The emergence of electrothermal water-based propulsion for CubeSats – with SteamJet Space Systems

Episode 27 of the Space Industry podcast is a discussion with Marco Pavan, CEO and co-founder of satsearch member company SteamJet Space Systems, about the performance, applications, and trade-offs of electrothermal water-based propulsion technologies for CubeSats and smallsats.

Contents

• Episode show notes
• SteamJet Space Systems’ portfolio
• Transcript

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Episode show notes

SteamJet Space Systems is a small satellite propulsion system manufacturer based in the UK specializing in electrothermal water-based propulsion for CubeSats. In this podcast we cover:

• The current maturity level of electrothermal water-based propulsion technologies
• Missions and maneuvers suited to flying water-based thrusters
• How water compares with other green propellants
• Future applications for this technology, such as in-orbit servicing and satellite de-orbiting

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The portfolio of SteamJet Space Systems

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Episode transcript

Hywel: Hello everybody. I’m your host Hywel Curtis. And I’d like to welcome you to the Space Industry by satsearch, where we share stories about the companies taking us into orbit. In this podcast, we delve into the opinions and expertise of the people behind the commercial space organizations of today who could become the household names of tomorrow.

Before we get started with the episode. Remember, you can find out more information about the suppliers, products, and innovations that are mentioned in this discussion on the global marketplace for space at satsearch.com. 

Hello, and welcome to the episode. Today I’m joined by Marco Pavan, CEO and co-founder of SteamJet space systems.

SteamJet is a small satellite propulsion system manufacturer based in the UK. And today we’re going to discuss electrothermal water-based propulsion for Q2. Firstly, Marco, thanks for being here today. Is there anything you’d like to add to that introduction? 

Marco: Thank you very much for inviting me here. You did a pretty spot-on introduction Thanks. 

Hywel: Electrothermal water-based propulsion. I wondered if you could first give us a bit of an overview of how such technologies have matured in, in recent years and why, you know, in some people’s opinions perhaps has it taken quite a long time to make this technology a reality for, for space missions.

Marco: First of all, it would like to just give perhaps like a very brief introduction about the electrothermal thrusters so just to make sure, basically we’re all aligned.We know what we’re talking about.

So electrothermal thrusters are very simple in principle, they’re kind of, uh, improvements from cold gas thrusters and cold gas thrusters are the really the simplest proportion systems that we can think of. Literally is pressurized tank usually containing gas which is connected to nozzle, through a valve and then opening the valve, releases this gas into, into space and that is creating thrust.

So cold gas thrusters are the easiest way to create propulsion, but obviously they are very inefficient. So in order to improve that then electrothermal thruster were created. And the main working principle this is we can heat up the gas before it gets expelled through the nozzle, in order to improve the efficiency. So electrothermal thrusters, do that by just using an electrical energy and warming up the gas in order to improve the efficiency of the system to create a, to create thrust.

Electrothermal thrusters have been widely used in the past, over the last decades. So they have a lot of flight heritage and it’s been used with many different propellants that have been used with pressurized gases, like Xenon and nitrogens, for instance, or even with liquid propellents. Now, if we look at electrothermal thrusters using water as propellant.

So water-based electrothermal thrusters then there’s been quite a lot of research in the years and, uh, this research, however, it hasn’t really created a lot of commercial options. Water itself is actually a very good propellant because as a very low molar mass, and therefore can potentially create quite an efficient propulsion system.

The main problem with water is that it takes a lot of energy to be converted into, into steam and eventually to make an efficient propulsion system. So what we did here is things that is, we find a way to basically convert water into steam by using very little power, and also by using a very compact design. So I think water being a propellant is extremely good.

However, as I say, it takes a lot of energy and a lot of times on these CubeSat and small platforms, you don’t have a lot of energy. What we did at SteamJet, we tried to make a propulsion system based on water, which is, which is actually feasible. It can, can be actually used on small CubeSats, and small satellites.

Hywel: Adoption took time because you needed the other parts of a satellite system to also be able to handle aspects of the propulsion system. So that’s really interesting.

And then also a lot of in the commercial sector, what we look at is, um, technology innovations that are driven by market requirements. Which, um, when it comes to the thrusters, is we talk about, are certain maneuvers or the different aspects of what the satellite needs to do. So I wonder if you could just explain what sorts of missions and maneuvers are ideally suited to fly in water-based thrusters.

Marco: Yeah, sure. This is a quite interesting question. I will say that, uh, most of the typical missions and maneuvers can be done using water-based thrusters, especially electrothermal thrusters.

And, uh, I would say we need to target mostly the low earth orbits missions. If we’re looking at LEO missions, then the main use case is the main maneuvers for propulsion, main use cases are station keeping. So keeping your satellite basically at the same altitude, and let’s say counteract drag, then obviously constellation management, which is becoming a hot topic because there are more and more constellation coming up. You need to make sure your satellites are positioned in the right spot in the orbit, and so constellation management takes care of that.

Then you can obviously do some small orbital changes, collision avoidance is also extremely important because there are more and more space objects now in space. And if you are on a collision orbit with another space object, you need some active propulsion system in order to avoid that collision. And finally the deorbiting is also quite a hot topic because we don’t want to introduce more and more space junk in space. We need to make sure that when the mission is finished, we can dispose of the satellite. 

The main limitation, I would say in the use of, uh, specifically electrothermal water-based propulsion systems are, if, for instance, you need quite a high Delta V if for instance, you need to do like a massive orbital change going from low earth orbit to a geostationary orbit. Then I think electrothermal thrusters are not the best technology for that. You need more efficient technologies, which usually have a higher, specific impulse, and they can provide basically better delta V. But other than that, I would say, most of the maneuvers and missions that I mentioned earlier can be easily done by electrothermal water-based thrusters.

Hywel: Yeah, those key parts on the lifecycle of a satellite, you know, to correct orbital position, the deorbiting. Yeah. Well, very important that as you say, collision avoidance increasingly important as, as the traffic, uh, grows. So you mentioned there the fact that it’s water-based electrothermal systems sometimes don’t have, or can’t produce the highest Delta V compared to other systems.

Could you expand on the comparison between a water-based propulsion with other popular propulsion technologies, things like FEEP and Hall effect. And maybe give us a bit of the pros and cons. 

Marco: Yeah, definitely. I would say starting from the pros, the main pros that we can identify are definitely high thrust, low power consumption and low pressure.

So just to expand a little bit on this, high thrust allows you to do your manouvers pretty quickly. And electrothermal thrusters can have 10 to 50 times more thrust than electric propulsion. Like the systems that you mentioned, and this basically reduces what is called the payload downtime. So especially if you are in a limited platform, like a CubeSat or a small satellite, if you’re using the propulsion system, you can’t use the payload at the same time.

Therefore the more you use the propulsion system, the less you use the payload. Therefore, if you have a system which has a high thrust that allows you to do the same stuff, but pretty quickly, then you can reduce the amount of payload downtime, and you can actually use the payload to generate revenues and to do the mission itself, which is a beneficial thing for the final user.

And in terms of power, also, if we compare, for instance, what we have been able to achieve here, in SteamJet, we can generate quite a good thrust using a half the power of electric propulsion systems, such as ion thrusters, FEEP, Hall effect thrusters.

Therefore, especially if you have a very limited platforms where like three unit CubeSats or even like six unit, 12 unit, still quite limited in terms of amount of power you can produce. Then obviously if you have a lower power consumption, you don’t have basically to design your EPS or your satellite around the propulsion system rather than the payload itself. So that is a very good, beneficial thing for also for the final user.

And finally, in terms of propelling itself, Water is a low pressure. Propellant is kept the pressure, which is usually below a hundred PSI or seven atmospheres. And if we compare that with the electrical propulsion systems, which in most cases used steel, highly pressurized gases, like Xenon a 70 bars.

Then we can understand that are really high pressure propellent tank, its way more tricky to be handled, especially on very small platforms and small CubeSats. So having a lower pressure makes everyone’s life easier at the end.

Obviously, there are also some cons, but if we can basically go back to what I said initially, the main, let’s say cons are related to the specific and total impulse. Obviously ion thrusters, FEEP, Hall effect, they can have very high, specific impulse and a lot of delta V that they can deliver to the satellite. So if for instance, if you need to do a very big orbital change, such as going from LEO to GEO as I mentioned earlier, then I don’t think electrothermal thrusters are the best option at the moment. So, yeah, this is more or less pros and cons of the two technologies.

Hywel: Just to follow up quickly. You said that you were able to reduce the power requirements are by up to half, is that half in order to produce the same amount of thrust – comparable thrust?

Marco: That is actually 10 to 50 times more thrust. 

Hywel: That’s fantastic. So you also touched on the properties of water as a propellant in the system.

So focusing on that aspect of it, water is obviously, um, referred to as one of the green propellents.. I wonder how you thought it compares as a propellant to other green propellant in that area? 

Marco: Yes. So I think here, we need to distinguish a little bit between doing proponents for electrothermal thrusters and potentially high performance green proponents for mono propellent systems.

So if we consider other possible propellents for electrothermal thrusters, which are butane ammonia and then obviously, water is still cheaper. It’s still easier to handle, it is nontoxic noncorrosive. So, and its also able to generate one of the highest specific impulse that you can have on this kind of technology.

So these are the most beneficial part of using water. And if we compare that with a high-performance green propellant using in a monopropellent system. Such as a S A MC one, five, or MP one of free, then it is true that those, those propellants are way less toxic than hydrazine. However, there’s still some risks associated to the fact that you’re using them at high pressure.

And they’re also highly energetic propellents themselves. So there’s a lot of energy stored. And so eventually water, which is kept low pressure and is non-flammable again, non-toxic is way easier to handle. You can potentially feel your propulsion system on one side and just ship it to another side without needing to any specific requirement or your not physically moving any dangerous materials. So it makes everything easier from this point of view 

Hywel: Excellent and yeah. And as you said earlier, um, low pressure is good for everybody. And I think that applies not just to propulsion systems. I think that applies to everything we do. Right. Just to focus then a little bit more on your own work at SteamJet so, you know, we’ve discussed the technology in general to whilst technical terms, but, um, we’ve mentioned your, your own products and service.

So what sort of stage of maturity are you at in SteamJet and what sort of customers and services do you foresee providing value to? 

Marco: Right. So while it Steamjet is quite a young company at the end, but we already have three products under development. Just to mention quicky we have TunaCan thruster, Steam Thruster One, and the attitude control thruster.

So in terms of technology readiness level, we are about TRL7. We, uh, both our TunaCan thruster and Steam Thruster One. And we are pretty excited because we have now two in-orbit demonstrations, which are coming up. One is actually for November 2021.

And so in a few weeks, actually, and the other one is Q1 2022. So this will allow us to test both technologies in space, the TunaCan thruster and Steam Thruster One. They have slightly different audience so that TunaCan thruster that is mainly targeting a small CubeSats. I would say up to three units or six units. The main, let’s say part of the, TunaCan thruster is that it has a very unique shape factor. That’s why we call it TunaCan thruster because it has like a tuna can shape.

So it can be installed in the so-called tuna can volume, which is available in CubeSat deployers at that means that especially if you have a smaller platform such as a 3U, you can just install the propulsion system outside the main CubeSat so that you still have all three units inside for your payload and subsystems.

But you also have propulsion capabilities as basically the propulsion system will be just installed outside and take the TunaCan volume of the deployer. So that is a major benefit for small platforms and the Stream Thruster One is based on our same, uh, steam generation technology. But it’s more for, let’s say, larger CubeSats or a bigger, let’s say still small satellites, but bigger, small satellites.

Basically it can fit different mission needs because we can just extend, customize the water tank to carry as much water as needed. And if we look about our customers, I would say anyone who needs propulsion but maybe to be more specific. Well, definitely satellite manufacturers. Also vertically integrated companies, which are companies, which are eventually creating everything in-house.

They usually the propulsion is still something that is outsourced and also agencies of course, and universities. So the plan is for us to make some features which is pretty simple to use and integrate into the satellite so that everybody can use it. 

Hywel: Best of luck with those IOD missions in, in November and next year. Just a final sort of application area one, the, you mentioned, well, you mentioned in passing, there’s quite a lot of talk recently about sort of using servicing satellites in particularly in LEO by refueling them using, you know, fuel tanks that already in orbit, as far as you can see, I know these applications are emerging, but as far as you can see, would that sort of service be limited to propellents like HPGP or do you see water as a potentially viable option.

Marco: I think that water, it is definitely a valid candidate for that. Perhaps even a better one. Let’s say, you know, if we look about water, then if we think about water, water obviously is inherently safe. As I mentioned earlier is no toxic. It’s very, very easy to handle. And it is also a very abundant here on earth, but also on asteroids and other planets.

And it can be used to produce the good propulsion so it can, it can be a very good propellent for, for, for propulsion, of course. So I see water as a very good option, not just for, in-orbit refuelling , as you mentioned that if we look, let’s say a bit farther, I see that as a very good option for refueling stations, also on asteroids or possible other planets.

Because obviously with water, you can potentially use different technologies. You can separate water into hydrogen and oxygen, and that have a lot of thrust, which could be used to escape gravity, for instance, from other asteroids or other planets. 

Hywel: Right. Brilliant. So just finally, aside from, you know, the examples you’ve just given, I wondered how you saw the market for, you know, electrothermal water-based propulsion technologies evolving in the next three to five years. If we look a little bit beyond the timeline of missions that are already booked for launch. I wonder how you saw things, things changing

Marco: Well, one, I would say common driver that I see in the next years is that, I believe water will become kind of a hot propellant will become more and more used.

And again, this is not just for electrothermal thrusters but used also by different technologies, as I mentioned. As you can have basically have a bi-propellent system with that, or you can use it with different technologies to increase the efficiency.

So, Water I believe will be the propellant of the future. If we specifically take a look at the market for electrothermal water-based propulsion systems, I believe that here, we’re going to see this as the, one of the best options for low earth orbit missions, as I mentioned earlier. The main reason is this. If we look back 10, 20 years, it was pretty difficult to put your CubeSat or small satellite in the orbit that you actually wanted, you were as secondary payload every time. And you were dropped off in the orbit of the primary payload, then eventually you had to make your way to the orbit that you decided.

And that required obviously big orbital changes most of the times. But if we look at the situation now, and if we’re looking also in the next three to five years, there are more and more small satellite launches coming up. There are more and more space stacks, which are actually able now to deliver your satellite exactly where you need it.

So you’re not going to be needing a lot of a big, massive army to change as it was 10 years ago. And this then opens up other possibilities for electrothermal thrusters because at this point that that the delta V budget for your mission is not that big anymore. So electrothermal thrusters can deliver what you need, which again, if I can just repeat quickly with the main use cases, which are station keeping, constellation management, collision avoidance, and deorbiting, those can be easily achieved with the electrothermal thrusters and at this point, electric trusters can actually provide you a budget compromise between performance and efficiency.

Because, as I mentioned earlier, you can have propulsion system, which is less intrusive in your satellite, can make sure that basically you’re operating your payload as, as long as you need. So for, uh, you can reduce basically your payload downtime, but can deliver you basically the performance that you need in order for you to maximize your, uh, your mission and your return of investment.

For this reason, I believe that a electrothermal thruster, especially water-based will be an extremely good options for. They are ready right now, but there will be even better in the next three to five years. 

Hywel: Excellent. Well, I think that’s a great place to wrap up the conversation there, Marco. Thank you very much.

You’ve shared, you know, lots about today about the different applications of water-based propulsion, the technical aspects that make it such a potentially attractive technology for certain applications and missions. And, um, yeah. Look into the use cases in the future as well has been really illuminating. So thank you for sharing all those insights with the Space Industry community today.

Marco: Well, thank you very much. It was my pleasure. And if anyone is interested, please get in touch with us. Visit our websites, steamjet.space, and we will be happy to discuss about our propulsion systems further. Thank you. 

Hywel: Great. Thank you very much. Thank you to all our listeners out there. If you’d like to find out more about the company, there’s also the satsearch supplier hub with the company’s product portfolio with all of the systems that Marco’s mentioned today.

And if you’ve got any specific needs for product quotes, technical documentation, introductions to the business or whatever else is required for a trade study or procurement purposes, mission design, but you’re more than welcome to use our free request system on the site.

Thank you for listening to this episode of the Space Industry by satsearch.

I hope you enjoy today’s story about one of the companies taking us into orbit. We’ll be back soon with more in-depth behind the scenes insights from private space businesses. In the meantime, you can go to satsearch.com for more information on the space industry today, or find us on social media, if you have any questions or comments. Stay up to date, please subscribe to our weekly newsletter and you can also get each podcast on demand on iTunes, Spotify, the Google play store or whichever podcast service you typically use.