Reactionless Drive: Difference between revisions

{{trope}}

 

 

This means that real-life and conceivable future spaceships are mostly containers full of stuff to throw out the back, with comparatively little volume for human habitation. Most [[Science Fiction]] stories, however are about humans, not reaction mass, so [[Science Fiction]] writers would prefer spacecraft to have much more of their volume dedicated to human activities.

For our purposes it is sufficient to define the drive as follows: "any form of propulsion not based around expulsion of fuel or reaction mass". In other words the drive will propel a vehicle, almost always a starship, without having to waste space carrying propellant. Sometimes authors will try to control these drives by requiring a power plant to make it keep working but more than a few will keep working forever.

 

 

{{examples}}

 

 

== Comic Books ==

* Most super heroes who can [[Flight|fly]] under their own power in space have some form of reactionless drive, [[Required Secondary Power|even if the comic's authors don't call it this]]. [[Superman]], for example, can accelerate, decelerate, and turn in Earth orbit, with no (obvious) rocket exhaust coming out.

 

 

== Literature ==

* ''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.

* The ''Cities in Flight'' series has the Dillon-Wagoner Graviton Polarity Generator or "spindizzy" which gets more efficiency when it moves greater amounts of mass.

* [[Isaac Asimov]] featured such a drive ''in The Gods Themselves''. It worked through the momentum being shunted into another dimension.

* In ''Fleeing Earth'' (''Terre en fuite'') by François Bordes (AKA Francis Carsac), the second civilization of humanity (after we mostly die out in another Ice Age) is [[Alien Invasion|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 a ship with a "space magnet" from moving farther (why the drive can't simply be shut off for the time being is not explained). Exceptions include a massive object traveling at very high speeds. 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.

* In ''[[Tom Swift]] and the Race to the Moon'', the plucky hero's spaceship is driven by "repellatrons." While there is no exhaust, these don't violate the Conservation of Momentum, because they work by pushing remotely against the Earth.

* In ''Stone'' by [[Adam Roberts]], 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 ''[[Sword of the Stars]]'' under Video Games. As Stone was published in 2003, and the game in 2006, I can only assume it was half-inched.

** [[Larry Niven]] proposed more-or-less this design in his "The Theory and Practice of Teleportation", originally a speech at [[Fan Convention|Boskone]] in 1969.

 

 

* The "ether propeller" of ''[[wikipedia:Space 1889|Space 1889]]''.

* Later versions of ''[[Traveller]]'' used reactionless "thruster plates" for spaceship movement.

 

 

 

== Web Original ==

 

 

== Real Life ==

* Since finding a technology that could really do this would be of enormous military and economic benefit, people have tried to come up with various methods for making this work. The [[wikipedia:Dean drive|Dean drive]] is probably the most famous of these.

That wonderful, wonderful Dean Machine! }}

* There is one confirmed way to get many of the benefits of this without breaking physics. If you make it so that the ship is not a closed system, then it doesn't have to carry fuel or reaction mass. Of course this just means that the reaction happens somewhere else. A sail is the form most familiar to us.

** A sail is not a truly ''reactionless'' drive - indeed, such a thing may not actually be possible. In the case of a solar sail, for example, the ship doesn't carry fuel but it still has reaction mass, because it's still a Newtonian reaction generating the sail's thrust. In this case the reaction mass is ''photons'' from the sun.

*** Magnetic sails transfer momentum without transferring mass. And so far, no one has demonstrated that photons have mass.<ref>Under the Standard Model of particle physics, photons don't have mass, but they do have energy and momentum.</ref> Some people insist that reactionless drives violate conservation of momentum ''by definition''. This is not the definition used in this article (see above description). But this is why Dr Woodward prefers "impulse engine" for a Mach Effect drive.

** A photon drive fits our definition; photons do exert pressure, and they are massless. A photon drive only consumes power. Unfortunately, a photon drive is horribly inefficient.

** The Ambient Plasma Wave Drive would use ambient plasma as its reaction medium, generating waves in it to propel itself. Sort of like how a propeller uses ambient air (or water) to create thrust.

* If you could produce a [[wikipedia:Negative mass#Negative mass|negative mass]] you could produce a ships that accelerates without using reaction mass. This occurs without violating conversation of energy because as the negative mass increases in speed its energy ''decreases''. Strictly speaking negative mass is not disallowed by any law of physics.

** In fact, most of current cosmological theories ''require'' our Universe as a whole to be of negative mass to match the currently known pattern of expanding. Well, they mostly express it as a negative energy, but E=mc^2, y'know...

** It should be noted that the ''Mach Effect'' DOES conserve momentum, the "equal and opposite reaction" is spread out over a vast amount of mass outside the engine (possibly the entire universe).

* The [[wikipedia:Electrodynamic tether|Electrodynamic Tether]] also achieves transfer of momentum without using any propellent, it's basically a simple form of magnetic sail.

* [http://arxiv.org/abs/0912.1031 Effects of the quantum vacuum] on magnetoelectric materials exhibit this, but again, it is unclear whether technological applications will ever be possible.

* Proponents of [[wikipedia:Heim theory#See also|Heim Theory]] claim you can get a reactionless drive with [[Faster-Than-Light Travel]] thrown in at no extra cost. Unfortunately, according to mainstream physics, the theory is most likely false.

 

{{reflist}}

[[Category:Speculative Fiction Tropes]]

[[Category:Spacecraft]]