Japanese researchers are using microwaves to propel free-flight drones, a project that could eventually pave the way for a new type of rocket.
Currently, most rockets generate thrust using controlled explosions from a solid or liquid fuel source, which can account for 90% of their total weight. However, new research published in the Spaceships and Rockets Journal demonstrates the potential of using an alternative fuel source: microwaves.
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Microwaves are a type of electromagnetic radiation. As such, they are packed with energy that can be converted into electricity, just as sunlight can be converted into energy by solar panels. In the new study, researchers generated electricity to power free-flying drones by sending microwaves directly to them.
“In drone experiments, microwave power is sent from the ground antenna to the drone’s antenna. A rectifier is used to convert RF [radio frequency] in DC [direct current], and direct current is used to drive the motors of the drone. We call it “rectenna” (rectifier + antenna), “one of the new study’s authors, Kohei Shimamura of the University of Tsukuba, told Space.com.
Previous studies exploring microwave propulsion used low frequency waves, but found that as the frequency is increased, the power transmission efficiency also increases. With this in mind, the research team used high frequencies (28 gigahertz) to lift a 0.9 pound (0.4 kilogram) drone off the ground.
Sitting directly above the source of the microwave beam, the transmitted power allowed the drone to reach a height of about 2.6 feet (0.8 meters) for 30 seconds. “We used a sophisticated beam tracking system to ensure the drone receives as much microwave power as possible,” Shimamura said in a statement. declaration.
In the experiment, 30% of the emitted microwaves were captured by the drone, and 40% of these microwaves were converted into electricity for propulsion.
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“These results show that more work is needed to improve drivetrain efficiency and to thoroughly assess the feasibility of this propulsion approach for airplanes, spacecraft and rockets,” Shimamura said. “Future studies should also aim to refine the beam tracking system and increase the transmission distance beyond that demonstrated in our experience.”
While the new research shows the potential of microwave propulsion, the technology remains largely in its infancy, especially when you consider its potential use for rocket flight.
“The big challenge is to follow the microwave to the rocket until it reaches an altitude of 100 km [approximately 62 miles]. To achieve this, it is necessary to control the phase of the propellant and the microwaves with great precision. In addition, phase alignment of multiple microwave sources with high power is a future challenge, ”Shimamura told Space.com via email. “Cost is a major problem as well as a technical challenge. Build a high power source of several MW [megawatts] is equivalent to building a nuclear fusion power plant, and the cost of launching a rocket is very high right now. ”
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