We Talk To The Scientist Whose Revolutionary Power Beaming Experiment Is Flying On The X-37B

Harvesting solar energy from space has been a topic of research for decades. The Naval Research Lab now has a plan to beam that energy down to Earth.

byBrett Tingley|
High Powered Microwaves photo


When the U.S. Air Force’s shadowy X-37B space plane was launched on top of a United Launch Alliance Atlas V rocket on May 17, 2020 from Cape Canaveral Air Force Station, it carried with it a revolutionary new system designed by Dr. Paul Jaffe of the Naval Research Laboratory (NRL). The device, known as a Photovoltaic Radio-frequency Antenna Module (PRAM), will eventually be able harvest power using solar panels and beam that power back down to Earth in the form of microwaves. 

While the module currently in orbit isn’t transmitting power to Earth, Jaffe and NRL investigators hope to someday be able to leverage space-based solar technologies to provide a revolutionary new source of power to nearly anywhere on the globe regardless of a lack of existing energy infrastructure. The War Zone recently spoke with Jaffe to learn more about the PRAM, power beaming, and space solar in general.

Before we get into our interview, here is a quick primer on Paul Jaffe's research and just how revolutionary microwave energy beaming from space could be. 

Space-Based Solar And Microwave Power Beaming

Paul Jaffe has been an Electronic Engineer at the Naval Research Lab since 1994. He began working on the original PRAM project in 2009. Jaffe would go on to earn his PhD as a result of a Doctoral Research Program while working on PRAM research. His 2013 dissertation described a “sunlight to microwave power transmission module” similar to the test module recently launched into orbit aboard the X-37B. Jaffe also holds a patent for “thermally efficient power conversion modules for space solar power,” granted in 2016 and assigned to the Secretary of the Navy.

In 2016, Jaffe and his team were named the winners of the first-ever Department of Defense (DOD) Diplomacy, Development, and Defense (D3) Innovation Summit Pitch Challenge, an initiative designed to foster innovation and collaboration on pressing national security issues far from the battlefield. In an NRL press release announcing the award, Jaffe stated that, if found to be successful and feasible, space-based solar-to-microwave power beaming has the potential to radically change the way power is generated and distributed on Earth. “It’s hard to overstate the significance and benefits of this concept if it comes to fruition,” Jaffe said.

In the same press release, Jaffe also stated that “other major powers around the world, particularly in Asia, are also investigating this idea in earnest.” Indeed, China’s state-run Academy of Space Technology tested such a system in 2019 and boasted that a fully-functional Chinese microwave beaming power station in space could be in orbit by 2050. Such a system could potentially beam power to rectifying antennas, or rectennas, on the Earth’s surface, providing power to existing installations or to remote areas without existing power infrastructure.

There are many other defense-oriented applications envisioned by the NRL. In 2010, Jaffe published the study “Defense Applications of Space Solar Power” in the Space, Propulsion & Energy Sciences International Forum hosted by the American Institute of Physics. In the paper, Jaffe presents a wide variety of defense applications that space-based solar power (SBSP) could augment, including providing power to a number of different installations, vessels, or distributed sensor networks, and even serving as a bistatic radar illuminator. As we cited in our previous reporting, Jaffe’s 2010 research also claimed that SBSP could be used in satellite-to-satellite power transmission or to provide UAVs with greatly extended endurance.

Jaffe lists potential applications of space-based solar in his 2010 publication “A Study of Defense Applications of Space Solar Power”, American Institute of Physics

More recently, Jaffe stated that the power beaming technologies involved with the PRAM module could potentially enable near-unlimited flight times on UAVs. “If we had a way to keep those drones and UAVs flying indefinitely, that would have really far-reaching implications, Jaffe said in a 2019 NRL press release. “With power beaming, we have a path toward being able to do that.” Keeping UAVs in the air indefinitely was also mentioned as a goal in 2014 by Thomas Mehlhorn, superintendent of the Naval Research Laboratory’s Plasma Physics Division. 

Other branches of the Armed Forces are pursuing similar technologies and concepts. Since as early as 1964, the USAF has been experimenting with power beaming and UAVs. In that year, Air Force-sponsored researchers were able to keep a small tethered helicopter aloft for ten hours powered only by a microwave power beam. NASA’s Jet Propulsion Laboratory tested the concept of beaming power to Earth from space using microwaves in 1975.

More recently, in 2019, the Air Force Research Laboratory (AFRL) awarded Northrop Grumman a contract valued over $100 million to develop space solar hardware that could provide “uninterrupted, assured, and agile power to expeditionary forces operating in unimproved areas,” such as forward operating bases far from traditional energy infrastructure or fuel supply lines.

“Energy is a strategic enabler and potential vulnerability for our nation and our Department of Defense,” U.S. Air Force Col. Eric Felt, director of AFRL’s Space Vehicles Directorate, said in a 2019 Air Force press release. “To ensure DoD mission success we must have the energy we need at the right place at the right time. The Space Solar Power Incremental Demonstrations and Research (SSPIDR) Project is a very interesting concept that will enable us to capture solar energy in space and precisely beam it to where it is needed,” Felt said. “SSPIDR is part of AFRL’s ‘big idea pipeline’ to ensure we continue to develop game-changing technologies for our Air Force, DoD, nation, and world.”

Now that you have an idea of what this potentially groundbreaking technology is all about, let's get to our interview with Dr. Paul Jaffe of the Naval Research Laboratory.

Paul Jaffe Talks Space-Based Solar Power

To help us understand this groundbreaking technology and its implications, The War Zone spoke with Dr. Paul Jaffe and the Naval Research Laboratory to discuss how the PRAM experiments are going thus far and what the future may hold for space-based solar and power beaming.

Brett: Why has it taken until now to get the first hardware specifically for solar power satellites in orbit?

Paul: These things definitely take time, and most of it is definitely a function of budget, like if we had 10 times as much money, obviously things would be able to go more quickly. But there is, I think, a very reasonable approach, which is “let's start with a small amount and if that proves fruitful then we'll add and expand from there and if it's not as successful then we'll investigate something else.” 

The original PRAM that started in 2009 was intended as a four-year program, which it was, and with that we started essentially with nothing and then ended up with a module, actually multiple modules, of two different designs, one of which we had to pass on. For the microwave conversion, we also tested those in actual space-like conditions.

Now, getting from there to space is a whole other story. Between 2013 and I guess it was probably 2015, when we started this process that led to where we got to the launch [in May], there's a whole lot that has to happen where we get more cycles of Shark Tank-like proposal and competition against other researchers and experiments. And also just like working to get something manifested, right, so we're effectively a passenger on X-37B.

We had many discussions back and forth with them about how we would be hosted and what they would provide for us and how we would behave. We are not radiating any power into space partially because it would be prospectively disruptive to the host. Right now we are radiating into an RF load, a radiofrequency load, and this allows us to measure very precisely how much energy the module is actually producing, which is obviously important for the experiment. We want to make sure that we are measuring and characterizing the efficiency accurately.

To send power to the ground at microwave frequencies from lower orbit would require much larger antenna apertures than are practical to put on X-37B or on most satellites. You would probably have to do like a whole custom satellite for that and that's much more expensive than being a passenger on a host spacecraft like we are doing for this experiment.

Jaffe and the Photovoltaic Radio-frequency Antenna Module (PRAM), U.S. Navy/Jamie J. Hartman

Brett: So that makes sense why you would use the X-37B for something like this than a more traditional space flight.

Paul: Just to be clear, we didn't pick the X-37B especially. We started the manifesting process in the mid-2010s, it wasn't like, "Alright, we're going to go in X-37B." We briefed to the space test program, and what they do is match payloads and hosts. And they say this one would be a good fit for this because of how big it is and how much it weighs and when this one is going to launch, and how much accommodation this has. So we could have ended up conceivably on another spacecraft or even on the space station, or we looked at actually geosynchronous spacecraft, we looked at some of the ISS resupply ones. But as we got close they're like, "Hey, we could put you on here, does that work for you?" And we looked at the trade-off and we said, "Yeah, you know, that'll accomplish what we're trying to do with this experiment."

The PRAM module currently in orbit., U.S. Naval Research Laboratory

Brett: Do you have any data back yet from the experiments?

Paul: We've gotten preliminary data on the order of, I think, several thousand records at this point, and we are in the process of putting it into spreadsheets and analyzing it, trying to see what's happening. So far, things are looking really good. They're comparable to the testing we did on the ground. One of the things that you might have seen, I don't know how much you would've delved into my 2013 thesis, but it's important for solar-powered satellites to generally be pretty efficient. 

The most important metric is what's called specific power or watts per kilogram, and that intuitively makes sense, because if you're going to be putting something into space, you want to get as much power down as you can, with putting the least amount of stuff in space. So if you think about the specific power watts per kilogram, it's very important for that to be high. If your hardware is more efficient, it's easier for that specific power to be high. And to have the specific power and efficiency both be optimized, you want to operate your electronics where they are most efficient under the temperature and illumination conditions that result in that.

Because the amount of power coming out of the solar panel changes, and we're driving the radio frequency electronics so there's actual power transmission, you want to try to match everything together so that the maximum power is coming out of the solar ray at the same level that the RF electronic can convert at most efficiently. All these things have to be matched, and they all have to stay matched at the equilibrium temperature.

This is one of the big things for PRAM, is like finding that equilibrium point, understanding it, understanding the thermal performance, understanding how hot the solar panel's getting, how hot the RF electronics are getting, how hot the antenna aperture would be getting if we had one and trying to match those things all up.

A lot of the testing we did on the ground was to find this point, but we could only simulate the space environment and the solar conditions to a certain degree of fidelity. So one of the biggest things we're getting out of the X-37B experiment, is since we're actually testing this in space, we're going to validate our operating point, and the assumptions we made of the equilibrium temperatures. For any future solar power satellite system, it's going to be super important to understand these points and to be able to engineer to them and to be able to show that you can operate at this and you can actually get the system power and efficiency this way.

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Brett: How much dwell time relative to a point on the ground do you have per orbit?

Paul: If you're thinking about a solar power satellite system in the future, the answer to that question is going to depend totally on the orbit that the satellite is. So if it's in geosynchronous orbit, which is where most of the solar power satellite systems that have been proposed to exist in, it's going to be in sunlight for more than 99% of the time during the year and it will have continuous 24/7 ground coverage obviously, while in sunlight, of a pretty large swath of the Earth, like in excess of a quarter of the Earth is where it could send the power beam. 

Now a power beam won't cover a quarter of the Earth, it'll send it probably to a specific location. But that would be available close to 24/7, 365. There are periods around the equinoxes at local midnight when the satellite would go into eclipse for some period of minutes, I think it might be slightly longer than an hour. There's a number of analyses and stuff have been done on these things. This is all for a single satellite, so if you have a single satellite in a lower orbit, the coverage will vary. And there's many different orbits lower or otherwise, but you can envision that instead of focusing just on a single satellite, that you would likely build a constellation. If you do judicious constellation design, you can ensure that no matter where you are at any point in time, that you could have power provided by a given satellite.

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Brett: You mentioned that keeping UAVs in the air indefinitely is one of the potential applications of this technology. Is that something you’re looking at specifically with the PRAM module?

Paul: Power beaming and space solar are constantly conflated. Power beaming is just moving energy without using wires or moving mass. So you could power UAV from the ground using power beaming, you could power a UAV from another aircraft using power beaming. You can power a UAV from space using power beaming. You could use power beaming to get energy to the permanently shadowed craters on the moon, or a whole range of different places. So the connection between PRAM and power UAVs is really only through the fact that PRAM is part of the system that is envisioned to use power beaming.

Space solar depends on power beaming in almost all of its incarnations, but power beaming is a totally separate technology that has many applications that have nothing to do with space solar, or even with space necessarily. Because you can't have space solar without power beaming, it makes a lot of sense to do the power beaming research first, right? Power beaming makes a lot of sense as a place to focus because without that being more mature, space solar is just harder to justify; and it's harder to design a system, a concept that makes sense because there are just too many unknowns.

Brett: What does the future of space solar look like?

Paul: The data we get from that is going to inform these efforts moving toward the next generation that will be built, and then the power beaming work, likewise, will inform whether it makes sense to pursue these other applications, the ones that use laser power beams or some other power beam. And along the way, we're always looking carefully at the nearer term applications, of which there are many for power beaming. 20 years ago, you wouldn't have thought about wirelessly charging your phones using the Qi standard or charging pad or something. As power beaming starts to become more of a technology unto its own, I think we'll see a lot more applications. 

And there's a lot of startups even within the last year or so that think they have the secret sauce that's going to make space solar economically viable. A lot of whom don't want their existence known just yet.

I think that if solar powered satellites become a thing, there's a couple paths they could take. This is another thing where history is kind of useful to look at, where if we were in 1950 and I was like, "Hey, we should be able to make it so that people can have a little handheld thing and we'll have this constellation of a dozen satellites, each of which will have its own atomic clock and they'll beam signals down to the ground, and we'll do a bunch of math on the device, and they'll tell people no matter where they are in the world, where they are,” you would think that I was crazy. In 1960, not only was even getting a satellite into space very difficult, but no one had put an atomic clock on a satellite at that point. And all of those things incrementally were advanced until the point where we are today, where we take GPS navigation kind of for granted.

Development for solar powered satellites might unfold like GPS, but it also might unfold like communication satellites where Congress recognized like, "Hey, there's a lot of utilities to be had here, and we'll pass the Comsat Act and set up the development framework that will let industry take the lead on this." GPS was all government developed and now, other governments around the world are trying to play catch up. 

Dr. Paul Jaffe is presenting a webinar on Power Beaming & Space Solar Innovation hosted by the Homeland Defense & Security Information Analysis Center on Thursday, July 30. More information can be found at http://www.hdiac.org/podcast/power-beaming/.

Contact the author: Brett@TheDrive.com