As a rocket approaches the speed of sound, what happens to the coefficient of drag (Cd)?

As a rocket approaches the speed of sound, also known as transonic speed, the coefficient of drag (Cd) typically increases. This behavior occurs due to the changing flow characteristics around the rocket as it accelerates through different regimes of speed.

At subsonic speeds, the airflow is smooth and relatively predictable, which means the drag coefficient remains fairly stable. However, as the rocket approaches the speed of sound, the airflow begins to compress, leading to shock waves forming. This alteration in airflow dynamics causes an increase in pressure drag, thereby increasing the overall drag coefficient.

Once the rocket exceeds the speed of sound, the drag may stabilize or even decrease due to the shock waves aiding in smoother airflow over certain designs, but in the critical transition from subsonic to supersonic speeds, the Cd is observed to increase. Understanding this behavior is crucial for optimizing rocket design to manage drag effectively during critical phases of flight.