Space Is Air when a work treats spacecraft as if they were aircraft; they bank into turns, keep their engines firing at all times, and may even have wings built into their design. Aircraft-style design can be justified if the spacecraft is capable of operating in atmosphere as well as in space (like the space shuttle), but the main reason that this trope exists is because audiences are more familiar with how airplanes work than with how spaceships work. Thus, creators treat spaceships as if they are simply airplanes in space instead of using realistic physics, in order to avoid confusing the audience. This isn't necessarily a bad thing — after all, it can be used to great effect to make things look really cool — but it does push things down toward the softer end of Mohs Scale of Sci-Fi Hardness.
The way airplanes work is dependent on the fact that they're travelling through the atmosphere. Wings provide lift, flaps and rudders can reorient the plane by redirecting airflow, and their engines must be on constantly in order to counteract the effects of friction and gravity wings generate lift only when there's airflow across them, so a certain minimum airspeed is absolutely necessary for them to work. Because space is a vacuum, none of these things apply to spaceships — wings and flaps are useless, and the engine only needs to be on when the ship is changing speed or direction. This means that spacecraft use dedicated thrusters to reorient themselves, and change direction in sharp bursts rather than gradually. If you see a spaceship changing direction without using maneuvering rockets, or making wide, sweeping turns, then that's because Space Is Air. Many movies who feel obliged to acknowledge the lack of sound in space will nonetheless accompany motions of spacecraft or planets with deep, low frequency whooshing sounds, as if they were creating rushing currents of air. This trope occasionally extends to natural phenomena; for instance, the Sun is sometimes depicted, particularly in children's fiction, as literally on fire, implying that space is full of air to let it burn. Comets are almost always shown moving in the opposite direction to their tails, as if they were moving through air and their tails were the trails they left behind.
A subtrope of Space Does Not Work That Way, and sister trope to Space Is an Ocean. Also a frequent cause of Space Friction, and may be why Batman Can Breathe in Space. If you see Old School Dogfighting in space, it's usually because this trope is in effect; it also dictates the appearance of many Space Fighters.
- Cowboy Bebop uses fairly realistic Newtonian physics for the most part, but during combat, Rule of Cool pitches the laws of physics out the window and they revert to Old School Dogfighting.
- Notably, in the dogfights, many of the ships do in fact drift a bit and disengage and re-engage thrusters for turning.
- Space Battleship Yamato combines it with Space Is an Ocean; capital ships act like sea-going vessels, while smaller craft act like airplanes, to the point of having dive bombers and torpedo bombers. Given that the show is very much in the style of World War II's Pacific theater Recycled In Space, it's to be expected.
- Superdimension Fortress Macross: Given that the Valkyries can literally turn into planes, it's no surprise that they act like planes even in space.
- The novelization of SDF's Westernized form Robotech handwaves it as the fighters being thought-controlled. Since most of the pilots were used to atmospheric craft first and foremost, their veritechs moved as if they were in an atmosphere.
- Later Macross installments do their best to avert this, showing their fighters using verniers and thrusters to move in space, as well as pulling off maneuvers that wouldn't work in an atmosphere.
- Star Wars may actually be the Trope Codifier, particularly with the Old School Dogfight between Space Fighters.
- The Wing Commander movie takes this trope even further than Star Wars by having fighters take off from runways the same way airships take off from Aircraft Carriers and ships drop down when they leave the runway.
- The Star Wars Expanded Universe has a lot of this, reflecting the films.
- The Elder Things from H. P. Lovecraft's At the Mountains of Madness fly through space with their wings. Note that this isn't Science Marches On, as Lovecraft knew perfectly well that "aether" was a debunked concept, despite referring to it in-story to justify this trope; he just liked the idea of space being full of aether more than that of it being vacuum.
- Justified in Polystom, which is set in a star system in which the space between the planets really is filled with air.
- While Warhammer 40,000 normally tries to avert this trope, the novel Pandorax plays it dead staight with no excuse or shame.
- Taken to a literal extreme in The Little Prince, in which the Prince leaves his planet by catching migrating birds. Still, the story is less a science fiction tale and more a Fairy Tale with planets in it.
- The Last Hero has the Disc's one-and-only spacecraft leaving its atmosphere and making an (unplanned) trip to the Moon. in the flat earth continuinuinuum, the atmosphere of the disc never completely ends, it thins, but does not diminish to a point where it is virtually non-existent. The intrepid travellers discover they can still breathe on the Discworld's moon, for instance. As the spacecraft has wings to steer with, tis comes in very handy.
- Although the earlier incarnations of Star Trek tend more toward Space Is an Ocean, later shows start to treat ships as much like airplanes as like sailing ships. Not only are there shots of ships making expansive, banking turns like an atmospheric craft, but combat between ships is increasingly depicted as an Old School Dogfight.
- Used extensively Buck Rogers in the 25th Century. With the same stock footage almost every time.
- Averted in Babylon 5 — the Starfury is clearly designed for operation in three dimensions and looks nothing like an airplane; the pilot is not even in a seated position, but standing.
- Even within the show, ships designed to operate in an atmosphere as well as space, such as the Raiders' delta-wing fighters or the Thunderbolt Starfuries, will have a more aerodynamic design at the expense of being less maneuverable in space combat. Raiders end up having to rely on superior numbers whenever possible, while the Thunderbolts are fitted with considerably more firepower.
- the new Battlestar Galactica generally averts this. In an early space battle, one of the Vipers does a head-to-tail 180 degree spin in order to fire at a bogey behind it, and most of the time the engines only fire when they change course.
- Doctor Who both plays this straight AND subverts it in "Victory of the Daleks". World War 2 aircraft (Spitfires actually) are given air-containing force fields and engine modifications that actually allow them to fly into space and attack the Dalek mothership (the air inside the force field allowing the propeller to function and perform the usual airplane banks and rolls). The whole thing is hand waved by saying the force field generators and engine modifications were made with Dalek technology.
- Used in BattleTech, where the rules for fighting in space are essentially identical to the rules for fighting on a planet — nevermind the fact that heat dissipation (a major factor in mech combat) would be completely different.
- This is how everything works in X-Wing Miniatures; if your fighter doesn't move like a plane, you're probably playing Scum and Villainy and sprung for Inertial Dampeners, because everyone else has to be in constant motion and can almost never turn on the spot. Justified on grounds of it being a Star Wars tie-in; piloting in space is always identical to piloting in atmosphere in the Galaxy Far Far Away.
- Practically every space combat sim in history uses this, since most of them are just following the example set by Star Wars. Examples include X, Strike Suit Zero, Tachyon: The Fringe, Terminal Velocity...
- Mass Effect: Averted for the most part, though the Normandy makes some suspiciously aerodynamic-looking maneuvers on occasion. Lampshaded by the pilot:
Joker: It takes skill to make a ship bank in a vacuum. Don't think it doesn't.
- Star Wars games make extensive use of the trope, as with the films and the novels.
- Star Fox has its Arwings handle exactly the same in space as they do in atmosphere — to the point where, in some incarnations (such as Star Fox 64), it shows the ailerons moving on the wings when you turn... which would do absolutely nothing in space.
- Allegiance tries to find a sort of compromise between this trope and realistic physics, mainly by including Space Friction, but turning it down compared to most games: ships still move like they're immersed in a medium, but inertia is important as well. The overall effect ends up being that spaceships feel like they're moving through water, rather than air. Most of them still look like aircraft, though.
- Optional in Space Engineers - if one engages a (small) ship's inertial dampeners it will handle like a plane, if one does not...steering will be difficult.
- Starfighters in the Wing Commander series default to flying like airplanes. However, beginning with Wing Commander III, some of the fighters gain the ability to disengage their inertial cancellers and "slide" without experiencing friction.
- Kerbal Space Program averts this as its entire raison d'etre. The game is essentially a rocketry simulator, complete with accurate Newtonian physics.
- There are parts for Space Planes (for mixed atmospheric/space flight) and even regular planes and it's possible to build spacecraft that look like planes, but these function realistically — i.e. the aerodynamics are only important while flying in the atmosphere during take-off and landing, and in vacuum Space Planes function purely as rockets (and all the wings, jet engines, and other plane bits become expensive dead weight until you're back in atmosphere).