Final answer:
Heat shields on spacecraft are crucial during reentry to protect against extreme heat generated by air compression and friction, with temperatures reaching as high as 15,000 °C.
Step-by-step explanation:
Heat shields on a spacecraft are necessary when it reenters the Earth’s atmosphere because at the high speed of entry air will compress and heat up, creating very high temperatures. This process occurs as the spacecraft moves rapidly through the atmosphere, causing the air ahead of it to compress. The friction from the spacecraft pushing against the air turns the kinetic energy of the spacecraft into heat. Subsequently, the spacecraft heats up and may glow red hot, with temperatures at the front of the heat shield reaching as high as 15,000 °C. The heat shield protects the spacecraft by absorbing this intense heat and preventing the interior and critical components from melting or burning up on reentry. This is why having a reliable heat shield is vital for the safe reentry of any spacecraft coming back to Earth.