Why do spaceships get cold if their heat turns off? What do they lose heat to if they're in a vacuum?

Question

It seems like space would work like a giant thermos. With nothing to transfer heat away, how come Apollo 13 became so cold when the heaters were turned off?

Answer 1

There are multiple types of heat transfer. Conductive heat transfer is the kind you're thinking of, which requires two objects to be in contact with each other. You're correct that there is nothing to conduct heat to in space, so the conductive heat loss of a spacecraft will be zero.

However, there's another kind of heat transfer, called radiative heat transfer. Any material with a temperature above absolute zero radiates electromagnetic waves (losing energy). For very hot items, the EM waves emitted are in the visible range, so we see the item as glowing red-, white-, or blue-hot. Different temperature flames are different colors for this reason (as well as stars with different temperatures). The hotter an object, the more energy it radiates away.

A spaceship might be at 20 Celsius (293 Kelvin). Deep space has a temperature of about 4 Kelvin. This means that far-away stars are radiating a tiny amount of energy onto the spacecraft, but the spacecraft is radiating a much greater amount of energy away into space.

The equation for the rate of energy (power, in other words) transferred between an object and its environment is:

P = epsilon*sigma*A*((T1)^4 - (T2)^4)

where epsilon is the emissivity coefficient (between 0 and 1), sigma is the Stefan-Boltzmann constant, A is the surface area of the object, T1 is the object's temperature, and T2 is the evironment's temperature.

Space has a very low temperature, so the net heat flow out from a warm spaceship is quite large. However, radiative heat transfer is not generally as fast as conductive heat transfer, so it took a few hours for the spacecraft to get really cold.

Answer 2

You have a couple things going on. First, you mentioned it is "really cold". When it is really cold, heat pumps do not work very well. When the outdoor temp drops below a point between 20° and 30° (this varies by installation) the heat pump can't put out enough heat to keep the house warm. There should be a temperature switch in the condensing unit that disables the compressor and forces the heat strips (emergency heat) in the air handler to run. This switch may not have been installed on your system or it may need to be adjusted. Next, the temperature variation in the house.... Due to the marginally warm air coming from the vents, any room that is better insulated and has less draft than the other rooms will be warmer. If the temperatures are always different in these rooms you may need to adjust the air flow from the registers. With warmer air coming from the vents this difference may not be so noticeable. Place a space heater in the cold room. Close vents in unused rooms. Use blankets when you can. If you must have the whole house warm, switch the emergency heat on as needed. It's cold out there! Expect to pay more to stay warm. The emergency heat will cost much more to operate.

Answer 3

The problem is that you are thinking of this is in the wrong way. The vacuum in a thermos isn't all that holds heat, even then it only holds heat for a short time. The vacuum of space doesn't change the fact that the ambient temperature is extremely low and as the capsule shut down the heat began to bleed off into space. Left long enough the heat would slowly disipate until the inside of the capsule was the same tempurature as space itsself. Heat is like water, it self-levels, moving from a higher area to a lower area until everthing is equal. Only in extremes like space there will never come a time when the temperature equalizes high enough to support life as we know it.

Answer 4

The heat does slowly radiate off in the form of infrared radiation, so a spaceship with nothing to heat it up will become cold, especially if it's in the dark (i.e., in interstellar space or behind another object). However, for the most part you're right, what with all the equipment they have on board generating heat, spaceships have more problems staying cool than they do staying warm.

Answer 5

In space, your average temp is just vector addition. Most spacecraft are "silver" colored, which reflects heat. They are designed that way because there is usually more heat generated inside them, then is received from the sun, and they want to radiate that heat.

The "heat" does not get absorbed by anything, it "radiates" off in the form of infrared waves. The silver skin of a craft is designed to radiate off excess heat - that means that it absorbes some heat, but more is radiated because of the head created by all the electrical stuff inside the craft.

So, when Apollo 13 turned off its power to save it for the re-entry, it got cold in there...

Ron.

Answer 6

I'm not a physics expert, I'll have a guess.

Every object with a temperature RADIATES heat evergy
(for an object at room temperature, this is in the form of
infrared light). This is how the energy is lost into space.

Remember that the sun heats the earth with infrared light through the
vaccuum of space.

Answer 7

Space is cold because there is not enough "stuff" in space to keep it warm. The lower atmosphere is warm because of all the air molecules constantly moving.

And in response to the person who said they have more issues with staying cool...in Apollo 13, all the equipment and computers were turned off and not generating heat.

Answer 8

There are two type of heat transfer. Conductance and radiation. In space there is no conductance but heat loss by radiation is the problem. It is the same way that our planet looses heat back into space.

Answer 9

The vacuum of space will prevent the heat escaping by convection, but does nothing to prevent heat loss by conduction.

Convection is heat transfer through a moving gaseous or liquid medium. Conduction is heat transfer through a conducting medium without perceptible motion of the medium itself.

When you bake something in an over, the air in the oven is heated by the heating element and makes the whole oven cavity hot through convection. When you touch the baking tray you get burned by conduction. (If you first hold your hand over the hot baking tray, you'll be able to tell it's hot thanks to convection.)