On beaming solar power from low earth orbit
innovationfrontier.org
innovationfrontier.org
Just to construct some massive structure in space is a monumental challenge. Every ton of solar panels or support structure needs some bus to get it to the right orbit and maneuver it in place. Even if you assume fully automated construction you need buses for all the construction robots and tankers to refuel them. Any collisions could scrap the whole project by making a debris cloud in the same orbital plane as the relatively fragile solar panels.
That all ignores the sourcing of raw materials, finished components, fuel, and buses to flit everything around. The "easy" answer is "use in-situ materials". In-space mining, refining, and fabrication are all entirely unsolved problems. Even the cheapest vapor ware SpaceX heavy lift rocket isn't cheap enough to build a space based solar plant with components from Earth.
The technical difficulty and cost would be ridiculous compared to just building ground based renewables. Ones of billions of dollars will get you gigawatts worth of off-shore wind power or ground based solar.
Unless you have access to literal magic there's no situation where space based solar ends up more efficient or cheaper than ground based renewables. The capital expense is literally and figuratively astronomical.
SSP only works if every piece of the orbital infrastructure is sourced and built outside of Earth's gravity well.
But that's not even the main concern with such system. The primary reason we won't see anything like this anytime soon is the simple fact that such system can easily be weaponised. An SSP is basically a potential space-based weapon. Even if there's no intention to use it as such, some governments are pretty much guaranteed to see it that way and proceed to install actual space-based weaponry in orbit.
Asteroid mining has a similar problem.
Any tech that can send a metal asteroid to Earth orbit can also smash it into Buenos Aires.
Spaceflight is a story of a military technology finding civilian use. That has a very different ring to it than civilian technology being used as a weapon, even if the effect is similar.
“A system described in the 2003 United States Air Force report[9] was that of 20-foot-long (6.1 m), 1-foot-diameter (0.30 m) tungsten rods that are satellite-controlled and have global strike capability, with impact speeds of Mach 10.“
That’s 1.725m2 of tungsten at 19,280kg/m2 = 33.2 metric tons and it’s still only doing Mach 10 on impact.
>About once a year, an automobile-sized asteroid hits Earth's atmosphere, creates an impressive fireball, and burns up before reaching the surface.
>Every 2,000 years or so, a meteoroid the size of a football field hits Earth and causes significant damage to the area.
https://www.nasa.gov/mission_pages/asteroids/overview/fastfa...
How would the US respond? Possibly Congress will respond by paying to build its own bigger one, again not for the economics, simply for the prestige.
I am not sure anyone will care that much about the “space-based weapon” angle. If it is a weapon, you just build your own and then you have one too, and now both sides have that weapon. The ability to have a (possibly illegal) space-based weapon yet publicly insist it is just a (completely legal) power generation demonstrator may even be attractive to military planners on both sides. However, in practice, a modest sized technology demonstrator may be quite limited in the damage it can inflict, unless it was enhanced with extra hardware that made it more obviously a weapon, and harming its plausible deniability.
But framing it as a weapons system, to attract military funding (which ultimately ends up as useful civilian technology) isn't so bad.
If there is at most one space based solar energy system visible from any given point on the ground, you can make strong safety claims based on wavelength and antenna size.
However, if you limit yourself to one in any given sky, you necessarily either (1) put them in high orbit so they do useful things in local night, limiting you to a small total count planet-wide, or (2) put them in a low orbit, which means you can’t use them in local nighttime.
If you want nighttime coverage and enough of these systems to be relevant to global power — and the current nameplate capacity of ground-based PV is just under a terawatt — you have to worry about multiple orbit-to-ground beams being directed at the same spot.
While you could have up to about half a dozen giant ground-station for half a dozen giant beams, that needs ground level transmission over a significant fraction of the surface to be relevant to global energy needs, at which point you might as well make a planetary scale power grid and get your nighttime supplies from a mixture of the rooftops on the other side of the planet and some convenient deserts your energy supplier is renting.
Geostationary orbit is a circle over the equator with radius 42241 km, circumference 265408 km.
Yes, it's "limited" in the sense that it's finite, but it's not exactly small.
In its current primary use, communication satellites, there is a problem with interference; things like residential TV-sat dishes need to be small, so they have limited resolution, so those satellites need to be relatively far apart. That is not an issue for space based solar power.
> put them in a low orbit [...] worry about multiple orbit-to-ground beams being directed at the same spot
From different directions, at different times.
The limit is not how many physically fit in geostationary orbit — I agree that’s fine — it’s that if more than one such system is in your sky (Edit: that is, above your horizon) then you need to care what happens if all the different ones in your sky (above your horizon) target your location at the same time.
>> put them in a low orbit [...] worry about multiple orbit-to-ground beams being directed at the same spot
That ellipsis is combining different scenarios.
No, you don't need to, because they don't need to.
>>> put them in a low orbit [...] worry about multiple orbit-to-ground beams being directed at the same spot >> >> That ellipsis is combining different scenarios.
Only if you insist that "about half a dozen giant ground-station for half a dozen giant beams" is the limit for what can be put in geostationary orbit, which you now seem to acknowledge is not true.
Hypothetical scenario: 1000 satellites evenly arranged around geostationary orbit, each beaming 1 GW to a ground station.
Now hackers point all the ones visible to NYC at NYC.
How do you guarantee this does not happen? I can only think of two options: (1) small number of big satellites (down side being centralisation); (2) low orbit (downside being no nighttime power because they’re now in shade at local night).
I say you must not allow this hypothetical to happen. This is a safely limit, and it never has anything to do with the volume of the orbit. It is still a limit.
What you just did there is called moving the goalposts.
The discussion up to that sentence was about constraints imposed by orbital geometry. You claimed incorrectly that the "limited" space available in geostationary orbit would allow "up to about half a dozen giant ground-station for half a dozen giant beams", concluded that it would therefore be necessary to use LEO instead (it's not), and (again incorrectly) jumped to the conclusion that this would necessarily imply multiple beams on the same target.
Neither you nor anybody else said anything about sabotage.
> This is a safely limit, and it never has anything to do with the volume of the orbit.
Actually you just threw away your original argument and made up a whole new one.
> How do you guarantee this does not happen?
I don't. I also don't guarantee that terrorists won't fly airliners into skyscrapers or put a nuclear device in a container and ship it to New York's harbor. Yet we keep building skyscrapers, flying airliners and shipping containers across the world, despite the obvious risks, because the advantages of doing so outweigh those risks.
The specific risk in question is not even all that hard to mitigate, especially when you're dealing with large stations in geostationary orbit, each targeting a limited set of fixed locations (which would be dedicated receiver arrays, not cities). You put fail-safes on station which are hardwired to track antenna orientation and shut down the beam if it strays from its target. Now all your hypothetical hackers can do is interrupt the beam until you regain control, which is irritating but nothing new:
If you are unable or unwilling to understand that all of my comments in this sub-thread are consistent, that there is no goalpost moving, and that I am demonstrating the flaws with each possible configuration and thereby excluding the whole, this conversion is over.
You falsely claim I said this is about limited space. I didn’t use the word “limited” until now, and wrote of half a dozen orbital components right next to saying why it’s bad to have more, without claiming it was impossible.
You falsely claim I’m moving the goalposts, when I said it was about safety of overlapping beams in first thing you replied to.
In point of fact, the half-dozen number wouldn’t even be geostationary in the scenario I was envisioning, which ought to have been obvious from even a cursory moment’s thought. If you feel like working out what this scenario actually was instead of arguing against things I did not write, feel free, but I won’t bother looking much less replying.
One misunderstanding is on me, but this many isn’t worth the effort.
This is what you wrote:
> put them in high orbit so they do useful things in local night, limiting you to a small total count planet-wide
Do you seriously wish to claim this is not a statement about limited space?
> You falsely claim I’m moving the goalposts, when I said it was about safety of overlapping beams
Nobody is disputing that your original argument was about the safety of overlapping beams. You moved the goalposts when you replaced that argument, which was based on your incorrect understanding of orbital geometry, with one about intentional sabotage ("hackers point all the ones visible to NYC at NYC").
> In point of fact, the half-dozen number wouldn’t even be geostationary in the scenario I was envisioning, which ought to have been obvious from even a cursory moment’s thought.
The article linked at the top of this page (you know, the thing we are supposed to be discussing) is about a development program which starts with a LEO demonstrator, followed by a larger MEO demonstrator, followed by GW-class stations in geosynchronous orbit. The latter are the standard commercial scenario which has been envisioned since the 70s.
If you had another scenario in mind, you "forgot" to say so. Again. Even while confirming that the "limit is not how many physically fit in geostationary orbit — I agree that’s fine".
> One misunderstanding is on me, but this many isn’t worth the effort.
No problem, it was obvious from your first reply that you're not interested in a factual discussion.
Charlie Stross does the napkin math here: https://www.antipope.org/charlie/blog-static/2021/09/fossil-...
I still doubt it will happen any time soon, because by the time we have enough launch capacity to use on things like this, the 0.2$/W will be a sizeable fraction of the costs of solar on the ground. The advantage is that you don't need batteries, but like photovoltaics, the floor on the costs of batteries is very low.
Also that's only to LEO which is useless for an SPS since the system wouldn't dwell over any receiver on the ground long enough to transmit a useful amount of power. You'd need all that mass in a geosynchronous orbit which trebles or quadruples that cost.
1. The current (public) Starship design has no facilities for cargo delivery. While it can lift a lot of mass it doesn't have doors to unload large payloads in space. SpaceX certainly can build cargo versions but that will require non-trivial changes to the craft. Cargo doors aren't load bearing structures.
2. Starship's "100t to orbit" is only to LEO. To get a payload to a better orbit you're going to need to also launch some sort of bus and lots of fuel. Even if it's just a buddy fueling Starship that's still more launches and rendezvous.
3. Musk's claims of $20/kg are unbelievable. He has a long colorful history or over promising and under delivering. A fully fleshed out Starship production pipeline will bring launch costs down but not that much. It'd be nice to be wrong but I'd take all of Musk's claims with a giant grain of salt.
4. You're vastly underestimating the amount of mass you'd need to put in orbit and then assemble. Solar panels aren't load bearing so they all need to be attached to some sort of support truss (like the ISS truss). Then you've got the power conversion system, thermal control system, maneuvering system, and power transmission system. Each of those systems will easily mass the same as the actual solar panels.
5. The ISS solar panels with the support truss elements mass about 60t [0], so they generate about 2KW/t. Assuming power conversion was 50% efficient (I think that's reasonable) a gigawatt SPS would need at least 1000t of panel assemblies with at minimum another 500t of supporting equipment/infrastructure. I'd argue the support structure would be at least 1000t.
6. To make that SPS even remotely useful you'd need it in a geosynchronous orbit, any lower and it would pass too quickly over the ground to transmit any power.
So an SPS, sending just a gigawatt of power to the ground, would require a minimum of 1500t (~4x ISS) launched into a geosynchronous orbit. That's in addition to the fuel and buses launched to facilitate construction. All of that is just for assembly. None of that counts the component construction on the ground of the space-qualified hardware.
Meanwhile a gigawatt of renewable power on Earth is orders of magnitude cheaper and doesn't require several square kilometers of rectenna on the ground. A bit of debris that breaks a ground based panel also won't cause a chain reaction that can destroy the entire installation.
Where am I horribly wrong?
1. "A 2,000 MW SSP system would require a ground receiver covering about 30 square kilometers"
2. The satellite would be in geostationary orbit, or 22,000 miles up, so a directed microwave beam would need to be sent that distance in as tight a beam as possible, so likely the transmitter side on the satellite would be a large dish (to go along with the large surface area of the solar panels, so maybe if the solar panels are solved, then a large dish is ok)
3. Now, if you flew an airplane through that 30 sq km area what happens, or various wildlife like birds fly through that area? Slight cooking?
4. Likely that receiver can't be located near a city because people would be freaked out about being irradiated by a giant microwave beam, so you need transmission towers going across the land to the city you are hoping to power
5. If something goes wrong with your giant power plant in the sky you need to spend serious money to go up and try to fix it.
Or, you can dispense with all of that say, ok lets put up a 30 sq km solar array and a battery bank with it and just live with the fact that you don't get sun all of the time. Far cheaper and easier to maintain and upgrade in the future.
If this was a discussion about doing this from a space solar farm beaming energy down to mars, then that would be a different story since putting mass into orbit around a planet is cheaper than getting it onto the ground -- so it may actually make some reasonable sense for powering a mars base for some period of time rather than deploying tons of solar panels down on the surface of mars, then on the surface you come up with a low cost way to create some receiver that is low mass and ideally would be just a bunch of wire on a spool that somebody drives back and forth building up over a month or something.
The sat does not need to be in geostationary orbit and in fact a better solution is to have a constellation at lower orbits. This also eliminates the last problem you posed because if something goes wrong with the sat you just de-orbit it before you had planned and write it off.
If you fly through the beam or walk through it you would not know. Do you feel a slight warming when you put your hand on top of your wifi antenna?
There are problems with space-based solar and beaming energy, but none of your objections make the list.
only that this turns the cost of something that is already very very expensive into something that is hideously ridiculously expensive.
30 square kilometers is 3e7 m^2. 2000 MW is 2e9 W. So you're looking at less than 70 W/m^2.
For comparison, the solar constant [1] is more than 1300 W/m^2.
So, no cooking.
Also, the receivers would be microwave antennas on poles, i.e. they wouldn't monopolize the land they stand on. There is concept art from the 70s showing cows grazing between/under them.
For reference, according to wikipedia [1] the US federal limit on microwave oven emissions (outside of the enclosure, ie, what you would experience if you smushed your face against the glass while watching your oatmeal cook) is 50 W/m^2, which is "far below the exposure level currently considered to be harmful to human health".
[1] https://en.wikipedia.org/wiki/Microwave_oven#Direct_microwav...
This is mostly an excuse to spend money on space programs. It has to be cheaper than ground-based solar power with batteries, which is working and works better every year.
It's one of those ideas, like automotive battery swapping, which were a bet against batteries getting better.
The distance is also large enough you need to be very certain about what’s going on outside your light cone.
He is a lot more optimistic than the average person in this comments section.
So the only advantage is the 24x7 availability. Which is a big advantage, but I'm not sure if it's big enough.
I do like one of the other suggestions to use this for Mars solar — Mars has a much bigger problem with dust blocking sunlight than Earth does — but I don’t see it being more than experimental here, at least not without a unified world government to remove political risks and a whole bunch of other tech that might make it redundant anyway.
How long stuff lasts is an interesting point I has not considered. More UV, micro-meteors, even the question of what light pressure does to the orbits over a few years, given the large surface area to mass ratio. I don’t know how similar or different conditions are in the ISS orbit versus any other.
That aside, I think optical mirrors are going to be the least acceptable with regard to security/defence types, as that’s the easiest to be surreptitiously modified into a death ray, just because all the elements are physically smaller. With RF you can at least make it so any modifications are ridiculously obvious, even if you still have to care about malicious combination of multiple systems.
But on the Moon? Not only will we probably only need at most a handful, the fact that the Earth-Moon distance is much larger than most orbits considered for space-based solar power means even a maliciously retargeted combination of system would be much less of a threat.
Though as he points out there’s lots of elements which are still impractical. Though I wonder if it could be worthwhile given that covering the Sahara with solar panels would change the global climate (particularly Brazil’s) (1). Space based arrays might be a possible way to avoid that. Or perhaps provide a power source for remote areas. A starlink for power would be intriguing.
1: https://www.techtimes.com/articles/257268/20210221/sahara-de...
No. No they don't. that's not what his conclusions are at all. How did you even get that?
He's comparing space-based vs. land, not space-based vs. nothing. His conclusion is that it's pointless to build solar power collectors in space for terrestrial power applications. In all cases, if you want power on earth, build the solar on earth.
His overall conclusion may reach that conclusion, but his EROI give SPS a net 10:1 to 4:1 energy returns even in his worse case. So regardless if its cost competitive to ground based arrays or not, it might have uses and would likely result in net energy gain vs input (including materials).
I get more energy than I spend, but it's never worth it.
Also the gas there is extremely expensive.
Or perhaps it’ll become possible to use for recharging electric airplanes in-flight. In that case the ability to “beam” worldwide might offset the cost of ground based grid of towers or ocean barges, etc.
To be clear, I think it’s very unlikely, just not infeasible. Particularly if antennae tech keeps improving.
Except local solar requires fewer resources of every kind than satellite solar. You're more likely in every way to get cut off from the space version.
> Or perhaps it’ll become possible to use for recharging electric airplanes in-flight. In that case the ability to “beam” worldwide might offset the cost of ground based grid of towers or ocean barges, etc.
That would be cool. But it's a very different problem from grid power. I don't think it counts as a reason to beam dedicated space power to ground stations.
Thus, there is no need to put solar panels in faraway deserts. Putting them above other land uses -- parking lots, buildings, reservoirs, pastures, cropland -- nearer to use reduces transmission costs. Shading reservoirs, pastures and crops also reduces evaporation, thus saving water. Where water is a limiting factor, partial shade increases yield. Where water is not the limiting factor, reducing water use cuts salt fouling, and enables other uses for the water, including restoring natural habitat.
There is absolutely no shortage of land suitable for solar arrays. You mostly see them on dedicated land (besides roofs) just because that is still cheaper.
While batteries+overproduction is cost effective for overnight and even over-winter, we are still in the scaling up process for battery manufacture, and if that turns out to have a limit for whatever reason, solving the nighttime/winter problem can also be done with intercontinental HVDC[0]. And if batteries can do nighttime but not winter, those connections only need to be north-south not antipodal.
[0] At least in principal, I don’t know anything about the geological or political restrictions.
But efficiency of power transmission technology has also radically improved, so that the chief downsides to distant generation are risk of failure of the transmission medium, and of political instability at the remote site or on the route. Anybody dependent on distant generation had better have multiple distant sources.
In practice, we will end up with both local generation and storage and long-distance HVDC backup, to accommodate different failures. Countries without trusted neighbors will need more storage.
But I do wonder if there might be better applications if you think outside the box.
Can standard PV installations be the receiver? Could this act as a complement to ground based arrays by using them at night or during winter by supplementing natural light? How does the math look for wavelengths that PV can capture?
The ability to inject extra power into the grid as required might make a small number of these cost effective for the whole planet, rather than as a bulk energy source.
Is there any way of extracting CO2 from the atmosphere or breaking down methane faster that could be done from low earth orbit with cheap enough energy?
Could these supplement the energy requirements of planes, boats or trains by beaming energy at moving targets? (Feels like the receiver would need to be too large for this to work well).
Is there any use for heating clouds? Can this cause rain to control weather? As well as the standard weather control thing, that could also help with terrestrial solar production.
space based mirrors could be really cheap and light. Think of a big mylar sheet held flat with this[1] mechanism.
When you double the brightness of light on a solar panel, you more than double the power output, so using a series of space based mirrors could really increase the return-on-investment of on-ground solar panels.
Probably not very wildlife friendly... Perhaps best to do it in a desert.
[0] basically a backwards laser. https://en.m.wikipedia.org/wiki/Coherent_perfect_absorber