Has to be done on
"Updaam" at
"Noon". This achievement requires a high level of stealth so make sure to equip silenced weapons and I use double jump in my video walkthrough.
Once in Updaam make your way over to the left-hand side of the map to find the "Condition Detachment" island. Cross the bridge, go up the first flight of stairs, bear right and go out then back in the two windows. Silently take down the guard in this room, then head out to the front of the main building, climb over the fake orange rocks to find a 1st floor window. Take a left to go through a door, do a quick 180 and jump to the 2nd floor window.
Here you need to listen to two guards talking, which provides you with the command 2-bit needs to launch the rocket. From here do your best to silently take down all guards on this floor and the floor above with the rocket. If anyone on the top floor detects you, Charlie will run away to his safe room and you'll be unable to kill him with the rocket.
Now that the floors below Charlie are now cleared, we can collect 3 batteries to power the rocket. The batteries can be found powering the moving boards/scenery. Once the rocket has been powered up with 3 batteries you can proceed to speak with 2-bit. He's found in a locked room beside all the computer equipment (mission control). Hack the door to open it, speak with 2-bit and command him to launch the rocket. The rocket should then kill everyone on the top floor, including Charlie if he hasn't detected you.
Tip: Enabling "One Shot Kill" and "Mark Mutiple Enemies" in the Gameplay options really helps!