Launching solar power from space

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Since the dawn of the space era, satellites have been solar powered. Now, the Navy is testing the revolutionary possibility that satellites could somehow beam solar energy down from orbit. For details on a newly launched experiment, Federal Drive with Tom Temin spoke to electronics engineer and principal investigator with the Naval Research Laboratory, Paul Jaffe.

Interview transcript:

Tom Temin: Mr. Jaffe, good to have you on.

Paul Jaffe: Thanks for the opportunity.

Tom Temin: Well tell us what you’re doing here. I saw a release and there’s a satellite that is very tiny, it’s a couple of maybe a foot or 16 inches across square, with a solar panel that’s now flying around. What are you doing here?

Paul Jaffe: So as you know, we have a big challenge with energy and certainly with its effects on the environment. Everything that we do in our society requires energy, whether it’s for economic purposes, civilian purposes or for military purposes. So there’s a big focus on making sure that we have a clean, constant reliable source of energy. Now what we are investigating is the possibility of collecting sunlight in space where it is brighter than anywhere on Earth, and where it shines uninterrupted. There is no nighttime, depending on the orbit that you select. And of course, there’s no clouds or rain. So this means that if we can take advantage of this tremendous source, and then send it to where we needed on Earth, it would be very powerful.

Tom Temin: And you’re not talking about dropping wires down 250 miles either, are we?

Paul Jaffe: Indeed not. The orbits that satellites exist in are pretty big in range. So you have like something like the space station that’s only a few hundred kilometers up. And then you also have satellites that are much farther away that are in excess of 35,000 kilometers, or more than 20,000 miles away. So the satellites that you might use for space solar, which is what this concept is called, might exist in a variety of different orbits. There’s arguments for some over others. Probably one way that your listeners could think about this in terms of GPS where we now take for granted the fact that no matter where we anywhere in the world, you can have a small device that will tell you exactly where you are. And the reason that works is because we have dozens of satellites in the GPS constellation that provide the service. So one thing that we’re looking towards potentially developing is something that would do the same thing for energy, where you have a whole series of satellites and no matter where you are in the world, you could put out a receiver and receive energy. So the experiment that we’re doing on the X-37 investigates one way that this could be done. And while we’re not actually sending any energy from the experiment to the ground, we’re testing an important component that will be used to build the system.

Tom Temin: And before we get to the means by which the energy could potentially get to the ground — what is the system you’re testing for the panel’s themselves?

Paul Jaffe: So the name of our experiment is PRAM-FX, the photovoltaic radio frequency antenna module flight experiment. And it has a solar panel on it and under that solar panel there’s a layer of electronics that does conversion to microwave frequencies. And then on the bottom layer of that experiment is an antenna. Now, because of the way we’re hosted on a spacecraft, we can’t actually radiate the electromagnetic energy from the spacecraft. So instead, we are putting it into a special device that we can measure the output and then calculate the efficiency and see what the thermal performance of our module has achieved.

Tom Temin: Got it. So as I understand it, then in any case, whatever the purpose of a satellite, when it generates energy from solar light, it is somehow producing an alternating current or a wave that could be a microwave or a radio wave or, you know, something you can pick up on your TV antenna, is that the general principle here that would be used to generate power also?

Paul Jaffe: Exactly. So sunlight and microwaves and radio waves are all part of the electromagnetic spectrum. And some folks may ask, well, sunlight already is an electromagnetic wave that we can collect on the ground, why would we do it in space? And the reasons are, in part kind of what I said before, where it’s brighter in space, and it’s uninterrupted, but also radio waves or microwaves get through the Earth’s atmosphere and through clouds much better than sunlight does. So the reason we do that conversion is so we can transmit more effectively to the earth.

Tom Temin: So the idea here is that this microwave then would pass across an antenna on Earth that would then by means of induction produce the current represents the power being generated up there?

Paul Jaffe: Yeah. I should mention, so there’s different ways that you can send the power wirelessly to the Earth. You can use either microwaves, which is what our experiment seeks to do, but there’s also proposals for using lasers instead of microwave transmission, which while they wouldn’t get through the clouds as well. They would let you use antennas and receivers that are a lot smaller. You could envision a possible concept where you might have a receiver actually at a high altitude like above the clouds that might be used. But the receiver on the ground in the microwave case is something called a rectena, which is a combination of the two words rectifier and antenna. And it’s basically a special antenna that converts microwaves back to direct current like we use for many of the devices in our everyday lives.

Tom Temin: That is to say, if these beams are coming down these microwaves, every single thing that’s metal that happens to be in their path would not be electrified.

Paul Jaffe: It depends on the intensity just like if you step outside, you don’t have to worry about the sunlight setting on fire. Similarly, the microwaves can be in a range of different intensities. This is actually something that is pretty easy to demonstrate yourself at home. We had earlier this year an astronauts on the International Space Station, Jessica Meir, do a demonstration to this effect where if you took a single element rectangle with a little light emitting diode on it and just held it up to the space stations WiFi and you can see how power is transmitted wirelessly.

Tom Temin: But it’s the basic old principle of induction, right, that we’re talking about just at a great distance.

Paul Jaffe: Uh, not exactly the same. So induction is something that happens in pretty close proximity, like if you’re charging your wireless toothbrush, or maybe if you’re sticking your phone on a charging pad. But sending waves is a definitely a different mechanism of moving the energy but it is still arising from electro magnetic energy.

Tom Temin: Aright, and once you have some understanding of the efficiency of this device that’s up there now, the PRAM, what happens next? How will you be able to see if you can transmit the energy down and therefore cause current in some manner down on Earth?

Paul Jaffe: Yeah, so the fact is that it’s still very expensive to do things in space. And even though we are seeing really encouraging developments with SpaceX and Blue Origin, with rockets becoming reusable and hopefully cheaper, it still is challenging to have things in space be economical, and certainly for space solar in order for it to be of interest even for DoD, which is used to paying more for energy since a lot of times it’s difficult to get energy to bases in different places around the world and requires a lot of cost and sometimes risk to soldiers, sailors and marines lives — that has to still meet a certain cost benefit. So what we are doing is figuring out from the results of the experiment, what the efficiency is, and also something that’s a little trickier to understand called specific power, which is how much power we can get down per unit mass. That turns out to be really important in determining whether something is going to be cost effective, because the more mass you have to put into space, the higher their costs, and you want to be able to get down as much energy as you can for that amount of math. That make sense?

Tom Temin: It does. Yeah, because launches are still expensive and it’s not clear even that the burgeoning or the just about to burgeon commercial launch industry is anything close to profitable or only profitable if the government is paying and not if private entities are paying. So you’re really doing pretty much close to basic research here, it sounds like.

Paul Jaffe: It’s definitely applied. But we are finding out the boundaries and the limits and what we learn will help inform the next generation of designs that we do to explore this idea.

Tom Temin: And to understand the efficiency of the program and the specific power implications that might have, how long does that take? Does it have to go around and around for months or can maybe 10 minutes of exposure give you the numbers you need?

Paul Jaffe: So because of the way we are hosted on the spacecraft, we’re not in full sunlight all the time. The reason for that is the X-37 B, the spacecraft that we’re on, is in a low Earth orbit, which means, much like the space station, it orbits the entire Earth in about 90 minutes. And because of the orbit it’s in, sometimes it’s behind the Earth. If you picked a different orbit as you likely would, for an operational space solar system, you can either be in an orbit where you’re never in the shadow of the Earth, or you’re only in the shadow of the Earth for a tiny percentage of the time, less than 1%. We’re not in that kind of orbit so it is going to take a little bit longer for us to get the data because we have to make sure that we’re not only in front of the Earth rather than behind it, but also that the spacecraft is pointed in the right direction. Since we’re just one of the payloads on the spacecraft, we can’t tell them where to point all the time. And we’re dependent on different times of the year when the orbit and the position of the spacecraft are both such that we can collect data.

Tom Temin: And as an investigator, an engineer with the Naval Research Labs, is this a full time program for you or do you have other experiements going on also?

Paul Jaffe: Yeah, so my focus has been on space solar but also on power beaming because power beaming is absolutely critical for space solar to work. So while this experiment examines an important component for a particular architecture that would use microwave powering. We also have activities going on in laser power beaming. We did a demonstration at the Naval Surface Warfare Center at Carter Rock last year, and there is actually a video of that on the NRL YouTube channel that shows where we sent hundreds of watts over hundreds of meters in a way that was safe and effective.

Tom Temin: It sounds like this has a lots of applications possibly for systems just that originate on Earth and stay on Earth for power beaming.

Paul Jaffe: Yeah, well, the ability to move energy without having to move a mass is extraordinarily powerful. So if you think about a lot of the things that we do today, like there’s a big increase in the use of drones for a whole range of different applications. And one of the biggest limitations for drones is just how long they can stay in the air, right? Like if you have a electric powered drone on a battery, if it’s flying for an hour, you’re doing pretty well. So imagine if instead we could beam power to it wirelessly, and now it could stay in the air indefinitely.

Tom Temin: All right. Have we covered it? You think?

Paul Jaffe: Yeah, I think so. I’ll mention one more thing about solar power satellites. And that is, it’s important to understand the geopolitical implications of them. If they are made to work, it means that whoever has mastered the technology will now be in a position to control clean energy globally, because the nature of the system is that it can provide energy anywhere in the world. And if another country is able to do that and provide energy to the growing demand in different parts of the world that will give them an outsized amount of power. So I think it’s very important for our country to continue our efforts in this region of technology.

Tom Temin: Paul Jaffe is an electronics engineer and principal investigator at the Naval Research Laboratory. Thanks so much for joining me,

Paul Jaffe: Tom. It was great, thank you.

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