ooooooh, where to begin.Ok. Newton said that every action has an equal and opposite reaction.When operating in a gravity well (like an aeroplane in earths atmosphere) in order to stay in the air the aircraft must generate lift equal to or greater than the force exerted by gravity - else it goes down. Gravity is a function of mass (or weight) - so the heavier an object is the more lift it requires to propel it into the air. A B747 weighs in at around 400 tonnes if memory serves correctly. This means that it must generate over 400tonnes of lift to get airborne and then must continuously maintain this to stay airborne because gravity is always trying to pull it down. An aircraft generates lift by aerodynamics, they must maintain airflow over a specially shaped wing surface to create the upwards force and to do this they must always be moving forwards.In deep space, well away from any source of gravity, there's nothing to pull you. If no force has been exerted on your spaceship it will just sit there and not move. Now if you pulse the thruster, just a split second of thrust, the ship will start moving. Now here's the big difference - it will keep moving. Once you've started moving you will keep floating along in the same direction on inertia.On Earth gliders will also do this, but because of air resistance the glider will slow down and (because lift is proportional to speed) it will lose lift and so descend (because lift will decrease below the weight of the glider).Now, if a spaceship will keep moving it means you don't need to keep them firing. It also means that if you pulse a different engine your ship will have had a new force act on it and it will start floating in a different direction (actually it will be a vector which is the sum of the original pulse and the new one).So... in Star Wars the X-Wing swoops and zooms around. It does the fancy banking maneuvers and rolls before diving down on you. This was does because the director wanted to emulate WW2 style dog fights. However it is completely unrealistic because in space there's 1. No reason to keep forward moment up, 2. No need to keep the engine burning continuously and 3. if the engine stops you just keep floating in the same direction. In Babylon 5 the Starfuries spin and rotate take advantage of a much more real to life set of physics (it's still not perfect but its far closer than Star Wars). Watch this video and you'll see some examples.As for why it's not atmospheric... because the series says so. However if you just look at the fighter you can easily see that it has the aerodynamics of a brick. Those wings aren't aerofoils, they are hollow I beams. Earth Alliance technology does not have antigravity so it has to rely on direct thrust and aerodynamics, and with a nuclear reactor onboard it isn't light. It has five main areas of drag and any attempt to turn would unbalance it and probably rip it apart. That's the Aurora. The Thunderbolt Starfury is a different beast altogether and is atmospheric capable.Hope that helps. And here is a nice montage of B5 space combat scenes which show off different styles of flying.