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This doesn't make sense to me. How is this radiation given off? Is it a natural phenomenon helped along by using certain materials, or an active system? How are "heat radiating fins" possible in deep space, where there are few particles which can transfer heat away from a spacecraft? And particularly in a ship/station with humans, where certain types of radiation need to be shielded against and internal energy must be conserved, how does this radiation transfer work?

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  • $\begingroup$ Radiation always occurs if the matter has a temperature higher than the absolute zero. The spacecrafts are covered with special materials, like MLI (which actually works as an insulator), white paint, aluminized kapton, silver teflon, beta cloth etc. To maximize the radiation some devices which are usually used are radiators (directly connected to the source of heat, like an elctronic device, and oriented towards deep space, which is assumed to have a temperature ok 3 K). $\endgroup$ – Rhei Jan 15 '15 at 19:32
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    $\begingroup$ This is relevant: space.stackexchange.com/questions/5246/… $\endgroup$ – Rikki-Tikki-Tavi Jan 15 '15 at 19:38
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How are "heat radiating fins" possible in deep space, where there are few particles which can transfer heat away from a spacecraft?

The particles that transfer heat away from spacecraft are photons, and they are created from nothing. The molecular motion on the surface of a solid material creates electromagnetic radiation (in form of photons) because it contains oscillating electric charge. In this case, the oscillation is the thermal motion of atoms in the material.


Addition: To elaborate on the "from nothing" part, I mean this in the sense of particle physics. The number of photons are not constant. They carry energy, and they are the means by which thermal energy escapes the radiator. This is different from and electron, for instance. You could make an electron from pure energy, but you would also need to make a positron in order to conserve electric charge. Conservation of the quantum numbers gets more complicated with protons and other matter. Materials are constantly creating new photons, and many of the photons from a space radiator will likely travel forever.


Is it a natural phenomenon helped along by using certain materials, or an active system?

Some materials are vastly more radiative than others. The theoretically perfect radiator is a blackbody (which is an academic physics concept). All materials fall short of this to some degree, but materials selected for a space radiators get pretty close.

Alternatively, some materials are very bad at emitting thermal radiation and very good at reflecting thermal radiation. These have their own use if you're trying to insulate something.

in a ship/station with humans, where certain types of radiation need to be shielded against and internal energy must be conserved, how does this radiation transfer work?

We shield against ionizing radiation. Some ionizing radiation particles are photons. Some are protons, electrons, and other particles. It's soup of different particles.

By definition, ionizing radiation will destroy chemical bonds. Particularly, we would like to minimize the disruption that this radiation causes to astronaut's DNA.

While thermal radiation and ionizing radiation can both be photons, that's like comparing a baseball to a speeding bullet. It's completely possible to both shield astronauts from ionizing radiation while dissipating their body heat (and energy use) into space. The spacecraft's heat is transferred to the radiator via a working fluid. This fluid passes from the interior through the shielding to the radiator and back again.

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  • $\begingroup$ Can you open "created from nothing". How it relates with conservation of energy, entrophy...etc? Do materials cool down equally while creating photons from nothing? $\endgroup$ – Guney Ozsan Jan 16 '15 at 17:31
  • $\begingroup$ @GuneyOzsan I tried to add more elaboration. I don't want to go into entropy because that shouldn't be in the scope of this question. I'm not sure what "cool down equally" means here. Photons carry energy and energy is conserved, so I see any other problems with closure of the energy accounting. $\endgroup$ – AlanSE Jan 16 '15 at 17:56
  • $\begingroup$ Thanks, you are right. I mean since photons carry energy, do radiating objects loose temperature in time with respect to their radiation? What is your opinion on this. $\endgroup$ – Guney Ozsan Jan 17 '15 at 0:01
  • $\begingroup$ @GuneyOzsan They lose heat by radiation. Temperature is an equilibrium concept. Temperature goes up or down based on whether the balance of heat flows is positive or negative. $\endgroup$ – AlanSE Jan 21 '15 at 19:10
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There are three ways heat can be moved:

  • convection, basically the heat moves because the object itself moves
  • conduction, the most intuitive one: when two objects touch, heat is transfered from the hotter to the colder
  • radiation, which always happen, is simply the natural emission of some electromagnetic waves, which takes energy, i.e. heat

Convection is only interesting when considering fluid dynamics and we don't touch anything (well, virtually nothing) while floating in space. However, electromagnetic waves don't need a support to travel; this is why light can travel from the Sun to us and we can communicate with our satellites. In other words, heat dissipation can and does happen, even in outer space.

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    $\begingroup$ A good answer, but not as detailed as I was looking for. The three types was interesting $\endgroup$ – Taejang Jan 19 '15 at 14:28

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