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?

5 thoughts on “The Heat of the Moment- Spacecraft and Heat

  1. Posted by Dave Collins on Facebook ( http://www.davesbrain.ca/index-left.html )

    The way spaceships deal with excess heat is with cooling surfaces. They boost the radiative ability. Many pseudo-serious rocket designs have giant fins on them for cooling.

    BTW, regards large ships: the larger the ship, the bigger the problem because of Galileo’s square-cube law (http://en.wikipedia.org/wiki/Square-cube_law). … See More

    A ship of one unit in length generates one unit of heat and has a radiatrive surface area of one unit.

    However, if you DOUBLE the ship’s unit length, you multiply its volume (thus inner machinery, thus heat generation) by EIGHT, while only multiplying its radiative surface area by FOUR. This means it’s twice as hard to radiate the heat.

    This is the same reason why large people sweat a lot and smaller people are cold a lot.

  2. Interesting. Would that mean then that it’s better to have smaller ships instead of larger ones to help deal with this issue?

    I forgot you’re also a engineering type!

  3. Posted by Dave Collins on Facebook ( http://www.davesbrain.ca/index-left.html )

    Well, what’s “better” is a matter of mission priorities. Everythng in the design of a spaceship is a trade-off between competing needs. There are probably factors much more critical(such as minimum size for drive and fuel) that will win out over heat dissipation.

    What you *can* deduce is that a ship might either have a method for dumping excess heat into the exhaust, or simply having disproportionately large cooling fins.

    “Engineering-type”. I like the sound of that. I would have you continue to believe this. It sounds better than “physics/sci-fi geek”….

  4. Hmm. Then it sounds like it would be difficult to actually make “generalist” spacecraft like the Enterprise, since ships need to be very mission-specific in order to accomplish their missions. Ultra-tech handwaving aside.

    I ponder this at the moment because I’m still designing the ships for my Twin Stars space opera series. I have rough ideas of what they look like, but have never really posted any because I keep scrapping my ideas. Now I’m wondering if I should take this heat issue into consideration and add some rocket fins! ^_-

    Also, since heat signatures would be a very good way of spotting spaceships, it would be a major issue in space warfare. After all, in real space warfare the guy who sees the enemy first usually just wins!

  5. Interesting. I wonder if it’ll ever be possible to recycle all the excess heat into a power source for the ships, in a green space way.

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