The Heat of the Moment- Spacecraft and Heat

Recently I was having an e-mail exchange with people who know far more about science than I do (which isn’t hard to find…) and an interesting tidbit came to light during the discussion. The thrust of the tidbit requires a bit of background, but the point is actually potentially a very important one for Sci-Fi writers.

First, the background… There are 3 ways in which heat is lost– convection, conduction, and radiation. In simplest terms convection is when it’s carried away by the atmosphere around it (like a cold day), conduction is when it’s lost by flowing into other parts of an object or things connected to it (like a hot stirring spoon), and radiation is when it simply radiates out into the surroundings as energy (like the sun).

Got that? Okay, now the interesting part.

In an atmosphere we’re constantly exchanging heat with the atmosphere around us (convection), our clothes (conduction) and radiating it from our skin. This of course applies not just to people but also machines, so a car is also exchanging heat with the environment (convection) and when it gets hot it’s emitting it into the environment (radiation).

But, what about in space?

In Space on ship or station, there is no atmosphere, so there’s no convection (except with the interior atmosphere), no conduction beyond what it’s attached to (nothing, in the case of a ship), and only radiation. You’d think that would be enough, because space is really cold, right? But the problem is that cold in space is actually the absense of heat, not an atmosphere, so it’s not absorbing heat from things in it. Things in space only lose heat through radiation, and radiation is actually the LEAST efficient of the three different means of heat transfer. Therefore, if something in space builds up heat it can take a long time to slowly lose that heat.

Thus it was explained by the person much more knowledgeble than I that a major problem in designing spacecraft is heat. Not keeping in it, but actually getting rid of it! Even a lot of small electronics generating small amounts of heat can add up quickly if there’s no place for the heat to go! And god help you if you have something that generates a lot of heat like a fusion reactor or perhaps a weapons system because you can only lose heat at a slow constant rate.  Where are you going to put all that heat? Because if you don’t put it somewhere it will cook the crew and perhaps the systems aboard the ship around it. Of course, you can have cooling systems, and will need them, but there may be limits to those too!

I’m reminded of the tactical boardgame Battletech I used to play when I was a teenager (you younger folks know it as the computer game Mechwarrior), where everything you did was limited by the inability of the mechanical war machines in the game to deal with the heat they were generating. It turns out that doesn’t just apply to mecha, it applies to spaceships too!

This could be applied a couple ways- one way would of course be as a weapon: lasers/microwaves heating your enemy into oblivion would be very effective. But, it could also be used to justify h0nking big-ass spaceships like the Red Dwarf or the ship in Aliens. Big ships with small crews because the ships mostly exist to deal with heat through their sheer bulk! Maybe that’s why oversize spaceships always seem to have lots of dark, steamy and dripping corridors in movies?