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X-37B testing beamed solar power from space

The U.S. Space Force’s X-37B mini-shuttle, presently in orbit for more than 300 days, is testing technology for capturing solar energy and beaming it back to Earth for use in the electricity grid.

Most of the robotic space drone’s duties on this mission, known as Orbital Test Vehicle-6 (OTV-6), are a tightly held secret. However, one known bit of research that the craft carries is the Photovoltaic Radio-frequency Antenna Module Flight Experiment, or PRAM-FX.

PRAM-FX is a Naval Research Laboratory (NRL) experiment that’s investigating transforming solar power into radio frequency (RF) microwave energy. PRAM-FX is a 12-inch (30.5 centimeters) square tile that collects solar energy and converts it to RF power.

Paul Jaffe, the innovation power beaming and space solar portfolio lead at NRL, said that PRAM-FX is not beaming microwave energy anywhere. Rather, the experiment is gauging the performance of sunlight-to-microwave conversion. To be measured is how the PRAM is performing from an efficiency standpoint and also from a thermal performance stance, he said.

The first results from PRAM were released in January, and showed an “8% total module efficiency,” which I think means it was able to beam down 8% of the solar energy that it gathered. This might seem poor, but if solar panels can provide that much of their energy for Earth use the pay-off could be quite large.

A much larger demonstration project will fly three different spacecraft in ’23 and ’24, each testing different components of the system.

Conscious Choice cover

From the press release: In this ground-breaking new history of early America, historian Robert Zimmerman not only exposes the lie behind The New York Times 1619 Project that falsely claims slavery is central to the history of the United States, he also provides profound lessons about the nature of human societies, lessons important for Americans today as well as for all future settlers on Mars and elsewhere in space.

Conscious Choice: The origins of slavery in America and why it matters today and for our future in outer space, is a riveting page-turning story that documents how slavery slowly became pervasive in the southern British colonies of North America, colonies founded by a people and culture that not only did not allow slavery but in every way were hostile to the practice.  
Conscious Choice does more however. In telling the tragic history of the Virginia colony and the rise of slavery there, Zimmerman lays out the proper path for creating healthy societies in places like the Moon and Mars.


“Zimmerman’s ground-breaking history provides every future generation the basic framework for establishing new societies on other worlds. We would be wise to heed what he says.” —Robert Zubrin, founder of founder of the Mars Society.


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  • Scott M.

    I never though that space-based solar power made sense from an economic perspective. The cost of lifting that much mass into orbit is just too high, even w/ something like Starship or Sea Dragon. BUT I would be quite happy to be proven wrong!

  • J Fincannon

    The PRAM provides an 8% efficiency of incident sunlight to output RF. Or, 104.1W hitting the solar array and 8.4W RF output at the spacecraft. This does not include the following losses: going thru a transmit antenna, through the atmosphere to the ground, thru that ground antenna, converted from RF to DC. Although the test was for LEO, it seems important to know that for real world power systems, you would need to have this thing at Geosynchronous orbit. If so, then the final power at the user on the ground for this 1 PRAM would likely be 1W. Even with a huge ground antenna, 35786 km is a long distance to send a RF signal.

    Using the PRAM module 8.4W power output building block to ramp up to a 10 MW at the RF output transmit aperture, the area of the PRAM being 30cm by 30 cm or .093 m^2, a geostationary power satellite would be 10,000,000W * .093m^2/8.4W or 110744 m^2 or 333 m by 333 m square surface or transmitter aperture (keeping the solar array size the same as the transmit antenna.. the transmit antenna is not allowed to be larger). Keeping the ground rectenna at 1 km by 1 km (pretty practical), this drives the transmission efficiency from the high value they have suggested of 78% down to 10%.

    The mass of the PRAM is a concern. The solar array is rigid panel. These are the heaviest kinds of solar panels. If all the electrical equipment in the PRAM image has to go with each module, then it is not going to be light.

  • Jeff Wright

    HLLVs are needed. Coyote Smith wants these to power drones for air support. China is to place a 200 metric ton demonstrator up-and some dingbat at Gizmodo or whatever gets worked up at this…. toy

  • Is the X-37B also harvesting manganese nodules like the Glomar Explorer?

  • Jeff Wright

    Shuttle bay moon pool huh? Now, Stratolaunch is big enough to drop a huge bomb on Fordow. I want “Glomar” to refer to secret tech-not this ‘neither confirm or deny’ stuff.

  • I would say that an 8% conversion rate is impressive for a first trial. Steam locomotives never were much more efficient than that, and they had nearly 200 years of development.

    Several books were published in the mid-70’s exploring SPS. Given the launch capabilities at the time, the only way SPS would be economically feasible would be to mine and produce the materials off-planet. Which, in itself, was far beyond our technical capability (and still is). The combination of heavy-lift, and improved solar cell tech, might make SPS at least viable, if not profitable.

    I’s also note that despite the hypothetical nature of the studies, the environmentalists were treating them as Real Things. Much written about birds being killed flying through the microwave beams to Earth. I don’t really see how that would be more damaging than the current wholesale bird slaughter committed by enviro-darling wind turbines. And, I’d think a flat antennae array would be more visually pleasing than hundreds of turbines stuck all over the landscape. Likely cheaper, too.

  • Steve Richter

    What about global warming? Would this capture solar radiation that would otherwise not hit and be absorbed the Earth?

    A solar panel in orbit absorbs solar radiation and then sends the energy down to Earth as a microwave. Would that increase the amount of solar energy that is absorbed by the Earth, thus increasing the temperature of the Earth?

  • Col Beausabre

    Give it time to improve the power generation, hook a powerful laser to it and you’ve got a death ray in orbit. The Death Star lives ! For those who scoff, the US Navy has deployed a laser weapon to the Persian Gulf. It can destroy drones and set speed boats like the Iranian Boghammers afire. and we’re about where guns were at the Battle of Cressy, the first recorded action in the West in which guns were used.

  • Col Beausabre

    In military space news, on Friday, Vandenberg Air Force Base cased its colors after six decades and assumed a new identity as Vandenberg Space Force Base

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