What happens if an Excalibur projectile does not acquire an adequate GPS signal?

Choosing that Excalibur projectile continues its trajectory to the ballistic impact point without arming and duds is accurate because the Excalibur is designed to rely on GPS for precision guidance and engagement. If it fails to acquire an adequate GPS signal during its flight, it cannot perform its intended function as a precision-guided munition (PGM).

Instead of arming and detonating on impact, which is typical behavior for standard munitions, the inability to obtain an adequate GPS fix means that the Excalibur would not arm itself, thus resulting in a failure to detonate upon impact. This would lead to the essential characteristic of behaving as a 'dud' since it hasn't been given the signal to operate as intended, rendering it inert upon impact.

The other options do not accurately reflect the design and operation of the Excalibur projectile, as they suggest alternative functionalities that contradict its reliance on GPS for effective targeting and arming mechanics.