BLACKSHIP ONE PRESENTS…
The One-Man Space Propulsion Company
Is it tough? Hell yeah, this is the hardest thing I have ever done. It has brought me to my knees, past my breaking point. Doing conventionally multi-million dollar level research on essentially pennies with little access to resources is incredibly demanding, and requires all of my spare effort and resources.
EP systems are nothing more than basic technologies just packaged compactly and strapped to the backs of satellites
Today, Blackship One, was fortunate enough to be able to talk with Michael Bretti, the founder of Applied Ion Systems, about his involvement in the electric propulsion space. We have an exiting interview planned for you today where Michael will walk us through what it’s like to work on advancing propulsion technology on a shoestring budget (see Michael’s Patreon page here).
Keep in mind, this is the second part of a five part interview series. If you’d like to start from the beginning of the series, you can click here.
Your open source project aims to help make electronic propulsion systems for nanosatellites such as Cubesats and PocketQubes more easily and affordably available. I’d be curious to know what additional obstacles you face when trying to miniaturize the technology to be compatible with the size restrictions of nanosats. Does the technology scale down well?
This actually touches upon one of the key fundamental challenges still facing EP. In general, it is much harder to scale EP down than up, mainly for the reason that performance relies heavily on the power that you can provide.
Depending on the type of thruster, different technologies and fuel selections can provide a wide range of thrust, ISP, total impulse, and range in a wide array from simple (like PPTs) to highly complex (like gridded ion). However, there are always trade-offs, and you can’t get everything for free. Often in the case where power is severely limited, the max thrust you can produce can greatly suffer, since thrust is primarily dependent on how much power you can provide for EP systems. Other factors like ISP can be inherent to the technology (for example, all things being equal, ion thrusters will have higher ISP than plasma thrusters), and in general, EP systems can provide very high ISP. For reference, at this level, typically various types of plasma thrusters can range from the low hundreds to high hundreds of seconds for ISP, where ion thrusters, like some forms of electrospray, can reach many thousands of seconds of ISP.
Certain technologies scale down much better than others, and at a certain point, there are only a few options that can be reasonably utilized. For more classical EP like Hall thrusters and gridded ion thrusters, the physics of operation makes it difficult to keep reasonable performance at very low power levels. Hall thrusters in particular suffer greatly at the lower power levels, and getting down into the tens of watts of power region, become less practical than other technologies that shine in this power region (like electrospray). However, at many kWs of power, Hall and gridded ion thrusters have far better performance, and are dominant in this power class of EP. There are even some cases, like MPD thrusters, that perform best in the hundreds of kW to MW range rather than single kWs and lower!
Many of these thrusters also rely on a lot of auxiliary power systems, which also translates to wasted power not directly converted to thrust, including heaters, neutralizers, valve control, etc. Even for more simplified systems with less auxiliaries, like in the case of RF power, there are tradeoffs in RF power levels and frequency required to ionize the fuel. Low MHz range supplies are much more efficient, but require much higher power at several tens of watts than say GHz level supplies, which can ionize propellants at only a few watts for a properly designed system. However, GHz level supplies conversely are much more complex, costly, and less efficient. In either case though, due to the requirement of gaseous fuel delivery (like Xenon or even water vapor), this limits the total system size miniaturization severely, and at lower and lower power levels, both thrust and ISP can suffer greatly, to the point that the size and power requirements really wouldn’t make sense compared to other forms of propulsion at that level.
On the other hand, there are EP technologies, like electrospray and pulsed thrusters (PPTs and VATs) that inherently can operate very well at low power levels of only a few watts and less. While lower power again still translates to reduced performance, performance still scales reasonably well with power and size that makes them viable technologies. In many of these cases, these types of thrusters also can rely on non-pressurized propellant feed and other forms of propellant besides inert gases used in their higher power class counterparts in EP, making propellant storage and delivery much more compact with little to no additional power requirements.
Yet even here there are some scaling challenges too. For example, for PPTs, while they can be run at extremely low power levels like less than 1W, the thrust to power ratio, and ISP suffers severely, limiting them primarily for use as attitude control rather than main propulsion. At this power level, you are looking at a few Joules of stored energy, even down to sub-Joule energy for pulsed delivery, making ISP in the very low hundreds, and thrust on the order of sub-uN to a couple uN max, and have non-linear scaling at the lowest end. Max total impulse that can be delivered, effectively determining delta-V and overall operational life, is also significantly lower at this range.
Other pulsed thrusters like VATs typically exhibit fairly linear scaling laws, at around 10uN/W, and with heavier metal fuels like titanium or aluminum, over Teflon found in PPTs, ISP is much higher, with generally higher total impulse capabilities. However, there are some trade-offs in terms of size, energy storage, and complexity here. Electrospray on the other hand has quite good thrust to power ratios and very high efficiency in this range. There are numerous types of electrospray technologies, with thrust densities ranging from a few uN/W up to greater than 30uN/W, with ISP ranging from 800s to over 8000s! Colloidal electrospray is more challenging of the electrospray to scale, relying often of pressurized feed and external neutralizers, suffering from the lowest efficiency of the electrospray classes.
Liquid metal fueled field emission electric propulsion (FEEP) electrospray can be scaled very small, providing good thrust at very high ISP and lifetimes, but still has some minimum power requirements for heaters for the liquid metal fuel, as well as the electron emitting neutralizer used to neutralize the beam. Ionic liquid ion source (ILIS) electrospray however requires no heaters or neutralizers, with self-neutralizing beam capabilities, allowing it to operate very efficiently at extremely low power levels, and providing very good thrust-to-power ratios and ISP, but currently suffers from the lowest lifetime and total impulse of all the electrospray technologies.
Taking all of this into consideration, I face the same challenges as many others in the field in terms of scaling. However, since I am working down to PocketQube class satellites, scaling becomes even more extreme. Where a 1U Cubesat is 10x10x10 cm, and can provide several watts of power, a 1P PocketQube is a quarter of the volume, at only 5x5x5cm, and can provide less than 1W power max!
Even here we approach the limits of space and power, and probably the minimum size a propulsion system can be reliably and effectively used at on this scale is 1.5P and up.
One of the advantages though starting with the most extreme case of scaling however is that going bigger becomes much easier. Especially in the case of these micro-ion and plasma thrusters, a common solution at the nanosat level is to parallel multiple thrusters, rather than use one single larger thruster. This actually works out very nicely in the case of electrospray thruster technology especially, and all companies out there providing electrospray solutions take this approach towards scaling, which is more advantageous for this particular type of propulsion rather than making physically larger single thrusters anyway. Going from a PocketQube class thruster to a Cubesat thruster or Cubesat cluster is honestly a huge breath of fresh air – I just have so much more power and room to work with!
Some of the biggest obstacles that I face in miniaturizing this technology beyond the typical challenges in the field however is doing such advanced research on such an incredibly limited budget with almost no resources. I am currently operating on a budget of only a few hundred dollars a month, I have to be extremely resourceful, and really plan out and prioritize development.
Besides my high vacuum test chamber and basic hand tools, I also don’t have any advanced manufacturing in-house. While I have plenty of access to outside CNC, laser cutting, 3D printing, and other manufacturing services, what I can do myself is limited, making modifications or changes on the fly a challenge. It is very common for me to rely on some hand filing or careful use of the Dremel to modify systems for testing! The lack of extremely advanced processes also helps drive my designs, allowing me to approach problems in new way that allow these systems to be developed and tested for many orders of magnitude less than conventionally.
Being a one-man propulsion company, I also have to literally do everything myself, and be an expert in everything. Beyond just thruster design and electronics, I have to do all the research, analysis, testing diagnostics, infrastructure, etc. Everything is completely designed and built from scratch at home.
My vacuum system was designed to optimize what surplus components I could obtain, and is incredibly small and compact, yet designed to be highly modular and simplified, maximizing its versatility as well as physical pumping speed.
I have faced every possible failure and setback with my testing equipment – pumps, cooling system, data acquisition, instrumentation, you name it, it has broken or failed at least once. Despite this, it forces me to become intimately familiar with every aspect of my system, allowing me to be able to troubleshoot any part of it quite rapidly. Heck even now, for every test currently, I have to run out to the local gas station and buy numerous bags of ice for the cooling system for my main high vacuum diffusion pump, for which part of the heat exchanger is a coil of copper tubing in a Styrofoam cooler!
I barely even have power currently to run my testing – power for the pumps is from the basement, where my vacuum system is currently located, but I have to run extension cords up to the first floor into the kitchen each test to power everything else. I’ve got a single ceiling bulb and a floor lamp to work with in an old space with dirt and wood plank flooring. Testing itself in these conditions is grueling, and I have to keep track of everything manually – multiple vacuum pumps, cooling systems, thruster control and feedback, test video recording, all while simultaneously troubleshooting, making adjustments, and live Tweeting every step of the test as it happens on the AIS Twitter page.
For electronics testing and assembly, I have a small spare bedroom that has been converted into a workspace (that also still serves as a closet for all my clothes). Since I generally work on multiple different systems simultaneously at any one point, it’s often so messy I can barely walk around in there. It’s nowhere near a luxury setup of the EP labs I have toured myself, and definitely introduces its own set of challenges, but it’s enough for me to get the job done!
What an incredible setup. I think your story and setup will inspire many others to want to get involved in the New Space niche. Let’s keeping moving along here. What are the three biggest limitations / obstacles of electric propulsion in the nanosat space and what’s being done to overcome those limitations?
This probably varies depending on who you ask, but for me, I think the three key limitations and obstacles facing EP in the nanosat space are scaling, supporting subsystems, and accessibility.
Scaling: For scaling, this goes back to the fundamental challenges of the technology itself which I touched upon extensively. Power and space are extremely limited on nanosats, and performance of any EP system is directly and primarily related to the electric power than can be provided.
This requires significant optimization, and in the extreme cases of miniaturization down to PocketQubes, every milliwatt can count. At the nanosat and picosat scales, optimization of every aspect of the system becomes crucial.
Everyone is working on their own different technology though, and each type of technology can be optimized in various ways. However, the field has progressed massively in terms of miniaturization in the last couple of decades. With the onset of the Cubesat revolution, there became an immediate recognition for the need for smaller and smaller EP systems, where before satellites were quite large and had much more space and huge power budgets to work with. Because of the advance of smallsats, shifting down further to nanosats and even picosats now, this has forced propulsion to shrink with the platforms, which has helped drive many original limitations of EP systems.
Subsystems: Second, unless you are flying an EP system purely for demonstration purposes, where you can just fire the thruster without worrying about the actual maneuver or orientation (except maybe if propulsion is used for attitude control itself), you need to rely on a lot of subsystems to support its use effectively. The first big part of this is onboard power. EP requires power, and the more you have, the better performance you can afford. While medium sized and large sized Cubesats can deliver quite decent levels of power, scaling down to small Cubesats and PocketQubes, this becomes a real challenge, especially for the PocketQube realm.
Improvements to solar cell efficiency, reliable deployable solar arrays, and battery technologies will only make the case for EP stronger and more viable. However, limitations in power also helps drive innovation in EP, like in the case of electrospray, which has gained significant interest in the past couple of decades due to its high thrust to power ratio and efficiency at very small scales.
Another subsystem that is required is attitude control, like reaction wheels, or using micro-EP thrusters as attitude control themselves. To be effective, the satellite has to be pointing in the right direction when you fire. Of course there are a lot of available systems out there that can accomplish this, but they are also expensive, require power to run, and need control algorithms to control the positioning of the satellite. This all adds cost, increased power demands, payload volume, and complexity to a mission. Again, the larger the satellite, the easier it is to accommodate this, but for the extreme end, this is a massive challenge.
Going back to PocketQubes, which really does well to highlight just the absolute extreme end, very few have flown active attitude control with reaction wheels, most relying on passive control via magnetorquers. Micro EP also isn’t mature enough yet to implement as attitude control here either, and would require some really tiny thrusters and creativity. Even with the AMSAT-Spain mission my two gPPT3s are flying on, the purpose is mainly a tech demo to demonstrate PocketQube control and operation of a thruster in orbit, and relies on passive magnetorquer control, and waiting for the satellite to passively align itself in the right orientation during its orbit, which occurs for a window of only about 15 minutes during each 90 minute orbit around Earth. To get propulsion to be truly effective at this level, beyond just miniaturization of the thrusters themselves, advances in more onboard power and active attitude control solutions are key.
Accessibility: Finally, I think accessibility is one thing that is largely overlooked in the field. Conventionally, EP is fueled through very large academic, government, military, and space agency grants. A system is developed through these funding means, and usually ends up targeting such end users. Yet no one seems to be looking to develop EP for all the countless Cubesat, and now emerging PocketQube teams, who would otherwise have a lot of interest in flying with propulsion that just can’t access it. Right now, EP is extremely expensive (like everything else in the space field), and is probably one of the most expensive and involved standard subsystems for a satellite out there (barring any specialized scientific payloads of instrumentation).
Very few Cubesats have actually flown propulsion, and the vast majority that are launched do not fly with any. Of course everyone in the field is aiming to produce lower cost systems (to an extent) and increase production capacity, but there is still a fundamental paradigm that such systems, and even space systems in general, can’t be developed and produced for far less than they already are.
I truly believe it is about the approach that is taken in the industry currently. As AIS has already demonstrated, you don’t really need millions of dollars to develop EP, and systems don’t have to cost exorbitant amounts.
Looking at average costs, at the nanosat scale, stuff like PPTs are on the order of several tens of thousands, micro-ion thrusters usually are in the $50k starting range, and going up to gridded ion, Hall, and RF plasma, range to hundreds of thousands still. I’m sure I am an outlier saying this (and many people in the industry will undoubtedly disagree with me), but this is insane.
Of course you need to account for engineering, R&D, production costs, market size, and other factors, but currently there hasn’t been any incentive to develop solutions for the low funded, low-cost platforms out there, especially when the bulk of your revenue comes through huge grants or government contracts.
One thing that makes AIS stand out is this focus on extremely low-cost, entry level systems that any nanosat team could utilize, and even any academic lab or program could acquire or even build themselves. I am looking at cost reduction levels up to an order of magnitude less, as well as open sourcing designs. Now, my systems can’t compete in terms of performance compared to all these other major multi-million dollar funded companies and labs yet, but I am not targeting critical military, NASA, or ESA missions.
For the nanosat community I am working with developing propulsion solutions for, this level of performance and reliability isn’t as crucial, yet having some propulsive capabilities at an affordable range opens up new options and missions that were previously locked away.
For things like PocketQubes, where orbital lifetimes are relatively short, on the order of months, maybe half a year, even doubling these numbers with low levels of minimal orbit keeping performance immediately increases value of the launch and mission significantly, allowing you to operate for much longer periods, and getting more bang for your buck.
Accessibility also goes beyond just affordability though. A major problem that plagues the field in general is lack of transparency and secrecy to the extreme. Transparency in particular is very bad, and there are many instances where companies (mainly new start-ups) just flat out misrepresent specifications, grossly overestimate or overhype performance capabilities of a particular technology, or present them in a way that to the average person reading it, sounds like an unbelievable and unmatchable system, but for someone well versed in the field, is merely out-of-context. Approaching companies for these systems can be a challenge and very discouraging when they are so reluctant to provide any details or information and require over the top levels of NDAs, even for just basic aspects of the system performance.
This is a large reason why I have decided to pursue and continue development through AIS as open source.
This isn’t black magic, and I think the more resources that are available for people to understand how these systems work and are designed, built, and operated, the easier it is to approach them, and lower these barriers of entry into this field.
This will not only allow the technology to advance further and faster, but improve usability having more people being able to access, and test these systems themselves.
Along the lines of accessibility, beyond the open builds, data, and educational resources I provide the community, I am also work towards developing educational kits that actually simulate the operation and control of all the fully integrated thruster systems I develop. These kits are 1:1 scale models of the real thruster, with the same input control, and similar readouts, to provide a way for anyone to access EP and get involved. Such resources can be used by enthusiasts, as well as students exploring the field of EP, without requiring the expensive and complex high vacuum systems needed to run EP, which is one of the biggest barriers of entries. It also allows nanosat development teams to begin exploring integrating and controlling the actual systems without having to worry about the full system integration and testing.
⚠️This concludes the second part of our five part interview series. In the third interview within the series we talk about the power requirements of nanosats that carry propulsion systems. Read the third part of the interview here.
If you’ve enjoyed this interview series so far and would like to help contribute to this open source space project, you can do so here.
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