Dead Space 3 side mission from the chapter 5: Expect Delays.
In order to start the mission, you have to go to the Mid Station, where you first must start the generator using an electric interface.
Inside the room you'll find a workbench and a crate. Go up the stairs to the panel, where you can locate a decoder which opens the second door (a side mission begins).
Leave the room and turn left, to the unlocked elevator which will take you to the upper level.