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"space is cold" I've always enjoyed thinking about this. Temperature is a characteristic of matter. There is vanishingly little matter in space. Due to that, o
by PeterHolzwarth 10mo ago
"space is cold"
I've always enjoyed thinking about this. Temperature is a characteristic of matter. There is vanishingly little matter in space. Due to that, one could perhaps say that space, in a way of looking at it, has no temperature. This helps give some insight into what you mention of the difficulties in dealing with heat in space - radiative cooling is all you get.
I once read that, while the image we have in our mind of being ejected out of an airlock from a space station in orbit around Earth results in instant ice-cube, the reality is that, due to our distance from the sun, that situation - ignoring the lack of oxygen etc that would kill you - is such that we would in fact die from heat exhaustion: our bodies would be unable to radiate enough heat vs what we would receive from the sun.
In contrast, were one to experience the same unceremonious orbital defenestration around Mars, the distance from the sun is sufficient that we would die from hypothermia (ceteris paribus, of course).
- zeofig 10mo agoA perfect vacuum might have no temperature, but space is not a perfect vacuum, and has a well-defined temperature. More insight would be found in thinking about what temperature precisely means, and the difference between it and heat capacity.
- bee_rider 10mo agoI think your second sentence is what they were referencing. Space has a temperature. But because the matter is so sparse and there’s so little thermal mass to carry heat around as a result, we don’t have an intuitive grasp on what the temperature numbers mean.
- zeofig 10mo agoI think otherwise.
- fc417fc802 10mo agoTo rephrase it slightly. It's not a perfect vacuum, but compared to terrestrial conditions it's much closer to the former than the latter. The physics naturally reflects that fact. To illustrate the point with a concrete example. You can heat something with the thermal transfer rate of aerogel to an absurdly high temperature and it will still be safe to pick up with your bare hand. Physics says it has a temperature but our intuition says something is wrong with the physics.
- margalabargala 10mo agoI think the better argument to be made here is "space has a temperature, and in the thermosphere the temperature can get up to thousands of degrees. Space near Earth is not cold."
- zeofig 10mo agoAre you actually making that article, or just "quoting" it as some kind of hypothetical? Regardless, without mentioning heat capacity, I don't see any point to your quotation in this context.
- margalabargala 10mo agoSorry to hear you can't see it. Let me try to assist you in understanding what you are missing. Yes I'm making that argument. Because it's true. The temperature of what particles do exist, 500km above the earth, is more likely to be in the thousands of degrees farenheit than below zero farenheit. The discussion being had, if you read comments above your original, is that it's widely thought that "space is cold" and therefore it's good for cooling. You're right that heat capacity means that the temperature of space is not relevant to its ability to cool a datacenter. You're wrong that making that argument is a good way to get people to actually change their mind. Instead, attack the idea at its foundation. Space is not cold, not in the places where the data centers would be. It's much easier to get someone to understand "the temperature at 500km where the auroras are is very hot" than "blah blah heat capacity". Now you see the point!
- deleted 10mo ago[deleted]
- teeray 10mo ago> Temperature is a characteristic of matter. There is vanishingly little matter in space. Due to that, one could perhaps say that space, in a way of looking at it, has no temperature. Temperature: NaN °C
- pfdietz 10mo agoTemperature is a property of systems in thermal equilibrium. One such system is blackbody radiation, basically a gas of photons that is in thermal equilibrium. The universe is filled with such a bath of radiation, so it makes sense to say the temperature of space is the temperature of this bath. Of course, in galaxies, or even more so near stars, there's additional radiation that is not in thermal equilibrium.
- fulafel 10mo agoRelated: what color is space?
- DoctorOetker 10mo agoAssuming merely attitude control, sure only radiative cooling is available, but its very easy to design for arbitrary cooling rates assuming any given operating temperature: Budget the solar panel area as a function of the maximum computational load. The rest of the satellite must be within the shade of the solar panel, so it basically only sees cold space, so we need a convex body shape, to insure that every surface of the satellite (ignoring the solar panels) is radiatively cooling over its full hemisphere. So pretend the sun is "below", the solar panels are facing down, then select an extra point above the solar panel base to form a pyramid. The area of the slanted top sides of the pyramid are the cooling surfaces, no matter how close or far above the solar panels we place this apex point, the sides will never see the sun because they are shielded by the solar panel base. Given a target operating temperature, each unit surface area (emissivity 1) will radiate at a specific rate, and we can choose the total cooling rate by making the pyramid arbitrarily long and sharp, thus increasing the cooling area. We can set the satellite temperature to be arbitrarily low. Forget the armchair "autodidact" computer nerds for a minute
- yetihehe 10mo ago> The rest of the satellite must be within the shade of the solar panel, Problem is with solar panels themselves. When you get 1.3kW of energy per square meter and use 325w of that for electricity (25% efficiency) that means you have to get rid of almost 1kW of energy for each meter of your panel. You can do it radiatively with back surface of panels, but your panels might reach equilibrium at over 120°C, which means they stop actually producing energy. If you want to do it purely radiatively, you would need to increase temperature of some surface pointing away from sun to much more than 120°C and pump heat from your panels with some heatpump.
- adrian_b 10mo agoWhen the cost of the solar panels does not matter you can reach an efficiency close to 50% (with multi-junction solar cells) and the panels will also be able to work at higher temperatures. Nevertheless, the problem described by you remains, the panels must dissipate an amount of heat at least equal with the amount of useful power that is generated. Therefore they cannot have other heat radiators on their backside, except those for their own heat.