Completion of all Week 3 challenges unlocks a new Blockbuster loading screen complete with another Battle Star to collect, hinted at by the hologram seen on the map:
The area of the new Battle Star is on the hill slightly south-west of Fatal Fields. To collect it, simply visit this location and interact with the star.
An image of the location in-game via Reddit user Agonyy95:
Note: You must have completed all Week 3 challenges for the Battle Star to appear.