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"So you can just slow down and make a sharp left in space?"
Isaac Newton turned the world of physics upside down when he observed his first law of motion:
A body in motion will tend to stay in motion at a constant velocity unless acted upon by an outside force.
This was earth-shattering stuff when he introduced the notion - in 1687! Sadly, most writers for science fiction TV shows and films are a little behind the times, and just don't get it.
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 with the road or the air to contend with, you can coast forever, 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 some friction in interstellar space, due to hydrogen particles. However, these are dispersed enough that they'd really only matter over huge distances - huge even by astronomical scales.
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.
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 obliterated by interstellar dust or 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.
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.
A form of Hollywood Science.
Examples:
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 a minivan. And let's not even talk about what the other spaceship looks like...
- 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.
- In Star Trek IV: The Voyage Home, a ship whose power is zapped by a probe is actually seen to coast to a stop.
- 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". (It was an excuse to throw the other, dying Decepticons out of Astrotrain.) 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 ...
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 Wait It Out until the universe decays enough to allow the engine to be shut down and repaired. 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. 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. Since a spaceship doesn't have inertia, turning off the engines causes it to come to an instant stop.
- E.E. 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.
- The whole concept of the ubiquitous sci-fi short story The Cold Equations revolved around the amount of fuel in a ship being precisely calculated to the point that a single stowaway (a young teenage girl, at that) could screw up the math to the point where the whole ship would be unable to make it to its destination without crashing unless she was jettisoned post haste.
- Extra load would be mostly irrelevant if planets were static "islands". They aren't. So the mission has limitation — not distance, but DeltaV. Though having tolerances so narrow that there's neither some mass they don't really need nor some extra fuel "just in case" (which would be norm in Space Trucker setting) while not having excessively tight security around spaceships and then checking dozen more times (like now) is a weird combination.
Live Action TV
- 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.
- This is still flawed, because the force of a traveling object is mass multiplied by velocity. If mass is lost in motion, the force of the motion is still constant, which means that velocity increases. Losing mass makes you go faster.
- False. Losing mass has no net effect in a frictionless environment. However the effect on you is based on which way you throw the mass and how fast, throwing it out in front of you is essentially giving some of your velocity to it (without affecting the net velocity of you and the object) which slows you down. Losing mass makes you accelerate faster. However the episode does misuse the idea of a maximum velocity (that's non-relativistic) in space.
- 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.
- Firefly, despite the evidence that all space travel is sub-luminal, has Serenity stranded in open space when its engine breaks down, and frequently features the notion of having "just enough" or "not enough" fuel to get somewhere. Because it's All There In The Manual, ancillary sources explain that Firefly's Artificial Gravity is also used as inertia cancellation and can move quickly using a relatively weak engine. When this system shuts down the ship comes to a dead stop as its inertia returns.
- Pretty much every other space-based Science Fiction series does this at some point as well. Space 1999, Farscape, the old Battlestar Galactica, and many others have all presented the victims of engine failure as effectively motionless.
Video Games
- In the arcade classic Asteroids, you can drift for about 2-3 screen's worth before coming to a stop.
- 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 FreeSpace 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 and Quasispace have 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. 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 Lets 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.
Exceptions:
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).
- 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.
Literature
- In the Honor Harrington novels, 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.
- Similarly, since the longest range sensors in the Honorverse detect ships by their engines, getting a respectable velocity going and then coasting from extreme sensor range to extreme weapons range (a process during which you may as well go have dinner and enjoy a good night's sleep before tomorrow's battle) is the bread-and-butter of stealth tactics.
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.
- 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.
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.
- 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.
- Attack Vector: Tactical is fully Newtonian, 3-dimentional starship combat. Each ship has a ship diagram records vectors in three axes, and momentum carries from one round to another. Vectors must be cancelled to change direction. Ships are tracked in orientation in three dimentions using tilted blocks in incraments of 60 degrees. The Physics Equations to explain motion and heat disapation, and everything else are in the rule book. To date this Troper has found exactly three people who thought the idea was cool: A Honda Engineer, and Particle Phyisist from CERN, and this Troper himself. 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 dimentional 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 travelling.
- 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 canncelling 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 manoeuvre like Star Trek ships it's done by firing the warp engines in reverse.
Videogames
- In ''Sword of the Stars', Human, Tarka, Hiver and Zuul 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 Liir playing this trope straight sounds like it's Hand Waved quite thoroughly by the fact that the ships wouldn't actually ever have a velocity, justifying the trope (unlike most of these examples.)
- 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.
- An interesting aversion happens in the novels based on the Wing Commander games. While the games themselves obey game-friendly atmospheric physics, the novels suggest that fighters and capital ships can attain indefinite speed with constant acceleration, or a sort of mind-bogglingly fast terminal velocity by employing drag scoops that collect interstellar particle matter to fuel the engines.
- 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).
- 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 you can change the direction the ship is facing 'in place' without changing your inertia, which makes no sense without using a turret (turning the whole ship would require thrusters, which should impact your inertia.) This error has led to what some players call the "Monty Python Maneuver", where you run away from enemy ships, then turn the direction the ship is facing (you'll still keep moving in the original direction!) and fire at the ships. Because all weapon speeds and ranges are absolute rather than based relativistically on the speed of the ship that fired them, you will be out of range of the enemy while they're still in range of you, even with non-lightspeed weapons.
- Another exploitation 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.
- The first example is a perfectly viable strategy (keeping your inertia but turning around violates no laws and is actually a good application of Newtonian physics).
- These are all also staple tactics in Star Control II combat.
- Avoided in the Frontier games by Frontier Developments, along with other space tropes. Ships that run out of fuel will continue to drift forever through a solar system.
- Although sometimes, if you have an autopilot destination locked in, you can just hit max time acceleration and you'll arrive and dock perfectly.
- "Orbiter" attempts to realistically simulate space flight...including the physics. However, it has only a Newtonian physics model, so you can go faster-than-light, and it allows you to turn down some of the realism (by, eg., allowing infinite fuel) in settings.
- 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!
- In the open-source space game Vega Strike, spacecraft behave more or less like this by default, but it's a compensation by the navicomputer as a convenience for Old School Dogfighting. Still, it's not completely aerodynamic: turning doesn't change the direction you're going. Turn off "Combat Mode", and the spaceship behaves more like the real world.
- 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.
- 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 travelling 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).
Web Comics
- Ennesby: "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.)
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