If there was air in space, the artificial satellites could not keep their orbits because of the drag, they would need to keep the motors constantly
(or at least frequently) working to keep the velocity.
Also, in that case they would not need to transport in the outer space vehicles (space shuttle, artificial satellites, space stations, etc.) any
oxidizing agent, they would only need the combustible part of the fuel.
They could then use other type of engine, like a turbine, or they could even use a normal four-stroke engine with a propeller



:gasp gasp: 



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