Radiating waste heat into deep space isn’t so difficult, on condition you shield your radiator from the sun. After all, space shows us a 3 Kelvin black-body and that’s really cold.
Right, but that is purely radiative cooling, which as I understand it isn’t nearly as efficient as conductive or convective cooling—there’s a reason that thermos bottles use vacuum flasks. As “cold” as space may be, you can cool things far more efficiently on earth by, for example, dumping heat into a lower temperature fluid. (I’m sure that some one with way more technical expertise could clarify what sized radiator would be needed to dump 5MW of heat into space.)
Sure, radiative cooling is less efficiënt than convective/conductive, but in space that’s all you’ve got, unless you vent precious matter (such as the flash-evaporative cooling the Space Shuttle uses when its payload doors are closed)
Radiator size is not the only issue here, temperature is one too. Radiative cooling becomes more efficiënt with rising temperature (look at the Sun, that’s a very efficient radiator), so all you need to make your radiator panels smaller is to make ‘em hotter.
I don’t imagine a FF spaceship at full trust using the kind of big, shiny radiators like the ISS has, I imagine them being rather small, sturdy and glowing hot. Using high-temp coolants such as molten metal rather than ammonia. Since energy is not such a scarce commodity on board a FF vessel as it is in a solar-powered one, a two-stage cooling process that steps up the temperature using some sort of refrigerator cycle can be used.
Actually both types of radiators would be needed, one high-temperature for the high-grade waste heat from the reactor and one low temperature for low-grade waste heat from electronics and life support.
Radiator size is not the only issue here, temperature is one too. Radiative cooling becomes more efficiënt with rising temperature (look at the Sun, that’s a very efficient radiator), so all you need to make your radiator panels smaller is to make ‘em hotter.
I don’t imagine a FF spaceship at full trust using the kind of big, shiny radiators like the ISS has, I imagine them being rather small, sturdy and glowing hot. Using high-temp coolants such as molten metal rather than ammonia. Since energy is not such a scarce commodity on board a FF vessel as it is in a solar-powered one, a two-stage cooling process that steps up the temperature using some sort of refrigerator cycle can be used.
Wouldn’t it be nice if we could just suspend the laws of physics when it suits us!
The laws of thermodynamics dictate that the temperature of the coolant and therefore the radiator must be lower than the maximum operating temperature of the device you need to cool. You cannot ‘step-up’ the temperature.
Well, you could build a device that cools the primary coolant and heats a secondary coolant to a temperature that is even hotter. One such device is a Peltier. However, you need energy to operate that device and you will generate additional heat that needs to be dissipated as well. This additional heat would be of a relatively low temperature and would require even bigger radiators.
In other words, heat voluntarily only flows ‘downhill’ from a hot body to a body that is colder. If you want to reverse that natural flow you need to supply energy and you will generate even more heat in the process. This is the reason why you won’t find a portable air conditioner that you can just put in the middle of your room. Its waste heat needs to be dissipated to the outside; otherwise you end up heating your room not cooling it.
Radiating waste heat into deep space isn’t so difficult, on condition you shield your radiator from the sun. After all, space shows us a 3 Kelvin black-body and that’s really cold.
Right, but that is purely radiative cooling, which as I understand it isn’t nearly as efficient as conductive or convective cooling—there’s a reason that thermos bottles use vacuum flasks. As “cold” as space may be, you can cool things far more efficiently on earth by, for example, dumping heat into a lower temperature fluid. (I’m sure that some one with way more technical expertise could clarify what sized radiator would be needed to dump 5MW of heat into space.)
Sure, radiative cooling is less efficiënt than convective/conductive, but in space that’s all you’ve got, unless you vent precious matter (such as the flash-evaporative cooling the Space Shuttle uses when its payload doors are closed)
Radiator size is not the only issue here, temperature is one too. Radiative cooling becomes more efficiënt with rising temperature (look at the Sun, that’s a very efficient radiator), so all you need to make your radiator panels smaller is to make ‘em hotter.
blackbody radiation is proportional to T^4 (where T = absolute temperature…eg Kelvin or Rankine).
I don’t imagine a FF spaceship at full trust using the kind of big, shiny radiators like the ISS has, I imagine them being rather small, sturdy and glowing hot. Using high-temp coolants such as molten metal rather than ammonia. Since energy is not such a scarce commodity on board a FF vessel as it is in a solar-powered one, a two-stage cooling process that steps up the temperature using some sort of refrigerator cycle can be used.
Why in the world would you want to do that? Who cares how big the panels are *IN SPACE*? There’s no drag, and surface area has very little correlation to mass in the absence of large dynamic loads. You say that energy isn’t scarce with FF..I beg to differ. Purposely *wasting* energy on an active cooling mechanism such as you’ve described necessarily means a bigger power source, and a bigger cooling system, and bigger radiator panels anyway. It’s basically the rocket equation to some degree. Efficiency = good. Passive cooling = efficient. Therefore, Passive cooling = good
Actually both types of radiators would be needed, one high-temperature for the high-grade waste heat from the reactor and one low temperature for low-grade waste heat from electronics and life support.
p.s.: you got your quotes wrong…
If you make the panels big enough, you’d only need a single set. The hull can also be used as a heat-sink/radiator with proper design. Again, simplicity is the key.
As we’re going off-topic once more and raving about space elevators and stuff, I would like to propose a more economic way for going into orbit and beyond in a near-term future. For that purpose I started a different thread Space and Aerospace Design in a Focus Fusion World. This post includes various other ideas floating around in this forum.
We’ll say 400 tons for energy conversion efficiency.
Even the absurdly high price of $2 / g would translate into $2000 / kg and $2 M / ton.
That comes to $ 800 M to power the USA for a year.
Current oil imports run around $ 600 B / year. The entire power industry is also of that magnitude.
With conservative calculations we see 3 orders of magnitude cheaper than current energy.
p-B fuel is simply free. Free in the sense that it’s so cheap it’s completely out of the picture compared to the other challenges.
p-B fuel is simply free. Free in the sense that it’s so cheap it’s completely out of the picture compared to the other challenges.
Correct. Take the waste from a typical desalination plant, extract the B-11, and use as fuel to power the desalination plant and waste reclamation. Then every byproduct becomes a valuable resource to sell.
It gives graphs for mineral imports, exports, and world production (US data). You can look at Boron, and I think the price evolution is the most useful. You can find the pdf of it here.
Most important are the recent numbers for word-wide Boron production and price.
4e6 metric tons
$800 / ton
So if we’re going by the figure of needing 400 tons for the task of powering all the energy needs of the world, that would come out to a total cost of $ 320,000 and would require 0.01 % of worldwide Boron production. I’d say this is case closed for the pB fuel availability. The fuel simply isn’t a consideration.
The important mineral would be beryllium for the focus and the onion—price and production on this PDF. That’s currently about 200000 USD per ton, with a current production of just 100 tons per year.
Just got an intriguing question from the FB site concerning potential alternate sources of B-10 and B-11:
“I’d just like to add that nuclear fission power stations already run processing to separate isotopes 10B and 11B - they want 10B for their shielding, so 11B is their by-product (80% of natural boron) and is what we want for fusing - so it would be good to find out if they stockpile the 11B…..”
What think? Would it still be cheaper to mine or to recover from evaporative desal plants?
The important mineral would be beryllium for the focus and the onion—price and production on this PDF. That’s currently about 200000 USD per ton, with a current production of just 100 tons per year.
Beryllium has a very important property: it is transparent to X-Rays. This property derives from the fact that it has a very low atomic number. It is the fourth element in the periodic table. The only ones before it are Hydrogen, Helium and Lithium. None of them are any good as electrode material.
Unfortunately, there is no classified element or compound with similar properties.
Remember, half the energy is generated in the form of X-Rays. Any material that absorbs X-Rays will convert them into heat.
So you have two problems:
1. You have lost X-Rays that you need to generate electricity.
2. More importantly, you need to cool the material. In fact, the amount of cooling that you can provide in such a small space may be the limiting factor as to how many ‘shots’ you can have per second. The amount of power that you can generate is proportional to the shot rate.
You could maybe use just boron, but this adds inefficiency and shortens the lifetime of the parts involved. But if the beryllium is handled in a cleanroom, or like radioactive material is handled, that should not be a big issue in my opinion. The problem arises if you handle beryllium like any other nontoxic metal.
You could maybe use just boron, but this adds inefficiency and shortens the lifetime of the parts involved. But if the beryllium is handled in a cleanroom, or like radioactive material is handled, that should not be a big issue in my opinion. The problem arises if you handle beryllium like any other nontoxic metal.
That’s right, if you handle beryllium very carefully, most problems can be avoided. But, of course, Murphy’s Law applies. People will be careless and accidents will happen. Both, at the factories that manufacture the Beryllium parts and at the generation sites.
That’s another reason why you won’t be hooking up a FF generator in your garage anytime soon.
Just because FF, if we can make it work, is far superior to any other energy source we know about it doesn’t mean it is exempt from any drawbacks. In balance there is no doubt that the advantages far outweigh the drawbacks, especially when compared with the alternatives.
Focus Fusion Society 
