What defines physical contact in the context of detonation?

In the context of detonation, physical contact is defined by the presence within a specific range that ensures a successful detonation event. The option indicating presence within 20+ mm signifies that the detonation mechanism is designed to react when an object, typically a warhead, is close enough to its intended target to ensure the detonative force can be effectively transferred. This range is critical because it establishes that the explosive device is no longer just in the vicinity but has reached a point where it can reliably initiate its function, resulting in the intended destructive effect.

Other options, while related to the processes leading up to detonation, do not accurately define physical contact. For instance, impact with a target (one of the other choices) signifies a moment of contact but doesn't capture the necessary conditions for detonation that rely on being within a designated range. Signal transmission pertains more to the communication or control mechanisms rather than the physical connection needed for detonation, and the launch sequence completion involves the procedural stages prior to detonation but does not define the physical presence required at the moment of detonation itself.