Comment by weinzierl
11 hours ago
I worked in aerospace for a couple of years in the beginning of my career. While my area of expertise was the mechanical design I shared my office with the guy who did the thermal design and I learned two things:
1. Satellites are mostly run at room temperature. It doesn't have to be that way but it simplifies a lot of things.
2. Every satellite is a delicately balanced system where heat generation and actively radiating surfaces need to be in harmony during the whole mission.
Preventing the vehicle from getting too hot is usually a much bigger problem than preventing it from getting too cold. This might be surprising because laypeople usually associate space with cold. In reality you can always heat if you have energy but cooling is hard if all you have is radiation and you are operating at a fixed and relatively low temperature level.
The bottom line is that running a datacenter in space makes not much sense from a thermal standpoint and there must be other compelling reasons for a decision to do so.
It's like a thermos flask where the spaceship is the contents and space is the insulating vacuum.
They address that issue in the link; The propose a 63m^2 radiator for heat dissipation.
Sure it is doable. My point is that at room temperature convection is a so much more efficient heat transfer mechanism that I wonder why someone would even think about doing without it.
The caveat to this is that that this also dependent on where in the lifecycle of the satellite you are at. For example after launch, you might just have your survival heaters on, which will keep you within generally an industrial range (e.g. >-40c), and you might not reach higher temps until you hit nominal operations. But a lot of the hardware specs for temperature often are closer standard "industrial" specs rather than special mil or NASA specs.
What is room temperature in this context? The temp of the space it's sitting in or a typical room temp on Earth?
Room temperature on earth. In physics room temperature is used as a technical term and actually pretty universally defined as 20°C (293.15 K).
Traditionally in European papers it used to be 18°C, so if Einstein and Schrödinger talk about room temperature it is that.
I've heard in chemistry and stamp collecting they use 25°C but that is heresy.
Maybe you did mean heresy, which would be funny (but a perfectly valid opinion to have)...
But I suspect that's a typo, and you meant 'heresay'? :D
Lay people associate space with cold because nearly every scifi movie has people freezing over in seconds when exposed to the vacuum of space (insert Picard face-palm gif).
Even The Expanse, even them! Although they are otherwise so realistic, that I have to say I started doubting myself a bit. I wonder what would really would happen and how fast...
People even complained that Leia did not freeze over (in stead of complaining about her sudden use of the force where previously she did not show any such talents.)
Well empty space has a temperature of roughly -270c...so that's pretty cold.
But I think what people/movies don't understand is that there's almost no conductive thermal transfer going on, because there's not much matter to do it. It's all radiation, which is why heat is a much bigger problem, because you can only radiate heat away, you can't conduct it. And whatever you use to radiate heat away can also potentially receive radiation from things like the Sun, making your craft even hotter.
> Well empty space has a temperature of roughly -270c...so that's pretty cold.
What is this “empty space” you speak of? Genuinely empty space is empty and does not have a clearly defined temperature. If you are in space in our universe, very far from everything else, then the temperature of the cosmic microwave background is what matters, and that’s a few K. If you’re in our solar system in an orbit near Earth, the radiation field is wildly far from any sort of thermal equilibrium, and the steady state temperature of a passive black body will depend strongly on whether it’s in the Earth’s shadow, and it’s a lot hotter than a few K when exposed to sunlight.
It’s not that dumb- if a human gets exposed to space the water in their exposed tissues will boil off, leading to evaporative cooling. In a vacuum, evaporative cooling can get you ~arbitrarily cold, as long as you’re giving up enough fluids. I don’t know whether you freeze over or dry out first, but I’m sure someone at NASA has done the math.
Wouldn't a body essentially freeze dry as a wet being exposed to vacuum? I.e. the temperature of the space is still irrelevant and the cooling comes from vaporization.
2001 did it pretty close to right, but watch it with normies and they'll laugh at it because it doesn't meet their expectations.