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Christian Carpenter Ignites Space Program at Aerojet Rocketdyne

Interview with Christian Carpenter, Program Manager & Space Architect at Aerojet Rocketdyne

Christian Carpenter Ignites Space Program at Aerojet Rocketdyne

Christian Carpenter heads the advanced space programs at Aerojet Rocketdyne, focusing on developing new product concepts and create new technologies.

Aerojet Rocetdyne's space programs include building new technologies in the areas of transportation architectures, power and propulsion systems, components, materials, and additive manufacturing. Carpenter specialized in the design of propulsion systems for CubSat, Small Sat, and ESPA Ring spacecraft and stages.

AMI: Could you briefly explain Aerojet Rocketdyne’s experience in additive manufacturing?

CARPENTER: We’ve been working on additive manufacturing for a number of years. We’re exploring applications for everything in aerospace-- from aviation through space flight. We’re primarily focusing on metallics for high temperature applications, and we’re doing everything from understanding applications to qualifying materials and processes.

AMI: We’ve read about the modular propulsion systems product line using additive manufacturing to create small rocket engines.  Could you tell us a little bit more about that?

CARPENTER: The Modular Propulsion Systems product line leverages additive manufacturing where it makes sense. The product line started with CubeSat scale systems and that allowed us to consider 3D printing of the entire propulsion system, as well as the engines, because it fits in the build volumes of most machines. At this point we’re developing liquid propulsion systems using 3D printed tanks made of titanium. We’re also evaluating whether 3D printing makes sense for small engines. There’s some fine feature sizes there that 3D printers can’t necessarily do right off the printer. They require post-machining so there’s some trades there we’re still looking at but we’re leveraging it to the maximum extent possible. For our larger systems, we’re looking at SmallSat class systems as well as CubeSat class. We’re looking more at components because the systems are roughly 24 inches by 24 inches so they’re not going to fit in most current machines. We’re looking at what components make sense to print and determining if we can combine components to reduce cost or assembly time, redesign components to be more cost and mass efficient, or to provide performance gains.

AMI: It’s my impression that the CubeSat is quite modest in size. How large is it?

CARPENTER: It’s about the size of the coffee cup.

AMI: That’s pretty small.

CARPENTER: MPS-120 is what they call 1U, which fits in a 10 cm by 10 cm by 11 cm envelope and in that we packaged an entire propulsion system that includes fill and drain valves, isolation system, piston tank and four rocket engines.

AMI: That’s quite amazing. Could you tell us about solar electric propulsion vehicles?

CARPENTER: We’ve been doing a lot in solar electric propulsion. Aerojet Rocketdyne’s Redmond campus produces more electric propulsion products than anywhere else in the world.  We produce resistojets, arcjets, Hall thrusters, and are developing gridded ion engines. We currently have 12 Hall thruster systems in flight right now on the AHF spacecraft. As we look to the future we’re looking at both smaller systems and larger systems than what we’re currently flying.  CubeSats and SmallSats systems will probably range anywhere from 2 kilowatts down to 50 watts, potentially even smaller than 50 watts. For larger systems, we’re looking at systems in the 10 kilowatt ranges all the way up to hundreds of kilowatts for large missions such as Mars exploration.

AMI: Is there any particular role for additives in such a system?

CARPENTER: There are a number of potential benefits for additive manufacturing, including cost and mass savings as well as performance improvement. We’ll be looking at how we can improve the efficiency of the system. I think we’re starting to see the tip of the iceberg as far as what we’re going to be able to do with additive manufacturing. Right now things are made with single materials, however multi-material technologies are becoming available and as those mature I think we’re going to start seeing a lot of interesting materials and applications especially in the electric propulsion area.

AMI: I’ve heard people talk about multi-material but I’m wondering how you control the fine-grained density of the various materials at which point in the process. I understand you can deliver where you wanted to be with the 3D printing but I’m intrigued to know exactly how you control the fineness of the mix between the various materials you want to work with.

CARPENTER: We are just starting to explore various ways to print with multi-materials. We’ve been looking at things like printing from one metal to another. We’ve also been looking at a combination of ceramic and metallic. Around here we like to talk about the possibility of directly printing a functional valve. If you have the technology to print a valve, you can make almost anything you want because of all the different materials and thigh tolerances that are involved, so we’re looking at all types of options.

AMI: One other new activity, excuse me if I have this wrong but its Zero-Erosion™ XR-5 Hall thruster propulsion system.

CARPENTER: The Zero-Erosion™ XR-5 is a Hall thruster propulsion system with 5 kilowatt input to the system. The system includes thruster, power electronics, and a flow controller.  This is the system flying on the AEHF spacecraft.

AMI: I was wondering is there a particular role for additive in any of that?

CARPENTER: Sure, we’re looking at additive for cost and schedule savings, such as, “Can we take existing parts, print those and get a significant cost and schedule advantage?” We’re certainly looking at that. As we move forward in new designs, we’ll be looking for performance improvements as well.

AMI: We understand that you guys were awarded a contract with a flight opportunities program office about developing a propulsion technology for the CubeSat, the MPS 120 which is chemical propulsion. Again how does additive figure into that if it does?

CARPENTER: The MPS -120 uses the 3D printed propellant tank. It’s an all titanium piston tank about the size of a coffee cup. We have gotten through our isolation demo and expulsion demo on that program and now we’re headed into hotfire (operational) testing for that system. The rocket engines that we’re testing are not currently 3D printed but we’re evaluating whether it makes sense to 3D print those in the future. We have already made 3D printed CubeSat thruster prototypes in-house to evaluate the opportunity.

AMI: Is the size difference between Bantam and the CubeSats making a significant difference of the involvement additive?

CARPENTER: Only in the way that things are assembled. I’m looking at a very small entire system while the Bantam is looking at a larger scale engine. The engine exceeds the build volume of the current printer so as a result we have to print components and put them together so those are really the differences. The physical size will come into how many components you have to make.

AMI: It sounds like from what you’re saying additive is likely to play a significant role in space technology going forward, do you agree or disagree?

CARPENTER: I definitely agree. I saw a recent NRC report that said it’s too early for additive but I don’t necessarily agree with that. I think you phase in technology when it makes sense. We’re at a place where CubeSat systems are becoming a reality using 3D printed parts.

AMI: Are there hundreds of them up now as we speak?

CARPENTER: There over a hundred CubeSats flying; very few have any kind of propulsion. The propulsion that has flown has been cold gas systems. We’re trying to create a new paradigm where CubeSats can move around in space and do missions that they can’t currently do right now.

AMI: Do you have any timeline in which you think they’ll be deployed in space on a functional basis?

CARPENTER: We’re hoping to see deployment in next 2 -3 years.

AMI: That sounds exciting. Is there anything you’d like to leave, anything you’d like to see coming along that would make your life easier?

CARPENTER: The most important thing for us is to start to qualify the single material processes, such as selective laser melting, electron beam melting and then as we move forward the qualifications of those multi-material processes like LENS™ and EBF3. Those are all going to be important as we move forward.

AMI: How important is qualification for material testing, processes and analyses?

CARPENTER: Qualification is very important including material testing, process qualification, and the analysis tools.  I think that analysis tools are one area that has a lot to do and mature because when analysing these additive components because you’re doing things that CAD and FEA programs aren’t set up to analyse right now. There’s a lot of work to be done to get through the qualifications but there’s also a lot of opportunities in the early phase for flight demonstrations that don’t require the full qualification you would need for a 15 year commercial type satellite mission. I think we also need so see more opportunities to fly these demo missions where the technologies can be proven earlier than waiting for the tools and processes to become available. We need to build early and fly often to prove technologies out.

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