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Tap into the experiences of NASA’s technical workforce as they develop missions to explore distant worlds—from the Moon to Mars, from Titan to Psyche. Learn how they advance technology to make aviation on Earth faster, quieter and more fuel efficient. Each biweekly episode celebrates program and project managers, engineers, scientists and thought leaders working on multiple fronts to advance aeronautics and space exploration in a bold new era of discovery. New episodes are released bi-weekly on Wednesdays. 

NASA Space Launch System Chief Engineer John Blevins discusses the rigorous engineering of the world’s most powerful rocket.

NASA’s Space Launch System is a powerful, advanced launch vehicle for a new era of human exploration beyond Earth’s orbit. The new super heavy-lift rocket, NASA’s first exploration-class rocket built for human space travel since the Saturn V, will send astronauts to the Moon as part of the Artemis missions. With its unprecedented power and capabilities, SLS is the only rocket that can send Orion, astronauts, and cargo directly to the Moon on a single mission. The Mega Moon rocket is designed to be evolvable, which makes it possible to fly more types of missions, including human missions to the Moon and Mars and robotic scientific missions to places like the Moon, Mars, Saturn and Jupiter.

In this episode of Small Steps, Giant Leaps, you’ll learn about:

  • SLS engineering best practices
  • Unique challenges of blending heritage, legacy and new hardware
  • SLS technical and engineering firsts


Related Resources

Space Launch System


Orion Spacecraft

Episode 78: Engineering Best Practices – Part 1 (Small Steps, Giant Leaps series)

Episode 79: Engineering Best Practices – Part 2 (Small Steps, Giant Leaps series)

APPEL Courses:

Developing and Implementing a Systems Engineering Management Plan (APPEL-SEMP)

Human Spaceflight and Mission Design (APPEL-vHSMD)

Manned Mission & System: Design Lab (APPEL-vMMSD)

Space Launch and Transportation System (APPEL-vSLTS)


John Blevins Credit: NASA

John Blevins
Credit: NASA

John Blevins is the Chief Engineer for NASA’s Space Launch System (SLS) Program, managed at NASA’s Marshall Space Flight Center (MSFC). Blevins previously served as the SLS Deputy Chief Engineer and Manager of the SLS Engineers Office. He has held positions at MSFC in the Combustion Devices Branch within the Propulsion Systems Department and served in various roles in the Spacecraft and Vehicles Systems Department, including Team Lead of Aerodynamics, Branch Chief of Aerosciences and Technical Assistant to the Structural Design and Analysis Division. Prior to joining NASA in 1999, Blevins gained industry experience at Honda of America Manufacturing and Sverdrup Technology Group. He is an Associate Fellow of the American Institute of Aeronautics and Astronautics, a licensed Professional Engineer, and an experienced pilot with airline transport pilot and flight instructor ratings. Blevins earned a bachelor’s in mechanical engineering from Tennessee Technological University and a master’s and doctorate in aerospace engineering from the University of Alabama in Huntsville.


John Blevins: We haven’t fielded an entirely new system since April 12, 1981, when the shuttle flew for the first time. That was the last time that we were at the same point in a vehicle that we are today.

This is just hard, rigorous work — good engineering work. You basically make a plan and then you work that plan, and you make sure that you stay technically rigorous. And that’s what gives you mission success.

It’s really going to be the most capable vehicle in the arsenal when it launches, and I think it really just opens up unique capability for our science partners. I’m most interested in the human flight side.

Deana Nunley (Host): Welcome to Small Steps, Giant Leaps, a NASA APPEL Knowledge Services podcast where we tap into project experiences to share best practices, lessons learned and novel ideas.

I’m Deana Nunley.

NASA’s Space Launch System — dubbed America’s rocket – will enable astronauts to begin their journey to explore destinations far into the solar system.

In the third segment of our Engineering Best Practices series, we’re chatting with SLS Chief Engineer John Blevins, who works at NASA’s Marshall Space Flight Center. John, thank you for joining us on the podcast.

Blevins: Oh, it’s my pleasure.

Host: How would you describe what it’s like to be the chief engineer for the world’s most powerful rocket?

Blevins: Well, it’s fascinating, first of all. Being the chief engineer is the convergence of so many different technical disciplines, more than I realized are even on the rocket before I was in that office, and then now getting to be the chief engineer. We do avionics. We do software. We’re responsible for the heating and the aerodynamics and the loads and the individual pieces of the elements. So, first of all, it’s fascinating.

It’s been a privilege to work with so many wonderful folks and to help discern the right course of action for the rocket and work with the program manager and communicate the risk as well as to make recommended technical changes and improvements to the rocket. So, I would say that it’s really an honor. There’s just a lot of wonderful people, a lot of great engineers – in fact, I believe the best and brightest of our country working on this rocket. So, it’s a privilege to represent them, not just on launch day, but every day when we go forward and we make decisions and we move as a team to build the best rocket for this nation.

Host: Could you trace the history of the Space Launch System from an engineering perspective. In other words, where did the concept originate and how did it evolve to where it is today?

Blevins: Yeah, that’s really a great question. A lot of people miss some of the nuances there. We were working on a program called Constellation back in 2000 and the country decided, ‘Hey, let’s do stuff only NASA can do. And let’s do this heavy launch vehicle. Let’s go where there’s not a market demand, but where we can make an impact and really do these exploration missions.’ Again, the Constellation Program had two phases, right? It had a low-Earth orbit phase, and then it had more of an exploration phase. And so, we picked up right there and took a look at what Constellation was doing. We did a little study between 2010 and ‘11 on heavy lift launch vehicle. And then we did this really ground-up study of, ‘Is that architecture the best architecture?’ We looked at all kinds of architecture from monolithic structure, if you will. It’s all hydrocarbon, a more Saturn-type-based rocket.

We looked at taking existing rockets and how do we combine those and how do we do the missions, even if that required assembly in space. And then one of the competitors – and that study is the one that won. And that was, ‘Let’s take a look at the assets that existed from shuttle heritage as well as add in some completely new pieces.’ And that really won on performance, on timing, on cost. And that started the Space Launch System. And then in 2011, I believe it was October 2011, Congress authorized the Space Launch System, and we’ve been working on it ever since.

And in fact, the first thing you do when you start a rocket like this usually is do wind tunnel testing. And my background is aerodynamics. So, the first thing I did was get a call from the chief engineer at that time, Garry Lyles, to run aerodynamics, and we got a wind tunnel model together. And we were in the wind tunnel in no time with my partners from Langley Research Center, Ames Research Center, Marshall Space Flight Center and Johnson Space Center. So, all of us got together and we made a great plan and we started and well, there’s a whole lot of testing and a whole lot of work ever since, but that was the original concept of Space Launch System. And really we’ve met that mission, right? We’ve got a rocket that is heavy lift, that it started with the intent to carry humans. And so, it’s considered those human-rating requirements since Day One. And it’s right on the cusp of launching.

Host: What are some of the technical or engineering firsts with SLS?

Blevins: Well, there are several. It’s the largest cryogenic propulsion tank. I think that’s probably the most visible when you see it roll out and you say, ‘That holds 700,000 gallons of cryogenic propellant.’ If you were to take the shuttle external tank, which is formerly the largest cryogenic propulsion tank, and you put it beside the Space Launch System to scale, if you just do that in a drawing, you’ll get an idea of how large this rocket is. It’s just super large and we need all that propellant to achieve the mission that we’re doing.

You also have the largest solid rocket boosters. They’re similar to shuttle. In fact, for a lot of people that messes up the scale, right? They look at the Space Launch System and they say, ‘Well, the boosters came up here on shuttle.’ And so, they come up here on Space Launch System. Well, these boosters are longer, they’re roughly 40 feet longer. And so they’re bigger. They’re more powerful for total impulse. And so, these are the largest solid rocket boosters made, too.

There’s a whole lot of other technical firsts that we’re doing. Really when I think about what we’re doing that’s first, I like to focus on the mission though. It’s the mission that we’re trying to achieve, right? We’re the big pickup truck, but what we’re achieving with this large vehicle is that we’re going to send a capsule, a human-rated capsule – the Orion capsule – further away than we’ve ever sent a capsule that a human’s on it.

So, the first flight is unmanned. And so, nobody’s on it, but we’re going to send that further away than we’ve ever sent anything with monitoring to make sure that next launch, when we do the same thing and we send humans further than they’ve ever been away from the planet, that we’re safe to do so. So that’s really to me the most important first that we’re doing is that further Deep Space exploration beyond where we’ve been.

Host: Are there unique challenges that come with using components that were originally designed for previous rockets?

Blevins: I’m so glad you asked that. It seems like my day is full of making sure that we’re balancing what the original intent for a part was versus what we need to use it for. So, a lot of folks wouldn’t recognize that up front, but when you take a heritage – or I like to call them legacy parts – and in fact, I divide the parts into three categories when I look at a component or just a piece of the rocket and I combine them into heritage. That means I took that part from some other program or some other flight vehicle, and I’m going to use it pretty much like that flight vehicle used it. So, there are cases on our rocket where we do that. So, like the forward attach that we use on the boosters that connects to the core stage, that’s almost identical essentially to the forward attach. And not only in hardware is that identical, but in function, it’s identical.

But there’s a lot of stuff that we took that existed and we wanted to use that. It saved us time and money and development, but it had constraints with it. And I call those parts ‘legacy parts.’ They exist, you can pick them up, you can hold them, but we’re not using them the same way. And some of those it’s quite different how we’re using them. One example, for instance, is the auxiliary power unit we used on the shuttle, we use on the core stage, we call it the CAPU, the core auxiliary power unit. And on shuttle, we used hydrazine as a working fluid through the turbines to create that power. Here we don’t. We use a helium spin that we transition to hydrogen. So, we’ve got a totally different working fluid, but many of the exact same components that we had before. And so that’s one where you’ve really got to pay attention to what you’re doing.

And there’s many others where it looks a lot like it did before, or it’s identical to what it was before, but we’re using it differently. And so that does bring new constraints to the design, but our team has really faithfully executed and made sure that we fit within the design capability. There’s been a few times where we’ve taken those parts and we had never tested them to what we’re going to do before. And so we’ve gone and tested them and we’ve made sure that they can handle the stresses, the loads, the torsion, whatever we’re doing on our rocket. And so that’s been really not just challenging but rewarding to go back and be rigorous with those existing parts and make sure they can fulfill our mission.

Host: If you had to identify the single toughest engineering challenge the team has faced in developing America’s rocket, what would it be?

Blevins: Well, first let me say that a lot of times we’re looking for a diving catch. And there aren’t any real diving catches. The rocket wasn’t about to fall over, and six guys hooked it up and kept it up, right? So there have been many challenges. Many of those are associated with those legacy parts that I just mentioned. Those that had limitations from before. Some of them are associated with new processes. We used friction stir welding for the tanks. This is the thickest aluminum friction stir welding anybody’s ever done in the world. And so that’s a first, and so there were challenges, making sure we got the welding schedule, the rotation and translational speed of those tools correct. And so, we solved all of those problems. But I would say probably the biggest challenge is just simply vision, really, for people outside of the program to recognize the capability of this unique machine.

Inside of the program this is just hard, rigorous work — good engineering work. You basically make a plan and then you work that plan, and you make sure that you stay technically rigorous. And that’s what gives you mission success. So, I would suggest that there’s been no huge technical challenges. There’s been many small technical challenges, but then making sure we communicate the vision and the capability of this rocket, it can do more than just carry people. In fact, it can be a great rocket to enable science missions we couldn’t previously do. So that’s been one of my challenges, at least as chief engineer, is to make sure that we communicate accurately the capability and the limitations of the system.

Host: Has anything in this process come easy or perhaps easier than you might have expected?

Blevins: There’s been a few things that did surprise me. And I hate to use the word easy because they came on the heels of hard work. I want to use Green Run as an example. We went down to Green Run and some parts failed early on during the first tanking and observations. And those were parts that were heritage. They weren’t even legacy. I mean, we were using them exactly like we intended to use them. And so that was a little bit disappointing. And we worked through that. Those are certainly sub-supplier parts to one of our major prime contractors. And so, it wasn’t anything anyone could foresee that minor changes had been made that weren’t fully evident. And so, we worked through that. Then we worked through valve timing and we’re interfacing the software in this very complex cryo system with this complex rocket for the first time. And really there was just a lot of work. It was very rigorous. Our heads were down working hard. We get through a hot fire that goes 62 seconds. We’ve made a lot of decisions on the fly that day. And we had achieved that. We found a limitation, that we had a very tight limitation on one of our software. And so we decided to rerun that test for a full duration. And when we re-ran that test for a full duration, it was an incredibly quiet day. Now, maybe we should have expected that, right? We’d worked through all the bugs. We had a machine and that machine’s going to operate very similar every time. And we’d learned a good bit about that machine going through the first process, but that second time, the full-duration hot fire for Green Run, it was a very quiet day.

There were no problems. The vehicle was doing what we told it to do, and it was doing it very well. And we were monitoring systems. And when it came time to light those engines at T-minus six seconds — that’s the timing on that test that we lit those engines, the same as an L-minus timing for launch — and we lit those main engines. And then we burned them for over eight minutes and roughly 20 seconds and depleted the tank and went through in a very aggressive profile with the engines and everything. Everything we did, we stressed that system and it behaved perfectly. So, if there was anything that surprised me about being easy, it is the results of the Hot Fire-2 for the Green Run and how well that new hardware — that core stage is largely new hardware, new lines, ducts, valves, new welding, new cryo tanks, new seals — it performed admirably. It was just great.

Host: John, what are some of the key lessons learned so far with SLS?

Blevins: Well, I think one of the key lessons learned is just staying in the game and doing rigorous work. We haven’t fielded an entirely new system since April 12, 1981, when the shuttle flew for the first time. That was the last time that we were at the same point in a vehicle that we are today. And during even shuttle, there was a lot of discussions and distractions. And you can certainly read about that. And we’ve still got some colleagues at the Marshall Space Flight Center and the Johnson Space Center and at Kennedy Space Center that experienced those events as young engineers on shuttle. And there was a lot of talk. There was also external pressures, and yet that team stayed in there and they flew that vehicle. And that’s really, for me, one of the major lessons learned is to not be distracted by artificial external pressures.

We have a mission to do that has been assigned to us by the U.S. government and we’re fulfilling that mission to do this accurately. And so doing good rigorous work and understanding what’s good enough that — I will say that one of the big jobs of a chief engineer is to listen to all the inputs and to recognize when good enough is good enough, or to recognize when one interest that’s being expressed competes with another interest. That’s also important, and to balance those. All of those have been personal lessons learned.

But as far as lessons learned for the vehicle, another good lesson learned that I think has been a trailblazer for other vehicles that will come behind whether they’re government or they’re commercial or even other countries is the combination of testing and analysis. We’ve changed to a model-based engineering that includes some models that have a lot of correlation in them. It helps us take away some of the conservatism that you would do in a more traditional approach. And yet it’s become very efficient. Some people might say, we’ve done a little bit less testing on SLS than we did shuttle. Well, that’s true, but we only did the testing we needed to answer questions. And that’s why we were able to do that. And we answered other questions with analysis and tools for analysis that we didn’t previously have. So, a lot of the investment over the last several decades for finite element modeling or computational fluid dynamics or internal thermal gradients and all of those things have manifest as a really much better way to build a rocket. And so we’ve done a good job that way. That’s been a good lesson learned.

Host: You mentioned your background in aerodynamics. What is it like going from being a technical leader to being a decision maker with SLS?

Blevins: Well, it’s been a growing experience for me personally. I really enjoy doing aerodynamics. And then the chief engineer at the time, Garry Lyles, who really started this program called me and asked me to come up and be his deputy. And I worked with him for several years. And one of the things I learned from Garry, and I’ve learned from working with other chief engineers at NASA, and that is really that the value that’s added to this vehicle is added by those technical workers, the leads that we have under me, the workers that we have doing wind tunnel testing and doing cryogenic testing. And so really what I’ve learned is to build trust with those folks. There’s going to be times where I make decisions that certain groups may not see fully, I may be weighing different risks on the vehicle, different technical views on the vehicle. And so, to make sure that they understand that I’ve heard them, that I understand where they’re coming from, but that I need to go a certain way. And maybe the way they want me to go may be a different way, but to build that trust between me and them has really been the key. You’re only as good as the people that you’re leading. They’re doing the hard work, and I’ve just been privileged to be part of that team.

Host: During this podcast series, we’re highlighting engineering best practices. Which best practices do you think have contributed most significantly toward getting the SLS rocket ready for mission success?

Blevins: Well, that’s a really good question. And there’s a lot of answers to that. Let me give you a few that I think have been incredibly significant in getting us where we are. It really starts with when you decide what you’re going to build and how you’re going to build it. And you’re going to communicate between NASA and the prime contractor. And so you start with these design and construction standards, that’s actually a best practice, right? Design and construction standards. How you plate wire, it can be how you build electronic components, it can be how you weld. All of those are really lessons learned, and we’ve learned those over numerous vehicles. And so you start there at the design and construction standards. Some of them don’t apply to every condition. And so you tailor those. And so that’s a form of best practices is making sure that we’re talking right up front, how we’re going to build the hardware and how we’re going to evaluate the hardware.

There’s also this balance between how we test and we do analytical. And let me just speak to testing a little bit. Testing comes in a lot of different ways. Some people, when they look at a program and they talk about testing, they’re just talking about the big structural components. And we do that. That’s an important part of testing. And maybe the most visible, in fact. You probably saw where we tested the hydrogen tank to failure, this large hydrogen tank. And we just ripped it open, right? We tested it to failure. It buckled. And then as we’re unloading the vehicle, it completely unzipped this over half inch thick aluminum sheet, just flapping as the gases on the inside came out. And so that was an interesting test.

But there’s also this testing before that, and that’s developmental testing. And so, we did a lot of combinations of analysis and developmental testing. I think that was a great best practice. We did some unit physics type problems in the wind tunnel, for instance, and we’d use that to make sure our model was validated. Then we’d expand that model to predict the environment. That actually made us more efficient, right? We did less testing overall because we did it testing intelligently.

And then of course there’s another type of testing and that’s the qualification testing, making sure that you test your parts so that they’re good for flight and they’re going to survive flight and you’ve got to do that without damaging the parts so that they don’t survive flight. And so all of those test programs built up. And I think that was a huge, best practice that we did. And it’s something the agency has long learned and done well.

Another really good thing that’s best practice is to have the right independent reviewers. We occasionally have areas that are extremely critical. In fact, we’ve got a category of events that we call critical events. So, you can imagine things like the commands that the ground sends to start the rocket, that’s a critical event. When we separate boosters from the rocket that’s a very critical event. When we take the ESM panel jettisons off of Orion and making sure they don’t hit the rest of the rocket, that’s a critical event. Making that translunar injection burn is a critical event. So in those critical events and all the inputs to those critical events, we tend to have external reviewers that take a different view and sometimes they’ll catch something that we didn’t do. And they’ll force us to go back and make sure we did things right. And so, I think independent reviews are actually a very good, best practice that we had at the right place.

And then finally, I’ll mention end-to-end integrated vehicle testing. And I think this is essential to the success of the vehicle. I make it akin to when you drive out to the edge of the runway and you pull the elevator back and you make sure it moves and you move the ailerons and you make sure they go in the right direction. We’re doing the same thing with the rocket. We’re telling it to point somewhere in space and we’re making sure that the nozzles deflect in the right position and we’re making sure the commands go from one system to the other. And that’s what we’re doing right now in the VAB as we prepare for launch.

Host: And let’s talk about the mission that’s right in front of us — Artemis I. At this point, what are your focus areas on Artemis I as SLS Chief Engineer?

Blevins: Well, at this point, we’re about to do an incredible test part of this ITCO test — the integrated test and checkout — and that test is the wet dress rehearsal. We’re sitting out there. We’re making all the preparations. We’ve verified all of our models and we’re ready to practice launching the rocket by doing the full tanking — 700,000 gallons of cryogenic propellant. We’re going to also tank the ICPS, the in-space upper stage. And so that’s what’s on my mind today is preparing for that imminent test for the wet dress rehearsal. And that’ll be the last major verification work that we do prior to launch.

Host: And you get past wet dress rehearsal, and then what really starts to get your attention?

Blevins: Well, when we get past wet dress rehearsal, it’s my job to help marshal the team that day for launch. And we’ve already prepared through several simulations. I get to sit in the Launch Control Center, represent all these engineers. We’ve got element chief engineers for each one of the elements and the OEM, the prime contractor, chief engineers. And as things come up that day, say it’s a temperature measurement or something that looks like it might inhibit our launch, we work through those problems and those guys bring that problem to me. And together we go to the launch director and we try to make sure we give the rocket the best opportunity to have a flight that day. And so that’ll be the next focus for me immediately after a successful wet dress rehearsal will be going into that launch preparedness.

Host: What excites you most about future possibilities with SLS?

Blevins: Oh, my goodness. We have a lot of opportunity for missions. It’s really going to be the most capable vehicle in the arsenal when it launches, and I think it really just opens up unique capability for our science partners. I’m most interested in the human flight side. That’s the side that’s expending the revenue to develop the rocket. And we’ve got those missions booked out largely through the rest of the 2020s. But I do think there’s a really unique part of NASA that I really appreciate and I think the public appreciates, and that’s the part that we do that’s unique telescopes and unique planetary missions and even interplanetary or interstellar-type missions. This vehicle will enable some things that couldn’t previously be done in the timeframes that they could be done. Now, let me add just a little bit of context to that, actually. If you were to build a new telescope and you could put a 10-meter shroud, roughly 30-feet shroud on this vehicle, you might would build that telescope to fit this vehicle because you can launch it in one launch and you don’t have the complexity or even mass penalty of making mechanisms that have to hook together. So, I think there’s just a lot of opportunity. I don’t want to limit the imagination of the audience. They may have additional things, but I think it’s just going to be neat to be back in the ballgame with a rocket that we have confidence that can be built and fly safely that can put expensive payloads or human payloads and go do missions. I think it’s going to be great.

Host: John, this has really been fun. I’ve enjoyed getting the opportunity to chat with you. Thank you so much for being on the podcast.

Blevins: It’s been my pleasure. Thank you.

Host: Do you have any closing thoughts?

Blevins: Well, I’ll just say that it’s really fascinating to be part of this wonderful mission. It’s the convergence of so many good technical practices and people and our country. And so it’s really a privilege to work on it and to represent the thousands of people that are working on it as we prepare to launch. And so, thank you for having me today.

Host: John’s bio and links to topics discussed during our conversation are available at along with a transcript of today’s show.

In the fourth and final segment of the Engineering Best Practices series, our guest will be Johnson Space Center Engineering Director Julie Kramer White. We’ll look forward to connecting with you when that episode is released April 6.

If you like this podcast, please follow us on your favorite podcast platform and share the episode with your friends and colleagues.

As always, thanks for listening to Small Steps, Giant Leaps.