Note: This is Side Ops and not a main mission, so there’s no ranking given out at the end. However, you are required to do this, as Mission 12 will unlock upon completing it.
You are required to do this Side Ops in order to continue with main missions. It is a relatively simple one that will force you straight into "Mission 12: Hellbound", so be prepared for that. Find the Landing Zone just north of Yakho Oboo Supply Outpost and use that for your long journey, meaning that D-Horse is perfect for this job.
You’ll likely pass through Aabe Shifap Ruins, which will trigger a boss battle against Quiet if you haven’t already done it (you’ll be forced out of the Side Ops anyway if you have to fight her). There are a few guard outposts along the way, so either check them out for any potential recruits or pass them right along on your way to the power plant.
The objective is to get to a door on the far end, which isn’t too difficult, as the southern side of the compound makes for a pretty good path. You will run into a few enemies along the way, but the height advantage by going on the roof of some buildings will help in scouting their locations. You can also just go via the ground, but there’s a higher chance of being spotted by any enemies on buildings. Once you reach the door, get ready for a cutscene, then Mission 12.