Enter your return speed. Find out how hot your spacecraft gets coming home.
Coming home from space is not the dangerous part. The dangerous part is the last ten minutes. When a spacecraft hits the atmosphere at 11 kilometers per second, it is not friction that heats it up. It is compression. The air in front of the capsule cannot get out of the way fast enough, so it piles up and gets squeezed. Compressed air gets hot. Hotter than the surface of the Sun. The heat shield sees 5,000 degrees Fahrenheit. The outside turns into a plasma ball. Radio blackout lasts about seven minutes.
The Apollo astronauts came back from the Moon at 11 km/s. Their capsule's heat shield reached about 5,000 F. The shield was a one-time ablative material: it burned away layer by layer, carrying heat with it. You cannot reuse it. Every Apollo mission threw its heat shield into the ocean.
Coming back from Mars is worse. A Mars return trajectory hits Earth at 11-14 km/s. The energy is double the lunar return. Some proposals suggest aerobraking at Mars first to slow down. Otherwise, the heat shield would need to be massive. This is one reason nobody has gone to Mars yet: the return trip will fry you.
The Orion spacecraft, built for Artemis, faces 5,000 F re-entry. Its heat shield is the largest ever built. It is designed to handle the lunar return speed. Even so, the capsule comes in at a shallow angle: too steep and it burns up, too shallow and it bounces off the atmosphere like a stone on water. There is a window. It is narrow.
Not friction — compression. The shock wave in front of the capsule compresses the air. Compressed air gets hot. At 11 km/s, that air reaches 5,000 F. The heat shield sits behind the shock wave, so the plasma does not touch the capsule itself.
The Stardust sample return capsule came back in 2006 at 12.9 km/s, the fastest re-entry ever by a human-made object. It reached about 5,000 F. It was carrying comet dust. It survived.
In theory yes, but it takes as much fuel to slow down from orbit as it took to get up there. That is the rocket equation problem. The reason we use heat shields is because the atmosphere is free. You just have to survive the fire.
You burn up. The peak heating and deceleration exceed what the structure and astronauts can handle. The Space Shuttle had a load limit of about 3 g. A steep re-entry could hit 10 g. Bones break. Then the heat shield fails. Then you are a meteor.