Quote from: randomly on 12/16/2013 08:19 pmThe concept is flawed because although you can passively achieve very low temperatures in space (eg JWST) this is only at very low energy flows. The only way to practically dissipate heat in space is via radiation and this obeys the Stefan-Boltzmann law that power radiated is proportional to the fourth power of temperature.You will need to dissipate a great deal of heat which forces your radiators to be massive if you are trying to do this passively.But you've neglected Landauer's principle. The energy you need to remove per computation decreases as you decrease temperature. You're using thermal engineering, but you also have to use the thermodynamics of computation. You have to combine BOTH. There is no other way for the concept to make sense. This is what you must add:E = k T ln 2This is the energy per computation. The colder you get, the less energy you have to dissipate through the radiator.
The concept is flawed because although you can passively achieve very low temperatures in space (eg JWST) this is only at very low energy flows. The only way to practically dissipate heat in space is via radiation and this obeys the Stefan-Boltzmann law that power radiated is proportional to the fourth power of temperature.You will need to dissipate a great deal of heat which forces your radiators to be massive if you are trying to do this passively.
Quote from: AlanSE on 12/16/2013 03:23 pm Even more important - progress in single-threaded processors has stalled. Going to lower temperatures will allow the speeds of single processors to continue to advance. In research, this has already happened. The most powerful single thread computations have been done at supercooled temperatures.That's why real engineers invented multi thread programming and GPU computing, instead of sending computers to space.Also although core speed has not increased much in the previous years, power consumption has been severely reduced.
Even more important - progress in single-threaded processors has stalled. Going to lower temperatures will allow the speeds of single processors to continue to advance. In research, this has already happened. The most powerful single thread computations have been done at supercooled temperatures.
The concept is flawed because although you can passively achieve very low temperatures in space (eg JWST) this is only at very low energy flows. The only way to practically dissipate heat in space is via radiation and this obeys the Stefan-Boltzmann law that power radiated is proportional to the fourth power of temperature.You will need to dissipate a great deal of heat which forces your radiators to be massive if you are trying to do this passively.If you go the active cooling approach it becomes vastly easier to actually do it on earth, it would also be vastly cheaper, especially from a maintenance and upgrade point of view.Also if there was some economic advantage you would see cryocooled processors in use, at least in niche applications. But you do not.
Radiating energy to cool yourself below 200K in LEO is an engineering challenge. The radiated energy per surface area will be minimal, and the radiator has to be carefully built to be shielded from both the hot earth below it and then sun. IR telescopes than need cooling have been sent into solar orbits or earth-sun L2 for a reason. Meanwhile, in Antarctica you basically get an infinite ~200K heat sink for free.
Regarding the revenue streams for private development of new space industries I want to know what people think of this proposal:Build low-temperature data centers in space to do cloud computingWhy? In short, because low-temperature processors have better performance. By that I mean, they can have faster clock cycles. Another motivation is that energy can be cheap in space, but this isn't very compelling. On the other hand, it's possible to expel energy by radiators at a very low temperature, depending on the heat input and size of the radiator of course. The physical underpinning of this idea is extremely well-established. We know that processors can go faster at low temperatures, but the fundamental law is that any computational operation requires a minimum energy due to the laws of thermodynamics. The most powerful single thread computations have been done at supercooled temperatures.If you imagine commodity computing, then there will be a price per calculation, and this price will be higher if the computation is performed faster. Even if a supercomputer in space can never compete with the cost-per-computation on Earth, it doesn't matter. It only needs to compete with a supercomputer on Earth that runs at the same speed - and that's a race that space data centers might be able to win 10 years from now. Additionally, computer science has extremely robust arguments that establish why not all problems can be made parallel efficiently. So we should expect the demand to remain strong.
The radiator design would be a nightmare, particularly if in LEO, and that is the most obvious place for it considering the time lag. The JWST is in a spot where low temperatures are easier to manage, but it's not as good for providing data services. In LEO, you would need both a sun shield and an Earth shield. You could need completely new, radical, radiator designs. Radiation would be an economics deal-breaker, so it would have to be shielded.
The concept is flawed because although you can passively achieve very low temperatures in space (eg JWST) this is only at very low energy flows. The only way to practically dissipate heat in space is via radiation and this obeys the Stefan-Boltzmann law that power radiated is proportional to the fourth power of temperature.You will need to dissipate a great deal of heat which forces your radiators to be massive if you are trying to do this passively.If you go the active cooling approach it becomes vastly easier to actually do it on earth, it would also be vastly cheaper, especially from a maintenance and upgrade point of view.
If cooling processors could be done with radiation only, we'd put them in a large room with black walls.
You can't passively lower your temperature below that of your environment. The proposal here is to put the data center in an environment that has a lower temperature than Earth's surface. A radiator on Earth can't get lower temperatures because its surroundings radiate back to it