Earth is a magnet. Also known as the magnetosphere. Electric motors or generators work by moving a wire (or lots of wires) through a magnetic field (by spinning them). Generators work by using mechanical force which forces the wires to pass through a magnetic field and generates electrical flow. Motors use electrical energy to make mechanical energy. Same principle works in Earth orbit- a wire in orbit will generate electrical energy. If you add more electrical energy to the wire it gains orbital speed (goes to higher orbit/gains mechanical energy), or if you take electrical energy from the wire it loses orbital speed (lower orbit/less mechanical energy)