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Part Minimum Temperatures, Surface Temperatures on Planets, Basic Thermodynamics

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Parts would have minimum temperatures, and some would passively radiate heat. When minimum temperatures are reached, the parts wouldn't explode or anything. They would merely stop functioning. However, based on a setting in the difficulty options, if a command module or spacesuit reached minimum temperatures, the kerbals could be at risk of freezing to death. Different kerbals would have different time limits for staying below minimum temperature, basically like gee tolerance.

Something else that should be added would be parts specifically meant for heating the spacecraft. Drills, converters, fuel cells, RTGs and active engines would passively generate heat. Liquid fuel tanks and idle liquid fuel engines would have an incredibly low minimum temperature. Landing legs and airbrakes, as well as xenon tanks and ion engines would have a fairly low minimum temperature. Wings (whose aerodynamics would simply not work quite right when too cold), command modules and passenger modules would have a medium minimum temperature. Probes, batteries, solar cells and reaction wheels would have a high minimum temperatures.

Finally, surface temperatures. Planets would all have ground temperatures, including the ones without atmospheres. However, part temperatures would be affected by the ground much more slowly than by the atmosphere. Therefore, you could probably last on Eeloo or Minmus for days without a heating system. You wouldn't have to worry too much about Jool's moons, as they are heated by tidal forces. With Duna you would probably want a heating system, seeing as it has an atmosphere. Also, unlike atmospheric temperature, surface temperature would change depending on whether it was day or night.

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Surface temperature should transfer heat much more quickly than atmospheric temperature, but only to the parts in direct contact with it. KSP already has a system for transferring heat between parts so the same system could transfer heat from the ground to the parts that are touching the ground.

Your spacecraft could get very cold when flying in space a long ways away from the sun or in the shadow of a planet, unless something on the inside were generating heat. RTGs should generate heat at all times.

I'm interested in giving a few parts a minimum temperature, but I think most things shouldn't be affected by the cold. All structural components, landing legs, struts, wings and lifting surfaces, docking ports, and panels should operate just fine no matter how cold they get. Fuel might be an interesting thing to have fail when it gets too cold, or it could have difficulty burning. Maybe some functions would happen slowly while the ship is cold. Getting any crew module's core temperature too low could kill any kerbals inside, though the kerbals would generate some heat and all parts with crew or passenger capacity would have internal heating which would draw electric charge to keep warm. That way you mostly could ignore heating, but in the event your power fails, it is possible for your kerbal crew to die from the cold.

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19 hours ago, thereaverofdarkness2 said:

Your spacecraft could get very cold when flying in space a long ways away from the sun or in the shadow of a planet, unless something on the inside were generating heat. RTGs should generate heat at all times.

Actually, in a vacuum there's nowhere for the heat to go, so it would be so slow you wouldn't even notice.

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On 7/25/2017 at 1:26 AM, Scotskerb said:

Actually, in a vacuum there's nowhere for the heat to go, so it would be so slow you wouldn't even notice.

Not exactly.  Heat can still be transferred by radiation, not only by dedicated radiators but by passive radiation (blackbody radiation) according to the Stephan-Boltzmann law:

P= A j^{\star} = A \varepsilon\sigma T^{4}.

Radiated power (W) from a body is the product of

  • A - area (m2)
  • e - emissivity (dimensionless value from 0-1 depending on the material of the body)
  • sigma - the Stephan-Boltzmann constant, 5.67x10-8 W*m-2*K-4
  • T - temperature to the 4th power (K)

Even a very cold body still radiates heat, just a very small amount. Halving the temperature reduces radiated power by a factor of 24=16 times!  Conversely, doubling the temperature increases it by the same factor.  For unmanned spacecraft with low-power electronics, heaters would likely be required to keep the bus above minimum temperature. However, for larger computers and crewed vessels radiators are actually necessary - all that heat would have nowhere to go and would accrue in the vehicle, eventually cooking your crew and electronics.

Currently, the game sets the failure temperatures much higher than they ought to be.  Obviously this is for balance purposes, and is probably a symptom of the fact that parts either exist or explode (with the exception of solar panels) with no grey area.  Setting a lower thermal bound on parts would require a non-explosive failure mode - something that (IMHO) should be integrated anyway, but this begs the question; what happens when a part freezes or overheats? Chemical batteries would burst or rapidly discharge, and propellant tanks more violently so. Structural parts could be unaffected, or they could fail (frozen struts become brittle and crack, overtemp I-beams melt and shed their connected parts).  Aerodynamic parts would be subject to the same constraints as structural parts, after all a wing is basically a plate with a convenient shape.  Moving parts would have to be inoperable in extreme cold, if solely due to thermal expansion or contraction causing joints to seize (unless they're made of Invar or some other special alloy). Electronics would probably not survive ultra-low temperatures for more than a few hours or days, and would definitely not function over 400K or so without serious reinforcement.  Motors - presumably fed by turbopumps i.e. moving parts would also require a minimum operating temperature.  Crewed parts would require some sort of active heating, which would imply active cooling as well in the form of a TCS.

On surface temperatures: while IRL planetary surfaces might provide a significant conductive heatsink, most landed objects in KSP don't rest on the ground, the stand above it on legs or wheels.  These would provide very little by way of conduction due to their relatively small contact area, so it is safe to say that even implementing a 'realistic' surface conduction mechanic would have little effect on the thermodynamics of the spacecraft - it would likely radiate away most of its heat before conduction became a major player.  Also, convection (referring to Duna's atmosphere necessitating heating) is already modeled AFAIK, but to what degree of accuracy I can't say.


tl;dr  I think more constrained thermal operating ranges is a neat feature, but complexity could rapidly scale out of control.  In real spacecraft design, thermal management is a very complex and multi-faceted issue.  The game as it stands has a pretty good balance and adding more complexity may get you more than you bargained for.

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