Comment by dahinds
8 hours ago
This isn't really true, though? The ISS does it with radiators that are ~1/2 the area of its solar panels, and both should scale linearly with power?
8 hours ago
This isn't really true, though? The ISS does it with radiators that are ~1/2 the area of its solar panels, and both should scale linearly with power?
ISS radiators run on water and ammonia. Think about how much a kg costs to lift to space and you'll see the economics of space data centers fall apart real fast. Plus, if the radiator springs a leak the satellite is scrap.
The point of the Starship program is to drop the cost of a kg going to space significantly - this isn't meant to be launched with rockets that aren't fully reusable.
The ISS creates radically less heat than a datacenter
Also, space solar is around 4-8x more efficient (24h/day full sun instead of ~4-8 on Earth), and 40% gain due to no atmospheric loss.
I don't pretend to understand the thermodynamics of all of this to do an actual calculation, but note that the ISS spends half its time in the shadow of the earth, which these satellites would not do.
Wouldn't they?
You would put these in polar orbits so they are always facing the Sun. Basically the longitude would follow the Sun (or the terminator line, whichever you prefer), and the latitude would oscillate from 90°N to 90°S and back every 24 hours.
From the linked article:
> By directly harnessing near-constant solar power
Implies they would not spend half of their time in the dark.
Radiator size scales linearly with power but, crucially, coolant power, pumps, etc do not.
Imagine the capillary/friction losses, the force required, and the energy use(!) required to pump ammonia through a football-field sized radiator panel.
Moving electricity long distance is a lot easier than moving coolant long distances, which puts a soft limit on the reasonable size of the solar array of these satellites. But as long as you stay below that and pick a reasonable orbit it's indeed not too bad, you just have to properly plan for it
The ISS isn't consuming and generating megawatts+ of power.
Yes but if the solar panel area scales linearly with radiator area, the problem doesn't get worse?
It does if you don't turn off the heat source every 30 minutes or so. Since the "datacenters" are targeted at sun synchronous orbits they have 24/7 heat issues. And they convert pretty much all collected energy into heat as well (and some data, but that's negligible). Those GPUs are not magically not generating heat.
Wouldn't the panels themselves need cooling too? The ones on earth generate heat while being in the sun.
There are commercial systems that can use open loop cooling (i.e. spray water) to improve efficiency of the panel by keeping the panel at a optimal temp of ~25C and the more expensive closed loop systems with active cooling recovers additional energy from the heat by circulating water like a solar heater in the panel back.
I would hope SpaceX is using more efficient solar cells than the ISS
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