Bat guano.
The kind of fuel that packs kilotons into a warhead doesn't give a rat's ass about air. LOL!
After separation from the third stage, the Trident D5 Post-Boost Vehicle(PBV) takes stellar sightings and updates its guidance systems.
The PBV is then able to receive GPS navigation updates to correct its velocity and position in space.
FYI, the accuracies achieved are still classified and even I do not know them.
But they are better than 90 meters CEP.
So the Trident D5 could be used as a carrier killer weapon thanks to its high accuracy.