How to controll vessel without crew?
You need to include a crew-less satellite part from the 'Pods' tab that is not the Command Seat. Right-clicking on them for more info will show "Unmanned" under the Command heading. Do note that if a satellite pod loses all power, the vessel will become effectively dead in space, and you cannot even throttle liquid engines on to generate power, so having a couple solar panels deployed once in space is a good idea.
If you are playing in career mode, the first satellite pod is unlocked by Flight Control for 30 science.