In-Universe:
The U.S.S. Defiant and the rest of the fleet destroy the powered-down orbital platforms as they continue on.
Production:
The Digital Muse V2 CGI model is used in this scene. This confirms that this is the same model used in the episode "Valiant' because the registry number on the nose is not the Defiant's NX-74205, but the Valiant's number: NCC-74210.
