Rare Replay

RDUs, or Radiation Dispersal Units, are collectible items spread throughout each carrier stage, and this achievement requires you to complete every last one in every stage. The bonus stages, including Shuttle Clear onwards, are not required for this achievement. RDUs aren't actually picked up, but rather are activated by driving near to them. Whilst there's not a fixed number of RDUs in each stage, your progress towards activating all RDUs in a stage is displayed with an on-screen counter.

Importantly, the first time that you attempt each stage, focus on clearing the carrier's path above any other objective. Once you've done this successfully, you can re-enter the stage at will in a free-roaming mode, without any pressure from the carrier's progress, or indeed any time limit at all - and this is the best time to go for a full clear of the stage.