Discover · Aerospace

Above a certain speed air stops behaving like air, and the leading edge becomes the whole design.

Format
Explainer
Published
2 April 2026
Read
6 min

Demo story Written as an example of the format. Real stories will be edited and fact-checked before publication.

Stagnation temperature

Air brought to rest against a vehicle converts its kinetic energy into heat. The faster you go, the hotter that stagnation region becomes — and the relationship is quadratic, so doubling speed roughly quadruples the temperature rise.

When air stops being a simple gas

Past a few thousand kelvin, molecules dissociate and then ionise. The gas no longer has constant specific heats, so the neat compressible-flow relations from a textbook stop applying and real-gas modelling takes over.

Three ways to survive it

Radiate the heat away with a hot structure, carry it away with a coolant, or sacrifice material deliberately with an ablative shield. Every hypersonic vehicle picks one of the three, or a combination, and the choice shapes everything else.

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