Helmet's right. Back to the "ultimate weapon."
Here's an interesting twist:
Dooku is Palpy's apprentice. But he's also the leader of the "Rebellion." So here's what I think: The Rebellion is all Palpy's plan (duh! 🙄 ) to gain special powers that allow him to create an army for the Republic (which he does). He then uses the army to force the Republic into his submission, making him Emperor. The Death Star is an extention of the army, which eventually becomes the Imperial Navy. Palpy plans to destroy the Rebellion, after he becomes Emperor, using the Death star on their bases. Palpy entrusted the plans to Dooku, who he could trust.
Only problem is, he couldn't trust Dooku, who "accidentally" let the plans slip into Rebel hands, planning to kill Palpy and take over. But then Dooku gets killed, ahd the plans find their way to Leia. We all know the rest.