Reentry Analysis for a virus spread

A returning spacecraft sheds nearly all its 7.8 km/s orbital speed as heat in the upper atmosphere. Too shallow an angle and it skips back into space; too steep and the deceleration g-load and heating spike to lethal levels. The ballistic coefficient sets how deep it plunges before the thickening air finally slows it.

The International Standard Atmosphere is the reference model all aircraft and instruments are calibrated against. Temperature falls steadily through the troposphere at 6.5 °C/km, then holds constant in the stratosphere above the tropopause. Pressure and density decay roughly exponentially — at airliner altitude the air is only a quarter as dense as at sea level.