History Main / ReactionlessDrive

* ''Literature/TheExpanse'': The Eros SpaceStation from ''Leviathan Wakes'' becomes a PlanetSpaceship of sorts as it becomes [[MeatMoss overran by the protomolecule]], capable of changing its trajectory without ejecting any mass. This is a problem for the protagonists as they have to chase the station to keep it within the visual range. The chase becomes all the more difficult by the station being able to accelerate at rates no human is used to.

SuperTrope of the AlcubierreDrive. The {{Ramscoop}} and SolarSail are sister tropes; each is a plain old reaction drive, but one that uses a clever trick to react with the ambient environment instead of needing to haul extra mass or stick to a base station. It is also very common for an incautious (or sneaky!) author to write something that's allegedly one of those two, but from the way it's described working is really a reactionless drive in disguise. The energy used to power one is sometimes derived from {{Antimatter}} annihilation, or the ship can be PoweredByABlackHole -- and sometimes the black hole ''is'' the drive.

[[quoteright:307:[[WebOriginal/OrionsArm https://static.tvtropes.org/pmwiki/pub/images/halo2_3133.jpg]]]]

* The greater powers of ''WebOriginal/OrionsArm'' have access to three kinds of reactionless drives for their spaceships, all largely based on the AlcubierreDrive but limited to just below the speed of light (attempting to hit c allegedly causes [[PhlebotinumBreakdown void bubble collapse]]). Like an Alcubierre drive, they depend on negative mass, and as per the setting's guidelines, elaborate {{justifi|edTrope}}cation has been provided as to their plausibility. Thematically, the lesser gods' Displacement and Halo Drives (pictured above) have only disposable engines located inside void bubbles and magnetically or gravitationally coupled to an external ship, since at their level, the only way to take down said bubbles is to destroy them chaotically. However, the highest archailects' Void Drives are true warp craft, with entire ships or fleets being contained within a void bubble and re-entering normal space smoothly upon reaching their destination.

* In ''TabletopGame/Warhammer40000'', reactionless drives are unique to [[HigherTechSpecies the Necrons]], who are also the only race to possess [[InertiaIsACruelMistress inertics]] and 'true' FTL travel as opposed to [[HyperspaceIsAScaryPlace using the Warp]]. In ''TabletopGame/BattlefleetGothic'' their unique access to these engines allow Necron ships to accelerate, decelerate, and turn at rates that are impossible for any other species. Their higher-tier ships have no true 'front' or 'back' and are capable of moving in reverse while still pointing all the big guns at their opponents, which is also something no other faction can do. To balance things out, Necron drives have [[MightyGlacier a slow top speed]] and races like [[FragileSpeedster the Eldar]] (whose ships use a SolarSail) can easily run rings around them speed-wise.

* In ''TabletopGame/Warhammer40000'', reactionless drives are a unique to [[HigherTechSpecies the Necrons]], who are also the only race to possess [[InertiaIsACruelMistress inertics]] and 'true' FTL travel as opposed to [[HyperspaceIsAScaryPlace using the Warp]]. In ''TabletopGame/BattlefleetGothic'' their unique access to these engines allow Necron ships to accelerate, decelerate, and turn at rates that are impossible for any other species, and their higher-tier ships have no true 'front' or 'back' as they do not need an engine to move and are therefore the only species capable of moving in reverse while still pointing all the big guns at their opponents while they do.

* In ''TabletopGame/Warhammer40000'', some of the more technologically advanced races have them. The Necrons do in addition to being the only race to possess true FTL travel as opposed to using the warp (if you can't go FTL in the real world, [[HyperspaceIsAScaryPlace go through Hell where you can! Just be careful about the daemons]]). The Eldar and Dark Eldar may possibly have them, while other races do not.

All spacecraft in existence today work based on Newton's third law -- for every action there is an equal and opposite reaction. Most toss stuff out out the spacecraft's back, creating a reaction force that accelerates the spacecraft forward.[[note]]Differences in engines mostly deal with what's thrown out the back, how hard it's thrown, and what you use to throw it.[[/note]] The rest rely on [[EnergyWeapon stuff]] [[MoreDakka thrown]] ''at'' the spacecraft and driving it forward as it's hit, [[SolarSail even if that "stuff" is just sunlight.]]

* Are mostly fuel tanks with a controlled explosion chamber in the back, with comparatively little volume for basic life support and human habitation, or ...
* Rely on an even MORE massive installation back home, and can't go anywhere out of that installation's range, because of SpaceFriction, or in harder science fiction, you can travel indefinitely, [[PointOfNoReturn but can't come back]], or ...

Most ScienceFiction authors, however, are writing about spaceships because they want to write about humans going places in them. They don't want to write about reaction mass, so ScienceFiction writers would prefer spacecraft to have much more of their volume dedicated to human activities. They typically want their spaceships to be able to operate within convenient distance of someplace interesting, rather than turning half the town into slag as they land and [[InferredHolocaust the other half as they leave]]. They want their spacecraft to flit from one PlanetVille to another, not just tool around wherever an earthbound laser can be shined on them. They DEFINITELY want it to go fast enough to get someplace interesting before everyone aboard dies of boredom. [[note]]Yes, even in hard sci-fi where they're all going slower than light; you still want to be able to at least reach other planets in the '''same''' star system.[[/note]]

Obviously this would be an awesome invention! So why don't we have them? Well, naively it would shatter the fundamental basis of all physics since UsefulNotes/IsaacNewton, as [[http://www.projectrho.com/rocket/reactionlessdrive.php detailed here,]] and modern theories predict effects too small to be useful. Thoughtful SpeculativeFiction writers have also noted that any sort of reactionless drive would provide those who possess it with an ''infinitely'' powerful weapon (compare WeaponizedExhaust, which is the use of a reaction drive as a weapon). Note that this would not be a problem if they required truly massive amounts of power [[note]] to accelerate at 1G a "photon drive" would need ~2.9TW per ton, or 32mg worth of mass converted to energy per second[[/note]] but many examples don't.

Supertrope of the AlcubierreDrive. The {{Ramscoop}} and SolarSail are sister tropes; each is a plain old reaction drive, but one that uses a clever trick to react with the ambient environment instead of needing to haul extra mass or stick to a base station. It is also very common for an incautious (or sneaky!) author to write something that's allegedly one of those two, but from the way it's described working is really a reactionless drive in disguise. The energy used to power one is sometimes derived from {{Antimatter}} annihilation, or the ship can be PoweredByABlackHole--and sometimes the black hole ''is'' the drive.

* ''Anime/{{Gunbuster}}'' features the Eltreum, a [[MileLongship 70 km-long]] carrier craft that uses mathematical computations and a load of other stuff to somehow warp the fabric of spacetime itself in order to move.

* Most super heroes who can [[{{flight}} fly]] under their own power in space have some form of reactionless drive, [[RequiredSecondaryPower even if the comic's authors don't call it this]]. Comicbook/{{Superman}}, for example, can accelerate, decelerate, and turn in Earth orbit, with no (obvious) rocket exhaust coming out.
* ''Comicbook/{{Planetary}}'' has a ship belonging to aliens called angels that uses an "informational drive". Running on the principle that reality isn't truly 3D and composed of matter and energy but is instead [[LeaningOnTheFourthWall a 2D plane of information emulating a 3D universe]], it absorbs the information around it to eject information that it's accelerating. Essentially, it's a ship that warps reality to manipulate its own acceleration, reaching the edge of the solar system in moments.

* ''Fanfic/RocketshipVoyager''. B'Elanna Torres dismisses the Dean Drive as crank science, but then goes on to explain several theoretical methods of FasterThanLightTravel, which turn out to be not-so-theoretical with the aliens who inhabit the far side of the galaxy. In the final chapter, she's drawn up a plan for a modified ''Voyager'' using what appears to be an AlcubierreDrive.

* The {{trope namer|s}} is Creator/LarryNiven's ''Literature/KnownSpace'' universe stories. The utility of this technology is made clear in the ''Literature/{{Ringworld}}'' books as it allows the ships to remain stationary relative to the Ringworld for extended periods.
* Cavorite from Creator/HGWells' ''Literature/TheFirstMenInTheMoon'' created anti-gravitational thrust. It ''blocks'' the earth's gravity in the same way lead blocks electromagnetic fields, allowing the moon's weaker gravity to pull the vessel up. Creator/JulesVerne famously [[SeriousBusiness called Wells out]] for falling back on such a device, though the one he used in his own space travel story-- a giant cannon-- hasn't held up much better in hindsight.
* ''Ender In Exile'' actually plays this one fairly straight as far as power goes. The starship engines work with a directional forcefield, dissolving space debris in front of the ship and propelling it out the back. Of course, it was the same dissolving technology that created the Little Doctor Device, a weapon that rips molecules apart, increasing by proximity of mass. Meaning that if someone drove the ship's engine into a sizable mass (say, a planet) the entire structure would unweave.
** That's still a reaction drive, just not carrying the mass; it's essentially a RamScoop. The "Park Shift" drives in use by ''Literature/SpeakerForTheDead'' seem to be true reactionless drives, somehow manipulating reference frames to spin the universe past your ship (at relativistic but subluminal speeds), but Card doesn't go into much detail. (The Park Shift drive is also an inertialess drive of sorts; a spacecraft can instantly switch from a dead-stop to going 99% of the speed of light without having to spend time accelerating.)
*** Unfortunately, the author can't seem to decide on how interstellar travel works in this 'verse. The instantaneous nature of the Park Shift is forgotten in a later novel where an admiral refuses to spend years decelerating his ships to quarantine a planet and instead opts to [[spoiler:blow up said planet]]. The prequel novels remove the Park Shift completely and just have the Formic ship using a typical RamScoop to travel between stars.
* The ''Literature/CitiesInFlight'' series has the Dillon-Wagoner Graviton Polarity Generator or "spindizzy" which gets more efficiency when it moves greater amounts of mass.
* ''Literature/RendezvousWithRama'' by Creator/ArthurCClarke gives one to the eponymous mysterious alien spacecraft, and acknowledges its impossibility in order to add to the mystery. "There goes Newton's Third Law."
* In the Literature/GiantsSeries by James Hogan, Ganymean starships such as the ''Shapieron'' achieve high-velocity (though ''not'' faster-than-light) travel by using a powerful gravity field to create a 'hole' in space in front of itself, into which it 'falls' continuously. The result is described by one Terran physicist as "like a four-dimensional tank track." While the ''Shapieron'''s drive is not FTL, the time-dilation produced by high sublight velocity, combined with the time-dilation produced by the drive's own mass, means that time moves much slower for the ship and its crew than for the Universe at large, allowing a single crew to make interstellar journeys.
* The Impeller Drive of ''Literature/HonorHarrington'' generates a pair of bands of extremely high gravitational distortion that allow a ship to go forward in a method that is likened to surfing. Top speed for unmanned items (such as missiles) is in excess of 99% of lightspeed under the right conditions. Manned vessels are generally restricted to 0.8c for military vessels and 0.6c for commercial, but that's a function of particle shielding not the drive. The real limiting factor is how great an acceleration that your crew can withstand, something that is increased by [[InertialDampening inertial compensators]]. One of the major disadvantages of the impeller drive is the fact that, even at low power, it's very difficult to hide from the enemy's gravitic sensors. As a side effect of the impeller drive, the top and bottom of any impeller-driven ship are virtually impervious to damage, as the wedges distort space to such an extent that no physical or energy weapon can penetrate it. The bow, aft, and sides are still vulnerable, though. Sidewalls are, basically, DeflectorShields that are also generated by the impeller nodes but are substantially weaker than wedges. The bow and aft remain vulnerable until the invention of bow walls.

* In Creator/AlanDeanFoster's Literature/HumanxCommonwealth series, faster-than-light travel is accomplished using the "KK drive". Invented by two human scientists named Kurita and Kinoshita, the KK drive projects a powerful source of gravity just ahead of the ship. This pulls the ship forward, which pulls the gravity projector forward, so the gravity source is still ahead of the ship... Given sufficient power, a KK drive ship can exceed lightspeed, at which point it moves into "space-plus," a version of {{Hyperspace}}.
* Creator/IsaacAsimov:
** In ''Literature/TheGodsThemselves'', he managed to come up with a [[ShownTheirWork fully thought through]] mechanism for this that ''doesn't'' involve abandoning conservation of momentum. There might not be anything to push against where you are in ''this'' universe, but what about the one next door?
** In ''Literature/FoundationsEdge'', the (First) Foundation produces a few top-secret starships that use a "gravitic drive" for maneuvering in normal space. These ships use no reaction mass. According to the next book, ''Literature/FoundationAndEarth'', the gravitic drive draws its power from the combined gravitational field of the entire galaxy.
* The eponymous technology in [[http://worldebookfair.org/eBooks/Baen_Library_Collection/038075357X.pdf Anti-Grav Unlimited]] are rods that act like "gravity magnets". Through experimentation, he not only manages to create a perpetual motion engine for his van (by welding two rods perpendicular to each other so that they're always being pulled up on one side and down the other), but also manages to rig rods such that he can make the van fly.
* In ''Literature/TerreEnFuite'' (''Fleeing Earth'') by François Bordes (AKA Francis Carsac), the second civilization of humanity (after we mostly die out in another Ice Age) is [[AlienInvasion conquered by aliens]]. When the aliens are defeated using a genetically-engineered virus, they leave behind some of their technology, including their primary means of propulsion in space called "space magnets". Apparently, there are certain energy lines between nearby stars that can be used for space travel by using these "space magnets" to allow a ship to be "pulled" towards a specific star. A ship with a "space magnet" can accelerate to close to 80% of the speed of light. Ships can also maneuver with these drives similar to how sailing ships can be still pushed by the wind even going in a perpendicular direction. There are limitations, however. It is discovered that there is a barrier of sorts at midpoint between the two stars that prevents any physical object from moving farther. Exceptions include a planetoid-sized object traveling at a high percentage of the speed of light. This comes into play when the Sun is about to explode, forcing humans to build giant "space magnets" that allow them to move ''planets'', such as Earth and Venus. Note that the Moon remains in Earth's orbit despite Earth itself leaving. There is even a scare halfway through the journey that the Moon might not have enough mass to pass through the barrier, but everything works out.

* In ''Stone'' by AdamRoberts, reactionless propulsion is achieved by extremely rapid teleportation in infinitesimal steps. This can even be applied to an individual, who can be wrapped in a protective shell, with life-support equipment and a teleportation device, and then sent off to their destination through interstellar space. The speed of this mechanism is affected by gravitational fields, where a stronger field requires more complex calculation (and thus less rapid steps). The reader may notice this sounds exactly like the Stutterdrive mentioned for ''VideoGame/SwordOfTheStars'' under Video Games. As Stone was published in 2003, and the game in 2006, I can only assume it was half-inched.
** Creator/LarryNiven proposed more-or-less this design in his "The Theory and Practice of Teleportation", originally a speech at [[FanConvention Boskone]] in 1969.
* In Creator/CJCherryh's Literature/AllianceUnion {{Verse}}, the FasterThanLightTravel drives that are used to enter {{Hyperspace}} can, while in normal space, be used to make instantaneous changes in velocity (piling on a ''second'' impossibility on top of normal Reactionless Drives).
* The ''Skylark'' in Creator/EEDocSmith's ''Literature/SkylarkSeries'' is powered by the direct conversion of matter into energy. This energy isn't jetted out the back; the ''Skylark'' simply accelerates.
* Averted early on in ''Literature/PerryRhodan'', whose classic "impulse engine" was basically just a fusion torch drive using proper reaction mass (if still impossibly little of it for the implied thrust values given, which led to a later retcon explaining that the drive had used primitive hyperspace technology to "supercharge" its exhaust all along). The occasional HigherTechSpecies of generally extragalactic origin (to say nothing of the really {{Sufficiently Advanced Alien}}s) could play the trope rather more straight even then; post issue-1000 time skip, so did "standard" Galactic starship drives.
* ''Literature/StarCarrier'': Ships bigger than 80 meters use an Alcubierre drive to accelerate to speeds fast enough to cross solar systems in hours. Ships smaller than 80 meters can generate a singularity ahead of the ship that allows far greater accelerations: whereas it takes the battle group's capital ships the better part of an Earth day to cross to Mufrid from the Eta Boötis Kuiper Belt, the fighter squadron Admiral Koenig sends ahead for a surprise attack crosses in about an hour and a half.
** On the other hand, gravitic acceleration is still limited by the speed of light, whereas the Alcubierre drive completely cuts off the ship from the normal space-time, folding space in front of the "bubble" and stretching it out behind it, and can accelerate the "bubble" (which is a non-event in space-time) to translight speeds (e.g. a ship using this drive can get to Alpha Centauri in less than 3 days).
** The author also convincingly explains the reason why ships don't need InertialDampening in this 'verse, despite enormous changes in acceleration (something like 5000 g's is common) and direction. Since ships pulled by a singularity as, effectively, perpetually falling into it (provided the ship continuously "extinguishes" it and reforms it farther ahead), both the ship and the people aboard are experiencing the same rate of acceleration, so no inertial compensation is required. Additionally, turning is achieved by flipping the singularity to the side and simply traveling along the curved space-time in a straight line (from the ship's point-of-view).
* ''Literature/TheStormlightArchive'' features a magical version of this. Windrunner Radiants can redefine what direction "down" is for them (or anything else they want), allowing them to fly at upwards of 80 mph without any effort on their part.
* The [[HumanAliens Bino Faata]] starship in Creator/MikhailAkhmanov's ''[[Literature/ArrivalsFromTheDark Invasion]]'' uses gravity drives, mounted on the outside of its enormous cylindrical hull, to move through space. Aboard the ship, ArtificialGravity is ubiquitous and is under local control (i.e. it can be altered in a specific room). The smaller combat modules used by the Faata as fighters and/or bombers also use gravity propulsion, as evidenced when dozens of them hover over the major Earth cities. After the starship's destruction, this is one of the many pieces of technology recovered and reverse-engineered by humans.

* In the ''Literature/GreatShip'' series, the eponymous PlanetSpaceship's true propulsion is a reactionless drive. The [[EnormousEngine massive array of 14 world-sized engines]] on its rear face are merely for adjustment. [[spoiler: When the Greatship is hijacked in the finale to ''The Well Of Stars'', the hijackers ignite the reactionless drive that the human captains were completely unaware of.]]
* In ''Literature/TheEnginesOfDawn'', FTL is usually acheived by hyperspace Engine. However, Eos University's Engine is destroyed during a terrorist attack. One student mentions that they can use the machine they're using to study black holes to create one a certain distance from the ship and use it to limp over to the nearby habitable planet so the Engine can be replaced. It doesn't need to be turned on and off, either, the singularity stays a fixed distance from the ship while the ship is pulled closer to it. Kind of like pulling yourself out of a swamp by your own bootstraps.
* ''Literature/TheKillingStar'' is all about why reactionless drives are a very, ''very'' bad idea. When humans develop near-lightspeed travel through reactionless antimatter engines, an alien race dubbed the Intruders destroy Earth with near-lightspeed missiles, annihilating the planet so thoroughly that only a deep-sea submersible was able to survive. The reason? Because the Intruders couldn't even ''risk'' having the same thing happening to them.
* In the ''Literature/NomesTrilogy'', the Nomes (who are the descendants of alien visitors who have long forgotten where they came from) have figured out how human aircraft work, and that spacecraft work the same way only more so. So when they encounter their ''own'' ship, it confuses the heck out of them, because it ''doesn't'' work on those principles.
-->'''The Thing''': Flames and smoke are not required.
* In ''Literature/WeAreLegionWeAreBob'', the SURGE drive (Subspace Reactionless Geotactic Emulation) is a relatively recent invention. Not many people actually know exactly how it works, only that it seems to push against space-time itself. Conventional drives are slowly being replaced on existing ships with SURGE drives. A SURGE drive's acceleration depends on available power and shielding (to protect against any high-speed collisions). Bob's original probe is capable of going at an acceleration of 2.5g. During his trip to Epsilon Eridani, he spends a part of it at a very high percentage of the speed of light, before flipping around and starting the deceleration. Later on, he builds better probes, which can push up to 10g. [[spoiler:The Others encountered later can move at even greater accelerations using their equivalent of the drive.]]
* ''Literature/SolarWarden'': All races use the AlcubierreDrive for transportation. It's why’s saucers can hover and maneuver so easily. The drive can also allow FTL and TimeTravel, since the two are linked.
* The Eros SpaceStation from ''Literature/LeviathanWakes'' becomes a PlanetSpaceship of sorts as it becomes [[MeatMoss overran by the protomolecule]], capable of changing its trajectory without ejecting any mass. This is a problem for the protagonists as they have to chase the station to keep it within the visual range. The chase becomes all the more difficult by the station being able to accelerate at rates no human is used to.

* In ''Franchise/StarTrek'', the nacelles may appear to be this at first, except they house the warp coils (for FTL travel, closer to Alcubierre Drives than anything else), and not the sublight impulse engines. The impulse engines are the red thruster-looking parts (e.g. the one on the back of the ''Enterprise''-D's engineering section), which are a type of fusion rocket.
** Also, ''Franchise/StarTrek'' ships are ''definitely'' the "power plant inside" version. It takes a ''lot'' to make that little blue (or red) light push the ship forward.

* One of the many ways Cylons in ''Series/{{Battlestar Galactica|2003}}'' have outstripped their creators technologically is by giving all of their [[TheBattlestar Baseships]] reactionless drives. In fact, due to the star shape and lack of outward features, it's sometimes unclear which way is their up, down, or forward. Their fighters still use normal engines, presumably due to power/size constraints.
* The ''Series/{{Firefly}}'' class of merchant space ships does spew a little bit of exhaust when it goes to full burn, but this exhaust is extremely rarefied and appears static against the backdrop of interplanetary space. Given the spacecraft's lack of internal space for storing propellant, the exhaust may merely be the (unaccelerated) fuel expended to power the Reactionless Drive.
* In ''Series/BabylonFive'', the First Ones and the Minbari use gravity drives to propel their ships without expelling matter out the back. Given that the Minbari provide ArtificialGravity technology to humans after the Earth Civil War, it can be assumed that future [=EarthForce=] ships will be using gravity drives as well.
** {{Subverted}} by the Centauri and most other races with ArtificialGravity tech: while they ''theorically'' could do it, they apparently find it too difficult with their current technology, and the artificial gravity merely facilitates the work of the thrusters. [=EarthForce=] ''Warlock''-class destroyers, the first Earth-made ship with artificial gravity, uses the same trick, as the ''Minbari''-designed ''White Stars'' and the ''Excalibur''.
* In ''Series/{{Salvation}}'', in order to divert an incoming extinction-level asteroid, tech billionaire Darius Tanz enlists the help of a brilliant student and his professor to develop the previously-thought impossible EM Drive (see RealLife below), which appears to violate Newtonian physics. Indeed, in order to develop it, they first have to get the help of an AI to go through all the possible frequencies and then use an extremely rare crystal that only shows up on meteorites to build the drive. And they manage to do it in a matter of days!

* The "ether propeller" of ''TabletopGame/{{Space 1889}}''.
* ''TabletopGame/{{Traveller}}'': Manoeuvre drives were implied to be either this or extremely powerful rockets. ''The New Era'' (3rd edition) replaced these with HEPLAR (High Energy Plasma Recombination) rockets which were much more limited, with the classic manoeuvre drives only becoming available at high TechnologyLevels.
* The Ion Drive engines of ''TabletopGame/{{Starfire}}'' are probably reactionless drives -- they let a starship instantly switch back-and-forth between a dead stop and 10% of the speed of light at the flick of a switch, so they definitely ignore pesky details of physics like ''inertia'' -- but we are never told outright whether they spew exhaust or not.
* In ''TabletopGame/{{Warhammer 40000}}'', some of the more technologically advanced races have them. The Necrons do in addition to being the only race to possess true FTL travel as opposed to using the warp (if you can't go FTL in the real world, go through Hell where you can! Just be careful about the daemons). The Eldar and Dark Eldar may possibly have them, while other races do not.
* The starships of ''TabletopGame/TwentyThreeHundredAD'' use a stutterwarp drive: the ship essentially teleports a short distance, and the "speed" one travels is dependent on how fast the engine cycles to make the individual jumps. While this is their primary method of interstellar FTL travel, they also use it within systems to move at the equivalent of sublight velocities.
* Judges Guild's ''Wilderlands of High Fantasy'' (Issue N) had a plethora of relic high tech items with little description, including anti-grav vehicles.
* ''TabletopGame/{{Rifts}}: Mutants in Orbit'' introduces the Traction Drive, which basically grabs the very fabric of space and pulls the ship along, like the caterpillar tracks of a bulldozer of a tank. It's very slow (to start), but has near-infinite acceleration.

* One of the drive systems in ''VideoGame/{{Ascendancy}}'' is a gravity drive which works by projecting gravitons in front of the ship, which then pull the ship forward. Presumably, the gravitons are removed after the ship passes, otherwise, they would then pull it backwards. It should be noted that this is by far not the fastest engine in the game and has no advantages other than be slightly faster than the one preceding it.
* The ''Normandy'' (both of them) in the ''Franchise/MassEffect'' games uses a "Tantalus drive" that propels the ship by creating mass concentrations in front of the ship that it falls into through gravity, principally for stealth purposes to avoid the use of heat-emitting thrusters. This has several limitations, chiefly that it also involves storing the ''Normandy's'' waste heat in internal sinks instead of radiating it, which must eventually be vented or they'll cook the crew. It's also extremely expensive: The oversized [[{{Unobtainium}} element zero]] core required gave the ''Normandy'' SR-1, a frigate, the price tag of a cruiser, and the SR-2's is even bigger.

[[folder:Web Comics]]
* In ''Webcomic/TheInexplicableAdventuresOfBob'' the Nemesites have been shown using both [[{{Ramscoop}} Bussard Ramscoops]] and some sort of Reactionless Drive called a "Grav Drive." Much of their technology is based on gravity manipulation, and this is apparently just one more aspect of it.
* In ''Webcomic/SchlockMercenary'' almost all futuristic technology is either possible, though difficult, according to our current understanding of physics, or is based on gravitics. Their engines create a gravity well in front of the ship.

* The greater powers of ''WebOriginal/OrionsArm'' have access to 3 kinds of reactionless drives for their spaceships, all largely based on the Alcubierre drive (see Real Life section below) but limited to just below the speed of light (attempting to hit c allegedly causes [[PhlebotinumBreakdown void bubble collapse]]). Like Alcubierre drive, they depend on negative mass, and as per the setting's guidelines, elaborate [[JustifiedTrope justification]] has been provided as to their plausibility. Thematically, the lesser gods' Displacement and Halo Drives (pictured above) have only disposable engines located inside void bubbles and magnetically or gravitationally coupled to an external ship, since at their level, the only way to take down said bubbles is to destroy them chaotically. The highest archailects' Void Drives however are true warp craft, with entire ships or fleets being contained within a void bubble and re-entering normal space smoothly upon reaching their destination.

* Similarly, in ''Webcomic/SchlockMercenary'' almost all futuristic technology is either possible, though difficult, according to our current understanding of physics, or is based on gravitics. Their engines create a gravity well in front of the ship.

* ''Anime/MobileSuitGundamNarrative'' has the Unicorn Gundam Unit 03, better known by its moniker of Phenex. Due to being made almost entirely out of psychoframe, a metal that reacts to human emotions and thought and is less understood than any other material humanity has ever discovered, the Phenex can move through space at truly ridiculous speeds in perpetuity so long as a human consciousness is strong and present enough to will it to do so, with no observable physical reaction occurring at any point of its operation.
* ''Anime/MobileSuitVictoryGundam'' featured the reactionless Minovsky Drive (a scaled down version of the system used to make battleships fly) on the Victory Gundam and it's successor, the V2, granting thruster-less levitation within atmospheres and in the latter case enough surplus power to sustain the enormous "Wings of Light".
** Technically the Minovsky Drive is not a reactionless drive, but a system to use the Minovsky particles from the fusion reactor powering the suit for propulsion directly, thus avoiding the need for dedicated reaction mass. It is more akin to a photon drive hybridized with an exotic fusion torch.

* The starships of ''2300AD'' use a stutterwarp drive: the ship essentially teleports a short distance, and the "speed" one travels is dependent on how fast the engine cycles to make the individual jumps. While this is their primary method of interstellar FTL travel, they also use it within systems to move at the equivalent of sublight velocities.

* Proponents of [[http://en.wikipedia.org/wiki/Heim_theory]] claim you can get a reactionless drive with FasterThanLightTravel thrown in at no extra cost. Unfortunately, according to mainstream physics, the theory is most likely false.

* Averted early on in ''Literature/PerryRhodan'', whose classic "impulse engine" was basically just a fusion torch drive using proper reaction mass (if still impossibly little of it for the implied thrust values given, which led to a later retcon explaining that the drive had used primitive hyperspace technology to "supercharge" its exhaust all along). The occasional HigherTechSpecies of generally extragalactic origin (to say nothing of the really SufficientlyAdvancedAliens) could play the trope rather more straight even then; post issue-1000 time skip, so did "standard" Galactic starship drives.

* Cavorite from Creator/HGWells' ''Literature/TheFirstMenInTheMoon'' created anti-gravitational thrust. It ''blocks'' the earth's gravity in the same way lead blocks electromagnetic fields, allowing the moon's weaker gravity to pull the vessel up. Needless to say Creator/JulesVerne [[SeriousBusiness had a fit]].

** A Bussard {{Ramscoop}}, likewise, doesn't carry it's reaction mass with it, but it still has to gather reaction mass from the interstellar medium.

* ''TabletopGame/{{Rifts}}: Mutants in Orbit'' introduces the Traction Drive, which basically grabs the very fabric of space and pulls the ship along, like the caterpillar tracks of a bulldozer of a tank. It's very slow(to start), but has near-infinite acceleration.

Some writers try to side step this potential danger by setting a maximum speed that the drive can go. Unfortunately while this eliminates the possibility of an infinitely powerful missile it still leaves the developer with an infinitely powerful energy source leaving the writer with most of the same problems. Other times, it may be limited to HigherTechSpecies or {{Sufficiently Advanced Alien}}s who presumably have some scientific understanding beyond the ken of "lesser races".

Most ScienceFiction authors, however, are writing about spaceships because they want to write about humans going places in them. They don't want to write about reaction mass, so ScienceFiction writers would prefer spacecraft to have much more of their volume dedicated to human activities. They typically want their spaceships to be able to operate within convenient distance of someplace interesting, rather than turning half the town into slag as they land and [[InferredHolocaust the other half as they leave]]. They want their spacecraft to flit from one PlanetVille to another, not just tool around wherever an earthbound laser can be shined on them. They DEFINITELY want it to go fast enough to get someplace interesting before everyone aboard dies of boredom. [[note]]Yes, even in [[MohsScaleOfScienceFictionHardness hard sci-fi]] where they're all going slower than light; you still want to be able to at least reach other planets in the '''same''' star system.[[/note]]

* Cavorite from Creator/HGWells' ''Literature/TheFirstMenInTheMoon'' created anti-gravitational thrust. It ''blocks'' the earth's gravity in the same way lead blocks electromagnetic fields, allowing the moon's weaker gravity to pull the vessel up. [[MohsScaleOfScienceFictionHardness Needless to say]] Creator/JulesVerne [[SeriousBusiness had a fit]].

Obviously this would be an awesome invention! So why don't we have them? Well, naively it would shatter the fundamental basis of all physics since UsefulNotes/IsaacNewton, as detailed [[http://www.projectrho.com/rocket/reactionlessdrive.php here]], and modern theories predict effects too small to be useful. Thoughtful SpeculativeFiction writers have also noted that any sort of reactionless drive would provide those who possess it with an ''infinitely'' powerful weapon (compare WeaponizedExhaust, which is the use of a reaction drive as a weapon). Note that this would not be a problem if they required truly massive amounts of power [[note]] to accelerate at 1G a "photon drive" would need ~2.9TW per ton, or 32mg worth of mass converted to energy per second[[/note]] but many examples don't.

Obviously this would be an awesome invention! So why don't we have them? Well, naively it would shatter the fundamental basis of all physics since UsefulNotes/IsaacNewton, as detailed [[http://www.projectrho.com/rocket/reactionlessdrive.php here,]] and modern theories predict effects too small to be useful. Thoughtful SpeculativeFiction writers have also noted that any sort of reactionless drive would provide those who possess it with an ''infinitely'' powerful weapon (compare WeaponizedExhaust, which is the use of a reaction drive as a weapon). Note that this would not be a problem if they required truly massive amounts of power [[note]] to accelerate at 1G a "photon drive" would need ~2.9TW per ton, or 32mg worth of mass converted to energy per second[[/note]] but many examples don't.

Supertrope of the AlcubierreDrive. The {{Ramscoop}} and SolarSail are sister tropes; each is a plain old reaction drive, but one that uses a clever trick to react with the ambient environment instead of needing to haul extra mass or stick to a base station. It is also very common for an incautious (or sneaky!) author to write something that's allegedly one of those two, but from the way it's described working is really a reactionless drive in disguise.

* ''Anime/{{Robotech}}'' has the Robotech Masters' motherships, that move through an unique reactionless drive. This actually backfires on them once, as they did not properly protect the drives and, once that was discovered, a small mecha was able to down their ''flagship'' with a single well-placed shot. Knowing well their technology and not being stupid, the Masters were able to track down the flaw and fix it in time for the rescue attempt on the flagship, during which th rescuing mothership was hit in another supposed weak point to no effect.

* To get to a ship that's entered the solar system quickly, the protagonists of ''Comicbook/{{Planetary}}'' pull out a ship that, according one member who can perceive the flow of information, "eats and craps out information" when activated. Essentially, they have a ship capable of FTL travel that works by rewriting reality so that it's already accelerating.

[[folder: Fan Works ]]

* Proponents of [[http://en.wikipedia.org/wiki/Heim_theory#See_also Heim Theory]] claim you can get a reactionless drive with FasterThanLightTravel thrown in at no extra cost. Unfortunately, according to mainstream physics, the theory is most likely false.