How do you make electric propulsion systems in your basement?
Propulsion systems for spacecraft come in various forms. One system that is of growing interest is electric propulsion. Compared to chemical propulsion, electric propulsion provides weaker thrust but for a longer period of time. This makes electric propulsion systems ideal for a variety of purposes – ranging from deep space exploration to station-keeping around Earth. Typically, one thinks of electric propulsion system development as being the realm of large, well-funded R&D programs. They can also, however, be developed by individual technologists as a hobby. To learn more, we spoke to Michael Bretti, who shares his at-home development of electric propulsion systems via his website, Applied Ion Systems.
Can you explain why you are interested in electric propulsion systems for nanosatellites and picosatellites?
My interest in electric propulsion systems comes from the fact electric propulsion is such a multidisciplinary field: it really combines essentially all the fields and disciplines I already love to study into one area. I only got heavily involved in electric propulsion recently and really almost by chance. There are many things that eventually led up to this being the area that I have really decided to focus on and pursue.
The key thing that really got me onto this path originally started way back in high school, when I began tinkering with high voltage. High-voltage generators with a 555 timer driving ignition coils and TV flybacks, Cockcroft-Walton voltage multipliers, spark gaps, creating ozone, drawing arcs from microwave oven transformers – all of these really got me hooked on the field of high voltage. Moving on from there, I found that there were entire applications for high voltage beyond just making arcs and sparks, which lead me to discovering a whole field of plasma engineering. Everything from thermal to non-thermal, atmospheric to vacuum, DC to RF – the entire field was absolutely fascinating and diverse. You could find applications of this technology in virtually any field and discipline. There was just something fundamentally epic about having the ability to control and manipulate the fourth state of matter and use it for so many practical applications!
At some point in my general interests and pursuits, I also took up an interest in propulsion systems through seeing amazing DIY hobby projects on the internet for pulsejet, small hybrid rocket, and turbocharger-based jet engines. These absolutely fascinated me. It was amazing that you could build jet engines yourself at home! Unfortunately, both pulsejets and turbocharger jet engines required access to welding and some custom machining (of which I had neither the resources nor knowledge at the time), though I did (unsuccessfully) try to build a weldless pulse jet with common pipe fittings and hardware. However, I was able to dabble with bench testing small hybrid rockets, starting first with simple engines made from brass fittings, small disposable oxygen tanks, and polyethylene tubing for fuel from the hardware store. Later, I experimented with tar fuel and cement-casted nozzles. Nothing remotely close to flight, to be clear – just simple bench tests to explore the fundamentals of the technology.
As I progressed in my own studies of these various systems for fun, I began exploring areas related to particle beam physics, pulsed-power systems, and x-ray generation. This further broadened my scope of interests. Naturally, electric propulsion came up, particularly with ion thrusters being related to ion beam physics, which I found interesting, though not my primary focus. I was still experimenting with high voltage projects, but throughout college and even a few years after graduating I didn’t really have the means to begin exploring vacuum-related projects.
A few years ago, however, I decided to bite the bullet and seriously commit to getting a vacuum system designed and running. I really wanted to get into these projects and figured I’d just have to start. I spent a year building up a large library of resources and becoming an expert in vacuum engineering, going through countless design iterations, reaching out to as many labs as I could for spare vacuum hardware, and scouring eBay for deals. I was able to acquire some free equipment through friends and connections I made who were also pursuing high-vacuum projects. I also patiently acquired parts on eBay and optimized my system design based on what parts I could find.
Since this was such a large investment in time and effort, and I anticipated working on this indefinitely, I also started the Applied Ion Systems websiteto document these projects and make my own contribution to the maker community with my experiences. I also joined Twitter, where I began posting about these projects’ progress.
Originally, my intent was to work on an old type of high-power pulsed electron beam system. I had all the designs, plans, and calculations ready. Unfortunately, there was the issue of shielding from the intense x-rays that would be produced. That, and getting the full system up with the multi-stage pulsed power driver, beam system, and instrumentation itself would take a lot more time and money. I ended up having enough spare parts to build a second, small chamber and wanted to tackle some unique project on the side that I hadn’t really seen done before at this level in the hobbyist community. Eliminating very high voltage systems and other projects that involved other risks and hazards, I thought: Why not play around with some simple thrusters to fill my time while working on the big stuff? It could be done on a smaller scale and much more safely than the big project I was working on, with simple materials and lower voltage supplies. Most of all, it combined my interests in high voltage, plasma systems, particle accelerator systems, vacuums, and propulsion all into one area!
I started with a very simple small-scale pulsed plasma thruster, sized for a cubesat. The thruster used Teflon fuel and required no external gas feeds, which simplified the design and kept costs minimal. Since the thruster also operated at fairly low voltages (relative to what I was used to) at just 1-2 kilovolts, feeding the voltage in through standard vacuum feedthroughs was not a challenge. Unfortunately, this first thruster never worked, but I was determined to get it firing. Through my initial posts of this one build, I captured the attention of several members of the nanosatellite community, who helped introduce me to various cubesat and PocketQube groups. I discovered, particularly at the PocketQube level, almost no work on propulsion being done at this scale. Really, no satellites at this scale had successfully used propulsion, and no propulsion actually existed on the market for this class of satellites. It was here that I saw that a real contribution could be made.
From there, I got more and more involved with the community, moving from simple prototypes to fully integrated systems. The more I dove into it, the more I was hooked, and the more it became my single major hobby. Before, I bounced around between different projects, but electric propulsion let me pursue everything I was interested in through one broad topic. People also took a real, genuine interest in plasma and ion thrusters at this level. This allowed me to gain a small following and some momentum in the nanosat and maker communities. Now, electric propulsion consumes all of my free time and resources. If I am not at my day job or spending time with the family, then I am focusing on and developing propulsion systems. There is just so much untapped potential to explore and advance!
And I think that’s part of the beauty of electric propulsion – it just covers so much! RF plasma, DC plasma, pulsed plasma, DC ion beams, pulsed ion beams, multi-polarity beams, and electron beams. Literally every type of fuel imaginable – solids, liquids, gases, plastic, metal, and water. You name it. And electric propulsion derives and shares so much from other fields. Ion thrusters are essentially ion guns seen in the particle physics and semiconductor fields. RF plasma thrusters share the same foundations as RF plasma torches and other RF plasma sources in research and industry. Pulsed thrusters have a history in pulsed plasma sources for physics and energy research. Electrospray finds itself in everything from focused ion beam milling to printing technology and chemistry. Neutralizers are just a type of electron gun. Everything is all connected in some form or another. It’s just not possible to get bored with all the topics you can cover in electric propulsion alone, and there is always something new that can be tried!
Another aspect about electric propulsion that I have really come to appreciate is the fact that its scalability lends itself to accessibility. Thrusters can be massive, multi-kilowatt beasts on the biggest of satellites, or they can be the tiniest of thrusters on the smallest satellites operating at only a few watts or less of power. While there are still many technical challenges to scaling smaller, the fact that it can be done very small makes it extremely exciting to tackle at this level.
And there are real-world applications and demands for this stuff. I already have two thrusters integrated onto the AMSAT-EA GENESIS N and L PocketQubes, all set and ready to go for launch in the next couple of months. I’m in talks for another thruster that could fly early next year. It’s no longer just tinkering with prototypes in the basement for fun but designing real, useable, deployable propulsion modules that could have significant impacts on the field. I can push the boundaries of what is possible at this level, beyond conventional development done in electric propulsion at the heavily funded NASA, ESA, academic, or company levels.
How do you go about engineering and testing propulsion systems at a hobbyist level?
This is a great question, and I actually get asked this often, but it’s kind of hard to put into words well. It first and foremost comes from a mindset towards approaching problems that has been the key driving force behind everything I do. Ever since I was little, I always had a fascination for making things. Obviously, there are times when you can’t access certain things – either they’re too expensive, difficult to get, or something else. In such cases, I end up turning towards trying to make those things myself. From robotics to musical instruments, the same principles always applied regardless of the project I took on. I had to try it myself. Every time I see something that interests me, I immediately think to myself: How can I build this on my own with little money and resources at home? It seems like a very simple question, but it immediately forces me to think of all possibilities, starting at my fundamental limits and working around those to achieve my goal. This is the driving force in everything I do and is a mentality I have cultivated for years. I am an extremely hands-on learner. I am constantly thinking about ways to build things in the simplest and most effective manner possible.
If we go beyond this basic philosophy to the actual practical side of engineering and testing, there are a lot of steps throughout the entire process. It first starts with an interest. I come across a technology that intrigues me, and I immediately start thinking of ways to break it down to its basic fundamentals and work with it myself. No matter how seemingly complex a technology appears, it is always rooted in some fundamentals that are shared across other fields. A lot of this initial stage, and in fact most of my time, is spent just sitting for hours researching and thinking about the technology. I download and consume as many papers as I can find, not only on the core technology itself, but on other related aspects as well. Everything from the physical thruster design to fuel, materials, electronics, total integration, etc. When I go through papers, I immediately identify diagrams, pictures, tables giving parameters (power, thrust, voltage, ISP, etc.), data, and the conclusions. I search both academia and industry. I look at all the different possible topologies and ways such a thruster can be configured and operated. I am always fascinated by the different ways of approaching these problems, and indeed there is never one right solution. I have also found that there is just as much incredibly valuable knowledge in some of the first pioneering works in these areas as there is in new, cutting-edge technologies.
Next comes sketches on paper. Once I have a general idea of the topology, I always just sketch it out to make something tangible. From there, I move on to initial CAD designs. Not anything final or concrete, but many different preliminary designs and configurations. At the same time, because this is a highly integrated system, I also need to think about how the electronics interface with the thruster at the top level. Especially at the nanosat and picosat levels, power and space constraints are the two major restrictions that determine both the tech class of thruster that can be used and the ultimate performance that can be achieved.
After the initial conceptual designs, I start looking at refining the designs from the perspectives of material availability and manufacturing. Because I am working on essentially a budget of maybe a few hundred dollars a month, I can’t afford any super custom stuff. Everything needs to be done with as many off-the-shelf components as possible; I need to minimize custom machining and very expensive materials. This has led me to heavily leveraging performance 3D printed materials. I integrate numerous features into the design, making it highly multifunctional. This allows me to integrate the thruster and electronics sides together more easily and spend only a fraction of what it would take to get these parts custom machined from solid stock. Of course, there are some things that can’t be avoided, like the custom CNC fabrication of the porous glass ion emitters for my ionic liquid electrospray thrusters I am working on. Even here, though, I have spent countless hours researching ways to design the parts in ways that make this normally cutting-edge propulsion technology more affordable at this level.
Once the models have been refined and the manufacturing details worked out, I begin working on the electronics for the thruster. Since I design the physical thrusters to integrate directly with the electronics, I already have a general idea of how the board should be laid out around the thruster, considering space and power restrictions, as well as components and circuit functionality. The electronics part of the design is probably more tedious and challenging than the physical thruster itself, because I am so limited in space and power at this level. There are also extra considerations, like high-voltage spacing and board tracking, that need to be considered for the high vacuum environment. For a PocketQube, which is only a five-centimeter cube for a 1P (where a 2P is two of these, 3P is three, etc.), and normally providing only a couple watts of power max, scaling at this extreme level is incredibly demanding. Right now, my propulsion modules are on the order of less than 0.5P total volume – that’s less than 5cm x 5cm x 2.5cm. They consume anywhere from a small fraction of a watt to a couple watts max. All of this is for fuel, high voltage, control, and the thruster itself!
After everything is finally designed, all the parts manufactured, and the PCBs are in, the system is soldered up and assembled for the first time. I find that, particularly with certain styles of 3D printing, tolerancing remains a bit tricky. This means there are always some hand modifications on the first iterations to get everything to fit right. Nothing a bit of dremeling, sanding, and filing can’t fix!
Then, comes testing. Of all the steps, testing is definitely the most exhausting. This is where everything comes together. The thruster electronics go through preliminary checks in air prior to final mounting in the chamber. This is to make sure the high voltage and control electronics are all functioning as expected. The thruster then needs to be carefully cleaned, assembled, and mounted into the chamber depending on the test run (lifetime, thrust measurements, general ignition, etc.). Each thruster has a very different mode of control and operation, and some are easier than others. Everything has to be wired up on the vacuum side, double checked, and then triple checked. Once the thruster is sealed up into the high vacuum chamber and pumped down, any wiring issues would mean many hours of repeating the process.
Despite all this preparation, you can never be fully prepared for what to expect during a test. Things behave very differently in high vacuum than in atmosphere. When you combine high voltages, tight spaces, plasma, and ion beams in the same picture, a lot of unexpected things can happen. Only once you are actually in the pilot seat can you get a real feel for the thruster in action. All the theory and background preparation are necessary to increase your probability of success, but the real world is always very different than the theoretical world. Running these thrusters is still a very hands-on and involved experience. Each type of thruster has a different feel. In all cases, I start up at bare minimum power, and then slowly creep my way up. I have to watch tons of things at once – vacuum, cooling, instrumentation, thruster control, power, checking that I am recording good video for test analysis, writing notes, taking data. So much is happening. When things go wrong or don’t work as expected, I really have to think on my feet and adapt to the situation. A lot of times, there is failure – arcing, flashovers, component shorting. But it’s seeing that plasma pulse or tiny ion beam coming from the thruster (and from the right area!) that makes it all worth it. Seeing that tiny thruster finally come to life after all that research, design, and testing – it’s a really exciting moment.
During testing, I also live tweet the entire test as it happens. From vacuum pump-down, to prep, to pre-test briefing, to actual testing, it gives others a behind-the-scenes look at what really goes on during advanced thruster testing. And I share it all, from completely abject failures to full success. It’s always an interesting ride with lots of twists and turns along the way! There is no other electric propulsion effort out there that bares it all so openly in its most raw form. Everyone can see and follow along closely during not just testing but from the very beginning of initial concepts and theories through to the end-of-life testing of a thruster.
But after testing, it does not stop there. No thruster design works perfectly on the first try, so numerous iterations of both the thruster and the electronics are done. After the first prototype, additional iterations are much faster since the initial groundwork is already laid out. However, running multiple tests is always physically demanding and very time-consuming. Yet each iteration, regardless of success or failure, always reveals something new to be learned. Each iteration always drives the design forward, no matter how small or large the step that is taken.
Since each phase of the thruster development and testing process can take time, between research, design, manufacturing, and testing, I always have numerous parallel developments. That way, there is never a point when I am not working on a thruster system. I think right now I have six active thrusters in development, between initial design and testing, as well as a few others I am researching in the background. I’m essentially covering almost every major form of electric propulsion out there.
What role do you envision electric propulsion systems playing in humanity’s engagement with space?
I would say that it is already playing a very important role in humanity’s engagement with space. Scientific missions such as Dawn and Deep Space 1 have already successfully utilized and demonstrated some high-power, state-of-the-art ion drives. There is work being done on a new generation of even higher-power ion thrusters like NEXT to support new deep space scientific missions. Of course, as humanity progresses towards venturing further out beyond the Moon, electric propulsion will play an important role in enabling this advance. But the advancement of engagement with space has already begun. And electric propulsion is not a new field either. It actually dates back many decades but has only started to gain more traction and prevalence with the reduction in size of satellites, as well as with the increased use of satellites outside of scientific missions.
Electric propulsion plays a large role in missions close to home too. The majority of electric propulsion systems flown are by satellites in the commercial sector, supporting these satellites’ orbit-keeping and orbital maneuvers. There are still plenty of commercial satellites that are launched with some form of plasma or ion thruster (typically Hall thrusters for larger satellites). They rely on these forms of propulsion for maneuvers, orbital transfers, and end-of-life capabilities. Numerous Starlink satellites, for example, are equipped with Krypton Hall thrusters. Amazon’s new Project Kuiper constellation is also looking to equip onboard propulsion (though the final technology has not been revealed yet). There are other constellations in the works, both government and commercial, that have announced some electric propulsion contracts to improve mission capabilities. And there are many companies around the world supplying new plasma and ion thrusters to the growing satellite market.
Going further down the scale, while most nanosats and picosats like cubesats and PocketQubes still operate without any form of propulsion, there is a huge amount of interest and investment at this scale for developing micro electric propulsion technologies. There are at least a dozen companies out there, along with countless labs, programs, and a new spinoff coming from these programs practically every month.
And now, with the effort at Applied Ion Systems, electric propulsion is seeing a new chapter in its development. Electric propulsion development is no longer reserved only for multi-million-dollar academic or government-funded efforts. It is something that can genuinely be advanced even at home. With the advent of cubesats and PocketQubes, combined with the ever-decreasing cost of launches, space has never been more accessible to the public. Especially with PocketQubes, more and more student, academic, and NewSpace startups can build and launch their own satellites and access space. A lot of these efforts are also being quite literally built at home or through small group efforts. This has just not been possible until recently. Heck, I would have never even dreamed a year ago I’d see the thrusters I built at home and fired in the basement actually being flown in orbit! When it comes to true accessibility, it is the makers, tinkerers, and enthusiasts around the world who take these normally complex and prohibitively expensive technologies and make them accessible to everyday people. And what better way can humanity engage with space when such technologies can be pursued even at home!