From Rise: The Vieneo Province
Reentry can be a very dangerous time, because you are impacting the air at a high speed, and there is not enough to help cool the ship.
Outside Air Temperature
Outside Air Temperature is displayed as OAT.
This is the air temp taken in Kevin.
Static Air Temperature
Static Air Temperature is displayed as SAT.
This is the air temp taken with a standard thermometer in still air and no sun shining on it.
- For the purpose practicality OAT(in K) and SAT(in C) are basically the same just different scales.
Ram Air Temperature
Often called Ram Air or RAT
This is a measure of how much the compression of the air is heating it. SAT+RAT= TAT
Total Air Temperature
Total Air Temperature is what you track to see how much the Air will heat your Air Frame
The lower the Dynamic Pressure and Air pressure the less TAT can affect you.
In space you may only be impacting a few molecules a second with the entire air frame.
Yes each molecule imparts energy but there are so few that you can still cool through radiation.
Air Frame Temperature
You will find this listed as AFT on most displays.
This is usually a direct reading of the most critical part of the ship.
This typically is were a wing meets the body.
The interaction of the two shock waves can super heat the air mass in a local area.
We can go in to the calculations for deriving the Total Air Temperature (TAT). TAT =SAT (static air temp) + Ram Air temperature. If you want to see the formulas to get to TAT please see. https://en.wikipedia.org/wiki/Total_air_temperature
For all practical purposes you want to stay under the following speeds at the following altitudes.
As density decreases the the effect of the ram air on the airframe decreases.
How to picture this.
Imagine you have 10 cups of boiling water. You pour all 10 right over your airframe. The entire wing get scalding hot.
Now you climbed to 6 Km altitude. You are at half the density. So you are only pouring 5 cups of boiling water on the wing. It get warm but not dangerous to your hand.
You continuing climbing. As you pass 20 km the density is down so low that you only have 2 ½ cups of water.
As you keep climbing yes the TAT is going astronomically high but the mass of the air is decreasing. Once you are over 100 Km you if you are at orbital speeds you are for all practical purposes you are exposing the skin to temperatures that would melt metal but the mass of the action is so low it has almost no effect.