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(CNN) – Scientists working for the Pentagon have successfully tested a pizza box-sized solar panel in space, designed as a prototype of a future system to send electricity from space back to anywhere on Earth.
The panel, known as the Photovoltaic Radio Frequency Antenna Module (PRAM), was first launched in May 2020, connected to the Pentagon’s X-37B unmanned drone, to harness sunlight to convert it into electricity. The drone circles the Earth every 90 minutes.
The panel is designed to take full advantage of light in space, which does not pass through the atmosphere and therefore retains energy from blue waves, making it more powerful than sunlight reaching Earth. Blue light diffuses upon entering the atmosphere, making the sky appear blue.
“We’re getting a ton of extra sunlight in space just for that,” said Paul Jaffe, a co-developer on the project.
The latest experiments show that the 12×12-inch panel is capable of producing about 10 watts of power for transmission, Jaffe told CNN. That is enough to power a tablet.
But the project envisions a series of dozens of panels and, if scaled up, its success could revolutionize the way power is generated and distributed to remote corners of the world. It could contribute to the largest networks of networks on Earth, Jaffe said.
“Some visions have solar space equivalent to or greater than today’s largest power plants (several gigawatts), so it is enough for a city,” he said.
The unit has not yet sent energy directly to Earth, but that technology has already been tested. If the project is turned into huge kilometer-wide space solar antennas, it could emit microwaves that would then turn into fuel-free electricity to anywhere on the planet at any time.
“The unique advantage that solar power satellites have over any other power source is this global transmissibility,” said Jaffe. “It can send power to Chicago and a fraction of a second later, if necessary, send it to London or Brasilia.”
But a key factor that must be proven, Jaffe said, is economic viability. “Building hardware for space is expensive,” he said. “And those [costs] they are, in the last 10 years, finally starting to go down. “
There are some advantages to building in space. “On Earth, we have this annoying gravity, which is useful because it holds things in place, but it is a problem when you start to build very large things, since they have to support their own weight,” Jaffe said.
The mission of the US X-37B space plane is shrouded in secrecy, and the PRAM experiment is one of the few known details of its purpose. In January, Jaffe and PRAM co-leader Chris DePuma published the first results of their experiments in the IEEE Journal of Microwaves, which showed that “the experiment is working,” Jaffe said.
The project has been funded and developed by the Pentagon, the Operational Energy Capacity Improvement Fund (OECIF), and the United States Naval Research Laboratory in Washington, DC.
A solution during natural disasters
The temperature at which the PRAM works is key. Cooler electronics are more efficient, Jaffe said, and their ability to generate power degrades as they heat up. The X-37B’s low-Earth orbit means that it spends about half of each 90-minute cycle in the dark, and thus in the cold.
Any future version of the PRAM could be placed in a geosynchronous orbit, which means that a loop takes about a day, in which the device would be mainly in sunlight, since it is moving much further away from Earth.
The experiment used heaters to try to keep the PRAM at a constant, warm temperature to demonstrate how efficient it would be if it were circling 36,000 kilometers from Earth.
It worked. “The next logical step is to scale it to a larger area that collects more sunlight, which converts more into microwaves,” Jaffe said.
Beyond that, scientists will have to test sending energy back to Earth. The panels would know precisely where to send the microwaves, and would not accidentally fire at the wrong target, using a technique called “retro-directive beam control.” This sends a pilot signal from the target antenna on Earth to the panels in space.
The microwave rays would only be transmitted once the pilot signal was received, meaning the receiver was in place below and ready. The microwaves, which would easily be converted to electricity on Earth, could be sent anywhere on the planet with a receiver, Jaffe said.
It also dispelled any future fears that bad actors could use technology to create a giant space laser. The size of the antenna required to direct the energy to create a destructive beam would be so large that it would be noticeable in the years or months it would take to assemble. “It would be extremely difficult, if not impossible,” he said, to turn solar energy from space into a weapon.
DePuma said the technology, if available today, would have immediate applications in natural disasters when normal infrastructure collapsed. “My family lives in Texas and everyone is living without power right now in the middle of a cold front because the grid is overloaded,” DePuma said.
“So if you had a system like this, you could redirect some power there, and then my grandmother would have heating in her house again.”
This story was first published on CNN.com, “CNN Exclusive: A Solar Panel In Space Is Collecting Energy That Could One Day Be Transmitted To Any Part Of Earth.”
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