Locate the radar station commandant's office on Lighthouse
Hand over the drive
Find military HDD with data
Obtain the military HDD with archived flight routes
How to complete the quest?
Go to Lighthouse, to the small area with the actual lighthouse, and get inside the radar station.
Find an office with a sign "Radar Commandant's Office" ("Кабинет коменданта РЛС"), and open the door with the key. On the table there is an HDD, that you need to take and give to Skier, so obviously, you need to extract alive with this HDD.
Find the military HDD on the map
Entrance to the radar station
Office of the commandant of the radar station