an interview with project sparrow

2:34 PM on Monday, January 3rd, 2022 (Claremont, CA)

Towards the beginning of this past Fall semester, I got to sit down with Jonathan Neeser, who is a full-time engineer that works on the combustion chamber design for Project Sparrow. While this interview write-up is long overdue, I’ve finally had some spare time thanks to Winter Break and am happy to recount the interview now.

Before we begin, some background information would most likely help those readers who aren’t ingrained in the collegiate rocket team culture. Project Sparrow is a student researched and designed (SRAD) project with the goal of designing, building, and testing a liquid-fueled thrust-vectoring rocket engine. This engine is not only a large technical feat for a student team, but also touts such engineering advances as being 3D printed, and regeneratively cooled. The students behind Project Sparrow are all part of a larger umbrella organization, DARE, or the Delft Aerospace Rocket Engineering group of the Delft University of Technology in The Netherlands. With over 190 members, they have multiple other projects in the works besides Sparrow, ranging from parachute research to SRAD avionics systems. Today, we’ll be focusing on Project Sparrow; below are selected excerpts from our discussion; ‘F’ denotes my dialogue while ‘J’ denotes Jonathan’s.

F: Just to start us off, could you tell us a little bit about yourself?

J: I’m a student of aerospace engineering here at the TU Delft, and I finished bachelors last year. I then took a year off of studying to work on Project Sparrow and I’m starting my masters right now. I joined Delft Aerospace Rocket Engineering back in 2018 when I started studying, and kind of bounced around on various projects until I ended up working with the cryogenic propulsion team, which was kind of the predecessor to Project Sparrow. From there I just started learning a lot more about how to design rocket engines, feed system testing, and the logistics of organizing test campaigns. During that time I also joined our Safety Board, which is responsible for ensuring safety during tests and all of our other activities. Last year was when I started working on Project Sparrow specifically, in which we want to make a liquid propellant rocket engine with liquid oxygen and ethanol. Within DARE we have mostly worked with solid and hybrid rocket motors, so we were really excited to now be able to test a liquid rocket engine using what we learned on the cryogenics team, and actually make a rocket engine we thought was useful for future larger rockets. Some years down the line, we hope that we can eventually make this thing small enough to fit into a rocket, and actually launch it. The goal here is to prove that not only can we do liquids, but we can also hopefully make an engine that is light enough and can have a long enough burn time to be useful. At the end of this past August we had our first successful short duration burn which was really neat to see. That was pretty exciting. On the second attempt, we sadly had an engine failure, which was the first time we tested our metal 3D printed engine. But we did have plenty to learn from that. Specifically my role in all of this was largely the thermal analysis of the combustion chamber, the injector design, the propellant feed system, and testing itself, where I served as test operator.

F: When thinking about a liquid rocket engine, that’s not exactly something you can just Google and make in a day. That being said, what is the design process that you guys take in order to do something that has never been done before?

J: The design pipeline can actually be quite problematic for student teams such as ours. What I found at the beginning of the year was that simulating underlying phenomena numerically is pretty much a waste of time. If you want to finish a project like this in a year, and especially if you want to start testing halfway through the year, you want to have a working design. You could spend an entire year trying to simulate your injector behavior, and not test anything. So, you’ve got to step back. And ideally you would design something by first principles, maybe some very basic empirical models, and then you would just go out and test it, test it, and test it again until it behaves more or less like you want it to. Sticking with the example of the injector, for this test campaign all we had time and resources for was one design and one design iteration. This is of course less than ideal, but there were a lot of limiting circumstances. We’re also very limited by COVID and a complete lack of workspace, which made this past year really interesting. So when it came to injector design, we went back to first principles design of fluid orifices, some basic calculations of things like resulting spray cone angles, some good principles used in previous designs, and trying to make something and hoping it works. And that’s where we as a student team struggle, with very low budget, little workspace, and limited time, because we cannot really afford to do that much testing.

F: Did you guys transition over to the 3D printed metal design from a prior one, and if so, what were you using before that?

J: We kind of designed two engines in parallel this year. Most of the focus went towards this optimized metal 3D printed design, with cooling channels. In parallel, we designed a battleship version of the engine specifically for ignition tests and to verify stable combustion on the same injection element. This is because we also realized that if we have any hard start, if we have any engine failure, we would rather have it on the steel tube with the graphite nozzle than having it on the really expensive, incredibly complicated 3D printed piece. In the end, while we did have a failure with the first 3D print, our first successful test was with this battleship engine.

F: How does a student team go about testing a liquid rocket engine?

J: First of all, finding a test site that would allow a bunch of students to come in and work with liquid oxygen is extremely challenging. We had to spend a lot of time presenting risk maps and explaining the safety features of our system before we were taken seriously. Acquiring the liquid oxygen also proved quite difficult. The Netherlands is also incredibly densely populated, so there is not just a desert we can go out to and test in. We really have to go through very official channels in order to do anything. We were lucky to find an Air Force base in The Netherlands that was interested in supporting us and they let us test in a facility that they usually test F-16 engines in. Without that we would’ve been screwed. They also have experience handling liquid oxygen which was extremely helpful.

F: How do you guys manage passing down knowledge between the different groups that come in, since students have a high turnover rate since they will leave upon graduation?

J: That’s an interesting question, and one that is quite challenging. In DARE, and even in between projects that are very closely related to each other, the knowledge transfer is rather poor. I would say that it used to be a little bit better because members stayed longer, since it becomes harder to spread knowledge among the team when people are not there for a longer period of time. This isn’t just knowledge about designing things either, because that knowledge at least can be taught to oneself. What is really crucial is some institutional knowledge such as how to conduct tests, how to test rocket engines safely, and things like that that need to be handed down a little bit better. We’ve tried for Sparrow just to document as much of the stuff that we did as possible. For the last test campaign for example we brought the new team in just to tag along, so we gave them tasks and tried to do a knowledge handover while testing which I think worked out really well.

F: Lots of people are of the idea that we are reaching a critical limit with chemical propulsion. As a propulsion engineer, what your thoughts on that?

J: I think that we are reaching some thermodynamic limits on the efficiency of conventional rocket engines. There were some really cool experiments that were going on for a long time in the 70s and 80s on really high chamber pressure designs. And I think people are going to continue to tinker with things like that, but the actual benefits to be gained are marginal to some degree. You can always make your engine a little more efficient, you can always get a little bit more mass into space and you can always make it a little bit cheaper, but I also don’t think that for getting something off of Earth into orbit there are a lot of viable alternatives. There are plenty of options that are interesting, but not too many that are currently feasible. I always like the idea of space cannons but I don’t think we’ll be using them any time soon. Project Harp was cool but I don’t think it’s coming back. Two areas that are a little bit more dynamic are very small space propulsion such as that for CubeSats, and propellant research itself although that has slowed a bit with the exception of  non-toxic monopropellants.

F: For you, why rockets, why aerospace engineering? What got you into it and why do you enjoy it?

J: I think quite simply put, it’s what I find incredibly interesting. It’s a little bit hard to explain, but I’ve always been really fascinated by rockets in general, and aviation as well, so going into aerospace engineering was always a bit of a natural choice. I really enjoyed flying any time I got the chance, and learning about aviation and rockets was fun. Specifically, being at TU Delft gave me a lot of opportunities to try out different things and that’s how I got into the propulsion engineering side of things; I got to try it out myself and learn it directly in a way that I probably wouldn’t be able to anywhere else. A society like this as opposed to a company or university, really gives us an opportunity to mess around and find out what we like. The ability to design something on your own and make mistakes, in a way that any other education doesn’t really allow you to is really wonderful. You really quickly discover there isn’t a lot of information on these topics, so you either have to guess or find out for yourself. Maybe that’s part of the allure for the whole topic for me, because it is so strange, and it is so niche.