Launch up to the cannon tower was a mission that Jak and Daxter completed to obtain a power cell in The Precursor Legacy. An unassigned mission that simply rewarded Jak for taking out the Cannon on top of the tower in the bay.
Once you have completed the "Find the blue vent switch" mission in Forbidden Jungle you can use blue eco from the newly unlocked vent located past the shallow part of the bay, on top of a platform that marks the start of a series of tall stone pillars. When channeling blue eco use the nearby Precursor launcher to jump onto the closest stone pillar. From here you can use another launcher to make another jump to the next stone pillar, where you can recharge yourself with blue eco at a second eco vent. Make another two of these jumps to reach the cannon tower. From here just defeat the two babaks operating the cannon and the power cell will be revealed.