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   Hippy Steve (exador23@m.ai6yr.org)'s status on Monday, 31-Mar-2025 05:46:20 JST Hippy Steve

   TIL. This is why capsules turn around and re-enter the atmosphere butt first…

   The heat load experienced by a re-entry vehicle is inversely proportional to the drag coefficient. counterintuitively, the greater the drag, the less the heat load. Through making the reentry vehicle blunt, air can't ‘get out of the way’ quickly enough, and acts as an air cushion to push the shock wave and heated shock layer forward. Since most of the hot gases are no longer in direct contact with the vehicle, the heat energy stays in the shocked gas and simply moves around the vehicle to later dissipate into the atmosphere.

   It's usually assumed that the mechanism of heating in reentry is by friction (i.e. viscous drag in the atmosphere). In fact, this is the predominant mechanism only at lower altitudes, as air density increases. During the fastest and hottest part of the descent, less familiar physics are in play. A reentering vehicle develops a very energetic pressure wave at its leading surfaces. The energy density is sufficient to cause atmospheric molecules to dissociate, and their component atoms to become ionized. The vehicle thus descends in a superheated shroud of incandescent plasma.

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     GreenSkyOverMe (Monika) (greenskyoverme@ohai.social)'s status on Monday, 31-Mar-2025 15:54:28 JST GreenSkyOverMe (Monika)

     in reply to

     @exador23 Wow!