Raddus unlocks at 4 stars.
Event requires you to complete 4 tiers with 4, 5, 6, 7 star ships and capital ship. Once you complete the 4 tiers you unlock the Raddus at 4 stars. This also unlocks a bonus tier that rewards 10 ship blueprints that is replayable every time the event returns. The bonus event can be refreshed 19 times for 999 crystals each time.
The event is expected to run 1-2 times per month but may change its frequency in the future
The below ships are required for the event: