The P-61 never carried any missiles operationally. It was the penultimate USAAF/USAF piston powered night fighter.
Your photo shows one assigned to the Navy to launch a Martin “Gorgon IV” ramjet air to surface missile. Twelve test launches were made.
Being a large airframe, it was used as a test bed for many occasions. The aircraft surviving at the NASM in Washington served as a test aircraft with NACA dropping models.

BTW: Pampa14, Please let us know if you read these responses to your questions 🙂