Japan's microwave technology is being used to power drones that fly for free. This could open the door to a new type rocket.
Current rockets generate thrust using controlled explosions of solid or liquid fuel sources. This can account for up to 90% of their total weight. New research in the Journal of Spacecraft and Rockets shows the potential of microwaves as a source of fuel.
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Microwaves can be described as electromagnetic radiation. They are jam-packed full of energy that can be used to generate electricity. This is similar to how solar panels can convert sunlight into power. Researchers used microwaves to generate electricity for fuel-free drones in a new study.
"In drone experiments microwave power is sent between the antenna on ground and the antenna on drone. The rectifier converts RF [radio frequency] into DC [direct current], and then the DC power is used for driving the drone's motors. It is called "rectenna" (rectifier+antenne), according to Kohei Shimamura, a University of Tsukuba researcher. He explained this to Space.com via email.
The setup of the drone experiment, which included the microwave emitting antenna as well as the free-flying drone. (Image credit: Kohei Shimamura)
Previous research on microwave-powered propulsion had used low-frequency waves. However, it was found that the frequency increases the power transmission efficiency. To lift a drone weighing 0.9 pounds (0.4 kg) off the ground, the researchers used high frequencies (28 gigahertz).
The transmitted power allowed the drone to reach a height around 2.6 feet (0.8 m) while sitting directly above the source. This was for 30 seconds. Shimamura stated in a statement that he used a sophisticated beam tracking system to ensure that drone received as much microwave power as possible.
The drone captured 30% of the microwaves emitted during the experiment and converted 40% to electricity for propulsion.
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Shimamura stated that these results demonstrate the need to further improve transmission efficiency and evaluate the feasibility and viability of this propulsion approach for spacecraft, rockets and aircraft. Future studies should also be focused on improving the beam-tracking system, and increasing the transmission distance beyond what was demonstrated in the experiment.
The new research shows the potential of microwave-powered propulsion. However, rocket flight is still possible with the technology's infancy.
The challenge lies in tracking the microwave to the rocket up to 100 km [roughly 62 miles]. To achieve this, it is important to control the microwave's phase with high accuracy. Shimamura also stated that aligning multiple microwave sources of high power with the phase is a challenge. "Cost is both a technical and major problem." A high-power source with several megawatts [MW] of power is the same as building a nuclear reactor power plant. The cost of launching rockets is very high.
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