Random Thoughts: SBSP for All-Electric Aircraft?

I haven’t blogged about Space-Based Solar Power (SBSP) much. At least not as much as Chris and some of my other cobloggers. While I try to be non-dismissive of ideas like this, I’ve never been able to convince myself that SBSP is going to make sense for terrestrial ground-power applications. As I’ve observed Liquid Flouride Thorium Reactor fission work pushed by former co-blogger Kirk Sorensen at Flibe Energy, and “new fusion” concepts being pushed by my friends at Helion Energy (and other groups at Lockheed, TriAlpha, and several other companies), I can’t help but think that at least one of these concept is going to pan out. If it does, I just don’t see how space based solar power is going to compete with small, local reactors, especially if the Helion guys make their concept work. It would be awesome if there were markets for SBSP though, because those are potential big drivers for all the sorts of in-space infrastructure (RLVs, depots, lunar mining, ISRU, etc) that us space fanboys like. So, I was trying to think of places where SBSP would actually be useful in a world where “new nuclear” (fission or fusion) pans out.

After thinking about it for a bit, the conclusion I came to is a similar one to what Chris Stelter (and frequent commenter Paul Dietz as well) thought of independently–using beamed power to enable all-electric aircraft.

Here’s my thoughts on why this might be a better market for SBSP than ground power:

  1. As safe as LFTRs are for ground-based power, I doubt anyone is ever going to be happy with a flying fission reactor1. And new fusion power systems, even if they can be made to work, look unlikely to have a high enough power density (W/kg) to make them practical for aircraft use anytime soon.
  2. Aircraft typically cruise at altitudes above 30kft, where you’re above clouds, and also above enough atmospheric moisture that many power beaming wavelengths become feasible that won’t work for ground power applications. Both high frequency microwaves and various laser frequencies as well. The fact that the lower atmosphere absorbs them efficiently means that any misses just heat up moisture in the air on the way down.
  3. While electric motors can often be more power-dense than gas motors, batteries tend to be much lower energy density than typical aviation fuels, which means that for a comparable flight, you’re going to have a much heavier aircraft, that’s going to need more peak power and thrust than a conventional aircraft.
  4. With SBSP beamed power, you only need enough batteries for the initial climb to cruising altitude (and some contingency power for emergency landings)–most of the flight can be under beamed-power, meaning the aircraft can potentially be much lighter, enabling either more cargo weight to be carried, or lighter engines and lower overall power consumption.
  5. With SBSP beamed power, you could potentially stay cruising fast for super long durations, possibly even indefinitely, even in local nighttime conditions. Imagine an AWACS or other similar military jet that could stay flying at 50kft around an area for days on end, without needing refueling.
  6. SBSP might even enable all-electric supersonic passenger aircraft. Those tend to be very fuel inefficient, and power hungry, but tend to have decent vertical cross sectional areas for power reception. Getting rid of the fuel might enable a much lighter and more cost competitive supersonic business jet. Once again, you use subsonic battery-power to get to cruising altitude, then kick it into high speed using the beamed energy.

A couple of other considerations:

  1. If my google-fu is working, it looks like a 777 produces ~150Mw of max power in its engines, and a 737 should be roughly ~1/3 of that. While 50MW is still a lot of beamed power, this is much less than the 1GW power levels usually discussed for SBSP applications.
  2. Since the target is moving, there’s no longer a big advantage to putting your SBSP spacecraft in GEO–MEO might make a lot more sense. Even a supersonic aircraft isn’t moving that fast with respect to a MEO spacecraft, so slew rates should be reasonable. There’s more radiation in MEO than GEO, but it’s also easier to get to delta-V wise.
  3. Using MEO spacecraft (4x closer) and higher frequency microwave or IR, you should be able to cut the spot beam size down to something quite reasonable. You’d need to make sure it wasn’t near a frequency used for communications, but because you’re focusing on higher-frequency radiation that doesn’t penetrate the atmosphere well, this should be solvable.
  4. For MEO you could initially get away with a few (say 6-9) equatorial birds, and just focus on markets below say 40 degrees North or South, or go with a few planes of satellites with modest inclination to enable covering most of the useful globe.
  5. For microwave based SBSP concepts, especially if you do a large reflector, you could theoretically use the same satellite for both power beaming (high power, very high frequency), and telecoms (lower power, lower frequency). You’d have a lot of power and aperture available, which might enable satellite roaming for normal sized/powered cellphones.

A 50MW transmitter is still no small project, but is probably not a multi-billion dollar demonstration either. Definitely need to dig more into the technical and economic details to see if this would close, but if it did, this is the kind of market that might enable large-scale space industrialization.

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Jonathan Goff

Jonathan Goff

President/CEO at Altius Space Machines
  1. Even though that’s where LFTRs first came from if I’m remembering my history correctly
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14 Responses to Random Thoughts: SBSP for All-Electric Aircraft?

  1. James Robertson says:


    FYI, the cruise power for a 737 is much less than 50 MW, because at lower air pressure the engines produce a lot less thrust. Another way to calculate the power is based on the aircraft drag: power = cruise_speed * aircraft_weight / lift_to_drag. I get about 10 MW assuming 511 mph, 150 klb aircraft, and L/D of 15 (airliners typically are in the 15 to 20 range). That should make the power beaming a bit easier!

    The 737-SBSP might still need 50 MW for takeoff and climb. Perhaps shorter range power beaming or batteries could be used for that higher power level.

    It’s also interesting to think about supersonic aircraft, since so much of their weight is fuel (~50%), power beaming might enable a large refduction in their size and weight. Consider a Concorde carrying no fuel: 1164 kts * 200 klb / 7 (L/D at Mach 2) = 76 MW.

  2. James Robertson says:

    Thanks for posting some well organized thoughts on this. Power beaming for aircraft is something I’ve also been musing about.

  3. Jonathan Goff Jonathan Goff says:


    You’re welcome! I’m glad you thought my quick blog post was well organized. 🙂

    I’m also glad you helped out with the numbers. I hadn’t had the time to dig into the power beaming math, but if a 737 only needed 10MW at cruising altitude/speed, and only 76MW for an all-electric Concorde, those are both really feasible sounding.


  4. Andrew_W says:

    Jerry Pournelle promoted this concept, with a system using lasers, in one his books (a step further out 1981).

    Can I just add that some people might think that electric = propellers, when in fact with enough power available electric jet aircraft are perfectly feasible.

  5. James Robertson says:


    I think your thoughts are better organized than mine! 😀

    I’ve just realized that in my excitement, I didn’t take into account propulsive efficiency in the power calculation. So that 10 MW is just the power required due to drag, not the input power. Propellers can be 85% efficient, but a ducted fan is probably better suited to a high-subsonic airliner, and quieter. I don’t know their efficiency, but I’d be surprised if it was less than 75%, and astonished if it is less than 50%. And of course you have all the rectenna, power handling and electric motor losses.

    I’ve also pondered using the beamed power to directly heat the air, but I haven’t run any numbers. That is probably less efficient than using an electric motor.

  6. Pingback: Beamed Power Electric Aircraft

  7. Paul D. says:

    I wonder if ultraviolet lasers could be useful here. They aren’t useful for reaching the ground due to Rayleigh scattering, but the same effect would diffuse much of the beam that missed the aircraft. The wavelength would have to be longer than the longest wavelengths strongly absorbed by ozone, unless the plane was well up into the stratosphere.

  8. Bob Steinke says:

    Batteries could also be used to bridge any short blackouts from switching satellites and recharged when the beam is on.

  9. David says:

    For military applications… or commercial ISR applications… maybe. But there are like 80,000+ flights over the US every day. Some (not small) fraction of those are up at the same time and you have to power each… that’s a lot of satellites, or some very large ones that can track more than one plane… and if I want to fly more planes we have to launch more satellites. Not sure how the business case closes here.

  10. Andrew_W says:

    David says:
    December 4, 2015 at 7:49 am

    I think you’re looking at it backwards, the bigger the customer base the easier it is to make the financial case for large infrastructure business projects to close.

  11. George Turner says:

    The problem I see is a descent under clouds that ends in a missed approach or a forced divert to an alternate airport. The batteries were mostly depleted in the initial climb to cruise so they won’t have much left in them – unless you can top them up at cruise. But you’ve also got short flights that won’t be above the clouds all that long.

    You might want to restrict the aircraft to cargo flights until they’re well proven at such contingencies.

  12. Andrew_W says:

    Seems likely that the batteries would be charged during flight and that the initial passenger flight market would be in long haul. The first aircraft would, I imagine, be hybrids with the normal complement of kerosene burning engines.

  13. Chris Stelter says:

    I expect such aircraft to be fully electric. With or without SBSP, we’ll see fully electric aircraft start taking to the skies. Limited by lithium-ion, they’ll only be able to do short routes. But in either case, it’s assumed that there’s sufficient battery reserve (this reserve requirement makes it hard to do electric aircraft, but not impossible).

    The reserve doesn’t have to necessarily cost you anything, either. Usually with lithium-ion or lithium-air batteries, you get your best cycle life by not completely discharging. So the bottom, say, 15% of your battery would remain unused just for cycle life reasons. You’d be able to dip into that reserve if needed.

    Also, an electric aircraft is capable of regeneratively braking. Instead of using airbrakes to slow to approach speed and altitude, an electric aircraft could slightly recharge its battery, adding to margin in case of a need for go-around.

  14. Andrew_W says:

    Chris, the low altitude electric battery powered short haul is at one extreme, while the high altitude long haul more suitable for SBS beamed power is at the other extreme, very different planes, I don’t see the former evolving into the latter.

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