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Background: My SciFi books are set 50-100 years into the future. My combat ships use fusion for power and direct thrust. (See previous question: "Performance envelope characteristics for a hard-sci-fi torch-ship") As many helpful people pointed out, one of the main issues with high power will be heat.

My ships are able to control, with a high degree of precision, plasma envelopes surrounding them. This is used in-atmosphere for magnetohydrodynamic propulsion. In space, the plasma-envelope is used for stealth by absorbing/reflecting radiation from radar etc.

My question:

If the ships have flakes of metal suspended in the plasma (something like: dusty plasmas) the flakes will absorb heat from the plasma and radiate it. If the flakes are mirrored on one face and black on the other and if the ship can control the orientation of the flake, is this a valid mechanism for preferentially radiating heat in a desired direction?

Plasma shell with radiating metallic flakes

Many thanks in advance! I am happy to share more info!

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  • $\begingroup$ (2) Plasma is simply hot gas, so ignoring how you're suspending the metal flakes, bear in mind that there's no such thing as a perfect mirror. We'll also ignore the question of just how transparent transparent metal really is. Defects in the transparent material and the material used to mirror the back of the metal are the limiting factor for how many photons they can handle. Too many photons and the metal will burn up from heat generated by non-reflected photons. Those metal shards would also play merry havoc with your own sensors, but you can control them. $\endgroup$ Dec 16 '20 at 16:18
  • $\begingroup$ I removed the 2nd question. I will post later as a follow on. $\endgroup$ Dec 16 '20 at 16:37
  • $\begingroup$ Regarding plasma and suspended flakes— the flakes are metallic and charged and would be suspended in the plasma within magnetic fields. (Also this is a technology to be used in micro-g). $\endgroup$ Dec 16 '20 at 16:38
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    $\begingroup$ I changed the tag to science-based, to soften things up a little. $\endgroup$ Dec 16 '20 at 17:23
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    $\begingroup$ "If the flakes are mirrored on one face and black on the other and if the ship can control the orientation of the flake, is this a valid mechanism for preferentially radiating heat in a desired direction?" Radiating heat by whom? By the ship? By the plasma? By the flake? Yes, the flakes themselves will radiate preferentially (not exclusively) along the normal to both flat faces; the "mirroring" and color have no effect. (And what is "mirrored" supposed to mean? There is no such thing as a mirror working at all wavelengths. Mirrors only work within a quite narrow range of wavelengths.) $\endgroup$
    – AlexP
    Dec 16 '20 at 17:36
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It might work, but..

Your concept requires several unknown/unresearched aspects to behave correctly. IF you can get a way for those mirror/nonmirror flakes to orient correctly, AND have them circulate correctly to collect the heat in the first place without clogging, AND have them carry enough heat AND have them not absorb too much heat from your plasma turning it into gas (which would then just float away), then the concept could work. I have no idea how you would orient the flakes other than along the magnetic lines though. You would be able to select IN or OUT, but not any other direction.

If your primary concern is for the cooling effect, then consider this:

There are similar concepts for space heat rejection that require a lot less hoops be jumped through to work, and would be just as spectacular for storytelling purposes.

Take a look at this link: http://toughsf.blogspot.com/2017/07/all-radiators.html
This is a webpage that devotes itself to all thing space coolant, both current, planned and theoretical.

Specifically, look at the Curie Fountain Radiator.

It is very similar to your idea, but requires a lot less finicky tech to be made to work. enter image description here
quote from the page, just incase it gets lost:

A Curie point radiator operates around the temperature at which metallic dust particles lose their magnetism. Iron, for example, loses its ferromagnetism at 1043K. The Curie point radiator uses metal filings or even liquid droplets. It is heated to above the curie point temperature and ejected into space, away from the spacecraft. A magnetic field is in place, but they are not affected by it. Iron can be released at temperatures of up to 3134K and collected at 1043K, but Cobalt has a Curie temperature as high as 1388K, is naturally black and boilds at 3400K, making it a better coolant. The small size of the particles or liquid droplets allows several megawatts of waste heat to be radiated away per square meters.

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I see some problems with the concept as it stands now:

  • Plasma can be depicted as a very hot gas, where atoms are dissociated. One usually needs RF frequency to sustain the plasma. I suspect those metal flakes won't do nice things while interacting with the RF radiation.
  • Assuming the RF radiation doesn't mess up with the flakes, they won't be aligned where you want them to point, but where the electromagnetic field configuration decide to align them, and it won't be a stationary configuration (remember, you need a RF frequency to sustain the plasma)
  • If the flakes emit more on one side than the other, they might be subjected to a force asymmetry as a consequence they would move, which again is something you don't want, because you want to point them in a specific direction, most likely away from your ship.
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  • $\begingroup$ In this case, the plasma heating will not be from RF radiation, be from circulating the plasma (gas) through the engine (fusion, sci-fi) to cool it. It would pick up heat and need to radiate it away. The flakes would be oriented by the magnetic fields, but this is one of the areas I am least sure about... $\endgroup$ Dec 16 '20 at 18:15

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