and the incredibly efficient RS-25 engine gets great gas mileage out of an already efficient fuel.

But even though LH2 has the highest specific impulse, because of its low density, carrying enough LH2 to fuel the reaction needed to leave Earth’s surface would require a tank too big, too heavy and with too much insulation protecting the cryogenic propellant to be practical.

To get around that, designers gave SLS a boost.


Next time: How the solid rocket boosters use aluminum – the same stuff you use to cover your leftovers – to provide enough thrust to get SLS off the ground.

Join in the conversation: Visit our Facebook page to comment on the post about this blog. We’d love to hear your feedback!