The vault activator discs were a set of two activator discs which could open the vault where the space ship of the Veil was kept. The vault could only be opened with both activator discs.
Androvax used both activator discs to open the vault. Then it was impossible to use the activator discs again as one of the disc lay on one side of the vault and the other one on the other side of the vault. Both disks were needed to open it. (TV: The Vault of Secrets)