Completing all of the challenges for this week unlocks another loading screen:
If you look in the background, there are 4 coordinates on the wall, A4, B4, A3, and B3.
Here is the location of the hidden Battlestar, which is between the four co-ordinates, posted by Reddit user Bfor45:
Simply interact with the star to receive a whole Battle Tier!
If you haven’t found the hidden Battle Star for Week 1, you can find the location below: