Radiators, Solar Panels, and Reactionless Drives [Spaceships]

AlexanderHowl · 05-24-2020, 12:09 PM

In more realistic settigs, massive radiators should be used for dealing with the waste heat of reactors and beam weapons. In general, a realistic reactor or beam weapon should have a 25% efficency during the TL of introductioj, meaning that there will be a lot of waste heat produced (at TL9, a SM+10 spaceship with four major batteries of beam weapons and two fusion reactors would produce 9.6 GW of waste heat). That would likely end up requiring around a square kilometer of radiators (solar panels would likely have a comparable surface area).

Radiators (and solar panels) are not very strong because they need high maximum surface area to volume ratios, but that usually does not matter when accelerating with high delta-v reaction drives (which tend to have a maximum total acceleration of 0.025g). Their lack of strength should matter when using reactionless drives though, as their accelerations are usually much higher than high delta-v reaction drives. In general, I believe that deployed radiators (and solar panels) should not be able to survive accelerations above 0.1g.

What does this mean? If you have realistic radiators (and solar panels) in the same setting as reactionless drives, they should depend on Fuel Cells and/or MHD turbines. Of course, you could have a reactor that recharges them when you can stop accelerating and can deploy the radiators, so it is not a major concern during non-compete operations, but it is important for combat. It would also give a good reason to use conventional guns/missiles, as spaceships could use them while maneuvering (unlike beam weapons).

DataPacRat · 05-24-2020, 01:15 PM

Quote:

Originally Posted by AlexanderHowl

In general, I believe that deployed radiators (and solar panels) should not be able to survive accelerations above 0.1g.

There are radiators, and then there are radiators. :)

I know of at least two-dozen different design proposals, from a few variants on the classic 'heat pipes that pump liquid through thin tubes spread across wide panels' to 'make 140-meter loops of buckytube filaments, wrap them around a drum to transfer heat to them, and spin it so the fibers make long loops in space to radiate with', to 'stretch out two arms, pump out molten tin from the one and let the droplets "fall" from the ship's acceleration, and collect them from the other'.

Bubble membranes, hula-hoops, Maragoni-flow that depends on surface tension, magnetic flux-pinned superthermal graphite foam, hot charged particles circulating in an external magnetic field, magnetically-recovered iron droplets, spraying hot lithium forward in a fountain... there are any number of options that don't depend on a rigid panel assembly that has to support itself against thrust. There just aren't too many existing GURPS stats for them. :)

Anthony · 05-24-2020, 03:55 PM

Reactor radiators operate at the cool sink temperature of the reactor, weapon system radiators operate at the operating temperature of the weapon. Neither has any particularly strong reason to match the temperature of the habitable portion of the ship, and the amount of heat they can eliminate varies with the fourth power of temperature. Also, unless you're needing to continually fire for a long period, it may be easier to just have some kind of phase changing material as your heat sink for weapons fire.

05-24-2020, 12:09 PM	#1
AlexanderHowl Join Date: Feb 2016	Radiators, Solar Panels, and Reactionless Drives [Spaceships] In more realistic settigs, massive radiators should be used for dealing with the waste heat of reactors and beam weapons. In general, a realistic reactor or beam weapon should have a 25% efficency during the TL of introductioj, meaning that there will be a lot of waste heat produced (at TL9, a SM+10 spaceship with four major batteries of beam weapons and two fusion reactors would produce 9.6 GW of waste heat). That would likely end up requiring around a square kilometer of radiators (solar panels would likely have a comparable surface area). Radiators (and solar panels) are not very strong because they need high maximum surface area to volume ratios, but that usually does not matter when accelerating with high delta-v reaction drives (which tend to have a maximum total acceleration of 0.025g). Their lack of strength should matter when using reactionless drives though, as their accelerations are usually much higher than high delta-v reaction drives. In general, I believe that deployed radiators (and solar panels) should not be able to survive accelerations above 0.1g. What does this mean? If you have realistic radiators (and solar panels) in the same setting as reactionless drives, they should depend on Fuel Cells and/or MHD turbines. Of course, you could have a reactor that recharges them when you can stop accelerating and can deploy the radiators, so it is not a major concern during non-compete operations, but it is important for combat. It would also give a good reason to use conventional guns/missiles, as spaceships could use them while maneuvering (unlike beam weapons). Last edited by AlexanderHowl; 05-24-2020 at 05:35 PM. Reason: Error in waste heat calculation.

05-24-2020, 03:55 PM	#3
Anthony Join Date: Feb 2005 Location: Berkeley, CA	Re: Radiators, Solar Panels, and Reactionless Drives [Spaceships] Reactor radiators operate at the cool sink temperature of the reactor, weapon system radiators operate at the operating temperature of the weapon. Neither has any particularly strong reason to match the temperature of the habitable portion of the ship, and the amount of heat they can eliminate varies with the fourth power of temperature. Also, unless you're needing to continually fire for a long period, it may be easier to just have some kind of phase changing material as your heat sink for weapons fire. __________________ My GURPS site and Blog.