Explore the developments and use cases for hydrogen-powered aircrafts with rocket scientist, aerospace engineer, professor, and CEO and founder of Hydroplane, Dr. Anita Sengupta, interviewed by editor of "97 Things Every Programmer Should Know," Kevlin Henney.
Kevlin Henney: Good afternoon, good morning, good evening, wherever you are, and whenever you are, reading this. My name is Kevlin Henney. I'm here at GOTO Copenhagen. Of particular relevance is timing-wise, we're actually recording this about halfway through the United Nations Climate Change Talks, COP 26.
I'm joined by Anita Sengupta, whose CV is ridiculously long, and covers, quite literally, multiple worlds. Possibly, the most stable and realistic thing we can talk about is that she is a professor of aeronautical engineering at the University of Southern California.
But of particular interest here, and for anybody who has an interest in technology and climate, Anita has just spoken about “The Future of Flight,” what it means from a broader point of view, in terms of climate change or our effect on the environment, but in particular, can we do better, is the short question.
Anita Sengupta: Hello, nice to see you. Thank you.
Hydroplane: hydrogen-powered flight
Kevlin Henney: Let's start at the end. Hydroplane, your current work, a startup, is about electric-powered flight. Most people, who hear that, will go, "The batteries are going to be too heavy." Some people might have a Tesla, and they'll go, "Oh, yeah, it's beautiful. It's silent. But then there's the range issue and the battery size issue.” When people think of an aircraft what comes to mind is big batteries. This is not the future. What is?
Anita Sengupta: I did spend about two years focused on electric vertical takeoff and landing aircraft, which are intended to be short-range, and powered by batteries. That's where I saw the true challenge of being able to implement energy storage onto aircraft. Batteries don't work if you want to have anything which has a range of more than one hour.
Kevlin Henney: Yeah, which is probably quite a lot of flight.
Anita Sengupta: Yes. In Southern California, you would be challenged to fly anywhere and land within an hour, just because it's such a busy airspace.
Kevlin Henney: So that kind of time range, that gives us drones, basically. We already know that one. I wouldn't say that's our comfort zone, but you say that to somebody, they go, "Oh, okay, we do have electric flight," but then it's that short charge thing.
How do we get further? When people look at flight, it is incredibly energy-intensive, the energy densities required, we have the dreams of the past. I still have the books from when I was a kid, where we'll have nuclear airplanes. Yeah, might not be such a hot idea.
How are we going to do this? Also, growing up, there was Solar Challenger, this huge glider-like plane with massive solar panels, but light as a feather, and clearly, utterly impractical, it could not scale. How are we going to do this and get beyond drone time?
Anita Sengupta: The solution, I believe, is hydrogen fuel cells. You would actually have onboard fuel, which is your hydrogen, but going through an electrochemical reaction to produce electricity to an electric motor, with hydrogen fuel cells.
Kevlin Henney: And hydrogen fuel cells have a really nice, long history, don't they? They keep cropping up. Everybody keeps talking about the hydrogen economy. But they have a really good engineering history in spaceflight.
Anita Sengupta: Yes, they were used onboard the Space Shuttle Program, as the energy storage means, because of their efficiency per unit mass.
Kevlin Henney: We've got that. You've got hydrogen, you've got oxygen, and you're going to get some nice energy from that.
Anita Sengupta: And I think, from a regulatory perspective, it's already used ubiquitously in the United States with hydrogen fuel cell-powered cars, for example. So, you can design a system which is safe for on-road use, including all the different off-nominal scenarios you might find, that have stored compressed hydrogen on board.
Regulations and design
Kevlin Henney: That's going to be one of the obstacles, isn't it? The safety, the regulations, and so on. You've got a start-up that's looking into this space. I guess you're tackling two things, really, aren't you? You're tackling the technology, the feasibility, what I guess anybody who's in technology would call the fun stuff. It's like, "Hey, this sounds like a really cool problem to solve." The engineering challenges, the joy of seeing something work. And then, there's regulation, which, clearly, there's a necessity for it, but that's not going to be fun and that's a very different world as well. So, do road vehicles that are hydrogen-based clear the way for you a little bit?
Anita Sengupta: I mean, it certainly helps, in the sense that there is government regulation in place for how to design a system from a reliability perspective for ground-based transport, how to design for different load cases, how to do fueling operations, for example. But for aviation, of course, it's always different, because you're not on the road. You're in the air.
So, with a car, you can pull off to the side, but with an aircraft, obviously, you can't do that. It does change things like reliability requirements, durability requirements, and that’s an engineering implementation challenge which you always have to deal with. I think the bigger issue, though, is, if a regulatory agency isn't familiar with the technology, you have to get the agency familiar. That means the FAA, and the European equivalent, have to become more familiar with the technology so that they can have their own regulatory structure that goes around it. So, there's that element of risk. But that also, once again, it's an engineering challenge which can be solved. And it shouldn't stop you from doing what is required to decarbonize aviation.
Kevlin Henney: I think the familiarity is a really interesting point because people like the FAA, have got decades of experience in a very particular field, conventional flight, and accompanied the field as that evolved and here's something new. And of course, there will be some point in the future where they will have the same, or equivalent, comparable expertise, in say, hydrogen-based flight.
You're generating electricity in-flight and during your talk, you showed us some images of a light aircraft. I'm not a pilot. I don't plane spot. I couldn't sit there and go, "Oh, that's what's different." To me, that looked like a very conventional light aircraft. It was more like we have a method of electric propulsion, fueled by hydrogen fuel cells, but the craft itself looked very conventional, very acceptable and unsurprising. It was only when you pointed at pictures and said, "Right, that one's hydrogen and the rest are conventional," that people would know. So, how much of that is just a byproduct of design? Or how much of that is intention?
Anita Sengupta: I would say it's mainly intention and the reason is why would you reinvent the wheel if you don't have to? If you have a perfectly good aircraft from an aerodynamic efficiency perspective, why come up with a new one? And when you're trying to develop a new technology, you have to raise a certain amount of capital, so we want to expend all of our capital into the new intellectual property, into the difficult engineering challenge, which is the power plant, and we can reutilize and retrofit existing aircraft.
Kevlin Henney: I presume that would also be useful from the pilot's point of view. If you got a flying license, then it still handles the same.
Anita Sengupta: Exactly. Basically, you just have to be a private pilot to be able to fly these types of aircraft. And then for commercial purposes, you would just have to be a commercial pilot to fly these aircraft for those purposes. I think it's a really good point, with regards to coming up with new platforms, because there's another new sector of advanced air mobility, which is eVTOL, electric vertical takeoff and landing. Those are brand-new aircraft, different designs, different flying skills required. In some cases, no one's ever done it before, so that's a huge challenge in and of itself, which adds additional risk to getting those types of technologies implemented. So, this one is pretty easy to implement, as long as you can show that you have the reliability for the power plant, as necessary to meet the requirements from the regulatory agency.
Kevlin Henney: So, that's quite nice in that sense of we're going to innovate along this axis, and in this space. Everything else stays more or less constant, a little more familiar, which I guess is good from an investment, but also from a practical point of view. People aren't thinking, "Oh, we're going to need all this kind of new infrastructure, retraining and all the rest of it." So, what kind of range are you getting on that at the moment?
Anita Sengupta: We're designing for 1,000 kilometers of range. That could meet a whole variety of use cases for small aircraft, whether that's humanitarian aid, disaster relief, any type of governmental use case, cargo, island transport, offshore transport. And also, if you have a shorter range, you can have multiple sorties or multiple missions before you have to refuel.
Kevlin Henney: And that will actually get you somewhere in California, distance-wise as well. So, how's that compared to the range of a regular light aircraft?
Anita Sengupta: It's the same.
Kevlin Henney: That's really cool.
Anita Sengupta: That was what we designed it for, to be compatible, because those aircraft already have a set of missions that utilize that endurance, and so we're achieving the same thing.
Kevlin Henney: So from a sales pitch point of view, it's, like, "See this? We're doing the same. But it's greener. There's less impact. We're producing water rather than CO2," and that's a very different story.
Anita Sengupta: Yes.
Use cases for hydrogen-powered aircrafts
Kevlin Henney: You mentioned a number of different use cases, and I think that's quite an interesting one because flight means different things to different people. For some people, it means holidays. For other people, they just say, "Oh, this is cargo. This is," whatever.
You're slicing through the uses and saying, "Here's where the strength of this lies." You're not trying to take on all of aviation at once. You're going for particular sectors. Again, it sounds intentional, but is it?
Anita Sengupta: It is. And of course, I am a general aviation pilot. I also do search and rescue flying, mission operations as well, so it's something I'm quite familiar with. And I also wanted to make it more accessible. People don't realize that general aviation actually is very accessible. Most general aviation pilots are not incredibly wealthy people. They're just regular people who are interested in flying, and there is a movement afoot to provide a more of an air taxi type of scenario, which is the eVTOL use case. Instead of having a brand new aircraft, where you have to wait ten years to get it, you can actually fly these as an air taxi, and complete that use case. And I was also interested in having a carbon emission-free platform for humanitarian aid, disaster relief operations, to make it accessible to people who really need it.
Kevlin Henney: I think you're right. A friend of mine has just started learning to fly. Another friend of mine who's a week or two weeks older than me, learned flying when he was 17 or 18. I remember because most people when they get carded, they pull out their driving license. But Orhan's thing was, we get stopped in a pub in London, he'd pull out his flying license, which was so cool. And everybody else was actually younger than him in the group. And so they thought, "Oh, well, you've got a flying license. You guys must all be old." That was a really good trick. So there is an accessibility that I think is underestimated there.
Anita Sengupta: And there are lots of governmental use cases. We were actually funded initially by Agility Prime, which is part of the Air Force. And so they see electric flight as something in the future, and they know that in order to achieve the range requirements that they would like to see for their humanitarian aid, disaster relief operations, they have to shift over to fuel cells.
Kevlin Henney: We're talking air, but am I using the right metaphor here by saying there's a groundswell right across the board? That's a lot of different people who are showing real interest, and it seems very feasible.
There's something else that I think is also interesting. You talked about the range, and there was a comment that you made, which I don't think I'd ever thought about. Although, in terms of routing, I've seen it come up before in the past. Often, when we think in terms of the environmental costs of flight, we tend to think of long-haul international flights. And you made a point that that's actually not where the weight of the environmental damage has been caused.
Anita Sengupta: It actually comes from regional flights, which are shorter range. So if you were cruising at, let's say 600 kilometers per hour, for a regional flight, going from city to city, that's where the bulk of the CO2 output comes from. And if you look at the power profile for an aircraft, you use your most power during climb. So if you're on a short mission, short cruise, you're always using up a lot of power because of that.
If you could address that market, decarbonize that market, by going with platforms like twin turboprops, for example, which is much more feasible, then you can actually reduce the CO2 output for the commercial aviation transport sector as a whole.
Kevlin Henney: So, it’s the takeoff and landing aspect, it's not the distance in the middle. That reminds me of the old bulbs, where the greatest costs were turning them on and off. That's when you get a spike, in terms of the usage, and it seems to be a similar thing. It's the upping and downing rather than the along-ing, if I'm allowed to make those verbs, that really causes the damage there.
Anita Sengupta: Yeah, you're cruising at a lower than 100% power level. I mean, you can choose to cruise at 100%, but most people don't. So that's why you can actually reduce your total CO2 output by having a more efficient power plant for these shorter-range use cases.
Kevlin Henney: Just thinking in terms from a European perspective, that kind of range, that's a good market, and even within parts of the regional U.S.
Anita Sengupta: There's another aspect to this too, which is, if you look at developing countries around the world, they oftentimes use much older aircraft, which means that they're less energy efficient. So they also have a larger bulk of the CO2 output because they're using less fuel-efficient aircraft to begin with. If you can bring in these aircraft to these markets, to support their regional use case, you can also have a big impact on reducing CO2. But of course, the United States probably still has the biggest one.
Kevlin Henney: For a developing market, the possibility that they could get into something that is cheap and clean from the ground level so that their old craft become the hydrogen craft, rather than a current generation, that's quite attractive. It allows them to grow a market, but without trampling all over the environment in that way.
Anita Sengupta: And the other synergy that exists here, too, is that in order to have green hydrogen, you have to have renewable energy production, so it's kind of a forcing function for different nations around the world to increase their renewable energy production, which can then go into the production of hydrogen for their aviation sector or their transport sector.
Green versus gray
Kevlin Henney: You raised a really interesting point there. Qualifying the color of hydrogen, so to speak, which is odorless and transparent, and all of the rest of it. There is the terminology, there's green versus gray. That's an interesting one, because we can't just say "Oh, we're using hydrogen, therefore there is no environmental impact." If I'm just in the general market for some hydrogen, which I can't imagine that I am at this point, but where would I likely be getting it from now?
Anita Sengupta: It would be gray hydrogen, which means that it's produced via a reforming process, which has CO2 as an output of that process. That's the reason why we really want to shift over to hydrogen which is produced from electrolysis, where the electricity for the electrolyzer comes from a renewable source, like wind or solar.
Kevlin Henney: And looking to countries that are going to grow into this, that's very attractive as well. That means they are more likely to be able to have a self-contained carbon-free economy from that point of view. Whereas currently, the supply chains and how kerosene and so on are distributed, clearly, are very anchored in certain countries and certain companies. So, the high degree of independence from that point of view.
Anita Sengupta: And there's always CO2 costs associated with the transport of fuel. So, if you can make your fuel on the site where you're going to use it, that is the way to really minimize your carbon footprint altogether.
Kevlin Henney: That's a huge implication here. We started with the idea of "Yeah, here's a light aircraft," but actually, the implications are quite staggering. So, let's stagger out, that's the air. Talk about land for a moment, because you were previously involved in the Hyperloop, and that is one area. Clearly, there are cars and other forms of ground transport.
Not everybody is going to take to the air to get from A to B. And in fact, some of the distances we're talking about, if we've got the means to do it by land, then sometimes we're going to favor that. So, where do you see electricity in this, but also some of the technologies that are more pushing beyond the conventional? I mean, we're very familiar with Teslas and hybrids, but Hyperloop is clearly something different. What else is there in the pipeline, or the loop line?
Anita Sengupta: There's definitely a movement afoot to decarbonize and electrify ground-based transport. There is a reliance on batteries, which you can use, but batteries have a pretty big carbon output as well, because of the rare mineral mining that goes into the batteries. And they have to be replaced and refurbished.
So it's not like it has zero carbon output. And they're also sensitive to weight. When you go to larger vehicles, like fleet vehicles, such as buses and trucks, they actually also will likely require hydrogen fuel cells for their power plant to be electric. There are synergies between the aviation use case and the large fleet vehicle use case, not to mention marine.
Other means of hydrogen-powered transport
Kevlin Henney: Let's take to water because there's an interesting picture emerging here. There are a lot of synergies that improving in one sector kind of lightens the load. It improves acceptability if nothing else, but certainly, actually smooths the technology path, and the idea of there is a hydrogen economy.
Marine is really interesting, because that's a bit of a blind spot. Most of the goods that we have, probably pretty much everything that I'm wearing and holding and carrying, and all the rest of it, ultimately, came to me by sea, and there's a huge cost to that.
Clearly, we can point to airplanes. They are obvious. But most of our goods, when we move away from the people to our goods, which form the basis, I guess, of many economies, there's a huge impact there, isn't there? Travel by ocean, I don't know how wasteful it is. I just know it is quite wasteful by comparison. So, what can be happening there? Is that just a hydrogen thing? Are there other things that we can be doing there? Where is that going to go?
Anita Sengupta: Hydrogen fuel cell power plant also works for boats, whether it is smaller boats or large container ships, so there's great synergy. And there's been a lot of. I actually showed it in the talk, there's been a lot of work where governments in the EU have taken a look at where do you see synergies? And you see synergies in terms of the amount of payload you're trying to push, and the amount of power which is required to push that payload between aviation and marine and large vehicles.
So it is an important thing to focus on because I think it's popular to focus on going after people who are flying on international flights, but that isn't the source of the CO2 problem that we're facing. Actually, from a transport perspective, marine is a big one, and we still have to provide goods and services to people. That can never go away. So, it absolutely is a way to decarbonize the marine sector.
Kevlin Henney: Here we are in a pandemic, and although a number of things about our everyday life have changed and gone through various fault lines of their own, not least of which is the number of flights that people are taking, actually, people are still being supplied with goods. And those goods are still being moved around the planet. That has not gone away.
Anita Sengupta: Exactly. And from a go-to-market strategy too, getting it into a use case which would be faster to get the regulation approved for, such as marine, will only help, because then it paves the way, economies of scale, for other sectors such as aviation.
Kevlin Henney: Let's talk a little bit about just nudging into space. I remember I have a book at home, one of those books I read as a kid. Here we are in 2021 and not only was I told about moon bases, I was promised hypersonic craft in this book. Concorde is just a stepping stone. We're going to be hypersonic within decades. We're going to be able to get from here to Australia, rather than spending 24 hours traveling, it's just going to be a few hours. And it's just a nudge briefly out of the atmosphere and back in again. So, where are we with that, and how does that fit with decarbonization?
Anita Sengupta: Well, I will say that it doesn't fit with decarbonization, but I think that suborbital vehicles are being developed for the purpose of space tourism, where you get to come up really high, you see a view of the curvature of the earth, and you come back down again. That could be used for something more than space tourism. It could be used for rapid transport. I don't know that that's necessarily a good thing, though, because of the carbon footprint associated with it. I think that's where regulation has to come in.
Kevlin Henney: It's one of those areas. It's kind of like, I was promised jetpacks and all the rest of it, and I think, how does that fit in? That's a little bit outside what we're talking about, but in terms of everything that we're currently doing in the world, in terms of our transport and our movement of goods, that's all fair game for the kind of decarbonization you're talking about.
In terms of transforming economies, but importantly, transforming flight, what kind of timeframes are we looking at? Obviously, I'm asking you to look into a crystal ball here. The danger is, we've been promised various things at various points. I think I read another article about how close fusion is, just last week, and again, that book that I've got told me it was before the end of the 20th century, and there's that. This feels very practical, what you're describing. I don't expect the industry to change overnight, but what kind of timeframes are we looking at here?
Anita Sengupta: I would say, from an automotive perspective, we already have hydrogen fuel cell-powered cars driving around on the road in the United States. And many gas stations actually have a compressed hydrogen supply, so you can actually fuel your car. It's probably not everywhere in the world, but certainly in the United States, and probably in Germany.
In terms of aircraft, I would say for small aircraft, it depends upon the weight of the aircraft. We'll see that within the next five years, obviously, with what we're doing, and Hydroplane. When it comes to a larger aircraft, it's a little bit more of a challenge, both from a regulatory perspective and because typically if you're carrying more passengers, you're going to go on a longer haul, you have to climb to a higher altitude, so that likely requires a change in the PEM fuel cell technology, with a different type of electrolyte, just so they can operate at a higher temperature, as is necessary for higher compressor powers. And so that is probably more like the 10 to 15-year timeframe out. And then for jet aircraft, that's probably more the 15 to 20-year timeframe out.
Kevlin Henney: I'm going to come back to almost where we started, and then a couple of other closing thoughts. Airships, and I know this isn't necessarily your space. So, again, what I was promised in these books was helium airships. But they were a little bit fuzzy about the power. They didn't mention that because they were just drawing pretty pictures, and this was for children.
This is the thing that we keep seeing. Roughly once a decade, somebody predicts the comeback of the airship. Could hydrogen fuel cells, could this direction actually be one that could potentially bring them back, say for haulage, if not passenger flight, at least cargo?
Anita Sengupta: I'm not sure. I don't know too much about airships. And certainly, that's maybe a slightly different use case. But I think the efficiencies of windborne flight, generating an aerodynamic lift from a wing, is probably the most efficient from an energy perspective. That's probably why I would say, go for that, just because at the end of the day, when you're trying to be more energy-efficient, you want everything about your system design to be the most efficient possible. I think that's where having wings allows you to achieve that, plus renewable energy to provide hydrogen through an electrochemical reaction with the fuel cell, is kind of the holy grail solution to all that.
Going into space
Kevlin Henney: Speaking of winged flight, let's move to another planet. You were involved in Mars Curiosity, which is, I have to say, my favorite probe. I still have a favorite space station. Sorry, ISS, it's Mir.
And Curiosity is just such a classic machine. You worked on that. Entry, descent, and landing sequence was part of what you did. And then we saw this year was such a good year for Mars. United Arab Emirates to Mars, China to Mars, and NASA came back with, as it were, the offspring of Curiosity, Perseverance, absolutely awesome.
But it took with it Ingenuity, which, as a programmer, I'm quite excited, because I know that like Perseverance, Curiosity was programmed in C, but this was programmed in C++, and it meant that Linux arrived on Mars, and that's just a small side note there. That was a proof of concept that actually having a little helicopter on Mars, whose atmosphere is ridiculously almost nothing, and it worked, and it seemed to work incredibly successfully. Is that something that you're thinking about, when looking to the solar system, there are a few atmospheres around. Does this open something up, or is that just a dead end, a proof of concept that was nice, but that was all we were going to ever do?
Anita Sengupta: I think it actually gets around a lot of the hazards of when you go to a planetary body where you don't have a lot of knowledge of what the surface terrain is like. If you're flying above it, you don't have to worry about driving over different rocks. You don't have to worry about the complexity associated with that. And you're able to travel longer distances and collect more scientific information, so I think it does lend itself to a variety of different scientific reconnaissance use cases. And there's Dragonfly, which is the mission which is coming up, which is an octocopter the size of a small car, which is going to be flying around on Titan.
Kevlin Henney: Yeah. Titan is ridiculously cold, but it's got an atmosphere about as thick as Earth's.
Anita Sengupta: Yes.
Kevlin Henney: And it's also just above lunar gravity, about a fifth of Earth's gravity. So, you've got the atmospheric density, and you've got very little gravity. You can carry a car around. But then there is a slightly different kind of thermodynamic element there. But that could allow you to stay in flight over quite some distance.
Anita Sengupta: Yes. And you can also have an airplane on Mars as well, which has been proposed in the past but hasn't been done yet. I think that would probably be the best way to cover large distances at the most energy-efficient system design possible.
Kevlin Henney: Speaking of large distances, let's go really large, warp drive. No, I'm not going to ask you about the decarbonization of warp travel. I do know that you're interested in Star Trek. As somebody who has an interest in that myself, they're not really into the whole flight thing except for spaceflight. But I have to ask you a couple of favorite questions. Do you have a favorite series? And do you have a favorite captain?
Kevlin Henney: Yeah, okay. Normally, if you led with TNG, then it was going to be Picard, but if you'd led with Picard, it might not have been TNG.
Kevlin Henney: I think the original Star Trek were on as reruns when I was growing up, plus they had the cartoon. Then they came out with the films and they had some interesting stuff in the original films. I have to say TNG partly cemented the deal, but I guess to me, doesn't have quite the same meaning. I'm a little more flighty with this, but I will say that Picard, definitely.
Okay, so, we're going to bring this to a close now. Thank you very much for your attention. I hope that's been of interest. There's so much here in terms of possibilities, and I think it really will be a case of “Watch the skies”! Thank you very much.