Re: How long does it take to get frostbite in space?

Hi Chris!

Thanks for your question.

It might seem counter-intuitive, but losing heat in a vacuum is hard. On Earth, heat is lost from hot bodies by convection and conduction, both of which require matter in contact with the hot body. There is a third method of heat loss called radiation (in this, the body radiates infra-red photons, which you may have seen demonstrated on IR/night-vision cameras). Radiation is not very efficient, but in the vacuum of space it's the only practical method available to a spacecraft or a person in a spacesuit. Indeed, all manned spacecraft need to contain substantial radiators to dump their excess heat.

The space shuttle, for example, has large radiators which line the inside of the cargo bay doors. There's a picture of these here. These radiators are so important that a shuttle would have to cut short a mission if, for some reason, the cargo bay doors couldn't be opened once on orbit. Similarly, as new solar panels are being added to the International Space Station, in order to generate more energy (which ultimately ends up as heat within the station) more radiators need to be attached. The 8 white panels in this picture show one of the ISS's radiators.

So if losing heat is so hard, it would be a good idea to avoid getting it in the first place? Naturally one way to do this is to paint or cover the spacecraft or spacesuit with a highly reflective covering to help avoid absorbing IR photons from the sun. This is the reason why you see so much white or bare metal on objects photographed in orbit. Another method, used on the Apollo missions, was to slowly roll the spacecraft, so that a period of baking under sunshine was followed by a period of cooling when these hot panels were in shade.

In a properly designed spacesuit, the duration limits are set by the use of consumables, notably air and - to a lesser extent - drinking water. Temperature control is important, and all spacesuits use water in flexible pipes held next to the body to transfer heat away to the PLSS (Primary life-support system) where a radiator dumps this heat into space. Layers of insulation and outer layers designed to reflect heat away ensure that the astronaut's temperature doesn't get affected when working in full sun or the shade.

Your second question asks about the temperature of space. Temperature is a product of matter - it is directly related to the kinetic (movement) energy of particles. In space, with no particles, the concept of "a temperature" is not applicable. However, an object in a vacuum will absorb heat from the sun, depending on the albedo (the amount of reflectivity) that the object has. Dark objects will absorb more heat, light objects less. Similarly, objects in sunshine will gain energy, objects in the shade will lose it. For the Moon, this change in energy gives temperatures for the lunar surface between -250C to 260C. Good insulation is the key here!

I hope the above helps answer your questions!

Andy