Space Friction

""So you can just slow down and make a sharp left in space?""

- Crow, Mystery Science Theater 3000

Most writers for science fiction TV shows and films are apparently still stuck in Aristotelian physics -- according to which a body in motion will always slow down even in vacuum -- and just don't get a single clue of how proper Newtonian physics work.

Basically, goes the misconception, if your engine breaks down in space, your ship will quickly slow to a complete stop. Your helm officer will say "We're adrift." This means something between, "We're moving at a random (low) speed and direction," and "We're not moving at all, practically speaking." Writers do this because if the engine in your car breaks down, you come to a stop, and if the engine in your boat breaks down, you drift at a random low speed at the whims of the currents. Based on these experiences, it feels intuitive to write that spaceships will act this way.

However, the reason these things happen is friction. On a straight road, with good tires, you can coast quite a long way on even a slight downgrade. In space, where there is no friction between the car and air to contend with, you can coast almost forever (albeit perhaps not in a perfectly straight line), or until you hit something, which, given how big space is, is astronomically unlikely. Which means that if your engine stops working in space at top speed, it's not going to give you any trouble getting to your destination. In fact, space vehicles spend most of their time outside the atmosphere with their engines off in this fashion. Stopping when you get there, of course, is another matter.

Note that there is a tiny bit of friction in interstellar space. The interstellar medium isn't a complete vacuum and, depending on what part of the galaxy you're in, there can be as much as one whole atom of hydrogen per cubic centimeter of space. This is still more rarefied than the best laboratory vacuum, however, and will only matter if you're going extremely fast -- as in sizeable-fraction-of-the-speed-of-light fast. Additionally, any object in space is affected by the minute gravity of all other bodies in space regardless of distance, so a coasting spaceship might not travel in a perfectly straight line; but this would result in a broken-engined ship perhaps missing its target or crashing into another, not stopping dead.

For that matter, the entire notion of "We only have enough fuel to get so far," is a little suspect: if you've got enough fuel to reach top speed, you've got enough fuel to go anywhere; once you reach top speed, you can just shut the engine off and coast. Of course, it would become a problem if you don't have enough fuel to stop at the end - or if, for whatever reason, you have to turn somewhere, or if your engine fuel doubles as power generator fuel, which would cause a black-out in your ship (which, if it comes up in a Space Friction plot, generally means the crew has a few hours to restore power before running out of air). None of this should be a problem if you know your situation before you set out and can plan accordingly (being boned in the event that you lose your fuel supply en route is possible, but then the problem is that you're either going to miss your destination... or you're going to hit it). Rocket engineers assess fuel reserves in terms of the ability to change velocity, known in the trade as "delta-v" (Δv), and every space mission has a "delta-v" budget. Note that it is possible to have not enough fuel to get to your destination if your spacecraft relies on Hohmann transfer orbits- if you don't apply the right amount of burn at the right times, you go streaking into space. However, in most fiction, spacecraft are well beyond being restricted by Hohmann orbits and so the above point is only valid in very, very hard sci-fi.

Heck, when it comes right down to it, the "top speed" of a space vessel is defined by the efficiency of the engines and their ability to accelerate a vessel whose momentum approaches infinity. Earth-bound vehicles have a top speed defined by the speed at which the engine can no longer out-perform friction (that is, the environment will brake the vehicle), and there's a point at which the vehicle will take damage from its surroundings (that is, the environment will break the vehicle). Space ships won't shake apart from going too fast, though they might be irradiated by blue-shifted cosmic background radiation. It's just that as their speed approaches that of light, they need ever increasing thrust to accelerate at the same rate. Furthermore, as the ship moves ever faster, collision with interstellar dust becomes increasingly dangerous, all the way up to nuke level or beyond at relativistic rates. Safety requirements may thus call for ships to not accelerate beyond what armour or shielding can withstand.

Exotic propulsion systems of the sort needed to exceed the speed of light are exempt from the normal laws of physics and can reasonably be presumed to expend energy even at a constant speed, just holding the laws of physics in check, but it's curious that the effects of such drives always cause space to behave exactly like an ocean.

Even in conventional space travel, though, there is a scenario in which a ship needs to constantly burn fuel, and that's when it's trying to fly along a non-ballistic trajectory. For example, to move in a straight line inside a solar system would typically be a non-ballistic path; you have to use thrusters to counteract gravitational effects from the star and planets. In space combat, non-ballistic paths are very likely to be used if for no other reason than to make it harder for the enemy to predict your motion. However, in these cases, when thrust is cut, rather than drift listlessly, the ship will either orbit something, crash into something, or leave the solar system, depending on its position and velocity.

A form of Hollywood Science. Leads to Old School Dogfighting.

Film

 * In Spaceballs, a spaceship brakes... and even emits a kind of shower of sparks, like a car would with burnt rubber.
 * Well, one of the spaceships looks like an RV. And let's not even talk about what the other spaceship looks like...
 * Lone Star's Space Winnebago actually leaves burnt rubber tracks. In space.
 * The Spaceball One, however, "brakes for nobody."
 * In Star Trek III: The Search For Spock: the Excelsior is accelerating up to transwarp, when Scotty's sabotage kicks in, everything breaks down and it coasts to a stop. Semi-justified in that the thrust was given by the defunct Transwarp Drive, a Phlebotinized engine that's probably not subject to Newtonian mechanics. Justified under Rule of Funny, as that breakdown is accompanied by a humorous "engine sputtering to a stop" noise.
 * Since Scotty made several 'improvements' in Excelsior he might as well program it to stop (decelerate). Or it might be an emergency measure that a ship losing main power in space dock will automatically come to a halt on thrusters.
 * In Star Trek IV: The Voyage Home, a ship whose power is zapped by a probe is actually seen to coast to a stop, while the Miranda class ship seems to continue on its direction - however while turning at a weird angle to indicate its out of control.
 * It could well be that most vessels will have some form of "emergency stop" procedure to prevent them from accidentally bumping into a planet or drifting off when it loses power. Not to mention making it easier to salvage said vessels. The Miranda class USS Saratoga's odd angle is a bit of a strange one though, perhaps it was just beginning to attempt a turn when the damping field got it?
 * Transformers: The Movie (the animated one) had a variation of this; Astrotrain, in space shuttle mode, pleads to his passengers to "jettison some weight, or we'll never make it to Cybertron". This seems to be an excuse to throw the other, dying Decepticons out of Astrotrain, but note that his engines were still on and burning brightly for some reason.
 * Parodied here.
 * Played straight in Mission to Mars, most notably where a character with a rocket pack tries to rescue another character who had done something silly - complete with fuel gauge running down. Kind of sad, as they'd done the space flight physics pretty well up to this point. Also, the friction from the space air doesn't seem to be affecting Woody - oh but that must be because he's not wearing his rocket pack any more ...
 * The space friction in Starcrash is so great that it leaves a trail by which you can track a spaceship.

Literature

 * Is a major driver in the plot of Poul Anderson's novel Tau Zero, where the Bussard-ramjet ship Leonora Christie suffers a failure of part of its engine. You see, Bussard-ramjet ships can accelerate near the speed of light using magnetic fields to fuse interstellar hydrogen to drive the ship; the reaction is self-sustaining once started. Problem is, as the ship accelerates relative to the rest of the universe, so does the oncoming hydrogen in the ship's path, which would result in the instant destruction of the ship if the fields fail. The ship has a special decelerator module on its engine for slowing down safely. Guess which portion of the ship's engine fails... resulting in the ship's crew having to keep on running until they find space empty enough to allow the engine to be shut down and repaired. There are a couple of false starts, as by the time they hit intergalactic space they're going so fast that even the incredibly thin intergalactic matter is still just too dense, and so on... and meanwhile time is dilating more and more. They then have the problem of finding a new home, as humanity is now long dead due to the eons that have passed outside the ship - and indeed the universe itself is running down. Their solution is... creative. Unlike most that use this trope, this is based on * real* science.
 * In Stanislaw Lem's The Invincible, the titular ship goes in continuous acceleration mode for several months by firing its main engine, and then needs only a few hours of deceleration using less powerful retro-engines.
 * Justified in the Lensman stories: the key to interstellar flight is a device that cancels a spaceship's inertial mass, so top speed is determined by the point at which a spaceship's thrust is exactly counterbalanced by the friction of the interstellar medium. With sufficiently powerful Impeller engines, this counterbalance speed can be many times the speed of light. Since a spaceship doesn't have inertia, turning off the engines causes it to come to an instant stop.
 * E. E. "Doc" Smith can't seem to decide if a spaceship is completely dead in space without its Bergenholm (the magic get-rid-of-inertia gadget) or if it still has its original speed achieved before starting the "Berg". However, with the speeds you can get with a Bergenholm, any possible "inert" speed is full stop by comparison.
 * In all the Lensman books he made it clear that when you turned off the Bergenholm you instantly reverted to the exact same speed and direction you were going in when you turned it on. What he didn't make clear was what that speed and direction actually was. When you are sitting still on the surface of the earth you are actually going east at up to about 1000 MPH due to the Earth's rotation, about 18 miles per second because of the Earth's revolution around the Sun, add to that the Sun's movement around the Milky Way, etc, etc.
 * Turning off the Impeller engines, while the Bergenholm is still engaged, causes the ship to come to a complete stop instantly (the moment they bang into that first hydrogen atom in the interstellar medium). Turning off the Bergenholm itself causes the ship to resume its "intrinsic velocity", i.e. the sublight velocity it had before the Bergenholm was engaged.
 * Wouldn't these two scenarios cause a spaceship to collapse horribly and almost instantly onto itself, even if it has almost no mass or is ridiculously tough? We don't much like it when our vehicles come to a dead stop from high speed in Real Life.
 * No - the dead stop when the impellers turn off doesn't matter because you have no inertia to go crunch with; the reversion when the Bergenholm switches off merely restores the status quo ante. The major problem occurs with combatants who go out in power suits, inert themselves for battle and then return "free" to their ships, or who land their ship "free" on a different planet from the one they left - or the same planet in a substantially different place or after a significant delay. At some stage, they must either re-sync their intrinsics or pray their Bergenholm continues to function. This becomes a plot point in the last book, where the intrinsics are so horribly different that each man on the planet's surface wears three personal Bergenholms - two on his person and one in his suit.
 * In Alistair Reynold's Revelation Space a character wonders why an interstellar light-hugger ship is aerodynamically shaped given that space is a vacuum. She is told that at 0.999c the interstellar medium is dense enough to almost function as an atmosphere as far as friction goes.
 * This is an accurate use of this trope, the insterstellar medium's tiny amount of friction at low velocities, less than a fraction of 1% the speed of light, becomes a lot of friction when moving at high velocities, just below the speed of light.
 * Just note that Alastair Reynolds writes Science Fiction and is an astronomer.

Live Action TV

 * One episode of Space: 1999 even showed one of the Eagle ships rocking in space.
 * Star Trek, unsurprisingly. In fact, in an instance where someone takes advantage of inertia (Star Trek: The Next Generation: "The Battle") by letting a derelict coast alongside them, everyone else is amazed by the notion - and, indeed, it turns out that his decision was prompted by his being Not Himself. In the other known instance ("Booby Trap"), it takes Geordi being inspired by ancient records to come up with the idea of escaping an engine-detecting minefield by pulsing the engines once and then coasting.
 * Though at least on Next Generation they have separate responses to the captain when the controls read all stop and when the sensors confirm all stop, implying that the all stop command requires the vessel to actively slow down.
 * It's also averted in some episodes - Final Mission springs to mind, along with Soldiers Of The Empire.
 * Farscape could usually Hand Wave this one, since Moya was a living entity, it was assumed her method of movement was energy-based... somehow. But it's specifically brought up when  with Aeryn in pursuit. He taunts her that while he has been trained to fly jets in a planet's atmosphere and gravity, Aeryn has not.
 * That's actually a potential aversion. Crichton presumably learned to fly in familiar Air Force fighter jets. Space combat would be extremely different to jet combat, regardless of what Star Wars shows us - consider the Starfuries on Babylon 5 and the way they coast, reverse, spin on their axes, and move nothing like any aircraft on Earth. Just because Aeryn's ship can fly in an atmosphere doesn't mean she's going to be any good at it. When you have the capacity to raze entire cities to the ground from high orbit atmospheric dogfighting probably isn't high on your list of training priorities, and her atmospheric flying experience most likely consists of ship-to-surface and back again.
 * Battlestar Galactica Classic & Buck Rogers in The 25th Century were terrible for this. The "fighters" always had to have engines on, & had to boost thrust to do anything worthwhile. The best stupid move was Buck's "brilliant" fighter jock tactic: barrel rolling around an axis, without ever changing direction. Somehow, this managed to throw off opponents. (Probably they were laughing too hard.)
 * Averted in Stargate Universe, noticeably in episode "Darkness", where Destiny uses atmosphere of a gas giant for braking when out of power for sub-light engines.
 * Averted in Battlestar Galactica Reimagined, the remake. Vipers can turn on just about any axis, and the visual effects always show thrusters on the sides of the fighters engaging when this happens. One of Starbuck's favorite maneuver is to flip her Viper end-over-end to point her guns directly at the enemy fighter following her, making it so that her bird is travelling backwards. During 4x09, The Hub, the show even uses
 * The reimagined BSG has several notable aversions. In the pilot, Boomer and Helo's raptor takes damage and starts leaking fuel. Boomer gets round this by shutting the engines down and letting their momentum carry them to their destination.
 * Another example comes during the Resurrection Ship arc, Starbuck shuts down the engines on her stealth ship and flies it right through the Resurrection Ship on thrusters alone. She goes completely unnoticed until she powers her engines back up again, at which point she's jumping out anyway.

Tabletop Games

 * In Battlestations by Gorilla Games, standard missions take place in deep space between rival vessels. At the beginning of every turn there is an "upkeep" phase where all your functioning engines produce power, ships systems drain power, and you lose a point of velocity.
 * Battlefleet Gothic averts this by forcing ships to take a command check to burn reverse thrusters in order to stop.
 * The Warp Rift unofficial rules for running on minimum power in order to avoid detection avert this, stating that ships continue on the exact same vector as they were on before shutting down unless the ship uses minimal thrusters to slow down.

Video Games

 * In the arcade classic Asteroids, you can drift for about 2-3 screen's worth before coming to a stop, depending what speed you're going. The arrow buttons work like thrusters, requiring reverse thrust to slow down.
 * In the MMORPG EVE Online, this is taken to rather ridiculous extremes for an otherwise acceptably scientific game. Not only does space have friction in EVE, but avid fans have actually done the math and determined that space in the EVE universe has the consistency of WD-40. When paired with the fact that a ship traveling on traditional propulsion methods actually has a top speed and an acceleration curve, it strains Suspension of Disbelief.
 * It's stated somewhere amongst the backstory that warp drives drag against the fabric of space, so a ship without a warp drive would be able to go as fast as its shields could handle (dust gets dangerous at high speeds), although it would be limited to slower-than-light travel.
 * The Apocrypha expansion of March 2009 removed a feature that caused one's ship to shake violently when entering or exiting warp, as if it were flying through an atmosphere. People complained, and it was returned in a subsequent patch.
 * Explosion shockwaves in space. Possible for faster ships to escape kinetic explosions among other things.
 * The Free Space video game series. Not that it's fun trying to chase after a ship that suddenly became disabled when it was on its afterburner. Besides, you've got to worry about that invisible barrier 150km away from your starting position that causes you to "collide with yourself" and blow up.
 * The FS Open project actually implemented real-world physics at one point: more as a proof-of-concept thing than anything else. After all, the engine was designed around Old School Dogfighting, so playing with "Newtonian physics" completely broke the AI and all game balance.
 * The PC game Inner Space averts this...but since the areas you play in are kinda small, you're more likely to slam into something than coast for very long.
 * In the Xbox 360 game Project Sylpheed, your ship steers as if there's air resistance in space, with this becoming more pronounced in atmosphere. In a related note of bizarreness, cutting the engines and coasting works even in atmosphere, despite the fact that the ship should fall out of the sky if it's not done in an effectively zero-G environment.
 * In Star Control II, Hyperspace has friction, resulting in a continuous need for fuel, and the ship slows to a stop when fuel runs out. However, space travel in solar systems and in battles obeys Newtonian physics, and fuel expenditure only occurs when using the engines to alter course. However, each ship still has a set maximum velocity, which only can be surpassed by slingshotting around a planet. Even then, if you apply additional thrust, it actually slows you down until you reach your "max speed" again. Yet the Arilou Lalee'lay, hinted to have perpetrated the various alien abductions and flying saucer appearances on Earth, fly saucer-shaped ships that stop and start instantly with no inertia, as often seen in depictions of flying saucers.
 * The Arwings in the Star Fox games have their engines firing constantly, bank into turns, and even open their wings for an "air brake"... in space. Now, this behavior is perfectly normal when the crew is on a planet, but in space, the Arwings would be accelerating constantly in one direction.
 * Shown in GuavaMoment's Let's Play X-Com: Apocalypse as a sign of Tynam's growing insanity and the excessive levels of Did Not Do the Research present in X-COM: Interceptor.
 * In the game Battle Cruiser by 3000 AD (possibly also the prequels and sequels in the same series). When you stop applying thrust you will eventually stop. But if you shut down all power to the engine you will go on with constant speed until you turn.
 * Possibly Averted in Freelancer. While ships do slow down when you reduce their thrust, the existance of a "Kill Engine" button which allows the player to make use of newtonian physics (Complete with realistic acceleration if the player uses the afterburner) suggests that the aerial-style movement is a product of the designs of the ships.
 * This was previously done in Tachyon the Fringe. Ships have a top speed, but with the clever use of afterburners and inertia, the ship's speed can nearly double. Of course, as soon as you reactivate the engines, your speed goes back to top speed. Not to mention all the banking and barrellrolls.
 * Ordinary functional ships in Escape Velocity limits this trope (there is a top speed, but the only circumstance in which such ships slow down on their own is if they had topped that speed with afterburners). Disabled ships, however, slows to a halt (presumably to make it easier to dock with them), and ships with inertial dampeners only move while engines are running.
 * This happens in the "planet-less" levels of Angry Birds: Space, making things difficult because any objects you collide with that should just continue to collide with other objects or otherwise keep floating until they leave the screen, will instead gradually slow and stop.
 * Fans of the X Universe series guesstimate that the universe has the viscosity of maple syrup. Many sectors also have the visibility of maple syrup.

Western Animation
"David X. Cohen: I wanna know how a ship can skid to a halt in outer space. Matt Groening: Yeah, that's the future for ya..."
 * Applied crazily in Futurama, in the episode "Godfellas" - when Bender is launched out of a torpedo tube, he keeps going. He's realistically able to slow himself a bit by throwing away pieces of treasure he had stored in his compartment, but runs out of objects to throw before he's stopped himself completely. However, the ship cannot catch up to him because it was moving at "top speed" when they launched him, so he was moving even faster.
 * Another episode stated that the ship went 99% of the speed of light (which was stated to have been increased some time ago), so the their speed would be limited by relativity, but then that raises the question of how Bender went faster and how anyone could ever get around as far as they could.
 * According to relativity no matter how fast you're going things can still move at the speed of light relative to you in any direction.
 * These, and many other scientific inaccuracies are lampshaded in the DVD Commentary:


 * The same episode mentioned in the first addendum also states that she ship isn't always moving, it ''moves the universe around it". ...So yeah, wrap your head around that.

Real Life

 * The Earth's atmosphere doesn't stop abruptly at 100-200 miles altitude; it tapers off the farther away you get until it's as thin as the interplanetary medium. At 200 miles high -- the usual altitude for Low Earth Orbiting satellites -- there's still enough ghost-fringe of an atmosphere to cause a tiny drag force. This is why satellites in Low Earth Orbit suffer orbital decay. Eventually, the satellite has to make some kind of orbit-correcting rocket burn, or it will re-enter the Earth's atmosphere and, most likely, burn to a crisp.
 * Skylab was a famous example of this. Its orbital maneuvering engines ran out of fuel and, with no re-supply missions able to be scheduled before the Space Shuttle entered service, it crashed into Australia.
 * In fact, there's enough air in Low Earth Orbit to maneuver. Using wings.
 * In the upper layers of the atmosphere, air drag can cause a satellite to speed up. As an initially circular orbit decays, the change in gravitational potential overcompensates for the energy lost to friction--until the drag force grows large enough.
 * Also, aside from the obvious need for an infinite amount of energy, one of the limiting factors in attempting to reach the speed of light is that the interplanetary medium does actually begin to have significant friction as an object accelerates towards it (even if it never reaches it).

Anime

 * Cowboy Bebop - in one episode, the Bebop is out of fuel, but the characters are unconcerned and are just killing time while the ship coasts to its destination. Despite this, Cowboy Bebop is not entirely a realistic series using Newtonian flight physics. There are plenty of occasions where the ships behave in Newtonian-correct ways (maneuvering thrusters, braking with forward-firing engines...), but plenty more when they don't (the dogfights in space, for instance, follow atmospheric flight patterns). The dogfights, however, may get a Rule of Cool exemption.
 * Outlaw Star operates similarly, but the dogfights definitely follow a more 3D style of maneuvering. In one episode, the Outlaw Star even rides a "stream of aether" using its parachutes.
 * Planetes did its research. Most of the early story was about collecting debris that were dangerous precisely because items in space never slow down or stop.
 * Macross handpicked a number of physics rules to abide by and it's pretty consistent with those, but then there are the ones it dislikes and rapes constantly.
 * Infinite Ryvius is about teenagers who are trapped on a ship drifting due to inertia.

Literature

 * In Honor Harrington, plenty of attention is paid to the difference between acceleration and motion - to the point that moving too fast can leave you blazing past the enemy's fleet without time to take a shot at him.
 * The longest range sensors in the Honorverse detect ships by their engines. Therefore, getting a respectable velocity going and then simply coasting from extreme sensor range to extreme weapons range is the bread-and-butter of stealth tactics. (During this process, you may as well go have dinner and enjoy a good night's sleep before tomorrow's battle.)
 * Averted in George Johanssons series Universums öde (~Destiny of the universe, 1979-1986). Humanity's nuclear-powered spaceships journey through the solar system by accelerating at 1G until they're halfway to their destination where they start decelerating at the same rate, thereby solving the problem of on-ship artificial gravity. Although you would need to reverse the floor and the ceiling to ensure you're being pushed in the right direction at the midpoint, which could create some problems for furniture and such.
 * Averted in pretty much every novel by Robert Heinlein which features space travel. In fact in many of his novels which showed fuel problems in space revolved around fuel needed to change course, to reach necessary speeds and to stop when needed against the weight of carrying said fuel. Heinlein was very good about that sort of thing.
 * An interesting aversion from the Wing Commander novels. While the games themselves obey game-friendly atmospheric physics, the novels suggest that fighters and capital ships can attain indefinite speed with constant acceleration for as long as their internal fuel supplies hold out, or a sort of mind-bogglingly fast terminal velocity by employing drag scoops that collect interstellar particle matter to fuel the engines.

Live Action TV

 * Babylon 5 and the new Battlestar Galactica portray spaceships moving realistically according to Newtonian physics, with Babylon 5 even showing damaged vessels with no engines gliding helplessly out of range of help. Ships with gravity-based technology can move in a more Star Trek or Star Wars manner; watch the White stars dart around the comparatively lumbering Earthforce Omega Destroyers which, having no gravity-based technology, maneuver far, far more like spacecraft we have today.
 * Yes, because vipers being able to bank-and-turn like a plane really follows Newtonian Physics
 * More like viper uses maneuvering thrusters to roll and change its direction, then uses the big thruster at the back of the ship to push itself into the new heading. Battlestar Galactica was actually pretty good at this... While fighters appeared to maneuver as in Old School Dogfighting, close-ups of those fighters clearly showed that these maneuvers were being accomplished through a combination of thrusters and the main engine. (Where all of the reaction mass for those thrusters came from is an entirely different question...)
 * While it would be theoretically possible to maneuver like this, since they were generally doing it in places where maintaining an orbit wasn't an issue, it would require superhuman abilities to keep track of the collective vector you built up doing it. Vipers are flown manually, remember?
 * In the Stargate SG-1 episode "Tangent", O'Neill and Teal'c are stranded in a death glider without engines. They continue to travel at constant velocity, expecting to reach the Oort cloud in several years.
 * Averted in Stargate Universe; Destiny and its shuttles move in the BSG fashion.
 * In Red Dwarf, Starbug's engine is disabled, and they're in trouble because they're headed right at a planet and traveling entirely too fast for comfort.
 * Firefly. The cut-off-our-engine-and-coast trick is used to approach Niska's space station without being detected.
 * However, in "Out of Gas", the engine breaking down seems to result in Serenity coming to an immediate halt.
 * The ship never actually stopped, but losing engine power meant losing oxygen and heat, and it happened while they were out in the middle of nowhere, on a course that would take weeks to get anywhere.
 * The ship's appearance of inertness, while also helping add to the theme of helplessness, is easily explained by the fact the space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. The only visible reference points we have in any shot in that episode are stars which are who-knows-how-many light years away and of course, the further away something is, the less it appears to move in reference to the viewer.
 * The Serenity RPG sourcebook explains it as a byproduct of the workings of the "pulse drive" used to accelerate the ship to relativistic speed for interplanetary travel. They apparently fiddle with gravity to reduce the ship's inertia, then fire the main engine (on a Firefly, the glowy bulb at the stern) to kick the ship to high speed. Cutting or losing power to the pulse drive causes all that inertia to come back, and the ship drops back to the speed it was at before you fired the drive.

Tabletop Games

 * In the Warhammer 40000 Gaiden Game Battlefleet Gothic ships specifically need to burn retros in order to go at less than their maximum speed.
 * Less than their maximum speed. Yep, it's both averted and played straight (more straight, to be honest)- under normal circumstances, you have to move half to all of full speed. Oh, and if you stop, you have to burn retros again next turn if you don't want to start moving again...
 * Avoided in Battle Space, the space-combat game that takes place in the BattleTech universe. What makes it more confusing is that it's a 3D space game played in 2D, so you have to take notes to each ships position, inertial direction, its pitch, yaw and roll rates, usually playing on a map which is about 300 times too small for any space encounter. A movement phase for a single fighter might take up to around 5 minutes (or more if the player needs to calculate ahead a few turns, which they undoubtedly will have to), which is probably one of the reasons why the game never took off.
 * BattleTech: Aerospace used acceleration and deceleration to pilot your ships. The hex maps had gravitational arrows and strength in the hexes - if you were going slower than the strength number in the hex you ended your turn in (if I remember right), you were pulled 1 hex in the direction indicated. Careful piloting could actually put your ship into a permanent orbit.
 * Attack Vector: Tactical is fully Newtonian, 3-dimensional starship combat. Each ship has a ship diagram records vectors in three axes, and momentum carries from one round to another. Vectors must be canceled to change direction. Ships are tracked in orientation in three dimensions using tilted blocks in increments of 60 degrees. The Physics Equations to explain motion and heat dissipation, and everything else are in the rule book. This game system is also the basis of Saganami Tactical Simulator, the Honor Harrington space combat game, and Birds of Prey, an air-to-air modern age fighter combat game.
 * Jovian Chronicles makes you track 2 dimensional vectors and has a "reality distortion level" that goes from Hard to Soft. Basically the game is Gundam in all but name.
 * Noble Armada makes you track two dimension vectors as well. Going so far as making you place a d20 next to the ship stem to signify how fast, and in which direction you are traveling.
 * Babylon 5 Wars actually had fully Newtonian physics, and you had to thrust in the opposite direction to slow down. You could roll you ship by assigning thrust points to "roll thrusters" on one side of the ship and canceling the roll with thrusts on the other side. With certain firing modes it was possible to damage all the roll thrusters on a given side of a ship and the main engines, meaning it was possible to have ships wildly spinning as the drove off the board.
 * The Kaufman Retrograde in Star Fleet Battles is a related tactic, in which ships go in reverse to keep the advancing enemy in optimum range as long as possible, but as (predictably enough) the ships maneuver like Star Trek ships it's done by firing the warp engines in reverse.
 * GURPS: Spaceships goes perhaps too far in avoiding this. Extensive (and accurate) calculations are available for people who wish to use them. It's made quite clear that with any sort of realistic engine turning it off for most of the trip will almost certainly be necessary. The existence of random debris in the void of space is mentioned but only in that if you spend enough time traveling at a good fraction of lighspeed it will wear away the hull after a few years, there's no way it could slow you down meaningfully.

Video Games

 * The indie 4X game, Star Ruler has newtonian physics on all the ships. The only thing restricting ships is their acceleration speed (and fuel), meaning you can have ships zipping through star systems at a sizable fraction of the speed of light. Ships disabled from crew death, power failure, or running out of fuel will cause them to drift along their path until the game kills it after a few minutes to save processing power. If you have stations orbiting other stations, and the core station is destroyed, the orbiting stations will be catapulted out of their orbit, then fall into orbit around the star; this can lead to stations spinning around a star at insane speeds, with nothing to limit their maximum speed.
 * Allegiance, a multiplayer-only space combat sim originally made by Microsoft and later made open-source and free, provides a partial aversion - a compromise between realistic physics and Old School Dogfighting. Ships have inertia, and turning your ship will not instantly change your direction of movement. In combat, your ship will usually be facing (and shooting) in one direction, and traveling in another. Competent players will use this to great effect, but it can also be a pain when you need to come to a quick stop to avoid ramming a wayward asteroid. There's even a retro-booster that a player can fire to slow down in a hurry at the cost of fuel, and although it's a rarely used piece of equipment, some veteran players swear by it. On the other hand - and this is where the compromise with Rule of Fun comes in - there is some space friction, and turning off your ship's engines will make you slowly glide to a stop (although how slowly depends on your ship's mass, and it often isn't enough to save you). In addition, each ship model has a maximum movement speed for gameplay balance reasons in addition to different rates of acceleration, and some ships rotate faster along certain axes than others (for example, Rixian Unity ships have fast yaw, but slower pitch).
 * In Sword of the Stars, Human, Tarka, Hiver, Zuul and Morrigi ships, while using some form of FTL to travel through interstellar space, use regular Newtonian reaction thrusters for tactical combat. Destroying the engine section of the ships of these races will cause them to drift helplessly away from the battle, at whatever speed they're going at, in whatever direction they're going at. They sometimes end up crashing into a planet or an asteroid, and get destroyed. Liir ships, however, don't use regular thrusters at all - they use "stutter warp" (a propulsion method involving fast, repeated short-range teleportation) for both interstellar and tactical movement. Destroying their stutter warp engines will cause them to halt wherever they are.
 * The trope is even more averted by the Kinetic Kill missile, a solid-body projectile that impacts into ships at a horrid speed. A ship hit by one of those will start flying and won't be slowing down again.
 * Actually, Tarka can research technology that allows them to use their hyperdrives for tactical combat by manipulating the hyperspace bubble to move the ship. Unlike Liir ships, however, Tarka ships with destroyed engines will continue coasting.
 * Also, even with destroyed engines, ships are usually able to slowly get back into battle by using their thrusters.
 * In Freelancer, there is no friction when you kill your engines, but somehow the friction reappears as soon as you start them.
 * Averted in this Freelancer mod, a Halo-universe-based mod which adapts the Freelancer system to instead use Newtonian physics.
 * Actually there is a slight amount of friction, and your velocity slowly drops. However in the scale of the game it is not easily noticable.
 * Averted to hell and back in the 2000 space combat/trading simulator-with-a-capital-SIMULATOR Terminus. The game uses painfully realistic physics - to the point where the extremely common fate of new players is to simply have to quit and restart, because they are drifting endlessly through the infinite emptiness of space, having burned just slightly too much fuel on an earlier acceleration or correction.
 * On top of that, it also factors in relative hull strength, overall mass, and acceleration. Got your ship doing top speed and try to make a 90 degree turn? Have fun dying. Loaded cargo ships are sitting ducks and it's entirely possible to overcompensate on a docking run and hit your target. There's a lot of effort put into making sure things behave right in space.
 * In Colony Wars 2, one mission has you tow a frigate out of harms way when its main engine failed; the problem is that it drifts to an asteroid and if you pull too much on the nose sideways, it'll create a torque and the sides may collide with the asteroid. Also, your own spacecraft drifts when your engine is disengaged; you'll rarely, if at all, have any time sitting put without any motion (although, you drift in a lateral motion, and like the asteroids there, you never stupidly rotate in place like most Hollywood asteroids do).
 * In earlier Elite releases, physics implementation was simplified, but in the later versions of Elite by Frontier Developments it's avoided, along with other space tropes. Ships that run out of fuel will continue to drift forever through a solar system. You can even stay on an elliptic orbit (evident only with time acceleration, of course)
 * Although sometimes, if you have an autopilot destination locked in, you can just hit max time acceleration and you'll arrive and dock perfectly.
 * Pioneer Continues in Frontier's vein. The development team have decided to stay with Newtonian, rather than Einsteinian, physics, so there's no top speed. Its behaviour is pretty close to reality for most situations, though.
 * Escape Velocity gets inertia right, but a whole lot of other things wrong. Once you're moving, you can stop holding down the arrow key and the ship will continue on its current direction unless you attempt to stop it. The problems appear when you realize that weapon speeds and ranges are absolute rather than relative to the speed of the ship that fired them. This error has led to what some players call the "Monty Python Maneuver", where you run away from enemy ships, then turn your ship 180 degrees (you'll still keep moving in the original direction!) and fire at the ships. You will be out of range of the enemy while they're still in range of you, even with non-lightspeed weapons.
 * Another consequence of the ability to turn in place is the carousel maneuver, which requires some very carefully timed thrusts but essentially allows you to almost orbit the enemy ship, facing them the whole while.
 * There are also several inertialess drives (which are not quite the same as Friction in Space, but behave similarly). These are on Vell-os ships and the Polaris Raven, which are intangible and warp-propulsed respectively. These ships are ironically harder to steer in combat, as they cannot coast or turn in place for the characteristing "joust" - they need turreted beams to avoid having to face their opponent.
 * This can actually lead to your massive Polaris Raven (just about the biggest, nastiest ship out there) being swarmed and shot to pieces by groups of small fighter craft. Their small size (and thus small inertia) allow them to basically make endless attack runs whilst remaining inside the minimum range of your weapons. A ship without inertia-less drive could rotate and catch them, but the Raven simply can't.
 * Independence War 2: Edge of Chaos mostly had Newtonian physics and slightly realistic scale to the systems, although shooting out the engines for some reason left the disabled ship spinning (if they were in a turn), but stopping. You could also override your ship's maximum speed, accelerating so fast that even missiles can't catch you, but consequently it took just as long to stop the ship, unless you engaged and then quickly disengaged your LDS drive, canceling all inertia and making your ship fly 1000 m/s in the direction it was facing at the time LDS was shut down. Fortunately, the ship's computer would automatically fire the thrusters to make the ship go in the direction you want it to, so you could do some Old School Dogfighting while still trying to deal with Newtonian Physics...unless you intentionally toggle off the inertial compensation.
 * The original I-War also would let you turn off the computer's compensation if you wished, leaving you completely at the mercy of Newtonian physics. While it would mostly fall under Awesome but Impractical for most players, mastering it would let you do some stunts that you'd have a hard time believing.
 * One key use of inertia is to speed up in the direction you want with the help of max-energy engines, then divert all energy to weapons when you have a good PBC solution without struggling to maintain that speed. Speed is key to survival in this game.
 * In Star Control, every ship has a "maximum speed" they can reach on their own, but don't slow down without a good reason and may even orbit a planet. In Star Control II combat, this nominal maximum is easily surpassed with a staple maneuver "Leyland whip" -- use of a planet's gravity to accelerate -- until the ship collides with something or fires thrusters. Some collisions do the same.
 * Orbiter, being a realistic spaceflight simulator, makes mincemeat out of this trope. However, it has only a Newtonian physics model, so you can theoretically go faster-than-light.
 * The Settings section in the game's launcher allows you to turn off some of the realistic restraints (e.g. allowing infinite fuel).
 * While Tachyon: The Fringe abuses the trope in normal flight, there is a button you can hold to continue moving in your current direction at the current speed. You can even spin around and fire backwards. A real pedant could use this system to fly the ship in a (pseudo) real fashion!
 * For example, it also allows you to fire your afterburners for a few seconds and then coast along in your current direction at extreme speeds, which is terribly useful if you need to get into or out of a particular fight very quickly, or if you just get impatient.
 * Another case that supports the trope is a mission to stop a capital ship whose engines are stuck from colliding with asteroids in an unusually dense field. After a while of you blowing up the asteroids, the captain of the ship will finally ask you to destroy its engine power plant. As soon as that happens, the large ship coasts to a stop within seconds.
 * In Vega Strike, spacecraft behave more or less like this by default, but it's a partial compensation by the navicomputer as a convenience for Old School Dogfighting and docking -- as such it's limited by the thrusters' force. One key sets "Zero" speed vector to match the target's, which makes docking easy. Turn off "Combat Mode", and the spaceship behaves more like the real world. Whether you'll want to use "Combat Mode" for, well, combat is a matter of style and controls -- sometimes dancing on thrusters manually without auto-compensators works better. One of stock tactics is whittling foes on fast fly-by if their weapons are more powerful but yours are shield-piercing.
 * In fact, the idea was copied from somewhat older I-War series, where it was a major gameplay feature. Complete with "dock-to-that-flying-thing-and-accelerate-it-sideways" missions.
 * Also in Babylon 5: I've found her.
 * In Origin's classic spaceflight sim/RPG Space Rogue you could toggle between 'Cruise' mode where (according to the manual) the computer automatically handled your main engines and maneuvering thrusters, letting you point where you want without having to manually counter-thrust to stop and apply min thrust in the new direction. You still had to fight your own inertia though. And you could turn this off completely for 'Newtonian Flight' if you so desired, allowing you to burn hard in one direction and then spin and coast backwards. This was a game breaking tactic since enemies always evade when perused, but stay locked on you if you're the one being chased, allowing you to fire away without much worry of evasion. You could also use the Newtonian Flight mode to slingshot around gravity wells...if you were really good at it.
 * The trope is explained fully in an overheard conversation from Mass Effect 2, in which a gunnery officer explains that a single misplaced shot from their powerful cannon will have the same force whether the target is a mile away or 10 light years away; and this causes a big problem when that 10-light-year target is an innocent merchant vessel (he even orders the private he's harassing to fully recite Newton's first law). When traveling with the Normandy inside a star cluster or solar system, releasing the "accelerate" button makes the ship fly on inertia alone while still burning fuel to slow down. As it's also possible to fly through a sun in ME 2, one can assume it's a Viewer-Friendly Interface for how Shepard directs the Normandy to go places.
 * There's a conversation Shepard has with a shop owner on the Citadel, discussing people who don't understand this trope, saying "You wouldn't believe how often I hear 'Why is the ship turning around? We're only halfway there!'"
 * In the first game, Joker lampshades this trope in a bit of random cockpit dialogue.
 * "It takes skill to bank a ship in a vacuum. Don't think it doesn't."
 * In the game Nexus the Jupiter Incident the earth designed vessels have huge thrusters on the back, and huge thrusters on the front. When you order you ship to stop, the ones in front fire like mad. In fact, you can clearly see a variety of maneuvering thrusters in operation. This is even true of the later alien vessel you get, which also has forward pointed engines (though far less obvious).
 * Although the Wing Commander series plays this trope mostly straight, in the later games some fighters have the option of "autoslide", which will make your fighter operate in a purely Newtonian manner for as long as autoslide is toggled. To actually change your vector requires turning it off and going back to playing the trope straight, however, then turning it back on when you're on the desired heading and have accelerated back up to the desired velocity.
 * Ace Combat 3 averts this in an anti-satellite mission starring an orbital fighter, and even puts the player through reentry procedure. Yes, a hard portrayal of space combat in the one sci-fi installment of a series devoted to modern air combat where the Acceptable Breaks From Reality are as numerous as the missiles hiding within its airplanes' wings. Yes, hard in more ways than one despite the objective of the mission boiling down to "gun down the defenseless, stationary targets within the time limit", because you're going to have to take a few tries to break air-combat habits, even if you're aware of this trope.

Web Comics

 * Schlock Mercenary: "We are inbound to Sol at point three-six cee, traversal shielding is at fifteen percent, we have insufficient power for full deceleration, and the ship is in two pieces. You tell me what we have averted?" (Also an inversion: their FTL drive probably still works, as it's powered by annihilating a randomly-selected fraction the mass being transported.)
 * Not so random anymore. Because it would be a mess if the drive annihilated you...