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:
- 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.
- 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.
- 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.
- 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.
- 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.
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:
- 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.
- 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.
- 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.
- 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.
- 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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