So, ballpark 7 MegaWatts, more during ascent, and add a bit if passengers want to watch movies, eat hot meals, drink soft drinks, etc.

On the plus side, if the airplane doesn’t have to carry fuel, carrying capacity could go up (with some redesign to make the plane strong enough to land fully loaded), so that 737 might be equivalent to a 747.

That 737-300 has about 125m² of wing area, and, guessing, about the same are for the body, so that would be 7MW/250m² = 28kW/m². The sun delivers about 1,400W/m², so that’s 20 times what the suns delivers on a cloudless day.

Now, most of the time, the ground station (or solar space array) beaming the energy wouldn’t be directly below/above the plane, so the required power/m² could go up a lot ⇒ I would make sure that any windows in the plane wouldn’t let the microwaves through.

Doable? Possibly, but on ground level, I guess it would be wise to use a lot more area for sending that amount of power up, to prevent killing birds.

A small battery, and/or a ground station at the airport could provide a bit of extra power during ascent, and the battery recharged during flight. I guess the extra power shouldn't amount to a lot more than 10kW...

Depending on the wavelength, it should be fairly easy to have the plane act as a Faraday cage to shield its passengers. I guess the geometry could be slightly tweaked as well to make a larger surface area, possibly using trailing metallic wires to improve the energy collection area at a minimal cost (I get that cylindrical wires are the worst aerodynamic shape, but it should be less of a problem behind the wing).

If the wavelength is low enough, a coarse mesh could collect power quite efficiently, but you'd have to worry a lot more about radio interference.

If you go slower, you need bigger wings (also no one really wants longer, slower flights in cramped airplane cabins).

Answering to a cousin comment, buses and trains can't compete when you need to cross water :)

So it seems drag isn’t taking most of that power.

Also, “I guess the extra power (for ascent) shouldn't amount to a lot more than 10kW” seems unlikely to me. It’s too low compared to the 7MW used at cruise height.

Also, if my math is correct, 1kWh lifts one kilogram about 360,000 meters, or 36,000kg (less than the weight of an empty 737) by 10 meters. So, 10kW would lift the plane by only 100 meters in an hour.

I like to approach problems this way. Plus, one can have dreams, can't they?

Once you've shown it can theoretically work, it's time to consider the side effects: best/worst. With the above, someone now controls a multi-gigawat orbiting power source.

Upsides: well, it can power useful stuff just about anywhere on (two third of) earth when there's nothing else to do. That would be really useful to compensate renewables, or other grid fluctuations. One could even imagine making airplanes slower of faster depending on demand.

Downsides: well, somebody really does control that :)

Might be a problem at the base station, but there should be multiple of those for greater fault tolerance anyway.

A 737 has a wing area of 125 square meters. To deliver 7.5MW to those wings will need 60kW/square meter.

That's a far greater energy density.

As for "time in beam" of a moving beam. Presumably one end of the beam is fixed, and depending on the target's velocity the beam might not be moving much at all (oncoming plane).

So, picking 30,000 feet for flight height and 250m/s for the plane’s speed, at 900 feet the beam’s speed would be 7½ m/s. That’s quite doable for birds.

More importantly, if the beam isn’t sent from directly below the plane, and the plane flies more or less directly towards or away from the beam’s source, the speed at which it moves horizontally goes down considerably (1/cos(α), where α is the deviation from the vertical, I think), and its width when flying through it in the direction of the beam’s source at constant height will go up considerably.

The beam’s width, and, with it, intensity, will likely be larger on the ground, but my gut feeling is this won’t be enough to correct for both these factors in all cases (corrections welcome)

That said, I was mostly imagining space-based stations.

In the above case, I talked about ground-based stations at airports. Unfortunately, those would require high angular velocities, but would already be in bird-restricted areas (airports use all sorts of tricks, including drones, sounds, people chasing them, etc, to scare away birds). You could also conceivably drastically lower the beam energy output by using multiple beams that concentrate at a single point.

Now, a fun calculation: what would be the tipping point between birds saved by not emitting carbon dioxide and birds killed by the towers, if there is one?

One last point: I'd hazard that the bird is likely to change direction if it starts running into a beam and it has time to (ie, it is not killed "instantly"). This drastically lowers the dangerous altitude range, as the bird is less likely to fly in the same path as the beam (how likely was it in the first place? One would need to go faster than the other to catch up, but not too much to actually dispense the lethal dose? I haven't done the math, but I'd say it's quite unlikely).

I don't know if this reasoning is correct or not, but definitely has nothing to do with the speed of light in air. I'm not even sure why you are bringing it up.

But the safety question is more serious. The beam is dangerous to birds, unshielded aircraft, and persons on the ground. I don't think it's great giving the US military even more power to start a fire anywhere on earth with zero warning.

They already have hydrogen bombs :-)))

This is a bit like complaining about a knife in a gun shop :-)

Single antenna apertures are limited to about 90 dB of gain, and I doubt that is near enough, but I’d have to run some calculations.

Are lasers like this detectable? If not, seems like a good way of creating targeted brain tumors. Disrupting soft infrastructure nodes etc.

If you get hit by a megawatt beam, you're going to get burned regardless of the wavelength (unless either it's short enough to pass through you, or somehow you reflect 100% of it).

As another comment points out, you can beam steer quite fast. You only care about angular rate, and an airliner at cruise altitude moves fairly slowly (eg you can follow it with your eyes easily).

Actually, yes, the article explicitly mentions the possibility of powering unmanned aerial vehicles.

Ya. The public report on the super-secret space plane touts that it is studying far-off green energy solutions when those same technologies have much more immediate military effects. It's like the USAF saying that it is studying lasers in order to build better CD players. Everyone takes such statements with a grain of salt. Nobody thinks that we are getting the full story behind these experiments and we chuckle a bit at the poor junior officer instructed to "be creative" with descriptions in public statements.

You're not wrong about low orbit sats in general, but it's only one of many potential military (and/or civilian) uses. And it's not the use the article focuses on.