 The next talks, actually two talks, will be about, yeah, somehow about saving the world and saving the environment. We will have two different ways of saving them. The first talk is saving the world with space solar power. It's held by Stefan and Anja, and they work as space engineers in Berlin at the Technical University. That talk will be followed by another approach, which is introduced to you by Christoph. He has a PhD in theoretical physics, and his former work was, yeah, he was working with higher loop perturbation theory in supersymmetric young mills theories. And now he is doing airborne wind energy, and that will be his talk also. Please give the three of them a warm applause. As you have heard, today we are trying to save the world with introducing you to two very different approaches of sustainable energy generation. We are the three of us, and we start with Stefan. Yeah, hello everyone, thanks for having us here. And me with our talk about space solar power. Of course we have an outline, and I will start the introduction with showing you this very nice picture. Here you see the Earth at night, also known as the Black Marble. It's a very interesting picture, because it illuminates you or it shows you where people live, or at least where people have electric energy. But there's more information in this picture. When you start comparing these pictures from different years, you also can see how certain regions are developing, and you also see where suddenly it gets dark, where there's been a catastrophe, or a war, or something like that. So the availability of electricity is an indicator for human development. We still have an increasing demand of power. This is also something we can see with that picture. But unfortunately, currently this power demand is largely covered by fossil resources. So yes, we need definitely renewable sustainable energy such as solar power, wind parks, water plants, or even other solutions. The thing with terrestrial energy plants is that they are bound to a certain location on Earth, normally. So you either need to decentralize them, having a lot everywhere, or you need a lot of the transfer infrastructure. The other thing is, especially when thinking about a wind or solar power, that the availability is very varying and is bound to certain conditions, so you need to start the energy. When talking about solar energy, of course, we have the day-night cycle, we have the atmosphere, so we have weather interferences. So why not go into space? There are some selling arguments or some really selling arguments about space solar power. As I already said, it's sustainable because it's sun-powered. Space generally is very, very large. So we can build quite big structures without covering any space, any area on Earth. It is possible to have sunlight on our satellites up there all around the clock, and we don't have an atmosphere, so there is no weather. So space solar power promised to have an unlimited constant and predictable energy source. That's cool, good. In addition, we don't need that much infrastructure to distribute the power on Earth. For example, if you would compare that to a huge solar field, for example, in the Sahara, you would need a lot of cables in order to get the power, for example, to Europe. This comes with some problems. But also, if solving the problem of power transmission, you can get energy to very, very remote locations on Earth, and you also can get the energy there quite quickly. And of course, the intervention in the landscape is, let's call it minimized to a certain way. This concept of space solar power actually isn't that young. There's a patent from Peter Glacier from the 70s who already proposed a method and apparatus for converting solar radiation to electrical power. And here you see, yes, there's a small red spot. I'm not sure whether you can succeed that. You already see that he introduces all the components that are in need. Of course, we need the Earth. We need some large area for solar, for sun collection. And we need some antenna in order to transmit this power. Since the 70s, these concepts were actually discussed all along. Since then, they were discussed. And the state of the art approach for that is called SPS Alpha, which stands for Solar Power Satellites by the mean of arbitrary large phase array. It's the best documented approach in that area, which comes with a phase one study financed by NASA in 2011 and 2012. And they suggest a satellite structure based in the geostationary orbit, which is non-moving, gravity gradient stabilized, that's collecting the sun with a very, very large mirror array and it transmits the power with a microwave beam. It looks like that, for example, or it could look like that. So like wine glass, it could look like a puddle. But there's three main components here. So we have the sun reflector mirrors. This is this very, very large shape. These sun-reflecting mirrors are made of actually solar sail materials or extremely lightweight, although they are so big. The core piece of this installation are the so-called hex modules, which you see here. And they host both the solar array, the solar panels, and the wireless power transmission modules. We come to that later. And then, of course, you also need the structure, which holds everything together. In addition to that, you need some support structures like little robots combining, fixing, exchanging modules, and so on, but they are not further discussed yet. But the NASA approach isn't the only one. There's also an approach from JAXA. This is the Japanese Space Agency. They call their approach Tethered SPS. It's also a gravity-grant stabilized approach, which you can see here. The idea is basically the same, but they don't have the mirrors. Their selling argument is, yeah, our system is so simple, we're sure it will work somehow. But they also say that it's not as efficient as the other approaches. In addition, there are Japanese scientists involved in the SPS Alpha study. But what I think is most interesting, there are also a lot of Japanese approaches driving forward the wireless power transmission. Then there's a quite new approach. This is from the Chinese Space Agency of CAST. And they suggest a multi-rotary joint SPS, which you can see here. So here in this yellow spot over here also is the transmission antenna. But they have their solar arrays bound in this structure, which is approximately 10 kilometers wide. And they adjust the position of their solar panels according to the sun position. So this is how they try to increase the efficiency. There's also a paper from Europe, which is quite old. But I'm not aware of current work on European ground here. If we summarize some of the core parameters of these three documented or still discussed approaches, we come to this nice table. So we are talking about a power transmission between one and two gigawatts. These entire structures have a mass of about 10,000 tons, metric tons, or even more. As the Japanese approach, the antennas are quite big. We come to that later. This comes with a certain energy density. But the total efficiency of these approaches are calculated. And there's also a little bit of a small wish list included. This total energy is in the range of more or less 20%. I put a question mark behind this 25% of the juxtaproach because they even said that they won't be as efficient as the others are. So don't take this number two serious. Maybe we miscalculated it. So yeah, with that, with those three approaches, I would say, problem solved, isn't it? Concepts. But there are some major challenges we want to point out here. At first, this is the attitude and orbit control. So this station is in the geostationary orbit. There are several TV satellites doing the same. And it's working quite well. But these TV satellites are about 1.8 metric tons. And this station we're talking about is about 10,000 tons, or 9 to 25,000 tons. So this is a huge difference. In the geostationary orbit, it's not a big deal to rotate. It's very slow. So we just need to point towards the Earth to hit the designated point on Earth. We want to transfer the energy to. And then we have a phased area antenna. So these little modules you saw before to form a beam which points exactly to the receiving point at the Earth for the energy. Another point is the orbit control. This means the distance from Earth and the speed the station is traveling with. This is another point. This is already for TV satellites. A little bit difficult to do. And now we have, as I said, these 1,000 metric tons station to lift up to the right distance for it to accelerate. There are several forces trying to push us out of the exact orbit. And we would lose the exact spot we want to point at. And there is the lunar gravity, the sun gravity, or solar gravity, and the flattened poles of the Earth. You know, the Earth is not a perfect sphere. It's more imperfect. It's more like a donut. You have flattened points at the poles which disrupt the gravity field. There are solar winds and radiation pressure. Solar wind comes from the sun. These are particles hitting the station and pushing it out of the orbit. And there is radiation pressure, the same. It comes from deep space. The station is huge. So you have a huge surface. This is different from the most TV satellites. So you have to overcome this. Luckily, we have nearly unlimited energy with this station. And we can use electrical thrusters so we don't need any fuel or propellant, maybe a little bit propellant, to bring up to the station. Another point is the power transmission. I think this is the most critical point. As I said, it's in the geostationary orbit. And I have an example here. I chose the MRSPS because the numbers are surround. But most of the concepts are similar, as you saw before. So I think about a one gigawatt output station. And in the picture on the right, on the top, you can see the yellow point is the sending antenna. This would be about 1,000 meter in diameter. So this is about 110 soccer fields placed in space. This antenna is sending microwave beam with 2.45 gigahertz or 5.8 gigahertz. These frequencies are chosen because of the low attenuation or damping in the atmosphere. We want to transfer the most energy. And this beam hits at the receiving antenna or in a literature called the REC antenna. And this REC antenna is going to be about 5,000 meters in diameter. This is 2,750 soccer fields, or about 20 times the Messer-Leipzig area. So you can imagine this is a big deal. If you think about wind parks are ugly, then maybe you think about this area. OK, so you can read more about, if you like, in the references. We have a link to this. Now I guess you wonder about the efficiency of this. Anya talked about already a little bit. I have the subsystems here, including. And I think the most important part is this microwave beam. This is the third position. And this is actually not tested. So this is just a calculated number. This 85% or 9 to 95% is just from the studies we read. Current tests are more in the area of 1% or a few percent. And the most studies are not really certain about the total efficiency. So we have 18 to 24% with these numbers. And from other studies, you have 13% to 25%. So this is most calculated. So now you would wonder if, wouldn't laser work for this? So microwave beam sounds nice. And you have this nice receiving antenna. But a laser would be much smaller, I guess. So yes, basically, you could use laser for this. And it would have a much higher energy density. So you could hit a really smaller spot on the earth to receive the energy. You don't have this five kilometers receiving antenna. But most of the research institutes don't want to talk about lasers. I think it's just a little bit too obvious that you have some. Yeah. OK. OK, so this is the most technical things, I think. For that. And if we talk about these extremely large structures, they have to be built. And since they're also meant to be in the geostationary orbit, where we have a certain radiation force, and we want these components to operate for quite a long time, they are usually quite expensive. And get all the certification for sending them up there is also very expensive. Somehow, the SPS Alpha approach has thought about that. And they are aiming at, although the numbers are varying very much, at a material cost of 250 kilograms, at $250 per kilogram, which still is some billion dollars. And this is also wish list. So they are aiming for this number in their third approach, where they think that they already have the mass production and have the certification. And the engineering and development cost are all covered up already. There's another thing, and this is the launch cost. So we are talking about a structure, which is maybe 10,000 tons large or heavy. Again, the SPS Alpha guys, they hope that they could launch a kilo for $600 into the low earth orbit and continue from the low earth orbit into the geostationary orbit with electrical trusters. Maybe if the BFR rocket will be available for the price of the Falcon 9, maybe. But this also would take some time. Just a reality check right now. For the prices the SpaceX provides on their side the Falcon Heavy, which was erected today. I don't know whether you have heard that. So also the Falcon Heavy has not flown yet. But SpaceX hopes that they could sell the Falcon Heavy for $90 million in order to lift 26 tons into geostationary orbit. But that would be approximately 400 launches for such a structure as the SPS Alpha, and also would cost some tens of billion dollars. In addition to that, there are some other costs, like the initial orbit installation costs, which comes with $11 billion and an operation of 100 million a year. So it's quite expensive. And probably this is also one of the reasons why we don't have space solar power yet. But still, I mean, we have technical problems. This is just money. Maybe it's also solvable, isn't it? Yeah, so you know about the concept. You know about the challenges. And let's assume we can overcome these challenges and someone is funding this big station. I think there are some considerations about if we want to do this at first. So this beam is, you need a precision of about $110,000 of a degree plus or minus to hit the spot at the Earth. So this is like you want to hit a hazelnut over 100 meters from a station flying with three kilometers per second. If there's something goes wrong and the beam is hitting the wrong spot, it's maybe, you know, it's not a good idea. Or if some of the antennas are not really working well, the beam is not forming right and it's straining somewhere. So this is one point. Let's assume everything works well. And the beam is still going through the space and it's going through the atmosphere. And there are some other satellites going. Maybe if for an accident they go through the beam, what happens then? Or if you can't order by accident, an airplane goes through the beam. So it's not even allowed to turn on your phone on the airplane. You can imagine what happens if this beam with 50 watts per square meter hits the airplane. I don't want to sit in this. So then you can't avoid the animals, birds, insect, whatever go through the beam. And yeah, maybe you have the same imagination like I have or we have. And it looks a little bit like this, maybe. Sounds pretty scary, I think. Doesn't it really a little bit sound like an energy weapon? So we thought about, OK, 50 watts per square meter. It's not like a nuclear weapon, but it could harm a lot. There is a high energy density. And you can really fast readjust this beam. So you can point it in one second to the receiving antenna. And the next second, you can just point it to some city. And a second later, you point it just back. It's really fast to change. It's not really defendable. I mean, you can sit in a bunker and try to hide and maybe put your aluminum head on. After all, it's useful. But still, this thing is 24-7 on. So it could hit your bunker all the time. And last here is there's a lot of interest from military institutions. So this is, I think it's a bit scary. And then you would ask, but is it legal to install this kind of application? So basically, yeah, you see, there is already the United Nations Outer Space Treaty. It was first signed from the Russian Federation and the United Kingdom and the United States. And now it's in the United Nations treaties. And most of the other countries signed it, too. It's about all activities of states in the space. What does it say about this case here? And it says there are no nuclear weapons or other weapons of mass destruction allowed in outer space. As always, there's a back door. If you install a military object in outer space with a scientific reason, then it's allowed again. So another point is in this treaty, you must not influence the Earth environment at all. There are no real studies about this, but I have a feeling it's going to influence somehow the environment. But I'm not sure about this. I'm not a lawyer. So finally, all this funding and this technology and the knowledge is necessary. So it's only possible by some few states to build this. And how do you prevent that certain leaders of states or whoever wants to build this misuse this technology? So I can't give you an answer on that, but I think there are some who shouldn't have this. And maybe you can think about this after the talk. And now we have some take-home words for you from Anya. So yes, the concepts are existing. And we don't say that they should not be discussed and that they are entirely evil. It's technologically feasible, at least that's proposed some studies. But I mean, it's still challenging. The technology is not there yet. But the moral questions are still open. So yes, it's still pretty science fiction. And as I said, we don't say we should not do that at all. But at least we should think about it and be critical with these kind or also with other new technologies. But right now, maybe we should think about, is there another solution to this energy problem? Maybe a more realistic, maybe a less problematic one.