Powering Airplanes With Microwaves: An Aviation Physics Challenge Amidst Many

Falling firmly under the fascinating science category of ‘What if…?’ comes the idea of powering airplanes with beamed microwaves. Although the idea isn’t crazy by itself, since we can even keep airplanes flying using just solar power (though with no real useful payload), running through the numbers as [Ian McKay] does in a recent article in IEEE Spectrum makes it clear that there are still some major hurdles if we want to make such a technology reality. Yet is beamed microwave power that much more far out than other alternative ways to power aviation?

Most of the issues are rather hard limits with the assumed technology (phased microwave arrays), with the need for 170 meter diameter ground transmitters every 100 km along the route (including floating transmitters on the oceans with massive power cables, apparently). Due to the limited surface area on something like a Boeing 737-800 you’d need to cram the full take-off power needs (~30 MW) on its ~1,000 m2 surface area available for receiver elements, or 150 Watt per rectifying antenna (rectenna) element assuming a wavelength of 5 cm.

The good news is that the passengers inside would probably survive if the microwave-like shielding keeps up, and birds passing through the beams are likely to survive if they’re fast enough. It’d ruin a whole part of the local radio spectrum from leaked microwaves, of course. Unfortunately beaming MW levels of microwaves across 100 km is still beyond our capabilities.

After this fun science session, [Ian] then looks at alternatives like batteries and hydrogen, neither of which come even close to the energy density (or relative safety) of commercial aviation fuels. Perhaps synthetic aviation fuel might be the ticket, but at this point beamed microwave power is as likely to replace aviation fuel as batteries or hydrogen, though more likely than countries like the United States building out a fast & cheap high-speed rail network.

19 thoughts on “Powering Airplanes With Microwaves: An Aviation Physics Challenge Amidst Many

      1. Yeah I don’t see that being practical short of using a battery/supercap to provide the surge power needed for takeoff.

        Planes are big, and the ones worthy of our attention have pretty significant minimum takeoff speed.

        Cruising power requirements will inherently be much lower.

    1. Indeed. Let’s put even more energy into the atmosphere. The attenuation effect turns that RF into nothing but heat. It’s small, but we are talking MW here. Not to mention the spectrum problems of all that RF flying around.

      Can it be done? Sure. Should it be done? ……eh…… gonna have to go with a hard “no” on this one.

  1. The fusion electricity seems more probable:)
    Is the problem with scattering of microwaves in water vapours e.g. clouds and fog solved? And the part about enough quick birds is particularly ridiculous:)

  2. “birds passing through the beams are likely to survive if they’re fast enough.”

    Dateline S.E. Asia 1970:
    One of the morning rituals was picking up “fried” birds under the tropospheric antennas.

  3. There’s a fascinating rabbit hole around the concept of scalar waves.
    1x of them is basically undetectable (no fear of birds getting fried).
    2x of them with a different frequency can deliver large amounts of energy to the intersection.

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