A proposal for a purely electric-powered commercial airline industry
Around 3-5 years ago, Elon Musk was teasing that he thought he had a clever idea for how to make electric-powered aircraft viable/profitable with, basically, current technology ... and he was basically daring people to guess it.
Regardless of what he actually did or didn't know, it got me thinking, and I came up with an idea. I thought I'd run it past the Tildes Team, see if it passes muster.
My idea, in a nutshell, is to build airplanes with only 25%-50% of the battery capacity required for their flight (making them much lighter, with much more capacity for people/cargo) ... combined with, I'll call them Maser Cells on the undersides of the wings ... coupled with low-intensity maser beam emitters at all the major airports.
Airplanes use a ridiculous amount of energy gaining altitude. For short flights, it can be upwards of 50% of their fuel spent just getting from takeoff to cruising altitude. My basic idea is for planes to get up to cruising altitude in large circles over the airport, powered by a combination of battery power and maser energy beamed up from the airport below. Then stay in a taxi-ing circle over the airport until the batteries are fully charged, before departing. Longer flights can plan their route to include one or more detours to pass over other major airports (or other recharging hubs, like the Tesla Supercharging network, but for airplanes) to recharge the batteries along the way.
Trans-oceanic flights would be more challenging, perhaps requiring some kind of recharging hubs located midway in the oceans.
To clarify, my "Maser Cells" are similar to traditional solar-electric power cells, except they are optimized to convert either laser or maser beamed energy into electricity. These things already exist (I forget what they're called), although getting them to a high-efficiency commercial-airline level of production, that would take some effort.
There is, potentially, a lot of inefficiency in the conversion rates, from ground-generated electricity to ground-generated laser/maser, then on the plane, maser converted back to electricity into battery, then from battery into electric engines ... perhaps there are ways to reduce the amount of conversions necessary, or to increase the efficiency of the conversions. Or perhaps this is what kills the idea.
Similarly, if this were actually implemented large-scale, to largely replace fossil-fuel-driven planes, we would be talking about a LOT of electricity requirements, a lot of laser/maser emitters at every airport, and a massive redesign of flight traffic management, to allow for hundreds of planes routinely in hours-long recharging flights over every airport, all the time ... potential choke-points at various recharging hubs (again, similar to what Tesla sees at overly-popular Supercharging stations on the ground) ... and doubtless lots of other issues I'm not thinking of.
Anyway, though, that's the notion.
ETA: This idea could be extrapolated to an extreme degree, with on-board batteries almost completely eliminated.
With clearly defined flight corridors, and ground-based maser power stations located every 10-20 miles along, planes could fly their entire route on power beamed up to them, with only 20-30 minute battery capacity for emergencies.
ETA #2: A person who owned his/her own rocket company might also consider putting the maser cells on the tops of the planes, and launching a bunch of solar-power-generating satellites, with maser emitters shooting power down onto them.
I guess my main point is, if this maser-energy delivery system is even remotely feasible at a commercial level, there's a lot of potential.
I don't know enough about the science to decide whether or not something like this is possible, but I will say that I think the idea of holding patterns over airports is basically a non-starter for a few reasons.
Traffic. Even if it only takes 30 minutes of holding, that will still cause a large amount of traffic, I think people underestimate how many planes can take off and land in 30 minutes, especially at big airports.
Area. Holding patterns are pretty big, like, miles big, realistically I don't think you could pull a holding pattern over an airport without causing some motion sickness.
Yeah this just can’t operate at the scale needed for commercial aviation, even if the efficiency loss and bad weather issues could be addressed.
O’Hare, just as an example, averages over 2,500 flights per day. The air space is actually dangerously thick with planes and air-traffic control is already one of the most stressful jobs out there with the number of split-second decisions with life-and-death consequences controllers are asked to make. And that’s with straightforward takeoffs and landings.
Add a bunch of planes circling around trying to stay positioned above maser beams and you’re adding a whole heap of stress to controllers and pilots both.
On top of that, there’s comfort for passengers to consider. Many many people are anxious fliers. And one of the most anxiety inducing parts of flying is turbulence and variable motion. Constant circling on every flight is not going to do anyone any favors, especially if they’re prone to getting queasy.
Residents near airports already hate planes going overhead because of how loud they are, which is why many have pretty narrow flight-paths to avoid bothering residents. You’d need bunches more airspace to make this work, and way more ground area dedicated to beam emitters.
At some point it almost makes more sense to put satellites in space to absorb solar energy and beam it down instead up from ground bases and airports. But then I doubt it’s realistic to put enough solar panels in the sky to supply the energy requirements of an airline industry that way.
I think it's a non starter simply because the infrastructure requirements would make high speed rail a much better option financially. I think the more reasonable way to go is replacing most flight routes with high speed rail, and then using synthetic fuel derived from atmospheric carbon for those where it's not possible, like intercontinental flights. You would still likely need to replace or retrofit much of the fleet to run on methane or hydrogen, since I don't think synthesized kerosene would be nearly as efficient to generate, but you could use biofuel as a stopgap.
I can't decide if having to fly a holding pattern several times during a flight to recharge via magic power beams is futuristic or retro.
Yeah, recharge time would also be a defining factor. If this could approach something close to the "80% in 30 minutes“ recharge capacity of cars, I think it would be very feasible.
OTOH, if an aerial recharge took 10+ hours, it would never work.
I think your 2nd edit is actually more viable with the maser power source located in orbit rather than ground based. With greater line of sight the plane doesn't necessarily need to hold over an airport, the plane can have power directed to it the entire time it's in flight, and you don't have to deal with line of sight being cut off by terrain. Getting enough power might be the biggest issue though. Solar power is "free" and abundant in space, but takes a lot of surface area, and a full sized airliner in flight takes an enormous amount of energy.
It seems like it would make more sense for this to be a proposal for a research project. For example, maybe test this form of power transmission on the ground. Before that, though, maybe do some reading about what's already been done?
Why masers? Wireless power beaming is a thing, but it typically uses lasers for long distance, as photovoltaic cells are actually fairly efficient with laser light. Microwaves are used, but that's typically for shorter range, more broad beaming. The type of cell that you're describing in the microwave range would just be a microwave antenna, sorta like you have for satellite TV.
It's my understanding that microwave power transmission is actually significantly more efficient than laser, as microwave generation is more power efficient than laser light generation, and unless I'm mistaken, rectennae are both more efficient and cheaper to build than photovoltaic cells, even ones tailored to work at a specific frequency.
EDIT: I forgot we were talking about MASERs. I know magnetrons are more efficient than lasers, but I'm not sure about MASERs. The point about power rectification should still stand though. Also, microwaves should have a much easier time punching through clouds and fog, as long as the appropriate frequencies are chosen.
I think one important limiting factor here that we haven't considered is power, and especially power per unit area for the transmission system. Modern turbofan engines, of the kind that are used on most commercial aircraft today, use a lot of fuel (On the order of metric tons per hour, even for a regional jet), and that fuel has a high energy density. Let's go through some math to see what that looks like for this idea.
I will be using the Airbus E-Fan X, itself a modified British Aerospace 146. I feel it represents the state of the art fairly well, as it was in development up until this April, when falling air travel demand forced the project to be cancelled.
The BAe 146 does its top speed at 426 kn of thrust, and it cruises at 404 kn of thrust, which leads me to believe that at cruise the throttle will be at around 94.8%. The E-Fan X replaces one of the four engines with a 2 MW electric version. For a hypothetical version of the aircraft that is the same mass and thrust with all four of these engines as electrical, this means the power usage at cruise would be 7.59 MW. I think this is a safe set of assumptions because the aircraft will need some battery capacity, and the energy density of jet fuel is on the order of 50 times greater than lithium ion batteries (43 MJ/kg vs 0.875 MJ/kg), so we are assuming 1/50th of the energy. In reality this would be less than 1/50th the endurance because an aircraft powered by fuel will be lighter at the end of the flight than at the beginning, allowing it to throttle down over time, while the electric aircraft will be the same mass throughout. I'll admit that battery technology is improving, but even a battery 5 times better than what is available now is an order of magnitude less energy dense than the fuels in use today.
Now that we have the steady state power, what does the power per unit area look like? For a best case scenario, we'll imagine that the aircraft is able to absorb power perfectly efficiently, with no reception losses, and no losses due to travelling through the air. As a first case, let's say the aircraft can absorb energy from a complete rectangle with a size defined by the aircraft's length and wingspan. The longest variant of the BAe 146 has a length of 31 m, and a wingspan of 26.34 m, for a total area of 816.54 m. Using the 7.59 MW figure from earlier, that's a power flux of ~9295.32 W/m2. Direct sunlight is on the order of 1050 W/m2, so in this case our theoretical LASER or MASER system is 8.85 more concentrated than the sun. I'm not sure that this counts as low intensity, but it's not super unreasonable.
A more realistic scenario that does not have the aircraft absorbing energy from area where it is not physically present would be to use the wing area. The engine nacelles are on the bottom of the wings, but we'll say the flat areas of those and on the bottom of the fuselage even out any losses there. The BAe 146 has a wing area of 77.3 m2, which gives us a energy flux of 98,188.87 W/m2 (significant figures notwithstanding). This is ~93.5 times more intense than direct sunlight. This is definitely no longer low intensity.
I can see a lot of ways such a powerful beam could be dangerous, because it's a big powerful beam of radiation and if it hits something it's not supposed to that thing might die, and it could also cause some pretty serious thermal concerns on whatever is supposed to be receiving the power. At least for photovoltaics, thermal issues also significantly reduce efficiency. I think a better bet for electric aviation in the near term is for slower flights using smaller, electrically powered prop aircraft, as the first commercial electric flight or the Eviation Alice choose to do. The beaming idea is promising for long duration, low power applications though, with some suggesting it as a way to power spacecraft on their way to other planets.
I read a sci-fi series that took place in the 23rd century. They had space planes that could get much higher than jets, and were powered by super capacitors. They'd charge them up, and then slowly discharge them as they flew. I wonder if that would be more feasible than microwave transmitters everywhere?