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Even if the "cost" of getting the required infrastructure into orbit (assuming Earth-based manufacturing) was close to zero, the energy requirements would still eat up the benefits.

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.

> An SSP is basically a potential space-based weapon

Asteroid mining has a similar problem.

Any tech that can send a metal asteroid to Earth orbit can also smash it into Buenos Aires.

It doesn’t even have to be intentional.

Any tech that can send a 1 ton roadster to mars can crash a 1 ton roadster into Buenos Aires at 20,000mph

Obviously. It all started as a way to drop bombs on London, and we are only now reaching a time where the majority of rocket models are not derivatives of ICBMs.

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.

Wouldn't the car disintegrate in the atmosphere?

The car would obviously be a poor choice as a weapon. A big tungsten rod on the other hand...

https://en.wikipedia.org/wiki/Kinetic_bombardment

Air resistance limits small kinetic kill weapons. Square cube law however means it’s less effective for larger objects.

1 ton tungston rod wouldn't burn up.

A 1 ton rod would loose most of it’s kinetic energy on reintry.

“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.

just make the large object split into many small kill weapons not far from the target(s).

A one ton roadster will burn up before it does anything, a large factory will not:

>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...

Think of the speeding ticket Elon will get.

Maybe China will build such a system, not because it makes economic sense, rather for national prestige, so they can claim to be ahead of the US in that technology. Even if they spend a few billion for a modest sized demonstration system, that’s only a fraction of their national budget.

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.

There's no need for space based weapons when hypersonic missiles can deliver megatonne grade nuclear arsenals "easily" today.

But framing it as a weapons system, to attract military funding (which ultimately ends up as useful civilian technology) isn't so bad.

Is it? Article claims 2 GW / 30 km², which is ~70 W/m², a fraction of solar irradiance in most places.

Sort of yes, sort of no.

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.

> put them in high orbit so they do useful things in local night, limiting you to a small total count planet-wide

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.

I think you’ve misunderstood the problem I’m describing, so I’ll see if I can rephrase.

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.

> you need to care what happens if all the different ones in your sky (above your horizon) target your location at the same time

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.

I don’t understand how you can assert what you’re asserting, especially as you appear to be claiming to read my mind despite the paragraph break you cut with the ellipsis.

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.

> Now hackers point all the ones visible to NYC at NYC.

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:

https://en.wikipedia.org/wiki/Ukraine_power_grid_hack

I am not going to make a further attempt to show you that my position is consistent or rephrase anything.

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.

>> You falsely claim I said this is about limited space. I didn’t use the word “limited” until now

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.

The game changer here is SpaceX's Starship. If you can lift 100T to orbit in one shot, that suffices to deploy around 6 MW worth of the current solar panels we use for the ISS, which clock in at around 120KW/2T. Solar panel efficiency has improved greatly since they were designed and built, so even accounting for the overhead of assembly, refueling, the transmission component etc, 10MW+ per launch seems quite feasible, particularly if Musk gets costs down to the mooted $20/kg or so.

Charlie Stross does the napkin math here: https://www.antipope.org/charlie/blog-static/2021/09/fossil-...

Interesting. That's 0.20$/W on launch costs, what is actually not a showstopper.

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.

Their math is wrong. The ISS solar panels plus supporting truss elements mass about 60t or 2KW/t. At the fantastical (unbelievable) $20/kg to LEO that's $10/W. That doesn't include the mass of thermal control elements, maneuvering systems, power conversion, or power transmission system.

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.

You're missing a few details.

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.

[0] https://space.stackexchange.com/a/9758

The naive engineer in me thinks that a baloon floating at 4k-5k meters above sea level, covered with solar panels, would still get most of the efficiency, but would also be cheaper and simpler to build.

Where am I horribly wrong?

Transmission loses would probably make a balloon a wash vs ground-based solar. Then there's the liability of some mass of solar panels floating over populated areas. At 5km an untethered balloon would have a fairly wide area it could land on. A 5km tether dragging around or falling on the ground could cause a lot of damage as well. There's also dangerous conditions when atmospheric conditions cause the balloon to lower its altitude, slacking the tether, and low altitude wind whipping it around. I don't see any utility of untethered balloons.