A Truely novice question about Heat.

[GarrisonChisholm]

Forgive me for the naiveté here evidenced, but I have a very practical general question stemming from the use of Nuclear Engines in KSP. Though I have not yet myself built anything that has "exploded" due to heat build-up, I read in the forums that it can happen with frequency, necessitating the use of radiators to dispense with waste heat. I have also read that some space-probes are designed IRL in such a way as to facilitate the radiation of waste heat.

My very novice question is; space is cold- why is "waste heat" an issue at all?

Edited September 18, 2015 by GarrisonChisholm

[Whizzkid]

I have a feeling that it is because space is a vacuum, therefore heat is more difficult to get rid of as conduction and convection do not work in a vacuum. The only way that heat can be removed in a vacuum is radiation.

[Kinglet]

I have a feeling that it is because space is a vacuum, therefore heat is more difficult to get rid of as conduction and convection do not work in a vacuum. The only way that heat can be removed in a vacuum is radiation.

Yep. Down on earth there is plenty of air to take heat, but in space there is nothing. Everything emits electromagnetic radiation when heated, which is why metal glows red when very hot. The glow makes things loose heat.

[Slam_Jones]

It's kinda hard to explain, but heat needs to be transferred to other matter. Generally, there's not a lot of matter in space to absorb the heat, so you need special systems to move the heat around.

[Red Iron Crown]

There are three modes of heat transfer:

1. Conduction: Direct physical contact between two objects, heat moves from the hotter to the colder.

2. Convection: Like conduction, but one of the objects is replaced with a fluid.

3. Radiation: Heat is shed as radiation from the object.

Only radiation works in space, so you need a lot of area to radiate with.

Finally: Space ain't cold. It's nothing, there's not enough matter for significant temperature.

Also: Moved this over to Gameplay Questions.

[The_Rocketeer]

Another little point is that in 'empty space' there's actually loads of energy floating around as various frequencies of EM radiation and very tiny, very high speed particles. Locally most of this stuff comes from the sun, but even in intergalactic space there's plenty of it around. A spacecraft might actually absorb more of this energy than it can give out. Lots of people assume that the ISS panels are all solar arrays, but actually several of them are radiators to shed a lot of the excess heat that harvesting solar energy can produce.

[Starwhip]

Finally: Space ain't cold. It's nothing, there's not enough matter for significant temperature.

True, and that's why matter not facing a heat source like the Sun (Provided it's thick enough to heat only "one side", i.e. a spacecraft) gets cold. It radiates all of its heat away into empty space faster than, say, conduction between metal atoms on the sunny side and the shadowed side can give it heat.

[GarrisonChisholm]

Another little point is that in 'empty space' there's actually loads of energy floating around as various frequencies of EM radiation and very tiny, very high speed particles. Locally most of this stuff comes from the sun, but even in intergalactic space there's plenty of it around. A spacecraft might actually absorb more of this energy than it can give out. Lots of people assume that the ISS panels are all solar arrays, but actually several of them are radiators to shed a lot of the excess heat that harvesting solar energy can produce.

I see- I suppose I should have been able to intuit this myself, but I appreciate the primer. Thank you all!

[Clipperride]

The "real life" example would be Apollo's BBQ roll. A slow rotation around the longest axis was set up so one part of the capsule would heat up, then roll into the shade and cooling. It was a difficult manoeuvre to set up as any slight error would become exaggerated over time causing the nose to start processing .