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The adiabatic processes of re-entering earth from a spaceship, creates intense heat. Heat in the range of 1700-2000 degrees Celsius.

I've read the the temperature in the air molecules generate a very hot plasma which glows in the red-orange spectrum.

But Di-nitrogen should only turn plasma 10.000 + degrees Celsius.

How is this possible? I'm guessing the 1700-2000 temperature is only at the spacecraft, while only the surrounding air are reaching these plasma temperatures. But I can't find sources.

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  • $\begingroup$ Okay I'm just finding this on wiki: "the air in the shock layer is both ionized and dissociated". So these plasma-temperatures are generated from the constructive interference of the pressure wave? $\endgroup$
    – nammerkage
    Commented Mar 10, 2020 at 10:12

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Nice question. By re-entering atmosphere spaceship transfers it's kinetic energy to impacting air molecules, thus molecules starts to move at a spaceship speed too. Knowing average molecules speed (which would be an aircraft speed) we can calculate shock-wave zone gas temperature : $$ T={m{\overline {v^{2}}} \over 3k_{B}} $$ Typical re-entry speed of Space Shuttle is about $7823 \,\text{m/s}$, this gives shock zone temperature $\approx 68'000 \,\,\text{Celsius}$,- seems more than enough to heat Nitrogen into a plasma.

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  • $\begingroup$ Thank you very much. Can you put some words on why the spacecraft isn't 68.000 degrees Celsius? $\endgroup$
    – nammerkage
    Commented Mar 10, 2020 at 11:25
  • $\begingroup$ Spacecrafts are protected with a heat shield composed of layers from special materials dissipating heat received. Also according to this decent answer in space.stackexchange there's an ablative cooling mechanism in action and besides at these altitudes air density is very small, so heat is transferred from plasma to spacecraft at low rates. $\endgroup$
    – Agnius Vasiliauskas
    Commented Mar 10, 2020 at 12:58
  • $\begingroup$ Good reference, the simulations referenced are close to your "back on the envelope" calcualtion. Thank you $\endgroup$
    – nammerkage
    Commented Mar 10, 2020 at 13:41

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