# How Sci-fi Doesn't Work

How Spaceships Move

We opened this article with a description of banking X-wing fighters and other spacecraft, from "Star Wars." You can see similar movements in the Viper fighters of the original "Battlestar Galactica" TV series. Designers modeled these spacecraft after modern jet aircraft fighters (like the F-14 and the MiG) and they engage in dogfights like those in "Top Gun." The banking of an aircraft is a consequence of air moving over the surfaces of the wing, ailerons and rudder. When a plane turns, the ailerons on one wing move up on one side and down on the other, which causes the aircraft to roll in the direction of the turn. Simultaneously, the tail rudder moves in the opposite direction of the turn and deflects air to make the turn. These combined air movements cause the plane to bank in the direction of the turn as the plane continually thrusts forward. They could not happen without air.

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While an aircraft moves through the medium of air, a spacecraft moves in a vacuum. Newton's Third Law of Motion ("for every action, there is an equal, but opposite reaction") governs the movement of a spacecraft. For a spacecraft to turn, it must fire a rocket thruster (eject mass as hot gasses) in the opposite direction from where it must go. There are three axes of rotation: pitch, roll and yaw. If the pilot wants to turn right, then the rocket thrusters fire left and usually the roll and yaw thrusters fire simultaneously. Such maneuvering thrusters are located in various places along the body of the spacecraft and allow it to move in all three axes of rotation. So, the turn of a spacecraft looks like an abrupt flip in one or more directions simultaneously rather than a smooth bank. You can see such movements of the Apollo spacecraft in the HBO miniseries "From the Earth to the Moon" and in the Viper fighters of the new "Battlestar Galactica" series on the SciFi Channel.

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Next, we'll learn about sci-fi mistakes with planets and asteroids.