Given that it was so easy to make things that would float in air, it was 
not much of a stretch to add an air turbine. This was nothing more than a small 
propeller, or series of them, mounted in a tubular foramen wrought through the 
body of the aerostat, drawing in air at one end and forcing it out the other to 
generate thrust. A device built with several thrusters pointed along different 
axes could remain in one position, or indeed navigate through space.