Spaceflight Insider

The European Service Module: A conversation with NASA’s Jim Withrow

The Artemis 1 Space Launch System (SLS) rolls to Launch Pad 39B on March 17, 2022. Credit: Scott Johnson / Spaceflight Insider

The Artemis 1 Space Launch System (SLS) rolls to Launch Pad 39B on March 17, 2022. Credit: Scott Johnson / Spaceflight Insider

KENNEDY SPACE CENTER, Fla. — In the lead-up to the Aug. 29, 2022, Artemis 1 Space Launch System (SLS) launch attempt, Spaceflight Insider had the opportunity to speak with a number of people involved in its design, construction, assembly, and flight. One of those people is Jim Withrow — NASA’s Deputy Propulsion Functional Area Manager for the European Service Module (ESM).

James "Jim" P. Withrow. Credit: NASA

James “Jim” P. Withrow. Credit: NASA

Withrow has been with NASA for 35 years — working the entire time at NASA’s Glenn Research Facility in Cleveland, Ohio. He grew up in Cincinnati and attended Ohio Northern University — graduating in 1987 with a degree in electrical engineering.

After graduation, Withrow came to Glenn to work on the Space Station Freedom power system.

Following the agency’s reorganization of the space station program, he began work as a microgravity aircraft (“Vomit Comet”) test director — flying around 18,000 parabolas over 13 years. After his microgravity aircraft work, Withrow moved over to work on the ESM.

The ESM is positioned immediately below the Orion Crew Module in the SLS stack and will power Orion to and from lunar orbit during Artemis missions.

A portion of our conversation with Withrow is below.

Jason Hutt, NASA’s lead for Orion human-rating, systems engineering, and integration, also participated in the discussion.

SpaceFlight Insider: Let me get your name?

Withrow: Jim Withrow, or James Withrow. I go by Jim.

SpaceFlight Insider: And Jim, you work for NASA?

Withrow: I work for NASA. I’ve been working for NASA for 35 years. I’m out of Glenn Research Center in Cleveland, Ohio.

SpaceFlight Insider: Tell me a little bit about what you do.

Withrow: I’m the Deputy Propulsion Functional Area Manager for the Service Module.

SpaceFlight Insider: You’re Service Module with NASA?

Artist's rendition of the European Service Module, and the Orion Crew Module, in Earth orbit. Credit: ESA

Artist’s rendition of the European Service Module, and the Orion Crew Module, in Earth orbit. Credit: ESA

Withrow: Yeah, so the Service Module is, obviously, it’s coming from Europe. NASA is managing the interaction with — the Glenn Research Center manages the interaction out of — the European Integration Office — the EIO we call it. So, we manage the ESA [(European Space Agency)] / Airbus work that they’re doing and the integration into the vehicle.

SpaceFlight Insider: They build it in Europe, for the most part, and they ship it here and it comes to the O&C [(Neil Armstrong Operations and Checkout Building at NASA’s Kennedy Space Center)]. And, obviously, the one for Artemis 1 is sitting out there on the rocket, but I understand the one for Artemis 2 is already here?

Withrow: Yep, and there’s already work underway on that.

SpaceFlight Insider: I’m trying to understand, since they build it, but you’re the NASA person on it, you do . . .?

Withrow: NASA is not completely hands off. We’re providing the OMSE [(Orbital Maneuvering System Engine)], the engines that were on the OMS [(Orbital Maneuvering System)] pods for . . .

SpaceFlight Insider: That came off the Shuttle?

Withrow: Yep.

SpaceFlight Insider: And that’s the main engine on the back of the . . .?

Image of STS-115 Space Shuttle Atlantis OMSE (center) taken from the International Space Station on September 11, 2006. Credit: NASA

Image of STS-115 Space Shuttle Atlantis OMSE (center) taken from the International Space Station on September 11, 2006. Credit: NASA

Withrow: That’s the main engine on the back of the Service Module. So, we refurbish it at White Sands [Test Facility in New Mexico]. We manage all of that — the refurbishment with White Sands. It goes to Johnson Space Center. We do the vibration testing on it — workmanship “vibe,” basically. And then the folks we have at Johnson package it up and it winds up getting shipped to Bremen. It gets integrated in Bremen, Germany, with some help from folks that have some experience working the Shuttle. We send them over and they help ensure that the integration goes smoothly. So, it’s not completely hands off. Glenn Research Center does all of the management of the pieces and parts that are moving around, to make sure that happens. In addition, the auxiliary engines, there are eight auxiliary engines on the bottom of the Service Module. They’re there for a backup in case the OMS doesn’t work. The Shuttle had two OMS engines. We don’t put two OMS engines on the bottom of the Service Module. So, you need a backup If the OMS doesn’t work. We have eight auxiliary engines.

SpaceFlight Insider: I’m not sure I knew that.

Withrow: So, the OMS engine is a 6000-pound thrust engine. The Service Module has eight aux[iliary] engines that are 110 pounds each. So, if in the event an OMS were to not function, those eight engines, and they’re not gimbaled, but they can work as a . . .

SpaceFlight Insider: They can fire in segments?

Withrow: Exactly. You can pulse certain engines. Other ones are running steady state. You can get the same effect, and you can . . .

SpaceFlight Insider: And they’re 110 [pounds thrust] apiece? And there’s eight of them? So that’s only gives you 880 [pounds of thrust]?

Withrow: 880, instead of 6000, but you can run them longer, and you can get the Delta V — the change in velocity — that you need.

SpaceFlight Insider: Let me ask you this: I know in one of the media / press conferences earlier this week there was a discussion about things that would be a “go” on this mission that wouldn’t be a “go” on Artemis 2. If the OMS engine didn’t function properly, could you still go to the moon with these eight smaller engines? Or would you?

Withrow: You would, you likely would.

SpaceFlight Insider: On this mission?

Withrow: On this mission, yes.

SpaceFlight Insider: But not on another?

Withrow: I don’t know that I can answer that. It probably depends. It depends on where you’re at. The upper stage is going to get you on the way, so you’re not using the Service Module to put you on a trajectory to the moon. But you can use it to turn around and come home if you need to. If you’re in lunar orbit, you’ll use it to come back home.

SpaceFlight Insider: And I know there’s graphics, but the ICPS [(Interim Cryogenic Propulsion Stage)] stays attached to the Command and Service Module until it does the trans-lunar injection burn, the TLI burn, and then after the TLI burn, that’s when the ICPS falls off?

Withrow: It comes off and then almost right away, after that, we’re doing an OMS burn, on this mission in particular.

Hutt: For Artemis 2, the OMS engine does the TLI.

SpaceFlight Insider: So, on Artemis 2, the TLI will be done . . .?

Hutt: By the OMS engine. It happens after ICPS sep[aration].

SpaceFlight Insider: Ok, so that’s a difference in the two missions.

SpaceFlight Insider: Jim, how is it working with, it’s being built by the Europeans in Germany, does that create any difficulties? Of course, NASA is spread out all over the place too, but does that create any difficulties, language difficulties or . . .?

Withrow: No, you know, I’ll give you a language example. The Airbus folks that we work with in Bremen, Germany, are, you have a lot of Germans working there, but they have hired a number of people from other countries too. You have Italians, you have French, you have some English, from England, working there, and the interesting way they work is that, let’s say they have a bunch of Germans and they’re working and they’re talking in German, and if they have a colleague that comes in that’s an Italian, they start speaking English to each other. Amongst their own team, they’ll switch to English. So, as far as the communication goes, from that standpoint, zero problem.

SpaceFlight Insider: Let me ask you this, do they work in metric, or do they work in . . . Which mission was it, years ago, that got confused and . . .?

Withrow: Mars [Climate] Orbiter.

SpaceFlight Insider: And that caused some . . .?

Withrow: Yea, they had an English-metric conversion problem, and they . . .

SpaceFlight Insider: So, what do y’all do with that? Does it matter?

Withrow: Oh yeah. And most of what I’ve seen, on the Airbus side, they’re working in metric units.

Hutt: But we own the requirements. So, Starship is operating in metric, but we’re operating in English units, so now we have to negotiate who is going to do the conversion.

Withrow: Yea, across the programs.

SpaceFlight Insider: So, I guess you’d want to pin that down, so if something gets screwed-up, you’d know who to point the finger at?

Withrow: So, yes, the Airbus folks, they think in metrics, metric units, and so they do their conversion and what passes on the ODN network, the Orion Data Network, is data that is normalized and agreed to. So, the requirements that we’ve been talking about, that’s all been managed.

Image of ATV-2 taken from the International Space Station on February 24, 2011. Credit: NASA

Image of ATV-2 taken from the International Space Station on February 24, 2011. Credit: NASA

SpaceFlight Insider: The Service Module is based on the European . . .?

Withrow: The Autonomous Transport Vehicle (ATV), except it’s a little, a lot, more complicated, a lot bigger. It didn’t have an OMS engine, for one.

SpaceFlight Insider: So the Service Module is more complicated than the ATV?

Withrow: Oh yeah.

SpaceFlight Insider: But the ATV was bigger, wasn’t it, because it had all the storage space?

Withrow: The physical, yea, they had, in essence, the crew module, what would be to transport either in pressurized cargo or unpressurized cargo. But the propulsion system, which is where I’m more focused on, the propulsion system is definitely bigger on Orion and the Service Module. Our Service Module is a lot more propellant, and more engines.

SpaceFlight Insider: What engine did the ATV use?

Withrow: They had eight R-4D engines which are . . .

SpaceFlight Insider: I’m not familiar . . .

Withrow: The R-4D is an Aerojet [Rocketdyne] product.

SpaceFlight Insider: Oh, it’s a Rocketdyne . . .?

Withrow: And it’s been around since the Apollo days and we have eight of those.

SpaceFlight Insider: That’s the same engines that you we’re talking about earlier?

Withrow: Yea, we call them auxiliaries. That’s when I talked about NASA delivering an OMS engine, and we refurbish it at White Sands and then we ship it to Bremen. NASA purchases the auxiliary engines, these R-4Ds, that are unique for this particular, they’ve been upgraded or modified by Aerojet to meet our requirements. NASA pays Lockheed, Lockheed pays Aerojet, Aerojet delivers them directly to Bremen, but, in essence, we sign off on them.

R-4D engines on the Apollo 17 Lunar Module. Credit: NASA

R-4D engines on the Apollo 17 Lunar Module. Credit: NASA

SpaceFlight Insider: The R-4Ds you said were Apollo heritage. What were they used for back then? Do you know?

Withrow: You know, I don’t know, specifically.

SpaceFlight Insider: I just wonder if it was Command Module, or maybe Lunar Module? Or, I don’t know what the little quad[ruple] things were? I don’t know. I can look it up.

Withrow: I’m not sure. I don’t know.

SpaceFlight Insider: I’ll Google it. [Note: Google reveals that the R-4D was the engine used in the reaction control quads on both the Apollo Service and Lunar Modules.]

Withrow: They’re found on many missions. We’re using them in a unique way, though. Almost every other mission that has used these engines run them steady state. So, they fire them up and they run continuously.

SpaceFlight Insider: Then you turn them off?

Withrow: Turn them off. They shut them off for a while. They’ll fire them up and run them again.

SpaceFlight Insider: So, they can be restarted?

Withrow: Oh yeah. Cassini is an example where it was used repeatedly.

SpaceFlight Insider: So, they have been used for a long time?

Withrow: Oh yeah.

SpaceFlight Insider: Because Cassini’s what – seventies, eighties? [Note: Cassini was launched in 1997].

Withrow: But we’re using them in a, we’re pulsing them. So, short bursts . . .

SpaceFlight Insider: Why would it be better to have one, ten second burn, as opposed, or vice versa, ten, one second burns? What does that give you?

Withrow: So, the steerability, the OMS engine has a gimbal on it. You can gimbal that engine and, based on the center of gravity of the vehicle, and you want to steer it to a particular location, you can use the gimbal to point the OMS, and make it — the vehicle — fly exactly where . . .

SpaceFlight Insider: And like we talked about earlier, you can fire-up which ones you need to go . . .

Withrow: Yea, and by doing that you can get the vehicle to go exactly where . . .

SpaceFlight Insider: And, if you burn this one for ten seconds, then you’d be . . .?

Withrow: You don’t want to . . .

SpaceFlight Insider: You don’t want to do somersaults?

Withrow: That would require the reaction control system [(RCS)] to kick in on the Service Module. And you don’t want to waste propellant. So, the most effective way is to pulse the aux engines to steer exactly where you want.

SpaceFlight Insider: So, there’s also a reaction control system on the Service Module?

Withrow: There is. There’s 24 RCS thrusters.

EFT-1 Orion RCS thrusters scarfed into the side of the capsule. Credit: Mike Seeley/Spaceflight Insider

EFT-1 Orion RCS thrusters scarfed into the side of the capsule. Credit: Mike Seeley / Spaceflight Insider

SpaceFlight Insider: Then there’s RCS thrusters on Orion too?

Hutt: Correct.

SpaceFlight Insider: Are they the same thrusters?

Withrow: No.

Hutt: They use different propellant.

Withrow: No, the Service Module uses a bipropellant. So, you use monomethtylhydrazine and dinitrogen tetroxide — N2O4. Some people call it MON. And you have those two react without ignition. You don’t have to create a spark to create ignition.

SpaceFlight Insider: Same way as the lunar ascent stage?

Withrow: Yea, the ascent stage was the same way. So they’re hypergols. They just react and create fire.

SpaceFlight Insider:  What about Orion? Are they hypergolic?

Withrow: No, no.

Hutt: No, not . . .

Withrow: The [Crew] Module uses a monopropellant. So, it uses the high purity hydrazine. And it uses a single propellant. And to get it to ignite it passes across a catalyst bed. And those engines are 160 pound thrust engines, and they’re cut, scarfed, into the side of the vehicle.

SpaceFlight Insider: How many did you say are in the Crew Module?

Withrow: Oh my, you’re going to ask me, and I don’t know. [Note: The Orion Crew Module has twelve 160-pound thrust reaction control system (RCS) engines.]

Stay tuned to SpaceFlight Insider for more Artemis coverage, including our conversation with NASA’s Jason Hutt on the Orion Crew Module.

Artemis 1 is currently scheduled for launch no earlier than 1:04 a.m. EST (06:04 UTC) Nov. 16, 2022, and we’ll be on-site at Kennedy Space Center for this, and any future, launch attempts.


Scott earned both a Bachelor's Degree in public administration, and a law degree, from Samford University in Birmingham, Alabama. He currently practices law in the Birmingham suburb of Homewood. Scott first remembers visiting Marshall Space Flight Center in 1978 to get an up-close look at the first orbiter, Enterprise, which had been transported to Huntsville for dynamic testing. More recently, in 2006, he participated in an effort at the United States Space and Rocket Center (USSRC) to restore the long-neglected Skylab 1-G Trainer. This led to a volunteer position, with the USSRC curator, where he worked for several years maintaining exhibits and archival material, including flown space hardware. Scott attended the STS - 110, 116 and 135 shuttle launches, along with Ares I-X, Atlas V MSL and Delta IV NROL-15 launches. More recently, he covered the Atlas V SBIRS GEO-2 and MAVEN launches, along with the Antares ORB-1, SpaceX CRS-3, and Orion EFT-1 launches.

⚠ Commenting Rules

Post Comment

Your email address will not be published. Required fields are marked *