Why does the rocket doesn't burn when it enters or exits the atmosphere?

Answer 1

At launch, the rocket is moving fairly slowly, and by the time it is moving fast enough to burn up in the atmosphere, it is mostly ABOVE the atmosphere. Also, the design of the rocket provides shielding and stabilization when it is launched.

Coming back down, many rockets DO burn up when they re-enter the atmosphere at high speed. It takes special shielding such as the space shuttle's tile belly and specific design such as its wings and stabilizer that allows the shuttle to return to Earth safely. Please note that when a small piece of icy insulation punctured one of Columbia's wings on takeoff, the resulting friction and off-center drag was enough to destroy Columbia and kill all the astronauts aboard as it re-entered the atmosphere at hypersonic velocity.

Answer 2

The rocket's heat shield protects it from burning up when entering or exiting the atmosphere by absorbing and dissipating the intense heat generated by air friction. The design of the heat shield and the materials used are specifically engineered to withstand these extreme temperatures, allowing the rocket to safely reach its destination.