What is the "rule-of-thumb" for a stable rocket?

The guideline stating that the center of gravity (CG) should be at least one body diameter in front of the center of pressure (CP) is essential for ensuring the stability of a rocket during flight. This rule-of-thumb emphasizes the need for aerodynamic stability; a rocket that has its CG positioned ahead of the CP is more likely to maintain a straight trajectory as it ascends.

When the CG is forward of the CP, any disturbances or external forces, such as wind gusts, that might cause the rocket to deviate from its intended path will result in a restoring moment that helps bring the rocket back on track. This means that if the rocket starts to tilt or rotate due to these forces, it will naturally realign itself in the correct flight path.

Maintaining this relative positioning of CG and CP is crucial for preventing instability, which could lead to errant flight paths or even failure of the rocket. Therefore, the rule highlights a fundamental aspect of rocket design that significantly impacts performance and safety during flight.