 lasers in space, lightsabers, what do you think about when I say space and airborne laser platforms? Death Star? What else? What do you think about when I say laser based propulsion for space travel? Freaking complicated navigation math with way too many variables. Okay, no seriously. In the next talks we will learn what's really behind those terms. Peter Buschkamp will teach us not only basic physics but he will also teach us about the boundaries of lasers in space. And we will learn about space travel with lasers which absolutely sounds like science fiction but apparently is already a reality. Peter Buschkamp works for the infrared group of the Max Planck Institute for Extraterrestrial Physics where he's building the world's most sensitive instruments for space observation. He's also active in the Munich Freifunk Community where he's building backbones and he was the head of the public astronomical observatory in Bielefeld. Are you sure about the Bielefeld part? Yeah. Please give a warm hand for applause for Peter Buschkamp. All right. Yeah, this is essentially a follow-up talk from last year. I don't know who was there last year. I talked about how to shoot lasers into the sky and use them for astronomical purposes, essentially to correct the atmosphere above us to get clean and undisturbed images here on the ground and not just from space telescopes on satellite platforms. So this year it's lasers in the sky. It's only 30 minutes. Sorry. I will give a brief overview of some topics. What is actually now already flying above our heads? What is what some people think should be flying soon above our heads? And some others are pure speculation. So first we'll talk about laser propulsion. Actually, this is the second reason how this talk came to be because I was talking to Liz and she wanted to do something about interstellar and interplanetary colonization. I said, okay, cool. Maybe we can combine it and then talk about also about photonic propulsion and so on. And then we just skipped it into the next talk to have more time for other stuff in the other talk. After that, we're talking about laser brooms, how to clear up the skies above us with lasers. It's going to be about laser sensing, which is routinely employed every day. If you look up the weather on your smartphones, there's a fair chance that you will be looking at some refined laser data that has been taken either from ground into space or from space to ground. And to finish, we'll talk a bit about laser communication. Of course, this is something a lot of people here in the audience are also interested in. It's the KS Communication Congress after all. And this is something that takes place above our heads, is being built right now and is actually pretty exciting. So first, let's talk about laser propulsion. Laser propulsion is a method of pushing something forward with just light. How does this work? Well, I mean, photons are not just there to illuminate things, which they do a pretty great job in. They also, of course, carry momentum. It's just a tiny bit. It's the energy divided by the speed of light. But still, there is a bit of momentum being transferred from a photon when it hits some surface. To get a rough idea how much this is, if you are in Earth orbit, you get the amount of photons from the sun, which is equivalent to the so-called solar constant, which is 1,361, I guess, if I remember correctly, watt per square meter. This translates, then, if you have a solar sail which you put into Earth orbit and just let the photons from the sun push it forward, which is equivalent to, well, it depends a bit on your orientation of the sail. And if it's a black sail, the photons get absorbed, or they get ideally reflected, if you have so, that means if you have an inelastic collision or an elastic collision for the physicist here in the room. But roughly, you get around 7 micro Newton. That's not much. Of course, this is not much. Well, you can scale up your sail. It's not just 1 square meter. Maybe it's 100 by 100 meters. The point is it may be just a very tiny fraction from each photon, but there are a lot photons, and this is for free. So if you maybe have a mission which you just want to push far away and you have time on your hands, maybe this is something you want to do because this is constant. It's not like a chemical rocket which burns off after some time. You don't have to bring huge amounts of propellant into space for that. This could maybe an option. Is this pure science fiction right now? No, actually not. This is a representation of a test solar sail satellite from the Japanese space agency, which has been launched in 2010. It's called Icarus. And there you get a rough idea of what this actually looks like because if you just, well, this is just a sail with something in the middle. But yeah, this is actually flying right now. They hope to, they last communicated with it in 2014. They hope to communicate in the next year with it again. And what you see here is in the middle, for example, there is the little payload. So some experiments, a little transmitter to communicate back to Earth. And these blue stripes you see around the middle. These are actually solar cells which then produce the electricity for the experiments on board. How big is this thing? It's 14 meters by 14 meters. So this is not much, but it's a nice technical demonstration platform. Of course, if you want to go really into serious propulsion with that, you'd rather look maybe at sails which are 100 meters by 100 meters or even a kilometer. We don't have a real clue yet how to make them, how to bring them into space, what to use actually as the sailing material, how to unfold it properly, but we'll eventually get them. Another thing you could be thinking of is of course not the sun, but of course to shine a big laser on this, maybe a ground-based laser, maybe a space-based laser. There is, of course, project star shot. It's going through the media all over the place right now. This is a very interesting concept which uses a ground-based or maybe a space-based laser. And of course there you have targeted and directed laser light so you don't have the one over R squared problem when you get far away from the sun. This is an option. Another option using lasers in a similar manner is not to just push the sail forward with your laser, but to use the laser actually to transfer energy to your spacecraft. And this is so-called laser-energized, laser-based propulsion. This is nothing like a sail, although this might look like it. I like these 60s and 70s space art. So on the very left you see a laser array here in some orbit around one of the moons of Jupiter. I think it should be Io because of the geyser there. Anyway, so this is sending out a powerful laser beam to one of these reflectors on the spacecraft itself in the front. Again, there's the payload at the very rear. Again, there's the engine. In the middle there's everything else. And so what we do here is we do have propellant on board. But unlike in the chemical rocket where we use the propellant for the energy and also the debris from the propellant, the dust and what comes out after the reaction for the thrust, here we use some external means of energy transfer on a propellant which gets then pushed out of the nozzle of our propulsion system and then pushes the whole thing forward. If you think of a normal jet engine, it's the same. Air is the medium and you use kerosene as the energy to actually drive the engine. Another very interesting thing which is being discussed in the scientific literature right now is the so-called photonic laser thruster. And for some applications, also in military application, there is the great wish for having formation flying satellites which also maybe are flying together like this and then they expand into a nice formation and have a nice long baseline between them and they should get together again for some radar, for some interferometry of radar on the ground to see where you know all this kind of stuff. This can be done with tethers or to just have a rope between those but if you have small satellites, you maybe want to think about something else and this is then what you do so you have a laser between those two vehicles, the mission vehicle and the resource vehicle can also be of comparable size, doesn't matter. The interesting thing is here, you do reuse the photons. It's not just that you shine them on a reflecting surface like on a sail or as we've seen in the other case but you have them actually enter like a laser cavity. There are mirrors to each side of this and so you reuse the photons and this is very efficient in pushing two small masses out of each other and then if you just switch it off they will self-gravitate together again. This is a very nice thing to have formation flights. At least it's proposed. It's not yet demonstrated in space but we'll soon we'll see this. Laser brooms. If you look at the earth from far away or maybe not even so far away within the orbit of our moon around earth and if you exaggerate a bit this is how it looks like. Earth is enshrouded by junk right now. This junk has been put there by us. We have 50 years of space exploration, upper stages of rockets, having collided, tanks being ripped off, satellites who have collided and this makes up a huge amount of space debris as it is called. There are around 30,000 objects of the size of 10 centimeters in space around earth. About 700,000 of the size of one centimeter so some thumb size and over almost 200 millions of them smaller than one millimeter so the ring you see here is the of course the geosynchronous orbit and in low earth orbit you also see this. Is this a problem? Yes, this is a problem. Here you see a nice image from ESA. I think it was in this September 2016. Sentinel-1A is one of the new class earth observation satellites from ESA and actually on the left you see how one of the solar panels looked like before the impact and then on the right you see there was some space debris hitting the satellite and there's about 40 centimeters in diameter damage on one of the solar panels and this roughly corresponds to some space debris junk piece of around five millimeters or even less. We have to think about if now space traffic is increasing and how to get rid of this. One concept is to actually shoot up this from the ground. Of course not in a matter that you now destroy these pieces and just split them up in even smaller pieces. This is not what we want to do. Of course not because we want to reduce the size. How do we reduce the size of these things? Well, if we get them into an orbit that they will just gradually go down in earth atmosphere and just burn up in the earth atmosphere problem solved. This is actually what is being proposed right now and if you take a commercial high power laser around five to ten kilowatt which you can buy and put it on a decent telescope you could move the orbits or the orbital velocity of space debris of around one to ten centimeters by one millimeter per second in only shining your laser at it. Again it's like a solar sail. It's just pushing the stuff with photons. It will have a slightly different orbit. It will then go into earth atmosphere and then just burn up. Of course this has also been proposed from space. Actually this is the same guy who is now in this project Starshot project. Lubin et al and Cosmo et al in 2015. If you want to look up those papers they're quite interesting reads. For example this is a proposed satellite that flies now in deeper space. They did not just think about deflecting space debris but also here targeting asteroids. This is a platform which has big arrays of solar cells to power the onboard lasers and then we just shine this laser at the asteroid for quite some time. It could be here. It could be maybe 10 years if we identify the threat to earth early enough. This is easy. Also by the way if you're interested in this stuff there is a conference about planetary defense conference. Just look it up so you can take part. People are discussing seriously about this. What you do then is not to just push the asteroid with your photons but here asteroids very often contain frozen material, frozen gases. So you supplement those gases and actually while the gas supplements from the asteroid itself it creates a bit of thrust of course. It's just like a little chemical rocket thruster and that gradually pushes things out of the way. This is the so-called D star light mission as it's called. There's also a D star which then proposes to have a dedicated shown on the left a laser platform with even more powerful lasers and then have an array of mirrors somewhere in space to direct this for example to an asteroid. Maybe this just needs half a day each day for five years to be deflected so it will not hit us in 30 years from now and then we turn this mirror in another direction and just to push a bit our spacecraft our solar sail spacecraft like the project star short thingy which we want to push through space. This could be done. It's shown here in detail how you would do this with an asteroid as yeah as said you just supplement the the gases there and use them as thrusters. This is of course not what we do have in space right now. It's being proposed. What we do have in space right now is laser sensing. Laser sensing is so-called LiDAR. It's light detection and ranging like radar and what we do is we do have a transmitter on a spacecraft. It shines down into the atmosphere. It's a pulsed laser just like the laser in last year's talk which we shoot upwards. So we know exactly when we started the pulse and where it is after a given time. So if the pulse travels down into the atmosphere it will of course traverse different parts of the atmosphere and thereby probe different layers maybe high clouds high winds more lower winds or something like that and it will back scatter and we of course know the time the light travels downward and upward and so if you make a graph of the signal intensity versus time we can learn about the different heights in the atmosphere. We cannot just do this with one laser we can maybe do it with two lasers and therefore use different wavelength that means looking at how the one wavelength is absorbed by the atmosphere and then looking at how the other wavelength is absorbed by the atmosphere and then correlate this and then maybe even learn something about the chemical chemical composition of the earth in our line of sight or we do something like Doppler shift measurements and there we can learn about for example how wind is blowing in the atmosphere so our timeline is essentially a set the distance from our spacecraft which then translates to altitude so a short is just means it's near to me it's the high atmosphere and the far away time signal is of course then the ground layer maybe. This is hopefully being launched next year this mission has been on the menu a bit longer it was a bit delayed this is ESA's new satellite for just profiling the wind and you see here an artist's description on the on the right the only actual instrument on this on the satellite will be this wind lighter and it will probe down into the atmosphere and give you exact measurements how the wind is blowing so this will then use this Doppler method where you send out a signal and just measure the the the shift in frequency from the return signal which is then influenced by if you have maybe hit something that is receding from you or coming towards you of course you have to calculate out the satellite motions itself and earth motion and blah blah blah and whatnot so this is hugely complicated and if you want to have a look at the instrument it's looking like this and this is another lesson we had this in in the talk before space technology is really really hard i'm not saying it's not possible it is possible it's it's it is being built but it's not just you don't just fumble something together and who has ever put i mean we have heard by andres talk about the the microscopes and how to build your own microscopes for for maybe doing laser microscopes to to enhance the resolution and how to build them on a on a on a on a typical optical lab bench here you do essentially the same but also you have to launch this thing and actually this is the most critical part because this will be shaken like hell and whoever has adjusted a laser ready resonator alone um mostly is not a fan of yeah just coming to my lab and kick my table a couple of times and let's see if it's still working this will be happening during launch and so you have to really make it perfect and test it and test it and test it and test it and test it again and when you think you have enough done enough testing you test some more um another thing of course you can make distance measurements this is used on the uh on the european um autonomous autonomous transfer vehicle the atv uh that docked to the international space station um this is how it looks like and there's a little lighter interface on the side and it sees the international space station then in false colors which mean this green stuff is very near near to me there's it's it's the flange where i have to dock and the red part is then is at the very back this is the trust structure of the international space station and the widest thing in the middle is one of the so-use capsules that is right now docking on the international space station so this is being used routinely now in space um and as said you can maybe see it in your uh weather app on your smartphone every day i'm not talking about this one this will be in the later actually maybe in the next talk you can also do gravitational waves and there you come have to communicate between different satellites not in terms of just exchanging data but you're actually flying a michelson interferometer in space and measure the relative distances between uh three satellites separated by thousands of kilometers in space to detect gravitational waves we'll learn about this in the next talk so in the remaining time let me briefly give you an overview of how our communication is actually affected by lasers in sky this is mostly developing right now so the first satellites who employ this on commercial platforms are already in space the next will be launched next year and the years after that um why do we want to do this laser communication i mean can't we just do the the the normal k a or q band uh radio frequencies which we are using i mean satellite tv it's it's working fine um the thing is of course with laser communications you do have a much higher bandwidth and that means you have several tens of gigabits per second port per channel it's very very efficient and this is actually interesting for space then again because you've learned in the previous talks that each kilogram you want to put into space costs you a real a lot of euros and so if you look at radio frequency you get about 0.5 megabits per second per watt so electrical consumption and kilogram if you're using it as a if you're looking at a laser communication system it's more in the range of 5 megabits per watt and kilogram um the communication terminals are smaller and they are um and if you for example have a satellite pointing just down on earth with its radio footprint the radio footprint is really really large if you do laser communications you can get down your even with a small telescope of about 20 centimeter size in diameter on your on your spacecraft you can get down your footprint um on the earth to about six kilometers so this is a very very tiny spot so if you're the only one who sits in the middle of the desert observing the signal so nobody is going to be eavesdropping on you also there are some ideas how to do this interferometrically and then if you actually were to intercept the signal you would destroy the interference pattern and this is not going to work out this is how it roughly looks like what we want to do so this is what we have right now it's the radio link between a ground station also called ground segment in in space lingo and this is the satellite bus up there yeah it's called satellite bus don't be uh it's just called like that um and it has the payload and on top so if you ever read payload and satellite bus satellite bus is the satellite and payload is the stuff you put on them to do the actual thing you want to do um this is for example in geostatic stationary orbit for satellite tv but there are other things also flying around in geostationary orbit or in low earth orbit and in low earth orbit you see that the orbit just vanishes behind the horizon there so if you have maybe a satellite that looks at um earth like probing the wind like we've seen before it is only visible from your ground segment from your ground station for a brief period of time who has done uh sdr radio on the NOAA satellites anyone oh yeah okay so those people do know what i'm talking about so you have about 10 20 minutes if you have a real nice position where you can see the satellite where you can record the weather image that gets transmitted from the but after then nothing so it would be nice for example to have an optical link high data rates as said to one of the geostationary satellites and then have them maybe over a hub then talk to your low earth orbit maybe then over other hubs when it gets out of the reach of the one geostationary satellite and so on so this could be really interesting again yes maybe radio also but as said high data rates um and all the uh uh plazas that come with the lasers um so for the technically inclined uh in this audience it's uh how do we communicate uh we have three different types of modulation this is the on off keying the oh okay uh that just means you to switch your laser on and off morseing it's what you have in your fiber line card maybe at home uh it's what you do from ground to space you have pulse position modulation this is what you have in your tv remote um and actually jump jump jump jump perfect so this is what you do from uh this is what you do from ground to space uh because this is uh very very immune to um disturbances by the atmosphere you still have to look through the atmosphere um if you have nothing in your line of side you can of course go to nicer modulation uh principles like binary phase shift keying uh or or higher um modulation schemes but this means then if you modulate the the phase that you do not want to have a medium in between which is disturbing your your phase and this is the atmosphere so this is only used for space to space links this is how a laser communications terminal looks like um you have the laser and everything uh down there somewhere at the bottom you have two um mirrors reflecting it then out of the uh central aperture at the very front it's about 13 centimeters usually and this is how it looks inside so the laser is at the very bottom there and then you have diverse mirrors in there to get actually the laser out um as I said different uh modulation schemes are being used different frequencies are being used typically if you want to reuse telecommunication equipment uh of the shelf you use 1550 nanometers you get this in the normal telecommunications industry if you uh want to for example imply a neodymiac laser the infrared part you go for the um 1064 nanometer um and people are working together uh in space so for example here it's the lunar laser communication demonstrator from from NASA talking to Issa's ground station in Tenerife and this is how it then looks like from space actually there's no video online but yeah um if you look at the communications unit there is the optical module this is the just the laser but of course internally you need controller electronics you need a modem um but the nice thing as said is if you um if you do this standardized you don't have this complicated setup yet for example seen in the experiment for the wind measurements with the LiDAR looking down here you just take commercial off-the-shelf units from telecommunication industry slap it together and you're good to go um you can also do this for deep space communication this was a mission proposed by NASA said it was canceled to do this up to Mars you can do this from satellite to satellite this has been done with the terrassa satellite from Issa and the NASA um and fire satellite and right now the Europeans building a data relay system around earth it's called the EDRS the European data relay system um it's hosted on a commercial satellite from Eutelsat and a dedicated satellite that will be launched later and you see here the laser links for example in red between the satellites or in green to the international space station and then they have also radio frequency links down the next step um is already in the works it will be the so-called globe net so position various satellites on a geostationary orbit around earth having intercommunication from satellite to satellite on laser based and of course the next step will be this one and my personal interest would be then to have this one is there anything else yes i know that in the abstract i did mention weird stuff communication laser based from submerged submarines to satellites in space yes this is being done um downside is you will not find any open access publications which you can show which can be streamed into the internet just google for it you will find really nice sets of information there it is that for certain frequencies in the blue and in the green actually the ocean is pretty transparent to these laser wavelength and so you don't need some uh some something floating on the surface of the ocean and then maybe have a fiber line down to your submarine and then no no no no you just shine the laser at the ocean and you do this the other way around too um just look it up it's pretty interesting some of the stuff has been declassified well actually this is the only source which i also have because i don't work in this kind of stuff and if i did i couldn't tell you um uh yeah so there's a lot of stuff going on in space above our heads right now and in the near future uh just watch out with your spaceship if you do the asteroids um we don't want to see that okay next talk thank you thank you very much for this amazing talk uh we perhaps have time for one short question a really short question so there's somebody already on the microscope he's waving uh do you get a short question number two yeah try okay it's just about how far the weather affects communication we had a company that had two locations and tried to do laser communication and it turned out fog is evil snow is even more evil so uh how is it from space to earth yeah um uh you do have these problems of course too um you do have the only thing you can do is maybe use modulation which is more immune to it otherwise if you have really dense fog you you're at some point just out and therefore uh the the ground link segments um are often still as you've seen of for example in the globe net and the european data relay system the ground links are all always at least back up with radio links so it's also getting a little too loud here to answer questions really so if you have any more questions just come here to the front and ask peter directly and now we want to end with a last big round of applause to thank our speaker peter