[Faint]

Yeah, no night, no atmosphere, constant power output, lot's of real estate, and panels in space do not need heavy superstructure to withstand weather or gravity, thus they could potentially be extremely light for the area (micrometers to tens of micrometers thick at most needed for light absorption). And in far future, if they are built of materials taken from moon or meteorites, you could also bypass most of the lifting cost for even that. Of course, that would need huge scale to justify the R&D to pull it off.

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.

[ZeroGravitas]

> constant power output

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.

[DennisP]

The satellites would be in geostationary, with phased-array transmitters, focused by a reference signal from the ground target. They actually could be repointed to various receivers. The ground stations would be relatively cheap so it wouldn't be all that important to maximize their utilization.

(Source: The Case for Space Solar Power)

[oceanplexian]

> They could potentially be extremely light for the area (micrometers to tens of micrometers thick at most needed for light absorption).

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.

[regularfry]

You might not be able to do a mylar-thick solar cell, but you can certainly make a mylar-thick reflector for a concentrator. Out of mylar.

[spacemark]

No night? Where are you putting these satellites? The only orbit that doesn't eclipse is sun synchronous, an already crowded orbit. Even GEO satellites experience eclipse.

[c54]

> Glaser had noticed that a satellite in geosynchronous Earth orbit (GEO), 35,786 kilometers above the equator, would pass through Earth's shadow for only a few minutes each year.

The article addresses this. To my mind 4 minutes per year is equivalent to the parent’s layspeak “no night” comment.

[cfraenkel]

4 minutes??? Not even close. Each eclipse varies from a few seconds for the first one to practically an hour in the middle, then gets shorter again, over roughly 30 eclipses each season (2 per year)

[mlyle]

So, let's cut down the pedantry a bit. Even in the most pessimal reasonable orbits, up to an hour of outage in the middle of the night for 3-4 months per year is a very different beast from getting just several hours of sun per day.

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.

[etskinner]

They address this in the article: Only twice per year are the panels in shadow, at the equinoxes. Presumably all the rest of the time they're slightly above/below the earth with respect to its orbit. It's the same reason the moon is lit nearly all the time.

[mlyle]

> It's the same reason the moon is lit nearly all the time.

The moon is 10x further away, so the Earth subtends/shades a much smaller angle.

[DennisP]

A geostationary satellite gets eclipsed more than the moon but it's still in full sun 99.5% of the time.

[mecko23]

Respectfully, I believe you are inaccurate on both accounts, sun synchronous orbits (SSO) only have no eclipse if their orbital plane is within a very degrees of the terminator, this of course widens with altitude but there exists far more possible SSOs with eclipses than without. Secondly with GEOs as with any very high altitude orbit the eclipse time trends towards zero so effectively at a GEO the eclipse time is minimal compared to the illuminated time. Of note the length for the eclipse time of GEO varies throughout the year.

[spacemark]

Respectfully, you are not correct that eclipse in Geo is insignificant. It drives many engineering constraints for spacecraft systems. Look I get why people are excited about space space solar power, but I've been in this industry for 15 years and when you dig into the numbers and understand the realities of spacecraft engineering, SBSP just seems like a fool's errand. It may not always be that way, but the technical challenges are extreme and costs are still nowhere near what would be required to make it work.

You can chalk my comments up to a grumpy engineer tired of the cyclical SBSP pushes that never go anywhere.

[mecko23]

Hmm, well I totally understand how it drives spacecraft design and I don’t know off the top of my head the length of greatest eclipse but it cannot be greater than a small fraction of the period (upwards of 1/12). This is significant for a spacecraft itself but as far as a regionally integrated power grid is concerned it is a clear improvement over current solar PV systems. I get that there maybe some fatigue here with the idea and blue sky optimism that comes with SBSP, I think there are valid criticisms to level at it orbit selection and corresponding ground tracks and eclipses are not one.

[mlyle]

> It drives many engineering constraints for spacecraft systems.

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.

[mecko23]

Why in this case would it cause significant problems? Are you referring to the heating (that would make sense with such a large surface area of panels)? Concerning cooling- with such short times in eclipse I can’t imagine that it would have enough time to have cooling issues beyond flexing of the superstructure (if made from metals). Be interested to hear though if I’m missing something.

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.

[mlyle]

> Concerning cooling- with such short times in eclipse I can’t imagine that it would have enough time to have cooling issues

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.

[spacemark]

It drives electrical and battery system requirements more than anything else. Thermal effects impact pointing/ADCS, which impacts propulsion, etc.

[mlyle]

There's no real intrinsic electrical or battery system requirements for a giant solar power satellite. The energy use is comparably trivial: no big transponders to run in eclipse like a comsat.

But you do need everything to survive the cold and thermal cycling.

[dabluecaboose]

Solar Radiation Pressure is non-negligible for navigation and attitude dynamics as well. Eclipse season changes things for the NAV team.

[sidewndr46]

You do realize the Earth doesn't have "night" as a globe-wide event right? If it's night here, it must not be night somewhere else.

[DennisP]

Yeah everybody knows that. But transmission by wire halfway around the globe would be pretty expensive, and carry geopolitical risks.

[sidewndr46]

Is transmitting power from a satellite in low-earth-orbit going to be cheaper?

[DennisP]

Possibly. Long-distance high-voltage wires get pretty expensive. At Starship launch costs with modern designs, SPS actually looks pretty economical.

[sidewndr46]

If someone has compiled a cost comparison of transcontinental HVDC links compared with the alternative spaceborne solution I'd certainly love to see it.

The space based solution is possibly actually more reliable, as there are actually less components involved that could fail.

[LargoLasskhyfv]

No protective atmosphere. More (micro)meteorites.

[pengaru]

> and carry geopolitical risks.

And a solar death ray aimed at the planet doesn't?

[DennisP]

As I noted in another comment, it's not a death ray. Even with a reference signal from the ground, it's not concentrated enough to cause harm.

Regardless, I don't think long-distance transmission is a viable solution to solar intermittency.

[ben_w]

One isn't a death ray; but if you only have one, then you need a global power grid anyway.

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.

[LargoLasskhyfv]

But it could be? Becaus phased array? See also https://en.wikipedia.org/wiki/The_Noah%27s_Ark_Principle

[ben_w]

Not for a single device with a fixed wavelength and size; unless someone figures out a way to cheat quantum mechanics and the diffraction limit, how well you can aim light is directly related to the size of your aperture (/antenna) in wavelengths.

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.

[sandos]

Conclusion: everyone will eventually live in orbit!

[XorNot]

I mean probably? We can't manufacture more real estate down here as easily as you could up there (once certain technologies are common place).