Electricity from Space: The 1970s DOE/NASA Solar Power Satellite Studies
spaceflighthistory.blogspot.com
spaceflighthistory.blogspot.com
and the study itself: https://www.nasa.gov/directorates/spacetech/niac/2011_Practi...
A book-length treatment of modern SPS designs is The Case for Space Solar Power. It has detailed cost figures but was written before SpaceX had accomplished much, estimating a cost at gigawatt scale of 15 cents/kWh. I plugged in Starship launch costs and it came to 4 cents/kWh, which is not bad for 24/7 clean power without storage.
What can be made in space that can allow moving this abundant energy? Obviously you can't haul ore up into space then refine it with a big magnifying glass and drop it back onto the earth. People talk about asteroids but they seem like they're a big delta-V away from where they'd be useful to put into Kia bumpers.
It's possible to grow extremely high quality crystals in microgravity, so there's your semiconductor and optics industries.
Bulk metallic glasses are easier to make in space for the same reason: crystals grow more slowly, and are easier to prevent.
High quality vacuum on a scale never seen before for experiments and industrial processes.
Imagine building the James Webb Space Telescope without needing to harden it against launch forces.
The implication of course is that surface area can be increased trivially by adding matter. And with a larger thermal mass, more energy will be required to heat the system to the same temperature, giving more slack in the system for radiative cooling to work.
Nevertheless -- finding ways to move refined products around that embody a huge amount of energy is the traditional way to approach this problem.
And anti-matter, if you could package it, is an obvious example....
Not really. The biggest difference between a panel on Earth and one in space is the space panel is illuminated 23 hours a day. So per panel you're getting 2-3x the illumination over the course of the day.
The drawback is even at the absolute cheapest pie in the sky Musk estimates of cost to orbit ($10/kg), a space solar panel is orders of magnitude more expensive than a ground panel. You could just deploy 3x the number of panels on Earth for 3x the price vs deploying in space at x\^3 the price.
Even with the near constant illumination of panels in space the losses from RF conversion, free space losses, atmospheric losses, and RF rectification eliminate a lot of your power gains. For those losses you also incur significant costs. So SBS is kind of a lose-lose problem. Every technology that would make SBS more practical could be applied on the ground for a tiny fraction of the cost.
Small nitpick, but as a GEO satellite navigator I want to point out that the solar panels are in sunlight constantly except for "eclipse season" around the equinoxes. During eclipse season it can be in shadow for about an hour.
How far does this interference extend? Thousands of kilometers from the receiver[0, see page 250]. Because the transmitter is far, the beam spreads out quite a bit due to diffraction and because the transmit power is gigawatts there's hundreds of megawatts of stray power. Making bluetooth headphones and bluetooth low energy tags work worse will probably make people angry.
Different frequencies could be used, but that requires allocating spectrum, which is a pretty difficult task politically. In the US, there are a couple bands in the sub-10 GHz range where power beaming works best that have few users. So it's not impossible, but still politically difficult.
I know super narrow notch filters up in the gigahertz are difficult, but has anyone thought at all about how narrowband the power transmission could reasonably be? Because then at least notching would be possible to squeeze out adjacent spectrum.
I'm not a huge fan of the artist(s) depicting space concepts in this particular article though (still better than most rendered art). I tried to do a bit of googling to find something better but in 10 minutes the best I could come up with was this site: https://www.kuriositas.com/2013/08/space-shuttle-concept-art...
I think there was more dynamism in the pre-CG concept art, often a bold use of color, sometimes an exaggerated use of shadow/light.
Anyway, space based solar power is the end game. Nothing on earth will ever provide the quantities of power (not even nuclear, fusion or fission) that capturing solar energy can.
Worth noting this isn't as much of a benefit as it's made out to be.
If you were designing a perfect power source, it would match demand, so produce more in winter in polar regions, and more in summer for regions with lots of AC. Similarly, you'd generally want more power during the day than at night.
This is part of the reason a mix of solar and wind that varies by latitude is an ideal mix.
Space power might get more bang for buck if it could target its power to different regions e.g. swapping from north to south as the seasons change, and/or following the day/night cycle and/or weather to maximise energy price.
(Source: The Case for Space Solar Power)
This is really the key, if you can make a solar panel that’s as light and thin as say mylar, and then unfold it when you get to space, we could put up several kilometers of solar panels without requiring much mass at all. It’s not like there’s wind or rain up there to wear it down.
The article addresses this. To my mind 4 minutes per year is equivalent to the parent’s layspeak “no night” comment.
Why?
- You still get better duty cycle from the panels
- The time the power is missing is very small
- The need for storage, etc, is low because it's a short period of relatively low demand that is missing.
The moon is 10x further away, so the Earth subtends/shades a much smaller angle.
You can chalk my comments up to a grumpy engineer tired of the cyclical SBSP pushes that never go anywhere.
Here the only thing it's going to drive are thermal requirements-- which are admittedly significant problems. There's no need to continue to use large amounts of power for comms, etc, like on most GEO birds.
And, of course, the grid needs to deal with the power disappearing for an hour in the middle of the night for short periods of the year.
As to power disappearing with an adequately geographically integrated grid I don’t forsee that as really too much of a problem. Currently the grid deals with short term outs fairly well especially if they are planned for months in advance.
Lots of thin structure with 70 minutes to radiate, with the only thing shining on it the earth's albedo subtending a tiny angle. I'd imagine it creates rather significant demands on structure and electrical connections.
I've not run the numbers on a GEO solar spacecraft, but the smallsat group that I'm mentoring that would be "thicker" than a lot of the GEO craft... gets down to -30C without heaters during its 40 minutes in eclipse while much closer to Earth.
> As to power disappearing with an adequately geographically integrated grid I don’t forsee that as really too much of a problem. Currently the grid deals with short term outs fairly well especially if they are planned for months in advance.
Yup, that's the point I'm making. A space based solar power craft has smaller problems from eclipse than a typical comsat. Batteries, etc, are not nearly as much of a concern. It's mostly the thermals that are left.
Have pizza: https://www.youtube.com/watch?v=lGDUmGlMJzU
But you do need everything to survive the cold and thermal cycling.
You'd need propulsion to maintain position and orientation. You'd also need a number of propulsion units to balance solar pressure gradients as the collector entered and existed the Earth's shadow as well as the thermal expansion/contraction of the structure.
It's likely not a lot of power but a non-trivial amount of fuel.
High-impulse ion engines, etc, are a good match for this task.
A structure 100m on a side would be just at the bounds of current technology (the ISS's control moment gyros). With 30% efficient panels that's only about 4MW before conversion and path losses.
The high impulse ion engines to desaturate the gyros would still need to be refueled regularly. I think you're hand waving a lot of complexity that even if completely solved still leaves a solution that's orders of magnitude costlier than solar panels on the ground.
The space based solution is possibly actually more reliable, as there are actually less components involved that could fail.
And a solar death ray aimed at the planet doesn't?
Regardless, I don't think long-distance transmission is a viable solution to solar intermittency.
If you have enough satellites to not need the distribution grid, and they're all in geostationary orbit, then many are over the horizon at the same time and they can (in principle) be combined on the same place.
If they're in a low enough orbit that you only get a few over the horizon at any given moment, you get a substantial penalty from Earth's shadow.
On Mars this would be a great thing for colonies; get past the global dust storms, and it won't matter if you have only a handful of sites; on Earth… pick which failure mode you prefer.
Convincing governments you've not cheated with a gigawatt optical laser on your satellites (optical wavelengths being smaller than microwaves makes them easier to focus with smaller parts), that's a separate question. I assume an Iranian one of these would get destroyed by Israel for the same reason they attack their neighbour's nuclear reactors.
Of course, there are loads of problems with the idea but I can see why it's intuitively appealing.
What is the "typically" you are referencing?
The 60% over a kilometer is not due to atmospheric absorption, it's due to losses at the transmitter and receiver (and beam spread exceeding the size of the receiver.) If microwaves lost 40% of their energy in a kilometer radar would have a hard time working.
Millimeter waves are more strongly absorbed in clear air, so they are not as good for this use case. They may be good for powering aircraft.
With modern modular designs using phased array transmitters, even getting that much focus requires a reference signal from the ground target.
Really though I don't see this scaling to energy production for the masses due to the beaming logistics.
It'll mainly be used to recharge drones that never land and possibly fry enemy systems / missiles / etc.
One cool thing we could do is slightly boost the amount of sunlight northern latitude cities receive. This will make solar panels there more viable and will make cities far more livable in the winter season. This could also be done seasonally. This is a cool example https://www.theguardian.com/world/2013/nov/06/rjukan-sun-nor...
There's solar heat based power stations, using mirrors that focus light on a point or a pipe to heat up oil; the question there is, would they become more effective if they get more light?
1 square meter of ground currently receives 1370 watts of energy (if my quick google is accurate); if this can be captured, you can do a back of the napkin calculation of how much you need. It's already been posited that filling a relatively small patch of e.g. a desert can fulfil all of europe's energy needs - no space things needed.
I assume someone has considered this scenario previously, but I imagine that SpaceX lift capacity and price might change the economics.
Not least by just putting normal solar panels on it and jettisoning the whole space part.
It's not exactly the same thing, of course, but it means 40 such ground stations would use as much metal as a 1 GW line looping all the way around the planet and back to itself, and a global grid is another way to obviate storage.
That's 1 GW with standard existing cables; I assume if you actually want to go that far one can improve the design as the optimisation goals are different. Parallel cables lower resistance.
I'm also not sure how much maximum current would scale in such cases.
But any benefit there also goes out the window if the SBS reciever is too large or dangerous or scary or ugly to have located all over the place.
Modern designs use a phased-array transmitter, and a reference signal from the ground for targeting. Overall energy loss is 40 to 60% according to the book The Case for Space Solar Power.
[1] https://www.nasa.gov/pdf/716070main_Mankins_2011_PhI_SPS_Alp...
IIRC, for n identical parallel resistors of rΩ, Σ = nrΩ, so this only gets better for bigger systems.
To even begin to make sense, space freight to would need to be 1/10th of Musk's overly optimistic $10/kg. You could ship the panels air freight and still beat those numbers by a huge margin.
That says nothing of the construction costs. Which for SBS will cost orders of magnitude more than day laborers in t-shirts assembling arrays on the ground.
Every aspect of SBS is ridiculously expensive and requires as-yet entirely undeveloped space-based construction technologies. There's no near-term horizon where it's anywhere close to competitive with ground-based solar. This holds even if you assume over-building surface solar to 3x to match the duty cycle of SBS.
As for construction cost, NASA's design would self-assemble in orbit. I linked the full study report.
https://spacenews.com/nasa-to-reexamine-space-based-solar-po...
https://www.esa.int/Enabling_Support/Space_Engineering_Techn...
https://spaceenergyinitiative.org.uk/
https://www.solarspacetechnologies.com.au/
Here's a nice recent summary (despite the publication date):
https://aerospaceamerica.aiaa.org/features/harvesting-sunlig...
Also neat that we ended up with complimentary energy generation and storage technologies to fix the "it gets dark at night" problem of solar electricity generation!
Weird, that's the first time in my life I've ever heard him referred to as 'James' rather than 'Jimmy'.