When astronauts return to Earth, they don’t simply “come down”—they slam into the atmosphere at orbital speeds of ~7.8 km/s (about 17,500 mph). At those velocities, air can’t move out of the way fast enough, so it compresses violently in front of the spacecraft. That compression drives temperatures up to ~1,500–3,000°C around the vehicle. Contrary to popular belief, it’s not friction that causes most of the heating—it’s the formation of a superheated plasma sheath as atmospheric gases are compressed and ionized. This plasma glow is what you’re seeing during re-entry. To survive this, spacecraft use thermal protection systems (TPS): • Ablative heat shields (like those on Apollo capsules) that char, melt, and carry heat away • Reusable tiles (like the Space Shuttle) that insulate against extreme temperatures • Modern materials (like SpaceX Dragon’s PICA-X) designed for high efficiency and reusability Astronauts also experience intense deceleration forces—up to ~3–5 g depending on t...