> Lets assume you truly believe the difficulty is the heat transport, then you correct me, but I never see you correct people who believe the thermal radiation step is the issue
It's both. You have to spread a lot of heat very evenly over a very large surface area. This makes a big, high-mass structure.
> how is it solved on earth?
We pump fluids (including air) around to move large amounts of heat both on Earth and in space. The problem is, in space, you need to pump them much further and cover larger areas, because they only way the heat leaves the system is radiation. As a result, you end up proposing a system that is larger than the cooling tower for many nuclear power plants on Earth to move 1/5th of the energy.
The problem is, pumping fluids in space around has 3 ways it sucks compared to Earth:
1. Managing fluids in space is a pain.
2. We have to pump fluids much longer distances to cover the large area of radiators. So the systems tend to get orders of magnitude physically larger. In practice, this means we need to pump a lot more fluid, too, to keep a larger thing close to isothermal.
3. The mass of fluids and all their hardware matters more in space. Even if launch gets cheaper, this will still be true compared to Earth.
I explained this all to you 15 hours ago:
> If this wasn't a concern, you could fly a big inflated-and-then-rigidized structure and getting lots of area wouldn't be scary. But since you need to think about circulating fluids and actively conducting heat this is much less pleasant.
You may notice that the areas, etc, we come up with here to reject 70kW are similar to those of the ISS's EATCS, which rejects 70kW using white-colored radiators and ammonia loops. Despite the use of a lot of exotic and expensive techniques to reduce mass, the radiators mass about 10 tonnes-- and this doesn't count all the hardware to drive heat to them on the other end.
So, to reject 105W on Earth, I spend about 500g of mass; if I'm as efficient as EATCS, it would be about 15000g of mass.
By saying that something is impossible to do cost-effectivey, one is implicitly claiming they have rigorously combed through the whole problem space, all possible configurations and materials, and exhaustively concluded it is not possible cost-effectively.
Imagine now instead of a pyramid, a cone. Imagine the cone is spinning along its symmetry axis. One now has a local radial pseudoforce, a fake gravitational force along the radial direction (away from the symmetry axis).
Now any fluid with a liquid-gas phase transition above the desired radiator temperature but below the intended maximum compute operating temperature (and there is a lot of room for play for fluid choice because the pressure is a free parameter) can be chosen to operate in heat-pipe fashion. Suppose you place the compute at a certain point along the outer rim of the cone, and fluid that condenses on the cone wall will flow to the circular rim at the base. the compute is inside a kind of "chimney" and the lower half of the chimney (and the compute in it) are submerged by the fluid. The fluid boils and vaporizes, and rises up the chimney and is piped to the central axis and flows out in a controlled distributed fashion. all of the pipes could be floppy aluminum foil (or mylar etc.) pipes, since they are all pressurized during normal operation.
Some of the liquid phase could be pumped up to the central axis at the base and cool the rear side of the solar panels as well. I don't see the problem. The power density of solar panel heating (and thus power density on the cone surface) are very similar and perfectly manageable with phase-transition cooling /condensing.
At some point you are just prodding until people hand you working designs on a silver platter.
It's both. You have to spread a lot of heat very evenly over a very large surface area. This makes a big, high-mass structure.
> how is it solved on earth?
We pump fluids (including air) around to move large amounts of heat both on Earth and in space. The problem is, in space, you need to pump them much further and cover larger areas, because they only way the heat leaves the system is radiation. As a result, you end up proposing a system that is larger than the cooling tower for many nuclear power plants on Earth to move 1/5th of the energy.
The problem is, pumping fluids in space around has 3 ways it sucks compared to Earth:
1. Managing fluids in space is a pain.
2. We have to pump fluids much longer distances to cover the large area of radiators. So the systems tend to get orders of magnitude physically larger. In practice, this means we need to pump a lot more fluid, too, to keep a larger thing close to isothermal.
3. The mass of fluids and all their hardware matters more in space. Even if launch gets cheaper, this will still be true compared to Earth.
I explained this all to you 15 hours ago:
> If this wasn't a concern, you could fly a big inflated-and-then-rigidized structure and getting lots of area wouldn't be scary. But since you need to think about circulating fluids and actively conducting heat this is much less pleasant.
You may notice that the areas, etc, we come up with here to reject 70kW are similar to those of the ISS's EATCS, which rejects 70kW using white-colored radiators and ammonia loops. Despite the use of a lot of exotic and expensive techniques to reduce mass, the radiators mass about 10 tonnes-- and this doesn't count all the hardware to drive heat to them on the other end.
So, to reject 105W on Earth, I spend about 500g of mass; if I'm as efficient as EATCS, it would be about 15000g of mass.