How far behind the center of gravity should the center of pressure be for stability?

For stability in rocketry, the center of pressure (CP) must be located behind the center of gravity (CG). This location ensures that any perturbation in flight, such as a wind gust or slight misalignment, will result in a restoring moment that brings the rocket back to its intended flight path.

A commonly accepted guideline is that the center of pressure should be at least one caliber (the diameter of the rocket's body) behind the center of gravity. This adequate distance allows for sufficient aerodynamic stability, which minimizes the risk of oscillations or spin that could lead to an unstable flight. A placement of one caliber ensures that the rocket can handle not only minor disturbances but also more significant aerodynamic forces without losing stability.

While shorter distances (like 0.25 or 0.50 caliber) may result in a rocket that is somewhat stable, they do not provide the same level of assurance as one caliber. A distance of 1.50 caliber could provide even more stability but might be unnecessarily far for many designs, making one caliber a commonly accepted minimum standard for effective flight stability.