Today's State of the Galaxy announcement stated:
First off, this event will require a new kind of event ticket, which will be earned via existing game modes. These tickets will become earnable once a player has met the prerequisites and unlocked the event. We are still working out the specifics of where the tickets will be earned, but we expect players to be able to earn these tickets every day.
Do these tickets unlock the event tiers, or are they used up with every battle attempt ? If I enter the battle and fail, do I need to earn more tickets before I can re-enter the battle and try again?