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Apr. 4, 2019
Dr. Paul Jaffe is an electronics engineer, researcher, and integration and testing section head at the Naval Center for Space Technology at the U.S. Naval Research Laboratory (NRL). In over 20 years at the NRL, he has worked on dozens of space missions for a range of defense and civilian agency sponsors.
Paul and I discuss power beaming into space and from space.
This episode was recorded on Mar 21, 2019
YuvalBoger (CMO, Wi-Charge, @TheChargeGuy): Good Morning Paul and thanks for joining me today.
Dr. Paul Jaffe: It’s my pleasure. Thank you for having me.
Yuval: So who are you and what do you do?
Paul: I am Paul Jaffe. I work at the United States Naval Research Laboratory. And for about the last 10 years I’ve been working on projects related to solar power satellites, also called space solar and also for power beaming, also called far field wireless power transmission.
Yuval: So at Wi-charge when we talk about long range wireless power, we usually think about distances of a few meters across the room charging your phone, that kind of thing. Your work is really far field, right? I mean how far is far for you guys?
Paul: So the idea for solar power satellites is to deal with power transmission from geosynchronous orbit, which is 36,000 kilometers away, so that’s quite far. We also have worked with and discussed with folks power beaming applications that are even farther than that. NASA has actually done some work on what’s called beamed energy propulsion, where you might be sending energy for hundreds of thousands of kilometers or even farther. So, but most of our work has focused on distances that are least 10 meters or more and pretty much everything between that and geosynchronous orbit.
Yuval: So let’s try to break the applications down. So one application sounds like it’s beaming energy from a geosynchronous satellite down to earth. So is that just to get more energy to areas to a point that maybe you couldn’t get energy otherwise? I mean, why would you want to do that?
Paul: So there’s two major contexts with motivation. So one is if you have, if you look at it broadly from like a grid electricity standpoint, there is a shortcoming to the way we get our energy today even though we’re making great strides and adopting renewable energy, most of our energy still comes from fossil fuels. And for this reason we are looking at solar and in particular, ways to improve the way we use solar. So the idea and the motivation behind using space solar is that you capture the sunlight in space where it’s brighter than anywhere else and you also have access to it affectively continuously, 24/7, depending on the orbit. And this presents not just a clean energy source, but one that could be constant, so reduce your need for storage. And then as you suggested, it’s globally transmissible. So even if you need energy in a place where there’s no existing grid infrastructure, you could get it transmitted to you straight from a satellite. And the sun remains the closest thing we have in our solar system to an infinite source of energy, so it’s attractive from that standpoint. For military applications or remote locations, there is attractiveness in this ability to get energy to a place where it’s a otherwise challenging to get.
Yuval: Have there been public demos or publications about experiments sending energy from a satellite down to earth?
Paul: So to date there has not been a meaningful demonstration of sending power from space to the earth. You could argue that our communication satellites do this everyday, but the amount of power they send is infinitesimal. If you go back to the 1970s which was when the Department of Energy and NASA spent quite a bit of money looking into this concept, there were some pretty fascinating demonstrations that were done. There was one that was done in 1975 in California using one of the antennas of NASA’s Deep Space Network where they beamed about 34 kilowatts of power over a distance of about a mile using radio waves. That remains today the largest amount of power that’s been demonstrated through power beaming. Since then, there have been quite a lot of demonstrations done around the world by the Chinese, the Japanese, Koreans and others using both, and the Canadians as well, using both microwave and also lasers. We’ve seen more recently a lot of really interesting demonstrations with lasers at a variety of wavelength, both at what we would consider to be like Ieye-safer wavelengths and other wavelengths as well.
Yuval: So we spoke about beaming energy from space to earth. Now there must be a need for the other direction as well. Right? Sometimes you want to beam energy from the earth to something in the sky. Are you also dealing with that kind of work?
Paul: Yeah, so there’s many situations where it is impractical or uneconomical to connect two places with a wire. And you may have a platform that is limited in its ability to store energy, whether it’s through a battery or fuel or some other purpose. And the ability to send power without wires would be great for just these kinds of contexts. So if you think about if anyone has flown like a toy hobby drone, you know that you usually have to spend about half an hour or 40 minutes or an hour charging the battery for that and then you can fly it for maybe 10 minutes. So if you would prefer to have a drone that you can position over a given location to give you the ability to provide constant surveillance, you really want that to kind of hang out there indefinitely. So if you could send power to that wirelessly, that would be very powerful.
Yuval: I’ve also seen, and this is more with regards to chi or contact charging, I’ve seen all these cool demos where a drone was charged and then flew and sort of met the smaller drone and passed some of the energy onwards. Is there any work on these kind of a long range power relays as well?
Paul: There are, yeah. Actually there was an instance in Japan where they had a drone that actually had a microwave transmitter on it and they used that to send power down to a sensor. There was also a demonstration some years ago where they had a blimp, a lighter than air craft, that used power beaming to charge up a phone on the ground. So there are definitely instances of doing power transfer. I’m less familiar with the ones that require the contact like you described, but certainly being able to charge something, whether it’s a sensor or a drone or something else from a distance, either upwards from the ground or from a high altitude platform downwards, these are all areas of interest. And it is driven as you suggest by kind of where the energy is needed and where it’s easier to get.
Yuval: So we’ve covered sky to earth and then earth to sky. What are the applications that you see for truly long distance terrestrial earth to earth power transfers.
Paul: So one of the ones that people have been talking about, although there’s not been a really compelling demonstration of it yet, is in the parts of the world that are still developing their infrastructure. So if you have a widely distributed, sparse population, it may not make sense to like set up high voltage transmission lines to get electricity to them. And if they don’t have sufficient resources near them to generate electricity, you have to figure out some way to do the distribution. So I’ve seen some companies proposing long distance power beaming laser links to connect these farther flung villages in places that don’t have infrastructure. So if that can be done effectively, that would certainly be an interesting application, although I suppose that remains to be seen.
Yuval: One of the things that at Wi-charge we care about a lot and are very proud of is the issue of safety. We have devices and technology that’s safe at the consumer level so you can install it at home without any concern. In contrast, as I think about soldiers or military applications, obviously they deal with lots and lots of equipment that’s very unsafe and are highly trained to do it. How much is safety a concern when you think about all of these longterm interspace or from space power beaming?
Paul: Safety is definitely a huge concern. I know when we talk about space solar, one of the first questions that people ask is, is this going to fry birds? And the answer to that question has to be no. Now whether you’re using laser or microwave, there will need to be integrated safety systems and means of controlling the beam. People have looked at these over time. Definitely, this is I think another area where there’s only been limited demonstrations. It is certainly easier to just transmit a bulk amount of power without worrying about the safety if you’re doing it in a controlled circumstance. But for something like this to be deployed, whether it’s for drones or for sending power between points on the ground, it is going to be absolutely critical to have reliable, demonstrable safety systems that are accepted by regulatory bodies around the world and by the users that are going to actually be using these systems. While it’s true that people in the military get trained, usually you want things to be as easy to use as possible so it’s not a distraction to whatever their mission is.
Yuval: You mentioned birds, and I think unfortunately some birds get injured or unfortunately killed with wind turbines a swell. But what do you do with planes? I mean, if you now have a high energy lane coming from the sky and you know, a plane happens to pass through it, that sounds like a dangerous thing.
Paul: Yeah. Well, one way to approach there is one of the pioneers of wireless power transmission, Dick Dickinson, has written about this and he has a collection of words that start with d that describe some of the courses of action you can take. So if you have a power transmission beam and something starts to impinge on it or get in the path of it, you have a few choices. You can divert the beam, perhaps send it to another place where there’s a clear path but no obstacles in the beam. You can dim the beam, just lower the power to a level where it’s not going to present a danger. Oh and I forgot the first d which is detect. You of course have to detect whatever’s going to a possibly enter the area where the beam is. And then you also have the option to douse the beam, to just turn it off. So by paying attention to these different options and aspects of beam safety, you have a lot of flexibility in how you can use it in a system that will actually be safe to use.
Yuval: When people think about long range power beaming, do they usually also want to use the same beam for data communications or is that really secondary?
Paul: That often comes up because the field of optical communications is also expanding and it has a lot of attractiveness because it means you don’t need to have a section of spectrum. People may know or may not that the radio frequency spectrum is really crowded. There’s no sections of unused spectrum waiting for a communications link, particularly if you look 10 gigahertz and below this is the proverbial beach front property of spectrum. So looking at optical coms is very attractive because you don’t need spectrum allocation to use that and if you’re going to be doing power beaming by optical means already and establishing that link, it’s a logical thing to want to add data to that. So certainly the combination of optical power and data together is of great interest.
Yuval: As we get closer to the end of the conversation, I’ve got two more questions for you. One is with regards to the transmitter size, the dish size. I mean I think that the wavelength that you’re sending on, the type of energy that you’re sending depends how much the beam diverges. So when you think about sending power beams to to drones, how big is the the dish or the transmitter on the ground?
Paul: Yeah, this is a classic trade off for power beaming systems. So the advantage of microwave, so call it about two gigahertz to 10 Gigahertz, is that they’re really good at getting through the atmosphere and through clouds and weather. The downside is they do require pretty large antennas sizes in order to have what we call a high beam collection efficiency. And this is usually going to be prohibitive for drones as we have them today. Like in order to capture a lot of energy, you just need big antennas. So this is why a lot of folks are more attracted to the optical region, to laser, to one micron wavelength, and to 1.5 micron wavelengths if you want to have a higher level of eye safety, because just from the diffraction limits, the shorter the wavelength, the smaller the apertures can be. And this is also why some folks advocate for using a laser-based approach for space solar, because you could make the satellites a lot smaller. You wouldn’t need a very large transmission antenna to get a high beam collection efficiency.
Yuval: And we see this in the consumer applications because people want small receivers that they can embed into the device and a small transmitter that doesn’t take up half their room. And that’s one of the reasons that we gravitated towards light-based power transfer in our consumer applications. If you were to look into a crystal ball, how soon would you guess that such a system for really long rage inter-space or from space system would be practical? Is that two years, 10 years, a hundred years? I mean, what’s your best guess?
Paul: It could be sooner than you think. The historical event I like to compare this to sometimes is we ended up going to the moon essentially in less than 10 years from when President Kennedy kind of charged folks to do it and when it actually happened. So clearly if there is the political will, a lot of things can happen very quickly. There’s not always that, so things can often take a while. You can also, I guess a counterexample maybe as you look at something like nuclear fusion that we’ve been working on for a really long time and still haven’t quite got there. So it’s a pretty big range. I think definitely at the consumer level and for the smaller scale situations where we would use power beaming, that’s likely to come pretty soon just because the hardware is smaller and a lot of the challenges are lessons. So I think we’ll see power beaming become more commonplace probably within the next few years.
Yuval: Paul, this has been very informative. Thank you very much. How can people get in touch with you guys and learn more about the work that you’re doing?
Paul: I encourage people to look at the website of the US Naval Research Laboratory, which is www.nrl.navy.mil and I also can be found on Linkedin and yeah, there’s a lot of exciting things happening in this area and I am honored to be on this podcast and talking about this topic.
Yuval: Excellent. Thank you so much for joining me today.