system
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human
How does space affect heat-seeking munitions/weapons?

Really three questions.

Hey folks. I'm a SciFi Writer. I have a few questions, to inform a short story I'm working on. Thank you in advance.

Anyhow, on to my questions.

1) I can remember reading or hearing that heat travels through space via radiation. How would this affect heat seeking missiles (suppose a craft is targeting another craft)? 

2) Since, according to Wikipedia, heat is a form of electromagnetic radiation, how would electromagnetic pulses affect this? Assuming the characters did some faraday cage stuff, could an EMP be used as a countermeasure (even if they can't directly disable the munition)?

3) In lieu of using heat to track, would it be viable to have weapons that track via light (ie the light of engines)? I've written it in so far like this (assuming heat is a no go), and the Humans use fast-moving reflective flachette to reflect light from their engines and the sun to fool such devices.
gpt
Heat seeking missiles / munitions detect infrared radiation to home in on their target.

Every object emits so-called thermal radiation, which is just electromagnetic radiation (just like light). The amount and wavelength of this radiation depends on the temperature of the object. Hot objects will emit more thermal radiation that has a shorter wavelength (= more energetic). On Earth, almost all objects we encounter emit most of their thermal radiation in the infrared part of the spectrum. This is why we often associate infrared with heat.

If an object is hot enough, its thermal radiation will start to shift more and more into the visible part of the spectrum (which has shorter wavelengths than infrared). This is where the expression "glowing hot" comes from.

Heat seeking weaponry detects the infrared radiation being emitted by the engines, which emit far more IR radiation than the surroundings. This will be the same in space as it is in our atmosphere, though the temperature of the engine of a spacecraft isn't necessarily the same as that of a jet engine.

While it's true that thermal radiation is a form of EM radiation, blocking it with a Faraday cage is effectively impossible. A Faraday cage requires the mesh width of the walls of the cage to be smaller than the wavelength of the radiation. IR radiation starts with wavelengths of the order of magnitude of a micrometer (and the range runs up to about a milimeter, but for hot objects like a running engine, this part of the range is not very relevant). So you'd effectively have to build a solid cage around the engine. In addition, the cage would, through heat transfer, heat up due to the engine it is surrounding. Unless the cage is very large (and heavy) compared to the engine, its thermal radiation spectrum will becomes just as obvious to detect as that of the engine. So no shielding thermal radiation.

As for your last question, yes, in principle that is possible, but the light emitted by the engines may be shielded in some way, by keeping the engines within a largely closed housing. Thermal radiation can't be shielded and the only way to become undetectable by thermal radiation scanners is to lower the temperature of the craft to be equal to that of the surroundings. Which is not going to be comfortable in space.