Hitting the atmosphere will also put an enormous amount of strain on the heat shield; it will experience pressures equivalent to being sat on by a jumbo jet. To keep it from cracking, engineers at Lockheed reinforced the heat shield with 2.5 inches of honeycombed aluminum that is stiff enough to handle the stress. The atmospheric drag created by the shield serves a braking function and will slow Perseverance to a few hundred miles an hour. Once the craft is about 7 miles above the surface—the cruising altitude of a passenger jet on Earth—it will use a small explosive charge to deploy its parachute. Shortly after, the rover will jettison its heat shield. That’s when things start to get truly wild.
When the heat shield clears the spacecraft, the rover will detach itself from the parachute and experience a few seconds of freefall about a mile above the surface. It’s