eli5: if space is virtually empty, does a space shuttle stay hot from when it exits the atmosphere because there’s less particles to absorb the heat? Or does it do the opposite and cool rapidly?

Question

I’m just curious as to the process and behavior of the surface temp of a shuttle once there’s virtually no particles in contact with the craft.

I’m aware space is cold due to the absence of matter,

But does a space shuttle take a much longer time frame to cool down with less matter available to transfer the heat of the craft to, or does the lack of matter cause the shuttle to cool rapidly?

In: 141

Answer 1

To quote Wikipedia [https://en.wikipedia.org/wiki/Heat_transfer](https://en.wikipedia.org/wiki/Heat_transfer)

>Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes.

Conduction, thermal convection, and transfer of energy by phase changes do need matter but thermal radiation does not. The visible and invisible light we get from the sun is thermal radiation.

Everything warmer than absolute zero emits thermal radiation. Most stuff we are used to including us is at a temperature so the thermal radiation is in the infrared range (IR). We can see it without the naked eye but a thermal camera can. You can feel IR radiation from the warm but not glowing objects when it heats up your skin.

The way the space shuttle and ISS get rid of heat is with radiators. On the space shuttle, they are on inside of cargo bay doors http://www.projectrho.com/public_html/rocket/images/basicdesign/shuttleHeatRadiator.jpg Overheating because of sunlight is a major concern for the shuttle so opening the cargo bay doors was one of the first thing done when it was in orbit.

ISS have large radiators that typically are close to perpendicular to the sunlight so they are as efficient as possible https://letstalkscience.ca/sites/default/files/styles/x_large/public/2019-12/Heat_Rejection_System_radiators.jpg?itok=JROfS9Pf

The system works like any other refrigeration system like a fridge or an AC but is shaped to optimize cooling from radiation instead of contact with air. The result is large flat areas to radiate the energy to space. If you use air you have large area too but in may stacked layers so blowing air with a fan is simple