Think You’re Stressed? Try Being A Rocket

You know how big the SLS vehicle will be. We described the tremendous power and thrust of just one of the RS-25 engines after last year’s test firings. You may have witnessed live as we fired one of the massive five-segment solid rocket boosters last March. Through all that, perhaps you can imagine how incredible it will be at launch when all four engines and both boosters ignite together to lift this 322 feet tall, 5.75 million pound rocket up through the atmosphere and toward deep space. Imagine the thunderous vibration in your chest even as you stand several miles away.

Artist’s concept of an SLS launch
Note: Actually watching an SLS launch from this close is strongly not advised (or permitted). Orion hardware is being tested to withstand sound levels that would turn a person to liquid.

We’ve talked about how it will feel to be there when the rocket launches. Now, let’s talk about how it would feel to BE the rocket, launching.

Envision the power generated at launch as the engines and boosters throttle up to 8.8 million pounds of thrust. The heat is incredible! The vehicle starts to shake. The engine nozzles, as big and solid as they seem, will warp under the pressure of heat when the engines ignite seconds ahead of the boosters. While still on the pad, the boosters are bearing the weight of the entire vehicle even as they fire up for launch – the weight of almost 13 Statues of Liberty resting on an area smaller than an average living room.

Then, you – the rocket – are released to fly, and up you go. More than 5 million pounds of the weight of the rocket pushing down are now counteracted by more than 8 million pounds of thrust pushing from the opposite direction. Remember those 13 Statues of Liberty? Now the bottom of the rocket is feeling the pressure of 29 of them instead!

And now things are heating up on the front end of the rocket as well. Approaching Mach 1, shock waves move over the entire vehicle. Friction from just moving through the air causes the nose of the vehicle to heat. The shock waves coming off the booster nose cones strike the core stage intertank and can raise the temperature to 700 degrees. The foam insulation not only keeps the cryogenic tanks cold, it keeps the heat of ascent from getting into the intertank structure between the hydrogen and oxygen tanks.

Computer model of a shock wave at the front of the SLS vehicle at the time of booster separation during launch.
Computer model of a shock wave at the front of the SLS vehicle at the time of booster separation during launch.

Are you feeling it yet? That’s a lot to handle. These impacts from weight (mass), pressure, temperature and vibration are called “loads.” It’s a key part of the “rocket science” involved in the development of the SLS vehicle.

A load is a pressure acting on an area. Sounds simple, right? There are all kinds of loads acting on SLS, some even before it leaves the launch pad. Tension and compression (pulling and pushing), torque (twisting), thermal (hot and cold), acoustic (vibration), to name a few. There are static (stationary) loads acting on the big pieces of the rocket due to gravity and their own weight. There are loads that have to be considered when hardware is tipped, tilted, rolled, and lifted at the factory. There are “sea loads” that act on the hardware when they ride on the barge up and down the rivers to various test sites and eventually across the Gulf of Mexico and up the Florida coast to Kennedy Space Center for launch. Engineers have to consider every single load, understanding how they will affect the structural integrity of the rocket and how they will couple and act together.

The Pegasus barge that will transport SLS
You’ve probably never thought of “riding on a boat” as rocket science, but SLS has to be designed to handle sea loads as well as space loads.

When SLS is stacked on the mobile launcher at KSC, there are loads acting through the four struts securing the core stage to the boosters and down into the booster aft skirts that have to carry the entire weight of the launch vehicle on the mobile launcher. Then there are roll-out loads when the mobile launcher and crawler take SLS more than 4 miles from the Vehicle Assembly Building to the launch pad. There are many more loads as the vehicle is readied for launch.

How do engineers know the rocket’s ready to handle the loads it has to face to send astronauts into deep space? Step One is good design – developing a rocket robust enough to withstand the strains of launch. However this is difficult as the vehicle needs to be as lightweight as possible. Step Two is digital modeling – before you start building, you run many, many simulations in the computer to a level of detail that would make any Kerbal Space Program fan jealous. Step Three is to do the real thing, but smaller – wind-tunnel models and even scale-model rockets with working propulsion systems provide real-life data. And then comes Step Four – build real hardware, and stress it out. Test articles for the core stage and upper stage elements of the vehicle will be placed in test stands beginning this year and subjected to loads that will mimic the launch experience. Engines and boosters are test-fired to make sure they’re ready to go.

Still want to be the rocket? Stay tuned for more on loads as we do everything possible to shake, rattle, and yes, even roll, the pieces of the rocket, ensuring it’s ready to launch in 2018.

Next Time: No Small Steps Episode 3

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What’s A Spacecraft Factory Like? Think Big!

“I’ve been to the Smithsonian,” said one awed observer. “I’ve seen crew capsules before. They’re not that big!”

Last month, welding concluded on the pressure vessel, the basic structure of the Orion deep-space crew vehicle. Workers from around the country who had prepared components and materials for the spacecraft were invited to NASA’s Michoud Assembly Facility outside New Orleans to see the culmination of their labor before it was transported to Kennedy Space Center in Florida for completion.

The Orion team at the Michoud Assembly Facility poses with the Exploration Mission 1 crew module pressure vessel
The Orion team at the Michoud Assembly Facility poses with the Exploration Mission 1 crew module pressure vessel prior to its transfer to the Kennedy Space Center ,where it will undergo final assembly in preparation for flight in 2018.

Even to those who helped build it, and even in that unfinished state, Orion was an impressive sight. Workers found themselves standing feet away from the core of a spacecraft that will travel around the moon, farther into space than Apollo ever went, and then return to Earth; hardware that they had helped create. And even though they had seen components of it, some expressed surprise at the size of what they’d helped build.

From a big crew vehicle to a big rocket to “the world’s largest dishwasher” (What’s that? Keep reading) “big” was the word of the day when the team at Michoud marked the completion of welding of the pressure vessel for the first Orion capsule to fly on a Space Launch System (SLS) rocket.

It was … well, a big deal.

Which is appropriate, because Michoud Assembly Facility is a big place. Originally built in 1940 to produce plywood airplanes for World War II, Michoud is one of the largest manufacturing plants in the world, with the main facility covering 43 acres under one roof. Michoud became a NASA facility in 1961. Among its contributions, Michoud produced stages for Saturn V rockets, and the external tanks that fueled every space shuttle flight.

The Orion pressure vessel at Kennedy Space Center
The Orion pressure vessel has now arrived at Kennedy Space Center, where it will be outfitted for its next mission, going beyond the moon.

Today Michoud is a multi-user facility, with government and commercial tenants. Walk through Michoud, and as you begin to understand just how big 43 acres is. As you come in, you see state-of-the-art tooling being used for Orion and SLS. Venture even farther, and you find private companies making use of the factory’s diverse array of equipment including some of the same tools that sent men to the moon. (The factory is also home to some big movies – just recently, filming has taken place there for “Jurassic World” and “Dawn of the Planet of the Apes,” among others.)

How big is Michoud? The factory is so large that if you don’t know what you’re looking for, you could walk through and totally miss the largest spacecraft welding tool in the world – not because it’s easily missed, but because it’s set apart from the main floor in its own separate chamber, behind one of many bay doors and a couple of mundane-looking doorways. Enter the chamber, however, and there is nothing mundane about the 170-foot-tall Vertical Assembly Center, a new tool built custom for SLS. Into the VAC are placed 27.6-foot diameter barrels, domes and rings, and it welds them together into giant fuel tanks for the SLS core stage. Then they go in the “largest dishwasher,” as SLS core stage manager Steve Doering referred to it at the event, a piece of equipment on the other side of the chamber that washes them post-welding.

Overhead view of the Vertical Assembly Center and a welded barrel stack
Core stage barrel sections are now being welded together to form fuel tank test articles in the Vertical Assembly Center at Michoud.

On the day of the event, visitors to the chamber of the Vertical Assembly Center were greeted by its first product – a stack of two barrels, about 40 feet high, which filled the entrance to the VAC chamber. By itself, the stack looms over visitors as they approach it, but it invites a quick mental calculation: The core stage of SLS will be five times taller still than that. And that’s still less than two-thirds the height of the entire rocket. It’s big.

Orion then traveled to Kennedy Space Center to be outfitted as a cutting-edge spacecraft. At the same time, the SLS fuel tanks are in production at MAF and will undergo testing before a complete SLS core stage is test fired and shipped to Kennedy as well. There, the core stage and the SLS boosters and upper stage will join Orion for stacking and then launch.

And that will be one really big day.

Next Time: Think You’re Stressed? Try Being A Rocket

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The Next Steps Are Here

Back in November, we debuted the first in a set of new videos, “No Small Steps.” Now, the next “Steps” is here!

The first video in the series explained why going to Mars is a very big challenge, and why meeting that challenge requires a very big rocket. (Hint: You need a whole lot of fuel.)

The second installment goes a step further, by discussing how NASA’s Space Launch System (SLS) builds on the foundation of the Saturn V and the Space Shuttle, but then uses that foundation to create a rocket that will accomplish something neither of them could – sending humans to the Red Planet.

Illustration showing a Saturn V and SLS launch, with the text The physics of sending a rocket into space haven’t changed, but our engineering has.SLS takes advantage of some of the best concepts and systems from its predecessors. Like the Saturn V, SLS is a massive, staged rocket. Like the space shuttle, it uses solid rocket boosters and RS-25 engines. But unlike either of those vehicles, SLS will be able to support human missions to Mars. How do you combine elements of two different vehicles and produce a new one with a capability neither of the others had? You take the best of yesterday and INNOVATE.

Today’s teams have the added advantage of a few decades of technology development. The teams that built the Saturn and Shuttle were pioneers of rocket science, but today we’ve not only built on their foundation but also improved on things like welding science.

And while they may not be as glamorous as making smoke and fire, advances in things like modeling and analysis, welding techniques and software development add up to be a very big deal.

Why? Because on the journey to Mars, there are No Small Steps.[/embedyt]

Next Time: Visiting the Rocket Factory

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