SLS Avionics: The Brain Without a Body

By Martin Burkey

If you compared NASA’s powerful Space Launch System (SLS) rocket to a human body, the avionics and software would be the nervous system and brain that monitor the body’s condition and makes and sends decisions. Just a few of the hundreds of operations that they make include: liquid propellant flow, engine throttling, engine and booster exhaust nozzle steering, trajectory updates, receiving and sending data to the crew and ground control, and responding to off-nominal issues such as wind gusts or an engine failure.

The avionics are required to work in environments of temperature, pressure, sound, etc. that no human body – and actually few machines – could tolerate. So everything from the boxes, to the boards, to the individual processors are “ruggedized” and tested at every step in development to survive launch.

Ultimately the avionics boxes and software have to work perfectly. But how can you be sure without putting it on the world’s largest rocket and seeing how it works? That’s the focus of the Integrated Avionics Test Facility – or IATF – at NASA’s Marshall Space Flight Center, where the computer, routers, processors, power, and other black boxes and software collectively known as “avionics” are being tested in preparation for the planned 2018 first flight of SLS.

Possibly the coolest thing about the test facility is that it can create an artificial vehicle operating in an artificial world and virtually “fly” SLS hundreds of times – from pre-launch activation and checkout to liftoff to core stage separation at about 17,500 miles per hour and 100 miles in space – to test the entire avionics package.

Expanded view of SLS showing various avionics locations.
Location of avionics aboard SLS Block 1.

Avionics can be found all over SLS: in the booster aft skirt and forward skirt, the core stage engine controllers mounted on the engines themselves, in the core stage engine section, intertank, and forward skirt, in the launch vehicle stage adapter, and in the Interim Cryogenic Propulsion Stage. Of course, avionics for the Orion crew vehicle are also linked in to the performance of the whole vehicle. So basically top to bottom.

An overhead view of the SLS IATF at Marshall Space Flight Center.
The heart of the Integrated Avionics Test Facility at NASA’s Marshall Space Flight Center. The Systems Integration Test Facility-Qualification is shown left background. The System Integration Lab is in the foreground. The SLS booster Hardware In the Loop facility is in the middle background.

Inside the test facility, the vehicle avionics boxes are mounted on a semi-circular, 18-foot-tall frame in the same relative position they will be inside SLS – right down to the length of the connecting cables. Outside the frame, several large towers house the equipment for simulating the SLS “world” and running test after test.

The virtual world of SLS is created by a pair of software tools, ARTEMIS and MAESTRO. They stand for A Real-Time Environment for Modeling, Integration and Simulation (ARTEMIS) and Managed Automation Environment for Simulation, Test, and Real-Time Operations (MAESTRO). (How do engineers come up with this stuff?) ARTEMIS is a suite of computer models, simulations and hardware interfaces that simulates the SLS and its virtual “world.” For instance, it simulates the Earth’s rotation, gravity, propellant tank sloshing, vehicle bending in flight, engine and booster pressure, temperature and thrust, and weather, from hot sunny days to cold stormy nights, and inputs from the Orion crew vehicle and launch facilities. In fact, ARTEMIS has far more lines of software code than SLS itself. MAESTRO serves as the test conductor for the virtual missions. This software configures and controls test operations, sets up the external conditions, monitors the tests, and archives all test data for analysis. That’s where engineers and software writers find out if their code needs fixing or supplementing.

The actual flight avionics for SLS will never be tested in this facility – only their flight-like equivalents. The actual flight avionics will be installed directly into the core stage at the Michoud Assembly Facility in Louisiana and tested there prior to flight. The test team at Marshall can already say that they’ve flown SLS “virtually” thousands of time to help ensure that SLS flies safely on its first real mission in a couple of years.

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A (much) Closer Look at How We Build SLS

By Martin Burkey

How do you put the world’s largest rocket under a microscope?

One piece at a time, of course.

NASA’s Space Launch System – SLS – will be the world’s most powerful, capable rocket. It will send intrepid explorers, their spacecraft, their landers, their habitats, and all their other equipment to survive and thrive in deep space.

But, first, it has to survive launch. SLS is an extreme machine for operating in extreme environments – 6 million pounds going from zero to around 17,500 miles per hour in just 8 minutes or so after liftoff. Some parts are minus 400 degrees F. Some parts are 5,000 degrees. Extreme.

So NASA works hard to make sure everything works as planned, including the largest part, the core stage – 212 feet long, 27 feet in diameter, and weighing more than 2 million pounds all gassed up and ready to go.

NASA and core stage prime contractor Boeing are building hardware at Michoud Assembly Facility in New Orleans, Louisiana for the first flight in 2018. Engineers have put the design through numerous computerized structural analyses and simulations, but that’s not the same as actually cutting, welding, and assembling giant metal panels, domes, rings, etc. on new manufacturing tools with new processes for the first time. Each time, the team starts to weld new flight hardware, they methodically go through a series of steps to make sure that first flight hardware is perfect.

SLS liquid oxygen tank weld confidence article comes off the Vertical Assembly Center at Michoud Assembly Facility.
A liquid oxygen tank confidence article for NASA’s new rocket, the Space Launch System, completes final welding on the Vertical Assembly Center at Michoud Assembly Facility in New Orleans.

“Perfect” is a relative term. Some technically-minded people consider welding itself as a defect in a metal structure because the weld is never as strong as the rest of the metal, according to Carolyn Russell, chief of the metal joining and processes branch at Marshall Space Flight Center in Huntsville, Alabama, with 32 years of experience in the field. Given the advanced state of welding technology, other people might consider the term “defect” as a bit extreme.

None other than legendary rocket scientist Wernher von Braun declared in the midst of Saturn V moon rocket development in 1966: “A lifetime of rocketry has convinced me that welding is one of the most critical aspects of this whole job.”

The first step to SLS flight hardware was establishing the “weld schedule,” – how the welding will be done. SLS uses “friction stir welding” – a super fast rotating pin whipping solid metal pieces until they are the consistency of butter and meld together to bond the core stage’s rings, domes, and barrel segments. The result is a stronger and more defect-free weld, than traditional methods of joining materials with welding torches.

The completed SLS Launch Vehicle Stage Adapter awaits testing.
The completed SLS Launch Vehicle Stage Adapter (LVSA) structural test article awaits transfer to a test stand at NASA’s Marshall Space Flight Center in Huntsville, Alabama. Measuring 56-feet tall, the LVSA connects the SLS core stage to the upper stage.

Based on the particular aluminum alloy and thickness, engineers establish the required pin rotational speed, travel speed, how hard it pushes on the metal Before committing the welding schedule to full size or flight hardware, the core stage team checks the process on test panels about 2 feet long. Test panels are made at Michoud and sent to Marshall, where they are nondestructively inspected, sectioned and then analyzed microscopically for minute defects.

A false color composite image of the metal grain in an LVSA panel.
A false color composite image produced by an electron beam microscope at NASA’s Marshall Space Flight Center shows the crystal orientation of a portion of the thickness of a metal panel for the Launch Vehicle Stage Adapter.

Marshall materials scientists study the samples under magnification in the search for cracks and voids, and to understand how deeply the weld penetrated the parts. They also undergo non-destructive evaluation, including x-ray, ultrasonic, and dye penetrant testing.

With weld processes tested for every part of the core stage, the manufacturing team can begin building weld confidence articles, or “WCAs.” There are WCAs for the engine section, the liquid oxygen tank, and the liquid hydrogen tank. Likewise, the WCAs are cut into samples that are again put under the microscope at Marshall. In theory, the WCAs should be perfect if the weld schedule was followed. In reality, it doesn’t quite work out.

WCA welding consists of lots of “firsts,” Russell explained. It’s a test of the tooling and factors like parts alignment and tolerances. Heat transfer from the welds to the surrounding metal is different once large parts are clamped together. It short, stuff happens. Adjustments are made. Weld samples are cut and again put under the microscope until the weld schedule is perfected.

All this testing and microscope-gazing has led to a major SLS milestone: the welding of structural test articles – STAs – and flight articles for the hydrogen and oxygen tanks, engine section, and forward skirt, which is underway now. The STAs will be shipped to Marshall next year. Secured into test stands – that are secured firmly to the ground – these test articles will be rigged with hundreds of sensors and then pushed and prodded to see if they can survive the stresses the flight hardware will experience – accelerating bending, twisting, etc.

Then, and only then, can engineers say that the giant core stage is ready for its launch debut. But that’s a story for another day.

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Meet the New Boss

Guest blogger Martin Burkey, the SLS strategic communications team’s resident expert on all things engines and stages, returns this week to introduce a man he’s worked with closely, new SLS Program Manager John Honeycutt. — David

New SLS Program Manager John Honeycutt
New Program Manager John Honeycutt speaks to the SLS workforce at his first team meeting.

Three golf putters lean against one wall in John Honeycutt’s office. They haven’t seen much action lately, and it may be a long time before they do again. Honeycutt, who takes his golf game seriously or not at all, was recently named to lead NASA’s Space Launch System Program, which is fast becoming crowded (pleasantly) with spaceship parts for testing and even flight.

He succeeds the program’s first manager, Todd May, who was recently named deputy director of Marshall Space Flight Center, where SLS is based.

Within NASA, he’s a known quantity with 25 years of experience on both the development and operation side and the challenges that came with both. As imposing a figure as he may be in person, he’s also surprisingly soft-spoken. He tends to do a lot of listening, asking questions designed to cut through knotty issues and reveal trends or issues lurking in the dense, detailed, “eye charts” typical of NASA presentations.

He’s collaborative, essential for working with other programs. He’s customer-focused, which makes him responsive to strategic direction from above. And he enjoys cutting up with his team on special occasions. Better judgment prevents me from posting the pictures.

Honeycutt grew up in Huntsville, a city that evolved from agriculture to manufacturing and to high tech thanks to military projects and NASA space programs. When he was growing up, it was just assumed that, if you lived here, you were going to work with the Army or NASA. His father is a mechanical engineer who was a metals expert first for the Army in the 1960s and then for a space shuttle contractor in the 1980s, and he continues to work in metals analysis today at Marshall.

The younger Honeycutt worked his way through college, managing a small grocery store, a gas station, and working in a hardware store. He attended college part time until he was about 24 and turned full-time student until he graduated with a mechanical engineering degree from the University of Alabama in Huntsville. Through the wife of one of his part-time employers, he soon got a job interview with Rockwell, the shuttle program integrator. And the rest, trite as it sounds, is history.

Honeycutt, 55, is no stranger to space hardware. If you could ‘letter’ in human space flight, he’d have the jacket. He worked in industry for nine years on environmental and structural testing as part of developing the International Space Station, as well as the main propulsion system, external tank, and launch support for the Space Shuttle Program before joining NASA.

Since joining NASA, he’s managed the shuttle external tank program, and he’s served as deputy manager of the SLS Stages office, SLS deputy chief engineer, and most recently as the SLS deputy program manager.

That’s all standard press release stuff, but his experience is worth mentioning just because he doesn’t consider it the most important aspect of his new job.

As program manager, Honeycutt knows that he can’t be just a hardware guy. He sees his main job as asking questions, seeing where people need help, especially when they don’t realize it, and challenging teams to push through barriers.

He also sees himself as program integrator. He places a high priority on getting the SLS team more closely integrated. It’s particularly important when things don’t go as expected… as they can understandably with the largest rocket in the world.

New SLS Program Manager John Honeycutt
New SLS Program Manager John Honeycutt

When he was named SLS deputy chief engineer, the program was not yet to its preliminary design review – PDR – one of the early design stages. The various hardware elements – boosters, engines, core stage, etc., were loosely coupled through various interface and performance requirements.

SLS has most recently completed its Critical Design Review – CDR – and the pieces that were once separate will start coming together in every sense of the word at every level for assembly and testing. Big rocket. Big integration job.

“In the earlier design stages, integration is not as strict relative to how communications takes place,” Honeycutt observed. “As you roll out of CDR and are pressing toward certification and on to launch, that transition requires you coordinate much closer. It will come to a point soon where I have to stand up and say this vehicle is certified for flight and can show how the pieces interconnect. We’re becoming more tightly integrated as a team, not just the SLS team, but its sister programs – Orion and Ground Systems (at Kennedy Space Center) – all under the Exploration Systems Directorate enterprise.”

Having worked on the hardware development side and the hardware operations side, he understands there’s a difference in how you approach challenges. That cross-cultural experience should help Honeycutt now as SLS moves from design into the “pencils-down”, design-complete, manufacturing and assembly that is gearing up.

The design is at least 90 percent complete by definition, and the vehicle is literally taking shape in factories around the country. Having been through challenges ranging from the Columbia shuttle accident to the destruction of Hurricane Katrina, and the ongoing lessons that every shuttle mission taught, Honeycutt knows SLS has more challenges ahead.

“I’m not going into this thinking we’re going to sail smoothly all the way up through Design Certification Review,” he says. “It’s up to me to look through things and see what’s coming.”

His decisions will be aimed at flying the first SLS mission on schedule and then having the second rocket ready as close behind the first as possible. Of course, that’s his job.

But Honeycutt has one more, longer-range personal goal that looks beyond delivering hardware to what that hardware will mean for the nation, and for the people who built it – a goal “for everybody working on this program to look back and say it’s the best thing they’ve ever done.”

To make that happen, it looks like a serious commitment to his golf game will have to wait.

Next Time: Passing A “Critical” Milestone
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