Could solar panels in space power military operations on Earth?

WASHINGTON – Getting an extension cord to a forward operating base is difficult.

Military outposts require a lot of energy, but they are often located in places without easy access to electricity. The U.S. military can’t exactly build a field of solar panels every time it sets up in remote locations, and fossil fuels can be expensive and difficult to transport into the field.

What the military needs is a source of power it can draw from anywhere on Earth with limited infrastructure, and the Air Force Research Lab thinks it could. well have the solution: a constellation of solar panels mounted on satellites that can collect energy in orbit and beam it down to Earth. Members of the ground services could connect to this power source from anywhere on the planet with mobile equipment, allowing them to power an entire forward operating base or simply recharge a radio.

It sounds like wild science fiction, but engineers at AFRL say it’s possible, and they’re working on a technology demonstration as early as 2024.

The initiative is called Space Solar Power Incremental Demonstrations and Research, or SSPIDR.

“The SSPIDR is like a technology development portfolio. So at the end of the day our goal is solar to RF [radio frequency] power beam – by taking the energy of the sun that we collect in space, converting it into RF in orbit, and diffusing it to the ground where it would then be converted back into power by a rectifier antenna, or rectenna ”, SSPIDR chief engineer Mandy Self told C4ISRNET.

AFRL thinks it’s doable, but getting there will be a journey. SSPIDR adopts an incremental approach, maturing several technological elements of the notional system and leading to three demonstrations. The flagship effort is Arachne – named after a woman who was transformed into the first spider, according to Greek mythology – which will be an orbit demonstration in 2025.

The main contractor of SSPIDR is Northrop Grumman. The company received a $ 100 million award focused on solar-to-RF conversion. AFRL is also working with other companies on high efficiency solar cells, deployable space structures and more, Self said.

Some of the technologies involved are already mature, Self said, but they need to be miniaturized. In fact, miniaturization is one of the main challenges in making SSPIDR a reality. The final size of the system in space is still a conversation, but it largely depends on the lab’s ability to miniaturize the various components and the ability to condense the entire structure into a launch payload. Currently, some of the technologies available are just too heavy to be used for a space mission, so a large part of AFRL’s effort is to rework these solutions to reduce mass and size.

Which leads to the most important aspect of any effort to collect energy from the sun: solar panels. Although technology keeps improving, there is usually a correlation between the area of ​​the solar panel and the amount of energy it provides. To power a small traffic light, a 1 square foot sign may be sufficient. SSPIDR will need a lot more power and panels than that.

“When it comes to solar-to-RF conversion, bigger is always better, so the more we can put in the better,” Self said.

SSPIDR communications manager Rachel Delaney said AFRL’s goal is to be able to generate 1,000 kW of electricity – enough to run a forward operating base, according to a study by the Naval Research Laboratory . For context, a GPS III satellite has four satellite arrays spread over its 48-foot wingspan that together generate approximately 4,500 watts of power. SSPIDR will have to increase the efficiency of the solar panels as well as the surface area of ​​its panels to generate the quantity of energy engineers sought.

To make this possible, AFRL wants to use foldable solar panels that can be condensed into a relatively small payload for launch and then unfolded once in place in orbit. This is not an unusual approach for satellites, but the scale of the SSPIDR solar panels could be new.

AFRL recently opened a new Deployable Structures Lab at Kirtland Air Force Base, New Mexico, which will help engineers develop solar panels that are not only large enough to generate 1,000 kW, but can also be efficiently retracted for the start. The new facility has enough space for the team to deploy a full solar panel while compensating for Earth’s gravity, helping them simulate the weightless space environment in which the satellite will operate. This will also allow AFRL to build the entire satellite with lighter and weaker materials. which may not withstand Earth’s gravity, but will function sufficiently in orbit.

An important innovation in space saving is a new “sandwich panel” designed by AFRL that both collects solar energy and converts it into RF.

“One side is solar, one side is RF, and the magic happens in the middle,” Self explained. “And we’re really trying to make it as thin and light as possible.”

On the earth side of things is the rectenna, which will take the RF signal emitted from space and convert it back into usable power. This technology is incredibly flexible, Self said. Larger rectennas can be installed on every building in a forward operating base, providing a continuous source of power from space. But it can also be used on a much smaller scale. Perhaps, Self explained, a smaller rectenna could be integrated into soldiers’ tents, allowing them to charge their radios and other electronic devices while they are in the field. AFRL even discussed a simple umbrella-shaped design that can be carried around the field – just unfold it and there’s power.

Anyone in the path of the harness can access this power supply if they have the right equipment – no cords are needed. And the beam is great. The final size will depend on what final product AFRL is capable of developing, but for now engineers expect it to provide coverage spanning tens of kilometers. And that’s with just one satellite. AFRL envisions an entire constellation of 12 satellites called Scorpio in medium earth orbit, emitting power to any location on the planet.

AFRL also partnered with the Naval Research Laboratory, which was working on a similar project. The Navy’s research lab sent its own demonstration project – the Photovoltaic Radio Frequency Antenna Module, or PRAM – into space aboard the secret X-37B space plane in May 2020. PRAM is testing a panel of solar-RF conversion developed by the Navy.

AFRL’s own demonstration project, Arachne, will go further by transferring the RF to another location. The experiment will test the first Northrop Grumman sandwich panel in space. The first panel is expected to be delivered in fiscal 2024, with a launch later that year or in early 2025.

Nathan Strout covers space, unmanned and intelligence systems for C4ISRNET.

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