[aorloff]

Reliably and efficiently transport energy generated in space back to earth, for starters

Or let me guess, its going to be profitable to mine crypto in space (thereby solving the problem of transporting the "work" back to earth)

[mlindner]

It's always better to generate electricity on the ground than attempt to beam it to the ground from space. The efficiency loss of beamed power is huge.

[amluto]

The efficiency loss of nighttime is approximately 100% if we’re talking about solar energy. At least at a most basic level, it’s not totally absurd to stick some kind of power beaming contraption in space where it is mostly not shadowed by the Earth and beam power to a ground station.

[ben_w]

Any process for beaming power from *outside Earth's shadow* to a point on the ground within the shadow (i.e. local night), necessarily can also send power from somewhere else on the ground that is in sun, even though the planet is in the way (ground->space->ground).

I wouldn't be too surprised by beamed power being used on Mars, because that planet has global dust storms during which nowhere on the surface is getting much light, but it doesn't make as much sense here: because of the atmospheric window, you either use 0.4µm-to-10µm-wavelengths or 10cm-to-10m-wavelengths* with not much in between, µm means lasers and the mere possibility you may have included lasers powerful enough to be useful means everyone else will demand something similar to the IEA nuclear inspection program or will put similar lasers on the ground and shoot them upward to destroy those satellites, while cm-wavelengths means each ground station is a *contiguous* roughly 10km diameter oval.

Given the expensive part of large-scale PV has shifted from the PV itself to the support structures they're on, the ground station ends up about the same cost as a same-sized PV installation, and because that's just the ground station this remains true even if all the space-side components are zero cost. Normal ground-based PV also has the advantage that it doesn't need to be contiguous.

It is also possible to use a purely-ground-based method to transfer power from the other side of the world; a cable thick enough that the resistance is only 1 Ω the long way around is already within the industrial capacity of China, but the same geopolitical issues that would make people hostile to foreign beamed power satellites also makes such a cable a non-starter for non-technical reasons.

* https://en.wikipedia.org/wiki/File:Atmospheric_electromagnet...

[aaronharnly]

I concur it’s not necessarily totally absurd — but when you consider that such contraptions require large — very large! — receiving arrays to be built on the ground, it’s hard to avoid concluding that building gigantic photovoltaic arrays in, say Arizona (for the US) along with batteries for overnight buffering and transmission lines would still be massively more efficient.

[hdjrudni]

Is that more or less absurd than making deals with our neighbours to share their electricity? Build some solar farms around the planet and then distribute it over wire.

I honestly don't know the answer. I know there's some efficiency loss running over long wires too but I don't know what's more realistic.

[mike_hearn]

In theory you can do HVDC over long distances. In practice that doesn't help much. Power would normally want to run north to south (not gonna do HVDC across the oceans anytime soon), and so the terminator hits you at the same time everywhere. It's got to be batteries if you want PV at scale.

The practical difficulties aren't really long distance transmission though. They're political and engineering. Spain had a massive blackout recently because a PV farm in the south west developed a timing glitch and they couldn't control the grid frequency - that nearly took out all of Europe and the power wasn't even being transmitted long distance! The level of trust you need to build a giant integrated continent-wide power grid is off the charts and it's not clear it's sustainable over the long run. E.g. the EU threatened to cut Britain's electricity supplies during Brexit as a negotiating tactic and that wasn't even war.

[Certhas]

HVDC would be a lot less connected than an AC grid.

The real question is, why do you expect Space to have fewer political and engineering issues.

[mike_hearn]

The political issues in space are mostly launch related, right? Once you have the birds up nobody cares about anything except space junk and bandwidth. They're getting experience of solving those with Starlink already. And if you can find a way to put the satellites really far out there's plenty of space - inferencing satellites don't need to be close to Earth, low latency chat stuff can stay on the ground and the flying servers can just do batch.

The politics on the ground is much harder. Countries own the land, you need lots of permits, electricity generation is in contest with other uses.

[queenkjuul]

There is absolutely nothing realistic about power transmission from space to earth, wired or wireless.

[queenkjuul]

We have these things called batteries, you charge them during the day, and drain them at night.

A solar+battery setup is already cheaper than a new gas plant. Beaming power from space is absolutely asinine, quite frankly. The losses are absurd, the sun already does it 24/7, and we know how to make wires and batteries to shuffle the sun's power around however we need to. Why on earth would we involve satellites?

[brd529]

Overview energy has done interesting work in this area.

[_fizz_buzz_]

Beaming energy always sucks. Without some very fundamental discoveries in physics nobody will every make this work economically. This isn't just an engineering problem, it's a physics problem.

[mlyle]

Beaming energy does suck, but it might be something to do before we launch thousands of terawatts of GPUs to space.

[mkull]

Why would you transfer the energy to earth? The energy powers ai compute = $

[Sparyjerry]

Dead on, You can transmit data to and from space and have the compute completed at potentially fractions of the cost.

[aorloff]

Tell me about your cooling medium in space

[rlt]

A large piece of aluminum with ammonia pumped through it?

[aorloff]

Nothing about this is sounding economically competitive with ground based solutions

[jacquesm]

Right up to the radiation limit and then you'll either have to throttle your precious GPUs or you'll be melting your satellite or at least the guts of it. You're looking at an absolutely massive radiator here, many times larger than the solar panels that collect the energy to begin with.

[DoctorOetker]

not really, for A_radiator / A_PV = ~3; you can keep the satellite cool to about 27 deg C (300K) check my example calculation (Ctrl-F: pyramid)

[pyrale]

Where does the heat collected by amminia get evacuated?

[littlestymaar]

Through thermal radiation, it's called radiative cooling.

But it's not trivial indeed, especially if you want good power density in your space data center.

[rlt]

Not sure why this is downvoted. Much cheaper to transfer data than energy.