On this episode of the SpaceGeeks podcast, Dan Leone talks to Jeff Thornburg: a propulsion expert who just capped a five-year stint at SpaceX where he led development of the company’s methane-fueled Mars engine, Raptor.

If you don’t feel like listening to Jeff’s episode, you can read a transcript below.

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Episode 26, Jeff Thornburg.

Dan Leone: This is the SpaceGeeks podcast!

[Intro music]

DL: Hi everybody, I’m Dan Leone with SpaceNews in Washington, this is the SpaceGeeks podcast and this is an episode about becoming the change you want to see in the propulsion business.

Jeff Thornburg: My mother begged me, pleaded with me, not to go into the aerospace industry. She was so adamant about it, she says, ‘I will buy you a car if you stay and go to junior college versus going to a four-year university.’

I said ‘no way.’

My name is Jeff Thornburg, and presently, I am the president and founder of Interstellar Technologies, which is a small company dedicated to advancements in propulsion and space technology.

I’ve been in this business now for almost 20 years after getting my start in the United States Air Force.

DL: Jeff Thornburg’s got a lot of calling cards, but I really have to call out the five years he just spent with SpaceX as a highlight. SpaceX, which managed to propel real space hardware into the news cycle the same week a new Star Wars movie came out, hardly needs an introduction.

But just in case you’ve been scavenging for scrap in the Jakku desert since the year 2000, SpaceX is internet gazillionaire and serial entrepreneur Elon Musk’s Hawthorne, California-based space-launch company. They just successfully recovered the spent first stage of a rocket used to launch communications satellites into space for a paying customer. One step on the road — so the refrain goes — to cheap, reusable rockets.

As for Jeff, he just left SpaceX in November 2015. He was most recently in charge of the company’s propulsion group, which is the part of SpaceX in charge of the rocket engines that make launches possible.

Landings too, for that matter.

JT: Raptor is kind of my baby there.

DL: Raptor’s a methane fueled engine that SpaceX is working on as part of its mostly-secret plans for a Mars exploration system.

And we’ll get to that stuff.

First, it’s worth taking a quick walk down Jeff’s resume because he’s made pit stops at pretty much every important type of employer in the space business. And there’s a method to the multi-pronged path that eventually led him to SpaceX.

Jeff Thornburg grew up in a small town in Central Illinois. For those curious about the vintage, he’s post-Apollo — but barely. Jeff was born less than a year after NASA stopped sending astronauts to the moon.

Still, the Apollo afterglow back then was fresh and strong, especially if you were a little kid, with toys to play with.

JT: You know, you’ve seen these lego movies — I’ve taken my eight year-old daughter now to [these movies] and, you know, kind of the joke in some of those are these old, beat up, Lego astronauts.

Well those were the Lego astronauts I played with when I was a kid. Those are the Lego sets I waited for at Christmas time, and you know, all of that just culminated into my interest in space.

DL: Now there was no internet back then to help a curious kid who liked Lego astronauts learn about space, but Jeff still managed to self-educate.

JT: I had inherited this encyclopedia set from my grandmother, and as a part of that set was this set of science yearbooks. And I used to just dive, as geeky as that sounds, I used to dive into those science yearbooks, and they had all these great features on the space program from the late ’50s to the early ’70s. And that was my internet as a kid.

And so then the set ran out in like the mid ’70s or late ’70s and I begged my mom to buy these science yearbooks starting from whatever year it was, ’80, ’81 on forward, and so that was, I looked forward to those every year, as crazy as that is, because that’s how I got all of the latest science and technical information as a kid about what was going on out there.

And I just loved it.

So that was kind of how I got my interest as a kid. And then really, my path into the industry was really through the U.S. Air Force.

DL: So, Jeff graduated high school in 1991, and, despite his mother’s misgivings, dove head first into aerospace engineering at the University of Missouri-Rolla. Like he said, he had help from the Air Force, which provided an ROTC scholarship that netted him bachelor and masters degrees in aerospace engineering — and nine years of active duty.

While he was on active duty with the Air Force, Jeff dabbled in planes for a while. But he knew what he really wanted was to get into the space corner of aerospace. Which he eventually did, in the year 2000.

JT: My first stop was the Air Force Research Laboratory and, um, I really at the time, I really was all gung-ho on electric propulsion, coming out of grad school. That’s where I wanted to be, it was the future, I wanted to work warp drive, you know: let’s bring on the exploration.

And the Air Force said ‘yeah, that’s nice, but we really need help with our liquid propulsion programs with the Air Force.’

And so really, my career started really at that point at the lab where I started working liquid propulsion technology programs. I had a lot of partnership programs with NASA and NASA Marshall specifically, Marshall Space Flight Center, and began my education on liquid engine systems.

DL: Liquid rocket engines are the big-kid engines. Rocket engineers sometimes look down their noses at solid propulsion, which can be effective, but is also much simpler than liquids. Solids, some people say, are really just fireworks.

The Air Force was especially interested in liquids. Around the time Jeff got to the Air Force Research Lab, United Launch Alliance — the Boeing, Lockheed joint venture that launches most U.S. government spacecraft — had just launched the first Atlas rocket powered by a Russian-made engine known as the RD-180. Some people thought then, and some people think now, that the U.S. ought to have its own liquid engine and not import one from Russia.

The Air Force and NASA have had fits and starts developing a new liquid engine, but ULA is still using the RD-180, for now.

And anyway, Jeff leant a hand with the Air Force’s liquid propulsion efforts around the turn of the century, but while he was with the service, he got hooked on the hard stuff.

Hey now, get your mind out of the trash compactor. I’m talking about hardware. As in rocket hardware.

JT: The time at the Air Force was really incredible, and it led to many other things in my career. I wanted, because I was gone all the time and working on hardware, I wanted to go work in industry. And so I left the Air Force for industry experience because I wanted to be right where the hardware was.

And that’s really my advice for anybody wanting to come in and grow their career is, you gotta go where the hardware is.

DL: Jeff checked some major boxes after he left the Air Force, and got to learn on the job from some of the country’s leading propulsion experts.

JT: I went to work for a small company that did a lot of small business research programs called Exquadrum in southern California, and then I went to work for Aerojet, before they were Aerojet Rocketdyne, for about four years. And then I went to work for NASA at Marshall Space Flight Center.

DL: Where, one day, he got a phone call from the West Coast.

JT: I was working at NASA Marshall on the J-2X engine program, and, and uh, that was during the time where Ares was kind of coming, the Ares program was kind of coming through a draw-down cycle, and I got a phone call one night.

My daughter was about three years old, and it was Elon’s assistant, and I wasn’t really too familiar with Elon Musk. I’d watched the SpaceX launches, it was, you know, late 2010, early 2011 at the time, and um, his assistant said, ‘Elon would like to chat with you, do you have some time?’

And I said ‘well no, I really don’t, cause I need to give my daughter a bath, but if you give me about an hour, I will, uh, I’ll give you a call.’

DL: [laughs] This is a really astounding thing to say to Elon Musk.

You should know that SpaceX isn’t exactly famous for having a family-friendly schedule or work environment. The space industry in general is very challenging and very demanding. The launch industry is particularly like this, and triply so is SpaceX, where Elon Musk wants you to work hard, work all the time, and work hard all the time. It can be an attractive environment for people who don’t have or don’t want families, but maybe not so much for people who would like to have a weekend, you know, like, ever again.

So it really made me chuckle to hear Jeff say he blew off Elon’s recruitment pitch to go be a dad for an hour.

JT: That could have been a very career-limiting phone conversation that night.

DL: Far from being limiting, that phone call opened the door for Jeff to have the moment of his career.

During our interview, Jeff recalled an Elon Musk quote about how engineers are like magicians.

And that reminded me of a quote that I heard — which maybe Elon’s also heard — from a 2013 movie called The Wind Rises, which was written and directed by the famous Japanese animated film maker, Hayao Miyazaki.

The Wind Rises a fictional biography of Jiro Horikoshi, a nearsighted aeronautical engineer who, as a young man, designed the infamous Mitsubishi A6M fighter plane the Japanese Empire used in World War 2.

In the movie, eccentric Italian airplane designer Giovanni Caproni speaks to Jiro in a dream and tells him, “Airplanes are beautiful dreams. Engineers turn dreams into reality.”

But Caproni said something else in the movie: engineers, like artists, are really only creative for 10 years.

So the actionable flip-side of the quote is this: if you’re an engineer, dance hard when the spirit moves you, because your peak years don’t last forever.

JT: Yeah, I, uh, it does speak to me a little bit. That explains very well the five-year timeframe I was at SpaceX.

DL: For Jeff though, reaching the peak wasn’t something he could do the way it happened in the movie. You can’t just use youth and enthusiasm and raw talent as a lightning rods for your magnum opus.

JT: When you’re talking about rocket engines, and rockets in general, but specifically propulsion with engines, it’s such a multidisciplinary field, it takes literally a decade or two to really know and experience enough to really understand those systems. And I mean in a way where you could create one yourself, or at least architect and help create technology.

I remember coming into the Air Force Research Lab as a young captain and being blown away by all of the things that I needed to learn. And, um, then that’s kind of how I constructed my career: I’m like, well, I want to learn more about rocket engine turbo pumps, so I’m going to go focus on that. And I did that at Aerojet and NASA. Then I’m going to come back and take all of that and work on propulsion and vehicle systems.

DL: Jeff felt like SpaceX was the place where he could put his head down and weave a new thing out of everything he learned during his years with the Air Force, NASA, and industry. This was his time to be creative.

JT: When I came into that job, I felt I had, had finally put all of the tools in my tool bag that I needed to help an organization like SpaceX be successful. That was the penultimate point where I was like ‘I can do this, and I can participate in some really crazy, revolutionary things.’

DL: And now, at long last, we finally get to talk about Jeff’s baby: the methane-fueled Raptor engine — which, okay, full disclosure, hasn’t flown yet, but it’s still very much worth talking about.

Methane is an interesting choice for rocket fuel. It’s not very popular right now and none of the major launch companies are burning any. Performance-wise, methane is sort of in the middle of the pack, compared with more popular kerosene and hydrogen options, but SpaceX, and Elon in particular, think the fuel has a future for reasons not entirely related to its flight performance.

JT: The reason why methane isn’t on par with um, kerosene and hydrogen is just because the country never really facilitized for methane. You know, there was a tremendous amount of work back in the ’50s and ’60s by Pratt and Whitney on facilitizing hydrogen for the RL-10. And hydrogen, in space, that’s where you want to go, that’s where you get your best performance. But because of the [low] density of hydrogen, you just end up with bigger tanks.

And so you made the comment about volume? Where kerosene is the most dense fuel, you end up with the smallest tank for the same energy. With methane you get a little bigger tank, and with Hydrogen, you have the largest tank. So really, the largest staged systems are the hydrogen systems. Methane kind of splits the difference, and it also splits the difference in performance: higher performing than kerosene, not quite as high performing as hydrogen, but from a facilitization, paying to be able to move the commodity and transport and deal with it, methane is much more cost-effective than hydrogen.

I can also say, from a performance standpoint, you can look at the classic kerosene first stage, hydrogen upper stage, which is — you know, [Werner] Von Braun had the right physics. The Von Braun physics, the physics in general, are still the same. It really is a question of programmatic decisions that the U.S. made over the years because of what they already had invested in.

DL: What Jeff’s getting at there is that the rocket industry, as it exists, has had plenty of time to gather, store, and learn how to transport kerosene and hydrogen. It isn’t that way for methane now, but it could be.

Now as far as why SpaceX wants a methane-fueled engine at all, well, there are some tantalizing rumors out there. And we know that, broadly speaking, these are related to SpaceX’s plans for Mars exploration systems. Exactly what’s going, well, it’s not widely known outside SpaceX. Every once in awhile, somebody who works at the company will tell you something like “hey, there are some SERIOUSLY crazy things going on back there!”

But no one’s willing to offer any specifics.

Jeff wasn’t either — not that I didn’t ask — but he did talk generally about some of the things you could do with a methane engine that perhaps you couldn’t do with a kerosene or hydrogen engine.

JT: The beauties of methane are that you get the higher performance than kerosene, but the idea is that you’re not dealing with some of the issues with kerosene. It’s a clean-burning fuel, like hydrogen.

And then, you’re kind of looking at two things: what does the fuel cost, and if you want to use and develop and exploration architecture for Mars or the solar system, where can you live off the land?

There’s all this in-situ resource utilization technology work that’s kind of been on the slow-simmer burner for many years within the government, primarily NASA. But as soon as you don’t have to take your propellent with you that you have to use to come home, now you can take a lot more stuff wherever you’re going. So, now that you don’t need to take your propellent to get home as part of your camping gear and you can make it on Mars or you can make it somewhere else, now you can take a whole bunch more stuff.

So if you’re talking about putting a colony or doing science missions or whatever, now you’ve just way expanded your envelope for all of the quote ‘stuff’ that you can take for whatever mission application you’re interested in.

Elon teases about, you know, coming out with a Mars plan soon? Here in the next few months, I think the public’s going to see some more information on where the company’s gonna go with that.

DL: So after Jeff got the Raptor team pointed in the right direction, he spent some time leading the propulsion systems for SpaceX overall.

Which, if anything, was a more stressful job.

Of course, Jeff knew going in that working for SpaceX was as much a commitment on his part as it was on his family’s.

JT: It was super challenging. My daughter, you know, would always ask me on the weekends, would this be the weekend that I would get a phone call and not be around? We kind of joke about that now, but, I mean, during that time period, that was just, that was another one of those challenging moments that just pushed you to see how far you could go.

DL: Jeff gives his wife and daughter a lot credit for helping him go as far as he did at SpaceX. As a family, they all believed in the mission, so to speak. And Jeff got his family time in when he could, even if it meant having that time in the cafeteria at work.

JT: You know, my daughter wanted to come for the free frozen yogurt. That’s what she loved. So, you know, I encouraged it. After school, there was plenty of free frozen yogurt trips to SpaceX. And the three of us would sit around and talk about our day and hear about what’s going on at school, and maybe if we had friends or family out, you know, walk around the factory a little bit and show people what’s going on.

If we were standing in the SpaceX production aisle right now, my eight year-old could give you the tour. She saw me give the tour so many times to people that she knows what’s going on in the SpaceX factory, which, I would have given my left arm for at her age, and she kind of just takes that for granted.

DL: But as well as things apparently went, Jeff decided, and quite recently, too, that it was time for him to leave SpaceX — and time for the Thornburgs to leave California.

He says it was a family decision.

But you know, a lot of senior executives have gone in and out of the revolving door out in Hawthorne at ludicrous speed. Elon Musk has a rep for chewing up colleagues and spitting them out. They say he’s a difficult man to work for. They say it’s a job that burns you out.

So I asked Jeff if maybe he felt a little bit burned out, or chewed up.

JT: I get that. I have gotten that question a few different times because, you know, it is a challenging environment to work in. And some people react different ways to that environment. the challenges of working in that very aggressive, very demanding culture never really bothered me.

To be frank, I’m probably going to be, maybe I’m going to be, like, the outlier here in some of these conversations. I left the company on very good terms, the company was very gracious when I left. I explained to them the family reasons of why I needed to make a change, and Gwynne [Shotwell, president of SpaceX] and Elon and the company in general were more than gracious with that entire transition.

DL: Now, down in Madison, Alabama, just southwest of rocket city and NASA’s Marshall Space Flight Center, Jeff Thornburg is president of his own company, Interstellar.

Which to be honest, sounded to me like just another LLC somebody stood up so they could consult between full-time jobs.

JT: I hope it’s not the LLC I create between jobs. Let me just start out by answering that question directly. I have had things in the back of my mind for many years. And I think, you know, with the family reasons needing me to relocate, it provided an opportunity to think about what it is that I could do if I could do anything in the world.

And Interstellar really is a vehicle for me to start exploring those things. I hope to be able to come back in the future and be able to tell you more about some of the things that we’re doing, but in general, the goals for the company really are to basically recreate the success that the industry’s having and provide opportunities to incubate new players and bring things to the table that people didn’t think existed.

I mean, one of my most favorite things about working at SpaceX was to do things like what happened last night [Dec. 21] with the landing. You know, you basically perform the magician’s trick: you do the impossible And the thousands men and women making that happen are incredibly talented, and they’re everywhere. And so, and it’s not the ones that I know about that I’m most interested in.

It’s the ones I don’t know about.

DL: Jeff thinks — and he’s not alone here — that the propulsion business has gotten stale. Liquid engines like Jeff’s worked on his whole career are about tapped out, in terms of efficiency, he says.

What we really need are new people with new ideas, Jeff thinks. Because the wind is still rising, and there’s a gale on the horizon.

JT: The fact that we don’t invest in research and development like we used to anymore, it’s going to be a dead end for us.

DL: Maybe with Interstellar, Jeff will find those people to help circumvent this dead end. Maybe he’ll help them find the place where they can have their five or 10 or however many years of magical creativity. Maybe one of them will be on this show, one day, who knows?

That’s all for this week, everybody. Thanks for listening. And have a happy holiday, whether you’re working, or playing, or doing nothing at all.

[Outro music.]

DL: The SpaceGeeks podcast is recorded and produced in Apple’s GarageBand. Some sounds were provided by the European Space Agency and NASA via the agencies’ SoundCloud accounts, other sounds were provided by the Internet Archive at archive.org.

Still other sounds were provided by my guitar, and a quaint old tool called reporting.

For SpaceNews in Washington, I’m Dan Leone.

JT: You missed the landing for Star Wars, but I have a lot more acquaintances that missed Star Wars for the landing.

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Dan Leone is a SpaceNews staff writer, covering NASA, NOAA and a growing number of entrepreneurial space companies. He earned a bachelor’s degree in public communications from the American University in Washington.