...who builds rocket engines? (with Nate Perkins and Doug Bradley)

Ever Wonder? / April 13, 2022
Doug Bradley (left) and Nate Perkins (right) in studio with a photo of NASA’s rocket for Artemis 1 behind them.
Image attribution
Courtesy of Aerojet Rocketdyne
NASA’s new rocket, the Space Launch System (SLS), rolls out to the launchpad at Kennedy Space Center for the first time on March 17, 2022
Image attribution
Courtesy of NASA
 Nate Perkins, mechanical design engineer on the RS-25 engine nozzles
Image attribution
Courtesy of Aerojet Rocketdyne
Doug Bradley, deputy program manager for the RS-25 engine
Image attribution
Courtesy of Aerojet Rocketdyne
Four RS-25 rocket engines during a test fire. An RS-25 engine is also on display at the Science Center!
Image attribution
Courtesy of Aerojet Rocketdyne

NASA is going back to the moon later this year with the Artemis I mission. And in March, NASA rolled out their massive new rocket for Artemis to the launchpad

Ever wonder who builds rocket engines? 

On this episode, we talk to two of those people. Nate Perkins and Doug Bradley both work at Aerojet Rocketdyne, the company that makes the engines for NASA’s new rocket. Nate and Doug work on a rocket engine called “RS-25.” Four of these engines are mounted at the base of the rocket and will be the first engines to fire when the rocket lifts off and heads to the moon. 

Have a question you've been wondering about? Send an email or voice recording to the podcast team to tell us what you'd like to hear in future episodes. 

Subscribe to our show on Apple Podcasts, Spotify, or Google Podcasts. To see a full list of episodes, visit our show’s webpage


Perry Roth-Johnson (00:06):

Hello! This is Ever Wonder? from the California Science Center. I'm Perry Roth-Johnson. NASA is going back to the moon later this year with the Artemis 1 mission. And in March, NASA rolled out their massive new rocket for Artemis to the launchpad. Ever wonder who builds those rocket engines? On this episode, we talk to two of those people. Nate Perkins and Doug Bradley both work at Aerojet Rocketdyne, the company that makes the engines for NASA's new rocket. Nate and Doug work on a rocket engine called "RS-25." Four of these engines are mounted at the base of the rocket and they will be the first engines to fire when the rocket lifts off and heads to the moon. Let's get into it. We have two guests from Aerojet Rocketdyne joining us today: Nate Perkins, you are a mechanical design engineer on the RS-25 nozzles—Nate, welcome to the show!

Nate Perkins (01:00):

Thanks, Perry. Good to be here.

Perry Roth-Johnson (01:02):

And we also have Doug Bradley, the RS-25 deputy program manager—Doug, welcome!

Doug Bradley (01:06):

Thank you, Perry. It's a pleasure to be here.

Perry Roth-Johnson (01:08):

I'm just beyond excited to talk to both you today. It's definitely not every day you get to talk to real life rocket scientists. Now I know that you and your team at Aerojet Rocketdyne are focused on building the rocket engines, the RS-25s, uh, for NASA's upcoming Artemis 1 mission. But before we dive deep into that, I just wanna give our listeners a big-picture overview, because folks might not be familiar with the mission or its new megarocket. Uh, maybe people were surprised when they saw some headlines recently and these really gorgeous photos from when NASA rolled out the GIANT new Space Launch System rocket to its pad in March. But let's just start with Artemis 1, first. Doug, what is the goal of the Artemis 1 spacecraft? What's it gonna do?

Doug Bradley (01:51):

Yeah, the goal of, of Artemis 1 is to test the entire system and to fly it without people on board. So we don't put anybody in jeopardy as we're testing out the system.

Perry Roth-Johnson (02:03):

There are more missions planned after Artemis 1. We have Artemis 2 and 3. Right? So can you just give us a sense of the goal of the whole Artemis program?

Doug Bradley (02:11):

Yeah, the, the big picture view is, is actually we're going to Mars eventually. And the moon is, is practice to go to Mars. Mars is, and you ask why, I mean, it's, it's exploration. I think humans are kind of wired to be explorers. Yeah. Uh, there's all, always all sorts of practical things that come out of the space program and, and just doing new things, but for the rocking and the mission itself, the, the end game is to go to Mars. But that's very difficult. Uh, uh, Mars, it takes over six months to get there. You have to spend six months or more on the planet until the, the planets are aligned properly again. And then it takes you six months back. Well, that's a, at least a year and a half trip. Long trip. So you have to get really good at space. And so we've been working up to that. We've gone to the space station. We've learned to, to live and work in space six months at a time. Some astronauts have stayed up as, as long as is a year. Now we're going to the moon and that's practice as well. We're gonna go to the moon. We're gonna stay there longer. In the Apollo days the astronauts stayed a couple days, we're gonna stay months now. We'll be building structures up there. The types of things you're gonna have to do if, if you want to go to Mars. So once we get good at going to the moon, then it'll be time to go to Mars and working out all those systems that, that are required for that. The immediate launches of Artemis 1 is unmanned un un-accrued, uh, just to check out everything else. Artemis 2, there will be crew on board, but we won't be landing yet. We still have to make sure that all the systems are working right in parallel with this we're working on the landers. And so Artemis 2 will be orbiting the moon. And then coming back if I was an astronaut, I'm not sure I'd want to go on that script. You're so close. Uh, but that's what they did in the Apollo days as well. A wonderful mission actually. And then Artemis 3 is boots on the moon, uh, first woman, first person of color on the moon and it'll be four astronauts there and they'll be there, I don't know exactly how long they're planning now I think they're still planning the mission objectives. Uh, but that'll be people back on the moon. That that'll be fantastic. I mean, I was, I was young when we landed on the moon the first time, but that was, that was exciting. It'd be great for, it'll be great for this generation to experience that same thing.

Perry Roth-Johnson (04:53):

Yes. Yes. As someone who went to space camp, when he was in fourth grade, I was always very jealous that I wasn't part of the Apollo generation. So I'm very excited for Artemis 3 when we get there. Um, but we're, we're, we're gonna focus on, on Artemis I and then take a, a closer look at your guys' engines and, and the rocket one, one point I wanted to clarify though, before we go there, since Mars is the ultimate goal, is the rocket that we see on the pad now gonna change very much when we eventually get really good at going to the moon and we're ready to go to Mars or is it gonna essentially look the same? Do you guys have like enough power already built into it to, to get all the way to Mars?

Doug Bradley (05:35):

We're almost there. Okay. What, the, one of the big changes they're, they're gonna change the solids a little bit, make them lighter basically. So you can that'll translate into cargo. Our engines can actually go a little higher in power level. So we're gonna go a little higher in power level. So both both of those things will be more cargo carrying capability. Right now, Artemis 1 has one upper stage engine, one RL-10, that's gonna change to four RL--10s. So you can imagine that the rocket will get bigger and taller, but the, the basic components will remain the same. So it's very much evolvable without having to go through more development and, and, um, expensive development. So that's part of the reason the rocket is designed the way it is. So it can be evolvable to those, those larger cargo carrying missions.

Perry Roth-Johnson (06:28):

I see, uh, Nate, this next question's for you for the younger crowd, uh, we're used to seeing things like SpaceX Falcon 9 do launches, SpaceX Falcon Heavy, you know, did one launch, um, people, uh, from the Apollo generation, obviously remember the Saturn V, uh, how does the rocket for Artemis 1, the space launch system, how is it similar or different from, from those other rockets that people might be more familiar with? Because this is the first time it's like rolled out, like I've seen renderings, but this, this is a new rocket.

Nate Perkins (07:00):

Yeah and, and really, it, it looks very similar, uh, visually to the, to the Saturn V. And one of the key differences from the other space companies like SpaceX and Blue Origin, you know, this particular, rocket's not a reusable rocket. So what what's really going on here is, you know, leveraging heritage technology, which, um, is really critical in this kind of stepping stone approach. You don't wanna reinvent all new systems from the ground up clean sheet when you've already, we've already done that. You know, we you've, you've done that with, uh, with the Saturn V and the Apollo program. You've built this rich heritage. Uh, we, we call it heritage in the aerospace industry. It's, um, you know, hardware that's been checked out, it's been certified certain technologies and, and specific designs like the space shuttle main engine, you know, we consider that really solid heritage with which to build new programs. So it takes out a lot of risk, uh, both in schedule and cost and, uh, and also technical risk, cause you've proven out these kind of systems. So you want to utilize those systems, uh, as we're doing with SLS to take out a lot of those unknowns, uh, especially when you're dealing with, with human safety, with our NASA astronauts, um, and you're dealing with, uh, you know, us taxpayer dollars, but when you look at the rocket, it's very similar to the Saturn V.

Perry Roth-Johnson (08:16):

It's really tall. Right,

Nate Perkins (08:18):

Right, right. Very similar height. Uh, but you know, it's, it's the most powerful rocket, um, you know, that exists. And it's also a good point to talk about, you know, some of the differences with the, the whole reusability kind of comment is, um, you know, that's a, it's a common criticism of SLS is, you know, why are we investing in this, uh, non-reusable technology? And really that comes a little bit back to the heritage comment, but also it has to do with how massive the rocket is. This isn't a small system, right. And reusability is a very non-trivial problem to solve. So as soon as you add reusability into a system like this, um, which, you know, during the origin of, of SLS, wasn't even something that was performed yet in, in space, then you're increasing risk dramatically and increasing cost. You're increasing weight of the components. So you're decreasing, uh, the amount of mass that you can put into orbit and put on the moon. So really, it comes down to leveraging our heritage technologies and it gives us the clearest path to an extremely powerful rocket, which will help us achieve those, those goals in space.

Perry Roth-Johnson (09:27):

I'm so glad you brought up, you know, that we're reusing heritage designs cause here at the California Science Center, obviously the space shuttle is near and dear to our heart because we have Endeavour on display. Uh, just for our listeners. When we say SLS, we're talking about the space launch system, the new rocket, uh, that your guys' engines are going on and you took the engines out of Endeavour to put on one of the space launch systems, rockets, the SLS rockets. So, uh, Doug, this is kind of like a pop quiz trivia question. Do you happen to know if Endeavour's engines are on Artemis 1?

Doug Bradley (09:59):

I'll answer that a different way. We have engines on Artemis 1, two of the engines on Artemis 1 actually flew on Endeavour.

Perry Roth-Johnson (10:07):


Doug Bradley (10:08):

One of them flew four times on Endeavour. The one, the other one flew once. So their experience flyers on Endeavour which is, which is pretty cool.

Perry Roth-Johnson (10:17):

Yeah. Yeah. And it's got even more personal connection to you. I understand. Right. Cause you worked on the shuttle program, uh, before the Artemis program. So, so how does all that feel?

Doug Bradley (10:28):

Yeah, that, I mean, it feels great. I was the, I, I worked in a lot of different, uh, positions on the, on the space shuttle program for the space shuttle main engine SSMEs we call them uh, started out as a designer and just moved around for different responsibilities. Uh, my last job was as chief engineer of the space shuttle, main engines for our company. Uh, that was just a tremendous job, you know, working with a fantastic team, uh, working on issues, working to get things ready for flight, uh, just like we're doing now. And so to see these engines fly again, and even though we're gonna drop 'em in the ocean, they're they're going down great because they're sending us to the moon. So it was a, a very satisfying program. And, and these engines, some of our guys describe them as our, our children, they were reusable. We got to know them very well. These different engines have different, uh, characteristics and you get to know them. So when you look at the data, you can explain, well, this temperature's a little high because of these things on this engine and we've got experience with those. So that's what what's, it makes us so confident to, to be able to fly these engines. We know them really, really well. We, we tested, we had over a million seconds of hot fire time on these engines.

Perry Roth-Johnson (11:46):


Doug Bradley (11:46):

Through the, through the shuttle, not these specific engines, but through the course of history of the shuttle program. And they're, they're just very reliable. You know, why people have asked why these engines, you run trade studies and you choose different engines. So why did we choose these? Well, the reliability was probably the, the key part of it. First of all, for safety, uh, but secondly, you need to be ready to fly when you need to fly. Uh, going to Mars is a two year trip if you miss the launch window because you've got an engine problem, you can't fly for another two years. So we don't wanna be in that predicament.

Perry Roth-Johnson (12:24):


Doug Bradley (12:25):

Uh, the engines are very, very high performance. So you've got reliability, high performance that translates into more cargo, as Nate was saying, it's, it's all about maximizing the amount of cargo that you can carry. That's that's people and, and cargo. Uh, the engines were very flexible. You can imagine in a long program like that, we tested them at all sorts of extremes.

Perry Roth-Johnson (12:51):


Doug Bradley (12:51):

And found out that they can, the, they can work in those extreme high power levels, different mixture ratios, how much fuel you're using with respect to oxidizer. And that opens up the space and the design areas for the vehicle manufacturers. If they need a little bit more thrust, well, we've already been there. If they're sizing their tanks in a certain way, then we can probably handle that mixture ratio. And then finally we had 16 of 'em left after the end, the end of the shuttle program. So we were with some modifications, we were not gonna be, uh, holding back the program with, with engine work. And that that's important engines are many times they'll be the, the critical path as we call it in getting a launch off. So for a lot of reasons, it was these, these engines were chosen. And for me it was very satisfying because I knew the engines really well.

Perry Roth-Johnson (13:50):

I love that. Um, you know, you hear pilots talk about aircraft almost how have their own personalities, you know, even though they're from the same, uh, assembly run. And I love that engines, you know, might have their own personalities that you guys feel like they're your kids, I guess now it's going off to college. Um, yeah. So I, I wanna veer more into, um, we kind of touched on, on the personal bits a little bit, but I want to veer more into like, how did you guys end up working at Aerojet Rocketdyne and becoming rocket scientists? Um, Nate, why don't we start with you? Like, like when you were a kid, did you know you wanted to be a rocket scientist?

Nate Perkins (14:30):

No, not, not at all. Actually, I was a skateboarder for years. Um, uh, and then, uh, yeah, I was actually a sponsored skateboarder, really skated in contest and things. Yeah. Oh, um, then eventually. Uh, but I knew I wanted to go to school cause I loved, um, science technology. I loved, um, I knew I wanted to learn more. I, I just love learning in general, just kind of a incessant learner and uh, so even while I was skating and stuff on the side, um, I, I owned a little skate shop business for a little while, right out of high school and then, uh, um, was doing classes on the side. So I didn't finish my undergrad until I was 28. Um oh, wow. Got a job here. And uh, immediately started grad school pretty soon after that and just finished grad school last year, actually.

Perry Roth-Johnson (15:20):


Nate Perkins (15:20):

Yeah. Some at some point during, during college, it just became crystal clear that that engineering was the right way and space in particular was what I was interested in. That's uh, my journey in a nutshell but no, I didn't know. that I wanted to be a rocket scientist at all.

Perry Roth-Johnson (15:36):

Nobody ever does. So like, it's, it's a, a weird question to ask. I know always, what about you, Doug? Were you always like a, a rocket fanatic when you were a kid?

Doug Bradley (15:45):

Not really. I was kind of all over the map, you know, when I was a kid fireman, uh, baseball player of whatever, although it, it probably was in my genes a little bit. My dad used to work on flight simulators with the original seven astronauts. So that was pretty cool. Um, and I grew up in the San Fernando valley and they used to test the Apollo rockets in the Hills, just north of us. And so we could hear them, you know, they were, they were obvious and sometimes see the smoke. So maybe it was maybe I was destined to do something like this, but it wasn't my plan really. I kind of interviewed here on a lark and I thought space, shuttle's pretty cool. I'll do that for three years. And that was in 1977. So been here ever since.

Perry Roth-Johnson (16:32):

One last, uh, question when Artemis 1 finally rolls out to the pad and it's ready for launch, where are you guys going to be Nate? Why don't we start with you?

Nate Perkins (16:44):

I'll probably be watching with my, uh, my wife and three year old girl. Um, not in, not at Kennedy Space Center, we'll probably be at the house. Um, but you know, depending on how things are then with, uh, with COVID and everything, it would be amazing to be, you know, in a, uh, in a mission center here, actually, you know, with the team, you know, enjoying it together. But, uh, man, it's gonna be something else seeing that thing fly.

Perry Roth-Johnson (17:11):

Yeah. I bet.

Nate Perkins (17:11):

So excited.

Perry Roth-Johnson (17:13):

All your hard work. And Doug, what about you? Are you going out to Kennedy? Are you staying in California?

Doug Bradley (17:19):

Well, I'll tell you what I have the great privilege of being able to go out to Kennedy for the launch and being outside, even. I spent a lot of time in the control room for shuttle launches, which is very exciting. Uh, but to see it outside and feel the, the vibration against your, you know, your chest pounding and the how loud and powerful it is. It's, it's fantastic. I mean, I'm in a part of my career now, since I've, I have enough general knowledge of the whole, uh, uh, vehicle and engines, uh, I'm kind of the answer, man. I'll be, I'll be the go between. If, if technical issues come up, then I can help. If there are general questions that maybe decision makers need, uh, I can help with that too. Uh, but that'll be outside watching that rocket launch. And so I'm, I'm pretty excited about that. Pretty pumped.

Perry Roth-Johnson (18:13):

Well, enjoy it. Uh, best of luck to both of you and the rest of your team. Uh, it's been fabulous talking to you, both Nate and Doug. Thank you so much for joining us on the show today.

Doug Bradley (18:24):

It's it is our pleasure. Perry. It's been great. We're excited to talk about people that are also excited about what we do in the space program.

Nate Perkins (18:31):

Yeah, absolutely. Thanks so much for having us and just like any of the listeners that are excited about space, please, please apply. That's not just engineering. That's, you know, material handling people, it's machinists, it's welders, you know, we need, we need help. We're we're going to space together. This is, you know, America's space program.

Doug Bradley (18:48):

Yeah. We're at a point in the company where we we've got a lot of work like Nate saying, you, you talked about how do you pick a career? Well, if you've already are kind of out of school and you've got some skills, whether it's in engineering or whether you're physically a, a, a skilled mechanic or technician we're we're hiring now, we can use more help. It's it's a fun team to on with with pretty cool goals.

Perry Roth-Johnson (19:12):

All right.

Nate Perkins (19:12):

Thanks so much for having us Perry really appreciate it.

Perry Roth-Johnson (19:14):

Thank you so much.

Perry Roth-Johnson (19:15):

That's our show, and thanks for listening. Until next time, keep wondering. Ever Wonder? from the California Science Center is produced by me, Perry Roth-Johnson, along with Devin Stewart and Jennifer Aguirre. Liz Roth-Johnson is our editor. Theme music provided by Michael Nickolas and Pond5. We'll drop new episodes every other Wednesday. If you're a fan of the show, be sure to subscribe and leave us a rating or review on Apple Podcasts. It really helps other people discover our show. Have a question you've been wondering about? Send an email or voice recording to [email protected] to tell us what you'd like to hear in future episodes.