Artist’s rendering of the Air Force Research Laboratory’s Arachne flight experiment on orbit.
The concept of collecting the sun’s energy above earth’s atmosphere and sending it back to earth to be used has been understood for well over half a century. If it could be made to work effectively, the technique offers many advantages over earth based solar collection, especially for geographical areas that don’t receive strong sunlight for large parts of the year. Obviously there is no night in space, so energy can be gathered for 24 hours a day. A space solar collector also has the ability to capture the 55-60% of solar energy that is lost with reflection and absorption on its way through the atmosphere of the earth. Of course, it is an expensive proposition to launch the solar collector into space in the first place, even if the technology was available to us. To operate, the collector would have to capture the solar energy in the first place and then convert it into a suitable medium, such as RF, to be transported back to earth.
The main technical problem that has been encountered so far is providing an actual conversion from solar power to RF without reducing the efficiency too much. In an attempt to find a practical solution to this problem and others, the Air Force Research Laboratory (ARFL) awarded Northrop Grumman a contract worth over $100 million to develop a payload that would include the key components of a prototype space solar power system. In response, Northrop Grumman developed a “sandwich tile” to provide a ground demonstration of the successfully conversion of solar energy to radio frequency (RF). ARFL and Northrop Grumman have now employed the sandwich tile to conduct an end-to-end demonstration of key hardware. The demonstration was part of the Arachne experiment. Arachne is the flight experiment in the Air Force Research Laboratory’s Space Solar Power Incremental Demonstrations and Research (SSPIDR) project, which aims to prove and mature essential technologies for a prototype space-based solar power transmission system capable of powering a Forward Operating Base. This series of incremental demonstrations will mature the critical technology elements that AFRL has identified as necessary for achieving a large-scale solar power transmission system. In support of the SSPIDR mission, Arachne will demonstrate technologies related to more efficient energy generation, radio frequency forming, and RF beam beaming.
The sandwich tile consists of two layers. The first layer is a panel of highly efficient PV cells which collect solar energy and provides power to the second layer. The second layer is populated with components that enable solar to RF conversion and beamforming. The ground demonstration used a solar simulator to illuminate the PV side of the tile and begin the solar-to-RF conversion process. Because the solar simulator was so intense, attendees viewed real-time RF output data on monitors from behind an industrial grade flexible plastic barrier. The RF energy peak appeared indicating successful power conversion and RF radiated power. Successful testing of the individual tile for the Arachne payload provides a building block for a square meter panel of tiles. Arachne is anticipated to launch in 2025.
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