High energy collisions between the orbiter and particles in the ionosphere. At MECO, the orbiter is only just out of the mesosphere (about 105 km IIRC) and there is still plenty of "air" for it to collide with. The energy transferred to the particles is re-radiated, some of it in the visible spectrum.1.Before ET SEP, you see some plasma "flames" surrounding the vessel. What causes it?
Almost all of it is due to adiabatic heating from compression at the shock front.3.During entry you see plasma flames. Is it caused by compressed air that heats, friction or any other? How much contribution each factor has in the heating?