[TeMPOraL]

> Is my borderline childish understanding of basic physics THAT off because I cannot see the value or utility (beyond a small smear of niche edge cases) of space-based compute?

Don't worry, most of the people online didn't get the memo on this.

One of the major selling points of orbital compute is power supply - more specifically, it turns out that, compared to beaming power from space, it's projected to be cheaper to move compute upwell instead - atmosphere losses for beamed power are just too big. Of course this doesn't matter if you can get cheap, clean power from elsewhere (e.g. nuclear).

This is in general data center case. Here, GP says the motivation is reducing C2 RTT, which makes sense for military applications.

[notahacker]

The unit economic tradeoffs aren't quite that straightforward (beamed power is lossy enough to require more panels[1], but solar cells and satellite structures have longer useful lives than inference chips so over longer time periods you likely end up launching more stuff into space with disposable datacentres anyway[2], particularly given the datacentres also need bigger radiators. Other issues which favour power being beamed to the ground are not exposing those expensive chips to radiation, and being able to replace them on cycles dictated by inference chip innovation or end-of-life rather than fixed cycles depending on a satellite propellant budget...

The other comparison point is of course plain old terrestrial power sources, including energy storage in the mix if it relies heavily on solar power without a sufficiently global grid. Not having to launch into space buys a lot of power.

C2 RTT times and edge computation of large datasets collected in space make much more sense since unit economics aren't the driving factor, but are unlikely to need datacentres on the same scale as inference compute for the general population (another reason why this use case makes more sense)

[1]but I think the underrated problem with beamed power isn't just the low maturity of the technology, but that as soon as you start talking about sending power to earth via RF or laser you're going to encounter political opposition that makes objections to terrestrial datacentres seem tame.... [2]chips can in theory be replaced on orbit, but the "million satellite" filings are disposable. Replenishing propellant for a few large power stations, potentially on longer cycles, is a simpler task.

[pantalaimon]

> but solar cells and satellite structures have longer useful lives than inference chips

The limiting factor on the lifetime of any satellite is fuel. Especially for large structures that are influenced a lot by atmospheric drag and solar wind.

[notahacker]

Sure, but periodically refilling a propellant tank for a few large SBSP structure on-orbit involves less complexity than replacing racks of inference chips distributed across constellations of satellites as proposed by current filings. Which is why the latter structures are designed to be disposable and the former not.

SPSP proposals tend to operate in higher orbits than ODC proposals too, as they're less affected by latency and radiation, so their station-keeping requirements are less propellant-intensive.

[TeMPOraL]

> beamed power is lossy enough to require more panels[1]

What kills that is simply costs of land. You have to put these larger rectennas somewhere, and land ain't getting cheaper.

[notahacker]

Non-exclusive use of farmland or wasteland (or even - at least until maintenance complexity is considered - offshore) isn't a major barrier; we have many many miles of wires and pylons crossing farmland for regular terrestrial grids already. A rectenna looks more like a mesh than a set of panels: the idea is that the visible light spectrum passes through and the target microwave frequencies don't, so unlike a photovoltaic solar farm the land underneath is fine for farming. Nominally the land is safe to be occupied or passed through by humans too, although they might take some convincing. It becomes a problem when people start trying to get the rectennae banned...

[mr_toad]

> Non-exclusive use of farmland or wasteland (or even - at least until maintenance complexity is considered - offshore) isn't a major barrier

Not now, but with solar power output doubling every few years how long before we run out of land?

[notahacker]

Never. As the post you apparently quoted without reading said, we're talking about a rectenna composed of pylons and wires structured as a mesh that doesn't interrupt farming and can theoretically be offshore, not panels here

Space based solar power has much bigger challenges in gaining acceptance, proving the physics works in real world conditions and delivering on its promises than the theoretical possibility that there is absolutely no unoccupied region of land or sea

[rayiner]

Could we have giant nuclear reactors in space? What's the power loss from beaming down power?

[TeMPOraL]

> Could we have giant nuclear reactors in space?

We could. The usual stumbling block is how to ship fissile material upwell without the risk of a launch failure spreading highly radioactive material over several countries.

> What's the power loss from beaming down power?

I think it's about 10% from atmosphere alone, but you have to add losses from other components in the system, including light -> current -> RF and RF -> current legs, and I've seen estimates ranging from 15% to 40% efficiency end to end; this random article includes breakdown with estimates, that multiplies down to 37.5% efficiency end-to-end.

https://www.sciencedirect.com/topics/earth-and-planetary-sci...

EDIT:

This system design gives 7-14% end-to-end efficiency: https://arxiv.org/pdf/2206.08373

EDIT2:

Also to spell out another non-obvious aspect of beamed power, it turns out that it's not the efficiency that's the limiting factor per se, but land - you can improve efficiency by building larger rectennas, but it gets very expensive very quickly once you consider paying for land under them.

[pantalaimon]

We already have a giant fusion reactor in space

[TeMPOraL]

Yes, and "beamed power" is exactly about tapping into it some more downwell. As outlined in other comments, it's not currently the best option.

[OneDonOne]

See:

SNAP-10A

BES-5 (oops, sorry 'bout that Canada!)

TOPAZ-I

Kiwi, Phoebus, and NRX (Mars here we come!)

RD-0410 (Dossvidanya Solar System!)

SP-100

TOPAZ-II

Kilopower

[laughing_man]

Everybody keeps talking about cheap, clean power. But where I live the price of power has gone up dramatically in recent years. Free power (well, marginally free, anyway) is a major plus.

[wazoox]

In France, where we have relatively cheap and clean energy, they plan to build GW DCs with GWs setups of diesel backup generators. When these will run, the pollution will be staggering.

[detritus]

My concern is more in the realms of cooling. I know there's the potential for lots of 'free' energy up there, but how do you then ensure your space-based array of GPU farms bleed all of the resultant heat?

[TeMPOraL]

This is like "how do you ensure you can bring back home all the groceries you bought" kind of problem. Space 101. We know how much heat we can bleed off, how, and how fast, and this gives us bounds on how much power we can use, and that is the starting point - you design everything around that.

[alephnerd]

From a Defense perspective, it's acceptable if multiple ODC fails and you have to re-launch another one. This is why these are being treated as part of a mesh. These aren't supposed to be a commercial DC and are intended to be a mesh of multiple racks in orbit.

The fact that the US, China, Russia, and India have already deployed ASATs means a Kessler effect if a question of when and not if.

[laughing_man]

The Russians put the first ASats up in the '70s. Their existence doesn't require use.

[alephnerd]

The difference is India and China had an orbital near-miss in 2024 [0] and both India and China now field ASATs.

It's a matter of time before Japan, SK, Iran, Israel, UAE, KSA, etc build similar capabilities.

[0] - https://www.bloomberg.com/news/articles/2025-09-22/india-pla...

[Dylan16807]

> it turns out that, compared to beaming power from space, it's projected to be cheaper to move compute upwell instead

This is damning with the faintest of praise. Beaming power from space is a terrible idea.