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Engage Thrusters

Season 1Episode 84Mar 22, 2019

Steve Barsi, European Service Module Propulsion Subsystem Manager, discusses the Orion spacecraft’s propulsion system, how it works and why it's suited for deep space travel. HWHAP Episode 84.

Engage Thrusters

“Houston We Have a Podcast” is the official podcast of the NASA Johnson Space Center, the home of human spaceflight, stationed in Houston, Texas. We bring space right to you! On this podcast, you’ll learn from some of the brightest minds of America’s space agency as they discuss topics in engineering, science, technology and more. You’ll hear firsthand from astronauts what it’s like to launch atop a rocket, live in space and re-enter the Earth’s atmosphere. And you’ll listen in to the more human side of space as our guests tell stories of behind-the-scenes moments never heard before.

Episode 84 features Steve Barsi, European Service Module Propulsion Subsystem Manager, discussing the Orion spacecraft’s propulsion system, how it works and why it’s suited for deep space travel. This episode was recorded on November 13, 2018.

Houston, we have a podcast

Transcript

Gary Jordan (Host): Houston, We Have a Podcast. Welcome to the official podcast of the NASA Johnson Space Center, Episode 84, Engage Thrusters. I’m Gary Jordan and I’ll be your host today. On this podcast, we bring in the experts, NASA scientists, engineers, and astronauts. All to let you know the coolest information about what’s going on right here at NASA. So if you are familiar with us, you may know that we’ve been reviewing some of the top technologies for spacecraft to survive in deep space. We’ve talked with experts that work on NASA’s Orion spacecraft, the one that will be traveling into deep space. And we’ve talked about life support, protecting from heat and radiation, and maintaining navigation and communication. And we’ll tell you all of those episode numbers at the end, if you want to check them out. So today, we’re talking about Orion’s propulsion system and how it will help maintain the vehicle’s course through the cosmos. We’re talking with Steve Barsi, European Service Module Propulsion Subsystem Manager based at the Glenn Research Center in Cleveland, Ohio. The service module is being built by the European Space Agency. It serves as the powerhouse for the spacecraft with 33 engines, one that serves as the main engine for major in-space maneuvering, a few auxiliary engines, and then the rest of them for basically steering.

We talk with Steve about the propulsion system, how it works and why it’s suited for deep space travel. So with no further delay, let’s jump right ahead to our talk with Mr. Steve Barsi. Enjoy.

[ Music ]

Host: Steve, thank you so much for coming on the podcast today to talk about propulsion and how we’re going to get to deep space and the energy needed. Thank you very much.

Steve Barsi: Thanks. It’s great to be here.

Host: Okay, so the topic is propulsion. I guess, when I think about propulsion, I thing about the movies and the, you know, the main pilot of the Starship Enterprise pushing forward and actually, you know, going warp speed into space. But I’m assuming it’s a little more complicated than that. So I kind of wanted to start by backing up and getting the very basics of propulsion. So if someone asks you, “Steve, what is propulsion,” what do you say?

Steve Barsi: So propulsion is just the mechanism by which a vehicle accelerates or translates through space. And so it doesn’t necessarily have to be a pilot. It could be an autonomous system with multiple classes of engine. It’s basically anything—it’s the mechanism by which you get from point A to point B.

Host: Okay, pretty important when it comes to actually flying in space, right? So it’s different from an actual launch, right? I guess that it is technically propulsion. But what we’re talking about is the Orion vehicle actually flying through space. And actually, it’s not like you see in the movies where you just see that glowing blue light at the back of the ship just constantly firing with a constant acceleration, right? It’s a little bit different when you’re actually trying to fly through space. I guess it’s more like coasting, right?

Steve Barsi: Well, there’s periods of active propulsion and there’s coasting.

Host: Okay.

Steve Barsi: So periods of active propulsion is when essentially any time you’re firing any of your thrusters or main engines. So it could be your reaction control systems. Those are the smaller thrusters. It could be your main engine. But when the engines are not firing, then you’re coasting through space.

Host: Okay. So are they scheduled then? Do you have to really know when you’re going to be firing all of these different engines?

Steve Barsi: So for the main propulsion system and the auxiliary engines, those burns are planned ahead of time, and you execute maneuvers based on the burn plan. For things like the reaction control system where you’re using it to maintain attitude, it’s not so much a predefined maneuver. You’re firing thrusters to maintain your spacecraft attitude.

Host: Okay. So basically you’re firing the thrusters to make sure you’re pointing the right way. And you’re not turning or any kind of — Okay, so that’s what it is. And this is interesting. I was reading about the propulsion system. There’s 33 engines, right? But only one of them is like the engine that you think about when you think about propulsion, right? The one that just fires and you just go, right? The other 32 are for what you’re — for maintaining the attitude.

Steve Barsi: Yes. So there’s a main engine on Orion.

Host: Okay.

Steve Barsi: And that’s, I think, what you’re kind of alluding to.

Host: Yes.

Steve Barsi: Around the main engine to the main engine at the center of the vehicle on the bottom on the service module, around that main engine, there’s eight auxiliary engines. Those essentially provide the same function. So they’ll provide similar translational thrust maneuvers, and they back up the main engine in case there’s a failure.

Host: I see.

Steve Barsi: It’s the 24 smaller thrusters that are used for attitude control.

Host: Okay. The main and then you got auxiliary and in the auxiliary control. Okay. I thought there was 32. That clears things up a bit. All right, so what are you firing, you know? Is it that nice blue light that you see in the movies? Or what are you actually using to make the propulsion work?

Steve Barsi: So the two fuels that we use, it’s a bipropellant system. The fuel is monomethylhydrazine . We abbreviate it with MMH. And then the oxidizer is called MON3. It’s mixed oxides of nitrogen.

Host: Okay, so the propulsion is a chemical reaction?

Steve Barsi: Yes. So it’s a hyperbolic system. So when the fuel comes into contact with the oxidizer, it just ignites. So there’s no igniter necessary on any of the engines on the service module.

Host: Okay, so how does everything work? Do you have the oxidizer over here and then the other thing over here, and then they touch? And when they connect and make that chemical reaction? It spits out the —

Steve Barsi: Yes. You have the fuel and the oxidizer in separate tanks. It’s actually two oxidizer tanks and two fuel tanks on the European Service Module. And downstream of those tanks you have valves and plumbing that essentially gets the propellant from the tanks to where you need it—to where it’s needed at the engine level. So you have plumbing and valves to get it to the main engine, to the RCS engines, and the auxiliary engines. And then, once the two propellants come into contact in the injector, or downstream of the injector, they’ll ignite. You’ll get a reaction and thrust is produced. And that’s what provides the motive force to get you to where you want to go.

Host: There you go. Just these two things meeting and then firing out. And just that little bit of force is really all it takes to make the thing go and to actually control the attitude and then to have that main engine, and the auxiliary engine is there too. So when you’re thinking about the fuel, you said you have two of the one type and then the two of the oxidizer, right?

Steve Barsi: Two tanks of each.

Host: Two tanks of each. How much are you bringing with you? Yeah, I guess you have to think about weight versus, you know, the mission itself and all those kinds of constraints.

Steve Barsi: So each tank holds about 2100 liters of propellant.

Host: Okay. Compared to, I guess, a car or like a — I don’t know. I’m trying to draw a comparison of how much that is, 2100 liters.

Steve Barsi: So a car is probably on the order of 14 gallons or so, so significantly more than what your car holds.

Host: Several cars, many cars. Okay, so the tanks themselves that are actually holding the fuel, I’m imagining like a circular kind of spacey-looking tank. Is that what it is? Is it a spherical tank?

Steve Barsi: So we’ve got several tanks on the vehicle. The propellant tanks are the tanks that actually hold the propellant. You might think of it as a cylindrical barrel with hemispherical domes on it.

Host: Okay.

Steve Barsi: So that’s kind of what the propellant tanks look like. The other tanks we have on the vehicle are high-pressure gas tanks. So basically we use regulated high-pressure gas to push the propellant out of the propellant tanks. And so those are spherical tanks and they contain our helium, which we use to pressurize the propellant tanks.

Host: So you have tanks that hold the fuel and then tanks to push the fuel?

Steve Barsi: Yes. So tank that hold gas that —

Host: Hold the gas that pushes the fuel? Okay.

Steve Barsi: Yes.

Host: Okay, this is a pretty complicated system. How much of the—this is all—I guess we should go kind of back to where is all of this, right? It’s not on Orion. This is on the European Service Module.

Steve Barsi: Right.

Host: What else is on the European Service Module?

Steve Barsi: So the European Service Module is essentially the powerhouse of Orion. So you’ve got your solar arrays there. You’ve got avionics boxes. The avionics boxes, they do a lot of the commanding of the valves on the propulsion system. But you’ve got the terminal system. And so there’s a number of substances that make up the European Service Module.

Host: Okay, the avionics boxes are computers?

Steve Barsi: So you could think of it as a pass-through. The vehicle computer is on the crew module side of the interface.

Host: I see.

Steve Barsi: But they essentially take commands from the crew module and then turn that into electrical pulses that open and close valves.

Host: There you go. Okay, all right. And then the thermal is to make sure that the vehicle itself is at a reasonable temperature?

Steve Barsi: Well, predominantly, the European Service Module in and of itself —

Host: Oh I see.

Steve Barsi: But yes, it’s the control temperature of the vehicle.

Host: Okay. And the European Service Module is where the solar arrays are, right?

Steve Barsi: Yes.

Host: So there you go. There’s your powerhouse. You have the actual electricity. You’ve got the fuel. You know, that’s a pretty important piece. So how is the European Service Module — Does it draw from any lessons we learned or any technology that we’ve used in the past, like any kind of Apollo technology or any kind of Shuttle technology? You know, what’s inside there?

Steve Barsi: Yes. So I think that probably the two vehicles you could probably point to are shuttle and ATV, the Automated Transfer Vehicle that the Europeans developed.

Host: That was a cargo vehicle, right?

Steve Barsi: Yes. That’s probably where we started. And so a lot of the, I’d say, original concept of the design, you can trace back to some kind of ATV heritage. I think there are a lot of some Shuttle influences in the design, and I think the biggest example of that is on the main engine and the thrust vector control system. So our current OMS engine, the Orbital Maneuvering System engine, and the thrust vector control, those systems have both flown on shuttles already. And so at the start of Orion, we had this inventory available that met Orion’s needs. And so we essentially repurposed those hardware to fulfill these objectives that we have on Orion.

Host: Okay. So they’re proven. You know they work. Okay, so this is the part—this is the main engine with those auxiliary engines that you were talking about?

Steve Barsi: It’s the main engine.

Host: Main engine, okay.

Steve Barsi: It’s the main engine. Again, it wasn’t just a drop and replacement from shuttle. We did essentially service the engine prior to delivery to Airbus. We added some redundant instrumentation. Shuttle had two OMS engines, so there was some redundancy there. So we added instrumentation to the engine itself to buy back some redundancy. Shuttle flew in low Earth orbit; Orion doesn’t.

Host: Yes.

Steve Barsi: So there was some thermal constraints on the engine that we just didn’t have to deal with on shuttle. So we modified the engine to essentially add a thermal protection to intercept any heat for those deep space missions. So that’s kind of the pedigree on the OMS engine, the pedigree on the thrust vector control. So it’s two actuators and two controllers. So the thrust vector control actuators, one end attaches to the OMS engine.

The other end attaches to the structure on the ESM. And basically on command, you can gimble the engine and pitch in yaw directions to vector your thrust in a certain direction.

Host: Okay. The idea is control?

Steve Barsi: Yeah.

Host: The idea is to make sure you’re pointing the right way. And the extra technology you need to move from shuttle to Orion is the extra constraints that deep space puts on you, especially thermal. Which direction? I guess both directions, right? Hot and cold?

Steve Barsi: Predominantly cold.

Host: Predominantly cold?

Steve Barsi: Well, actually, I take that back. It is both on the hot and the cold. The cold because there are certain attitudes where we’re pointing the nozzle to deep space. And so the nozzle is acting like a radiator just pulling heat out of that engine. On the hot side, there are attitudes when we’re pointing the tail towards the sun, and we have solar energy just impinging the engine and warming things up. So it’s a mixed bag, both hot and cold provided some challenges for modifying the engine for use on Orion.

Host: I could imagine. It’s not as easy as, you know, just fire the engine and go. Just where is the engine? Where’s the sun and how it’s facing the engine? You have to think about all that whenever you’re flying. That makes flying a little bit more difficult. [Laughs] Okay, so let’s talk about the European Service Module a little bit more. We kind of went through all of the different, I guess, components of what’s inside of it. So where are we at with it, you know? Where is it being built? I think you mentioned Airbus. Airbus is one of the, I guess, prime contractors of it too?

Steve Barsi: So Airbus is ESA’s prime contract. On the propulsion system, the Airbus folks in Bremen, Germany are the primary group of people responsible for the propulsion system. But they leverage a number of resources and suppliers, both within Europe and in the US, that make up the entire propulsion system.

Host: Okay yeah. How we how it working with them then, to make sure everything comes together?

Steve Barsi: It’s certainly been a learning experience. But the vehicle is built. It was delivered to KSC. So the first vehicle is back in the US, and we’re taking all those lessons learned and applying them to the build of the second ESM.

Host: Okay. So was it tested in Germany or is it going to be tested here? A little bit of both?

Steve Barsi: A little bit of both. So before, you know, any component leaves your supplier, you do testing at the lowest level possible. So that could be at a valve level. It could be at a sensor level. Those parts are delivered to Germany. They get integrated. You test them at the next higher assembly. Ultimately, you install that assembly into the vehicle and you do a number of tests at the European Service Module level prior to shipment. So those tests were completed and the vehicle just arrived at KSC. And over the next several months, it’s going to be subjected to a number of integrated spacecraft tests. And it will go through a battery of tests, both functional tests and test during environments, so acoustic testing, thermal vac testing, thermal cycle testing, just to shake out the system prior to flight.

Host: Yeah. Getting, you know, any kind of things that you’ve missed. That’s really what you’re going to do. The poor thing, you’re going to just blast everything at it?

Steve Barsi: Yep.

Host: All right. So it’s a lot of things for the European Service Module itself, right? To make sure it’s going to withstand the environment of space, you know, launch, everything in between. So what about the propulsion system, testing there? How do you make sure that everything’s going to fire the way you want it to?

Steve Barsi: So it’s the same thing. So the first thing that gets done, they’ll mate the European Service Module to the crew module adapter. We’ll do a number of approved tests and leak tests on those joints that we just welded up. There’s a battery of functional tests that get performed where you’re opening and closing valves, making sure that the Service Module is communicating with the vehicle. And the Service Module is a part of that integrated spacecraft assembly testing. So it’ll see acoustic testing and thermal testing as well. And we’ll be checking out the system along the way to make sure it’s still healthy.

Host: Okay, so it’s part of that whole integrated testing, you know. Why would you test the system separate if you can just do everything altogether. You’re getting similar results, even better actually, because that’s how it’s going to be positioned and everything.

Steve Barsi: Yep.

Host: So that makes sense. Okay, so let’s talk about the missions coming up. You know, we’re testing a lot of this right now. We have the European Service Module, I guess, in Florida right now. Crew module is being tested. We had a couple podcasts about the escape system. We’ve got a lot of tests going on here. Everything’s going to come together and you’re going to launch everything and test it and EM1, Expiration Mission 1. So what are we looking forward to for propulsion testing on EM1? What’s that going to look like?

Steve Barsi: So we saw qualification testing in front of us. So that’s our integrated subsystem testing down at White Sands, where we’re firing multiple thrusters, the main engine, the auxiliary engine, and the RCS in an integrated fashion, doing different burn profiles. Just shaking out the system at the propulsion subsystem level. And from a propulsion standpoint, that’s probably the most important testing we can do to qualify the subsystem, because we get all the interactions with the different engines firing. And for our purposes, it’s pretty important from an overall spacecraft certification. But once we pass the propulsion qualification subsystem testing, there’s really no additional testing outside of the normal integrated spacecraft test that the rest of the vehicle is going to go through, at least from a subsystem level, that we’d say we’re ready to fly.

Host: Okay. Well, that’s coming up soon then. It seems like, you know, a lot of these boxes have been checked. You know, one thing that just came up, just based on what we were talking about. You know, testing and then we’re actually going to fly this in deep space, right? This is for EM1. I was thinking about the fuel. You said the fuel was MMH, right? And they have an oxidizer? Why those? Why did you choose those kinds of fuel for deep space versus, I guess, other types?

Steve Barsi: Well, the other class of fuel was cryogenic, and any cryogenic fuels have the challenge of being able to keep them cold for long duration deep space missions.

Host: Okay. So this works for this mission profile. Deep space, you know that it’s going to work. It’s going work where you want it, how you want it, that kind of thing.

Steve Barsi: Plus the pedigree of the — I mean, that was the fuel system that’s been used on multiple vehicles.

Host: Proven.

Steve Barsi: Yeah.

Host: Yeah, that kind of helps too. So I guess, EM2. Now we’re looking forward to actually putting crew on the vehicle and testing it with crew. Any differences there or is it pretty much the same?

Steve Barsi: So there are differences. I mean, at the subcomponent level. We’re re-building valves that, you know, we might not have been for EM1. We’re using different sensors in some cases. I think the biggest addition for EM2, at least from a propulsion standpoint, is the addition of helium cross feed. So that allows you to essentially pressurize one propellant tank in the event you have some anomaly or blockage in another part of the system. So from a crew survivability standpoint, it was important to add that capability.

Host: Crew survivability. Redundancy? Is that what it really what it comes down to?

Steve Barsi: Yeah. So if there is some blockage or leakage in the system and you find yourself in an inability to pressurize one of the propellant tanks, cross feed will give you a capability to get the crew back.

Host: Okay. There you go. Which is, you know, that’s one of the main things about flying people is crew safety. Making sure you can get them back. So what about the actual control of the propulsion, for EM2 or for, I guess, any mission really? Are the crew actually — Do they have a stick and are they controlling where the thing is going to go and where the thrusters are firing? Or is a lot of this automated? How is everything controlled?

Steve Barsi: It’s mostly automated. I think for future flights there will be some manual control of the reaction control jets. But for the most part, the burn plan will be something that’ll be defined prior to launch.

Host: Okay. Do you have a good idea of the plan for propulsion during some of those missions actually going around the moon and everything? So like once the spacecraft actually separates from the rocket, right, SLS, at what point are those main engines firing? At what point are the, you know, the thrusters firing to control the attitude? Do you have a good understanding, even right now, of when things are going to happen?

Steve Barsi: I think a decent understanding.

Host: Okay.

Steve Barsi: I think from our perspective though, from a propulsion standpoint, we’re giving the vehicle a capability. And so basically what we’re saying you can fire your main engine up to X number of seconds. You can fire your auxiliary engines for this duration. You know, how you choose to use up that total amount of burned duration is something that the mission planners have something at their disposal when they design a specific trajectory.

Host: There you go. That’s the difference between the engineering side and the operation side. You just define this is how long you can fire a thruster. And it’s up to the operation folks to say, all right, we want to fire here because we want to go here and make sure that it’s having a backup for this. Okay, that’s cool. So are you working pretty closely with the operations folks then, to understand what they’re mission needs are to actually define the requirements for building the spacecraft?

Steve Barsi: Yes. And it’s always a give-and-take. I mean, on one hand, from a mission planning perspective, you want to maximize your amount of capability. And sometimes that doesn’t always mesh with what the hardware can actually do. And so there’s a give-and-take between trying to maximize the vehicle capability and stay within the component or engine capability that they can deliver to the system.

Host: Okay. Is there any kind of cross-disciplinary sharing, especially within Orion too. So are you the propulsion guys talking with the avionics guys talking with the life-support guys? Is there some cross-disciplinary stuff there to make sure everything just works together?

Steve Barsi: It is. So we are very close couple with the avionics guys. Without commands to fire the engines, our propulsion system isn’t going to do anything.

Host: There you go.

Steve Barsi: We are working closely with them. And from a thermal standpoint too, we do work closely with the thermal team and trying to understand and make sure our propellant doesn’t freeze in our lines, for instance. And cause a blockage. So we do work closely with the thermal team as well.

Host: That’s important. So, at what point, you know, with this testing you have to understand the risks that are associated with actually flying this thing in space. So the balance of, or I guess the challenge really, of mitigating the risks with understanding how the thing is going to work and making it work efficiently. So efficiency versus risk. How do you measure that?

Steve Barsi: It’s a judgment call.

Host: Of many people on the team, right?

Steve Barsi: Yep, yep. But ultimately, I think we’re charged with delivering a system that we believe is safe to fly. And so in some cases, that might not mean that we’re able to chase something down to the nth degree. But again, we believe that we’re minimizing risk to the spacecraft from a technical standpoint.

Host: Yeah. Minimizing risk. Because ultimately, you’ve got to hand this technology over and say, “Okay, put humans on it. Go fly it,” you know. That’s pretty important. You talked about building a capability, especially from an engineering standpoint. You design the propulsion system to work, and here you go. You guys do with it what you want, right? So looking forward to, you know, missions even beyond EM1, EM2, we’re talking a lot about the moon now. We’re going back to the moon. We’re going to have missions to the moon. But then, even beyond the moon, right? So thinking about the capability there, is a lot of this translatable to many different profiles, just even beyond the moon?

Steve Barsi: Yes. So again, from a kind of fixed data point, your tanks can only carry so much repellent and your gas tank can only carry so much helium. But what you do with that, you do have a lot of flexibility in terms of what set points you’re operating the engines with, for instance, where you can buy back some capability based on specific engine performance.

Host: Okay, there you go. So the answer is “sort of.” There’s a lot of other factors, right? You know, you’re not just going to blast Orion off into Mars. There’s a lot of other considerations, you know. Because the vehicle itself is designed for, I think, up to three weeks, right? For a crew to actually survive on. So if you’re going to go to Mars, you’re probably going to need a Mars transit vehicle. There’s a lot of other considerations there. Propulsion is pretty interesting. Are there other things you’re looking forward to for, I guess, upcoming tests or even something in the near future for propulsion on Orion and the European service module?

Steve Barsi: I’d say the biggest thing I’m looking forward to, from a test perspective, is one of the last — It’s a qualification test we run at the subsystem level at White Sands, is a full-up test with all the engines firing. And it’s stressing from a propellant demand perspective because you’re firing all the engines.

Host: At the same time?

Steve Barsi: At the same time, yeah.

Host: That’s got to be a sight.

Steve Barsi: Yes. So that’s probably one test that I’m really looking forward to.

Host: Yeah. It’s kind of like, I was talking with, I think it was Ronnie Bacchus on a couple episodes ago about Orion’s heat shield and thermal testing. And I was like, that’s got to be an engineer’s dream, man. You got to do the thermal testing. All you’re doing is shooting fire at the thing, right? That’s pretty fun.

Steve Barsi: Yep.

Host: It’s when things, you know—you get to do those sorts of tests, those are really exciting. And to really not only just, you know, the exciting part of just the visual. Like wow, this is so cool. I get to shoot fire at the spacecraft. I get to you know, really push this thing to the limits, but really to push your knowledge too. Yeah, everything that you put into this vehicle is being tested. You’re really giving it a run for its money. If it comes out the other end, you know you did your best. Thant’s not bad. Well, Steve, thank you so much for coming on the podcast today and describing propulsion. This is absolutely fascinating, and it sounds like you thought a lot of this through and are working with a great team to make sure everything comes together. So it’s very exciting.

Steve Barsi: Thanks. It’s been a pleasure.

[ Music ]

Host: Hey, thanks for sticking around. So today we talked with Steve Barsi about Orion’s propulsion systems and how it’s going to get us through deep space. So that wraps up all five of our technologies from the article, “The Top Five Technologies Needed for a Spacecraft to Survive Deep Space.” You can check out the episodes on Houston We Have a Podcast in no particular order. Episode 66 was titled “5,000° Fahrenheit.” Talked about Orion’s heat shields. Episode 69 “Navigating Deep Space” on the navigation and communication systems. Episode 75 on “Radiation Shielding,” and Episode 78 called “Livable Space” on the life-support systems. You can go to some of our social media accounts, especially NASA Orion and the NASA Johnson Space Center. Use the #AskNASA on your favorite platform, Facebook, Twitter, or Instagram. Submit an idea for the show and just make sure to mention Houston We Have a Podcast so we can find it. This episode was recorded on November 13, 2018. Thanks to Alex Perryman, Norah Moran, Pat Ryan, Greg Wiseman, Laura Rochon, and Rachel Kraft.

Thanks again to Mr. Steve Barsi for coming on the show and taking the time out of his schedule while he was here in Houston. We’ll be back next week.