Radiators on spacecraft

[Geronimo]

I understand solar arrays on space craft, but what is the purpose of having radiators? I tend to see them quite often when looking at space probe designs, and a lot of custom packs for KSP seem to have them - but I don't get what benefits they have.

[AeroPelican]

I think they hold and disperse heat so the probe or station does not become overheated.

[Cby]

Well real radiators are used to vent heat from things on the ship.

On parts from mods, they are completely useless except decoration. Maybe in the future a plugin will require something that needs to rid itself of heat. Maybe even in the actual game itself.

[nhnifong]

Electronics operate better at colder temperatures, but they generate heat while they operate, and that heat must be dissipated, or it will build up and destroy the component (or force it to be turned off)

The three ways to get heat away from something are conduction, convection, and radiation.

Conduction is when two things are touching and their temperatures equalize, for example, holding a metal rod to a hot object will conduct heat up the rod, and the other cold end, which you are holding, will eventually get hot and burn your hand. heat conductivity is roughly related to density.

Convection is the heating of a nearby fluid, and then moving the fluid away. this is why computers have fans (yes, gasses and liquids are both "fluids") Heat fins use conduction to get heat away from the source, into themselves, and since they have a high surface area, they touch a lot of air, which the fins equalize with, and is then convected away (blown away) and replaced with cooler air.

Radiation is the emission of photons. Hot objects, emit radiation and the color (frequency) changes with the temperature. Radiating away some of their energy causes them to cool down. radiation comes from all atoms in the material, but only the radiation emitted near the surface tends to escape.

In space, where air and water are not abundant, convection is not practical, at least, you can't just vent the hot air into space or you would run out of air.

You can conduct heat into cold mass and jettison the mass, but you're going to run out of mass.

The only way to get rid of your heat is to emit it as photons. So a space radiatior uses a large heat conductor, which has a maximum surface area with an unobstructed view of space. (if photons were emitted from the radiator only to be re-absorbed by other parts of the craft, it would be pointless. and since the surface is all the matters, they tend to be thin. And they tend to not have parallel fins. and they tend to be far away from the ship, so that the photons emitted, are not reabsorbed.

#edit

They also tend to be perpendicular to the solar panels. because you dont want them absorbing solar radiation. Generally you don't want any parts of the ship absorbing solar radiation except the solar panels.

Edited August 31, 2012 by nhnifong

[Elios]

Convection flat out doesnt work in a vacuum

the engineers that built the APU sub systems found that out the hard way when the blew up an APU in a vacuum chamber test

the heat had no where to go so it started to heat the fuel line which for the shuttle APUs is Hydrazine not fun stuff and BOOM

another fun fact about cooling on shuttle the cooling loop is the things achilles heel its the one system that if it fail would basically make them have to de-orbit on the spot if any one of the 2 coolent pumps failed

but just about every thing makes heat so you have dump it over board and the only way to do that in space is radiate it out

you can do other tricky things like use flash evaporators but your going to run out of water at some point

thermal control is a big issue on spacecraft would be nice to see it added to the game at some point

[Binky]

IIRC, there was a problem with the radiators on Skylab due to a malfunction at launch. The temp inside rose to almost 50C before the first crew fixed the issue.

Definately not a nice place to be at the time, I'd say

[Rickenbacker]

Yep, that would have been a fascinating and challenging mission to go on - basically putting a huge thermal blanket on the outside of Skylab to keep it from overheating.

[Tommygun]

IIRC, there was a problem with the radiators on Skylab due to a malfunction at launch. The temp inside rose to almost 50C before the first crew fixed the issue.

Definately not a nice place to be at the time, I'd say

I thought it was that one of the insulating panels broke off during launch allowing the Sun to heat the metal skin?

But it was a long time ago, so I'm not 100%.

Edited September 1, 2012 by Tommygun

[Tauge]

Actually, what happened was, the micrometeorite/sun shield was torn off during launch taking one of the solar panels with it. The other solar panel could not completely open due to part of the damaged sun shield wrapping around the remaining solar panel. This left the unprotected workshop in the sun causing the temperature to get...unsafe. Eventually NASA was able to get the panel partially open, giving them enough power to reorient the station to allow the temperature to drop some, but was still unsafe. When the Skylab 2 crew arrived, they attached a collapsible sun shield over Skylab, which brought the temperatures to more comfortable conditions. On their second walk, they were about to fully extend the solar array.

So Skylab's issue wasn't due to an inability to cool the station, it was due to an inability to keep the station's living quarters out of direct sunlight.

[Elios]

NASA can come up with some great fixes on the fly top 3

1. CO2 filter rig on Apollo 13

2. Skylab sun shade

3. ISS solar panel "cufflink"

[Alchemist]

Radiators on the real spacecrafts usually are either rotating panels that are being turned in the plane of the sunlight or they are mounted on the rear side of the solar panels or in some other place that is supposed to be in the shadow (depending on the craft's attitude control profile). And they are used to cool the internal pressurized volumes and other systems of the craft by radiating heat that is both produced by the internal systems and gets inside from the hull when it's exposed to the Sun.

In KSP... well, there's a radiator module in muMech, that displays its temperature (and nothing more - you'd make the part work as radiator by increasing its heat conductivity and dissipation). I've also added radiator abilities to PowerTech solar panels (or you can make just a radiator with the same module) - they can increase heat dissipation when deployed and produce heat based on exposure to sunlight. Still, there's nothing yet to produce dangerous amounts of heat except the engines.

[Tommygun]

NASA can come up with some great fixes on the fly top 3

1. CO2 filter rig on Apollo 13

2. Skylab sun shade

3. ISS solar panel "cufflink"

Good list, but you left out the Hubble fix.

[Elios]

hubble fix wasnt a we need it now thing so it doesnt make the top 3

they had time to build hardware

the others were all improvised

i would rate some of the antics on the later hubble missions over the COSTAR fix

like just ripping the hand hold off lol im sure a few engineers couldnt stand to watch that

the 3 i listed had be done fast and with what was on hand

1. would of killed the crew and was rigged what what was on hand in the CSM at the time

2. would ended skylab be for the first crew even got there and they needed a fix in less then 48 hours

3. would crippled the ISS other wise and was done with what ever crap they had on the ISS

COSTAR was cool just they had time to build custom hardware for it

Edited September 1, 2012 by Elios

[Maddmatts]

RTG's also need radiators to produce power efficiently. I remember watching a vid of a team sending an unpowered rc airplane to the upper atmosphere via weatherballoon. They had to mount all the electronics to copper sheets to keep them from burning themselves out in the thin atmosphere.

Edited September 1, 2012 by Maddmatts