Nuclear Torch Rocket

A Nuclear Torch Rocket is a rocket engine that operates by hyper-energizing the fuel beyond the limits of mere chemical reactions — usually by invoking nuclear power or antimatter to generate plasma to be propelled out the nozzles. Like a chemical rocket, it still relies on the Equivalent Exchange of Newton's Third Law,^note "For every action, there is an equal and opposite reaction" but can get much higher acceleration out of the same mass of fuel.

This has several advantages over chemical rockets, chief among them that a "torchship" (as they're sometimes called) is much more fuel-efficient: much less of the mass the engine can propel must be devoted to carrying fuel, freeing the ship from the Tyranny of the Rocket Equation. A torchship also effectively has Artificial Gravity while under thrust due to the much higher sustainable accelerations. Often they have big habitable and payload sections, whereas a chemical rocket generally may only fire the engines in small bursts to conserve fuel (fuel economy is so poor it's measured in seconds worth of acceleration by rocket scientists). The engine also gives the crew a very powerful Emergency Weapon by allowing them to flamethrower their enemies with blasts of radioactive fire, and gives the writer a ready-made source of dramatic tension if something nasty happens to the reactor. However, it also generates a lot of waste heat, enough to melt their own components into radioactive slag if not properly maintained, and is often likened to flying on the recoil of a Wave-Motion Gun — to the extent that oftentimes the Fictional Geneva Conventions ban their use near inhabited planets.

It helps that it's actually a pretty "hard" sci-fi concept that would more or less work as advertised, satisfying the eggheads in the audience.

Compare the Orion Drive, which also utilizes nuclear reactions, but emanated in an instant in an uncontrolled blast, whereas a torch engine burns for longer (like a torch). Contrast with Reactionless Drive, which bypasses conventional physics altogether. See also the Ram Scoop, which gathers interstellar hydrogen for use as fuel and is often a component of a Nuclear Torch Rocket.

This trope specifically excludes fission-fragment rockets, as the only advantage these have over ion drives is that they don't lose power the further they get away from the Sun.

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Examples:

Anime and Manga

• Touched on in Space Battleship Yamato. The ship's main gun fires the engine's plasma in a colliminated stream. Since it has the ability to vapourize a continent, the engines must put out energy equivalent to approximately 1.33 petatons (that's one-and-a-third quadrillion tons) of TNT. Constantly. It still takes the ship most of a year to get to their destination (this is a near-light drive, and they still have to use an FTL engine when they want to go somewhere in a hurry).
• Mobile Suit Victory Gundam utilizes a fusion torch crushing minovsky particles to power its ships, and a certain Humongous Mecha. The minovsky particles allow a much greater thrust for much less waste heat, to the point that, like Star Trek, a casual viewer would mistake it for a reactionless drive.

Comic Books

• In The Adventures of Tintin, "Explorers on the Moon" has Professor Calculus' experimental nuclear rocket move the character's ship (paid for by the Syldavian Space Agency) fast enough to get to the moon inside a day (it takes three with Apollo-era oxygen/kerosene engines), and it moves fast enough to generate a comfortable 1G. Hilarity Ensues when it's turned off for the deceleration burn halfway there and everyone floats around helplessly for a bit. The engine is handwaved to be small enough to fit into the rocket by saying it's made of a super-material called "Calculite," which has a melting point in the millions of degrees

Fan Works

• The Cochrane Drive from Rocketship Voyager uses "contraterrene" (an old-timey word for antimatter) as fuel to accelerate between planets. The ship moves fast enough that it's built like a skyscraper to take advantage of the pseudogravity effects. It's also theorized that the slightest hiccup would blow the ship into gamma rays, but they have an emergency release lever to make people feel better about that.
• The Sudden Contact Codex offhandedly mentions that Terran battlecruisers use fusion torches for propulsion. UED Space Fighter drones use nuclear reactors, which causes them to spew clouds of nuclear waste while in-flight. This is used as an Area Denial tactic.

Films — Live-Action

• The Venture Star from Avatar uses a dual-propulsion method: going from Earth, it uses a Solar Sail to get moving, and an antimatter rocket to slow down. Going from Proxima Centauri, it does that in reverse.

Literature

• The Expanse has the Epstein Drive, a kind of fusion rocket. It can generate multiple G's of thrust, during which everyone sits on couches and takes drugs in order to survive the crushing force.
• In Heaven's River, the Quinlans have figured out how to build fusion torch ships. They have a higher acceleration than the SURGE drives used by human ships, but they can't sustain them indefinitely, which is why they're still confined to their system.
• Larry Niven's Known Space has fusion rockets as a basic engine (most species use reactionless drives). It's noted that humans like torch engines because they double as guns. Ring World has the main character's ship equipped with torch drive retros for this very reason.
• The Rocheworld series has torch engines become viable after the crew of the Solar Sail ship Promethius discovers a high-temperature superconductor on an ice planet of the Barnard's Star system (the aliens native to the planet utilize it biologically in their nerves, if you were wondering) which would allow fusion plasma to be controlled without the magnets losing their, ah, magnetism due to overheating. Earth's government launches a followup mission to the Barnard's Star system that takes a fraction of the time it took the Promethius with a solar sail, but the torch ship still gets there just as the last of the Promethius's old crew all die of old age.
• Fusion torch drives are common in Robert A. Heinlein's near future stories set in a Colonized Solar System.
  • In Farmer in the Sky the teenage protagonist asks why his Colony Ship has an engineer for the torch drive if it never shuts off. He's told that if there's a problem with the drive, the engineer is expected to sacrifice his life fixing it.
  • The Green Hills of Earth: The interplanetary hitchhiker main character loses his sight trying to fix the fuel rods on a fission-powered ship, and later sustains a fatal dose of radiation repeating that trick.
  • A torch-powered rescue ship trying to save a plague-stricken ion drive ship way off in the Black is the main focus of Starlift. The torch ship is capable of making 16 G's (that's sixteen times Earth gravity), and is flown by a drone pilot, since that would basically reduce any living crew to yucky stains on the back wall. It's powered by a total-conversion-of-matter-to-energy reactor.
  • Discussed in Have Space Suit – Will Travel. The protagonist does some in-head calculations, and reaches the conclusion that at the constant thrust equaling eight gravities it's capable of, the alien ship could do Alpha Centauri and back within a quite reasonable timeframe.
  • A good portion of Double Star is set on board Bonforte's personal torch ship Thomas Paine, first as she makes a three-gravity speed run from Earth to Mars, and then as she makes a normal one-gravity run from Mars to Luna.
  • In Space Cadet (Heinlein), the cadets train on 'jeeps' fueled by monatomic hydrogen. One of them blows up during the course.
• Aeon 14: Fusion and antimatter pion thrusters are commonplace throughout the franchise. Ships typically carry both, because AP drives aren't allowed to be used near inhabited worlds or stations because of the gamma rays they give off: in Attack on Thebes they're even weaponized by the Nietzschean Empire in a Scorched Earth tactic.
• RCN: Spaceships have three main types of thrusters, two of which follow this principle. Plasma rockets are used primarily in atmosphere and work by stripping electrons from reaction mass (typically seawater) and propelling it out the nozzles. The High Drive, which is used in space only, is a matter/antimatter thruster, so using it too close to a planet's atmosphere is a good way to disable your own ship: in Some Golden Harbor Daniel wins a confrontation with a cruiser in his corvette when the cruiser dips too low into Dunbar's World's atmosphere and blows out its own High Drive. Ship-to-ship missiles in the series also use matter/antimatter thrusters exclusively, which effectively makes any warship a Glass Cannon because no hull built by man can withstand that kind of kinetic energy.
• Kris Longknife: Fusion torches, typically fueled with seawater, are used for starship propulsion almost exclusively throughout the series. The books often use a metaphor of demons of nuclear fire chained in the reactors, and bad things happen if the containment is breached.
• The Space Odyssey Series:
  • In 2010: Odyssey Two, the Soviet spaceship Alexei Leonov is powered by the "Sakharov Drive", which uses a pulsed thermonuclear reaction to expel its propellant mass (usually liquid methane or ammonia; water can also be used, although it's less efficient). It's implied the Chinese ship Tsien uses a similar system. (Averted by the American Discovery, returning here from 2001, which is also fusion-powered but uses magnetic acceleration, rather than heat, to expel its propellant.)
  • In 2061: Odyssey Three, ships use a similar but more efficient drive based on muon-catalyzed fusion, which uses water as a propellant, and allows relatively inexpensive travel from one side of the Solar System to the other in a matter of weeks. (For comparison, Leonov's mission to Jupiter and back took five years.)
• Early Perry Rhodan books have "Impulse" engines, which are fusion torches that further supercharge their reaction plumes with primitive hyperspace technology.
• Starsnatcher has two variations. The first are antimatter-matter drives. Due to overheating concerns, they usually do not accelerate faster than 0.5 Gs, but they can hit multiple Gs if the situation calls for it. They are kept far from inhabited worlds and are only accessible through space elevators. The second are more exotic drives based around clean matter-energy conversion through monopolium. They are basically like antimatter drives without radiation-related drawbacks.
• A novelisation of Space: 1999 has an accidental version when a huge nuclear waste dump reaching critical mass causes this effect, pushing the Moon out of orbit. This is an attempt to handwave the Artistic Licence – Physics of TV series which had a huge explosion (that should have destroyed the Moon) be the cause, though it still doesn't explain how Moonbase Alpha can visit a new planet every week or so.
• Used by James White in several of his stories. In Lifeboat, the radioactive and explosive potential failure modes are invoked to justify the passengers and crew of a spaceship evacuating to escape pods rather than remaining with the ship until an automated rescue vehicle can reach them.
• In Tales of Pirx the Pilot, spacecrafts be one-man patrol ships or freighters with a mass of many thousands of tons are powered by nuclear rockets. The dangers of their usage (ie, the nuclear reactor failing and exploding) are often touched.

Live-Action TV

• The Impulse Drive from Star Trek is presented as a Reactionless Drive on-screen, but is canonically a fusion rocket. It's just that the reaction plume is invisible, and makes it look like the ships are being pushed around by their tail-lights. They also require a fair bit of Techno Babble to produce more thrust than a fusion rocket should, especially when pushing a million-tonne starship.
• In Andromeda, the Bellerophon is an ancient STL starship launched by Earth not long before First Contact with the Perseids, resulting in humanity being given slipstream travel. The ship has a massive fusion torch for a drive. While the ship is unarmed, she can use the drive's Weaponized Exhaust to cook enemy ships, although it uses up a lot of the fuel. The ship's been traveling the galaxy for about 1500 years, still committed to its mission of discovery thanks to Time Dilation, even though humanity has settled countless worlds in three galaxies since then.

Tabletop Games

• Transhuman Space has rules for building hard sci-fi spaceships with several options for nuclear drive systems. Fusion torches are specifically used for deep space voyages to the outer system as they have low thrust and high endurance compared to the fusion pulse drives (with or without antimatter catalysts) used for rapid travel in the inner system.
• Urban Jungle's "Astounding Science" supplement is based on 1930s pulp sci-fi so atomic rockets are standard. In the sample adventure a rare isotope called "tellurium-307" is needed for interplanerary travel and Counter-Earth has depleted their supply so they intend to invade Earth for more.
• Attack Vector Tactical is a space-based Turn-Based Strategy where all the ships are fusion torch-powered, giving them the ability to maneuver like contemporary warships, since they don't have to worry about the strict delta-V budgets of modern rockets. The tungsten heat shields protecting their drive's delicate superconducting cages make the ships look rather like flying maces.
• DropShips and WarShips from Battletech use fusion rockets to move to and from a star system's jump points and typically provide artificial gravity by acceleration (so much so that spacecraft engines are rated in G output). The JumpShips that move the DropShips between solar systems have fusion drives too, but the engines are so weak that they are commonly used only for station-keeping.
• Starships in Traveller usually use much more efficient (if less plausible) reactionless drives, but the third edition of the game removed them as part of a Retcon to make the game more Hard Sci-Fi and used the HEPLaR^note "High Energy Plasma Recombination" drive, which was a nuclear torch drive, instead. Later editions of the game brought back reactionless drives, but retained the HEPLaR as an alternate drive technology that some groups in the setting still use.

Video Games

• The most powerful sublight engine in Stellaris is the Impulse engine, which are described as "fusion-powered thrusters."
• In Mass Effect, Fusion torches and matter/antimatter thrusters are two of the four main types of space engines used in the setting (the others being chemical rockets and ion engines). Fusion torches work by venting plasma from the ship's power plant, while only military ships use antiprotons for combat maneuvers. These are combined with mass effect fields to enable Faster-Than-Light Travel. Mass Effect's "Bring Down the Sky" DLC shows building-sized fusion rockets being used to reposition an asteroid for Asteroid Mining; the plot is kicked off when batarian terrorists hijack it for an attempted Colony Drop.
• EV Nova: Most ships canonically use nuclear thrusters, with the Valkyrie considered somewhat outdated for still using chemical rockets according to its Flavor Text. These are primarily of the fission variety, either uranium- or thorium-based (the Starbridge is considered cutting-edge in part for using the latter, but mostly because its design pumps more power directly from its thorium furnace into the engines but then recoups of some of it through turbines placed behind the engines), and additional reactors can be purchased from outfitters in the Federation storyline; otherwise you're limited to buying black market ones, which are illegal and have a tendency to wear out (uranium) or explode (thorium), the opposite of how it ought to be (real thorium reactors are immune to meltdown). Vell-os and Polaris ships use Reactionless Drive instead: the Polaris are a Higher-Tech Species and Vell-os ships are constructed entirely with the pilot's Psychic Powers.
• The Far-Future Tech Game Mod for Kerbal Space Program has various fusion plasma rockets, such as Spherical-Tokamak, Inertial Confinement, and Antimatter-Catalyzed Fission engines, as well as nuclear salt-water rockets.
• Endless Sky has atomic engines as the most mass-efficient and most-powerful per-outfit engines, but they're expensive and use lots of energy and fuel and create a lot of waste heat. The Hai have more-efficient atomic engines and the Sheragi developed powerful nuclear engines before going extinct, while most more advanced aliens favor either ion or plasma-type engines, or even their own more exotic technology.
• Terra Invicta has many of these ranging from various NERVA-type nuclear thermal rockets, liquid and gas-core rockets, every proposed type of fusion rocket, and the below-mention Nuclear Saltwater Rocket, referred to as the Neutron Flux Drive and Neutron Flux Torch.

Webcomics

• 21st Century Fox: In one arc Jenny has to present a proposal for a fusion scramjet-propelled Jupiter probe to a Congressional committee. One senator (a sheep) freaks out whenever he hears the word "nuclear" and tries to fillibuster, which leads Jenny to resort to repeating "nuclear" until he runs bleating from the room. In a later arc, Jenny and Jack ride a people-safe version to Venus while the crew make nuclear physics puns.
• Freefall uses fusion rockets as sublight engines. Luckily, the AI on most ships is smart enough to refuse to turn them on while planetside.

Web Original

• Atomic Rockets has an entire section on these, and their various types. It also notes that the exhaust plumes of any kind of torch drive could obliterate a small city, and therefore the military would want to keep a very close eye on anyone who has such a ship, since they're effectively riding around on the recoil of a Wave-Motion Gun. It also notes that a fusion rocket would want to have the reaction well away from the ship, contained within a well-insulated/shielded magnetic cage, lest the ship "glow blue-white for a fraction of a second before vapourizing." One interesting tidbit of information it mentions is that, if you're using a fusion torch, the atoms in the fusion plasma can be manipulated to "point" in a certain direction simply with a strong enough magnetic field (way stronger than the ones used in MRI scanners), allowing you to "aim" the neutrons emitted from the nuclear reactions for thrust, as well as the energetic plasma, and you also get a beam of other subatomic fragments going in the opposite direction, which can be captured for power, or directed away for yet more thrusting power.
• Orion's Arm has several variations of fission, fusion, and antimatter propulsion in use by sub-singularity sapients. Post-Singularity transapients tend to use matter conversion drives that use magnetic monopoles to generate antimatter within the reaction mass while the archailects have Reactionless Drives.
• Fen Space has fusion torch engines that utilize Green Rocks, outright called "Handwavium" In-Universe, to achieve ordinary-hydrogen fusion, with physics-defyingly incredible velocities without melting the engines.

Real Life

• A common idea, called a "Nuclear Thermal Rocket" (NTR), is to use the heat of a (usually) conventional nuclear reactor to heat hydrogen gas (any other fuel isn't worth it; hydrogen gives the best returns for its weight but is a nightmare to store and carry around). Some theoretical designs have a reactor added to a conventional rocket, to be turned on for interplanetary travel, which is called a "Bimodal nuclear thermal rocket." This has proved problematic for both political (most people and countries mess their drawers at the word "nuclear") and practical (the darn thing needs a few tons of shielding to keep from frying the astronauts, the fuel is constantly trying to escape, etc) reasons. A few were tested by the United States in the NERVA project; but never used on anything (due to parts of the reactor being carried away in the rocket exhaust for the early ones, and primarily budget cuts for the later ones [after they fixed the problems with erosion of the fuel elements], coupled with the cancellation of all the heavyweight high-delta-V missions that would've required the NTR in order to meet their delta-V budget). Both the U.S. and the USSR later solved the shielding and reactor erosion problems for the relatively-simple solid-core NTR, but a combination of budget cuts, worries about contamination downrange if one failed to reach orbit (or if one decayed from orbit and disintegrated in the upper atmosphere), and (for the U.S. at least) an aversion to nuclear technology except where absolutely necessary, meant that neither country ever actually launched one. Much of the NTR research since then (led by several governments, including the aforementioned two) has focussed on the gas-core NTR, which has a theoretical performance vastly in excess of even the solid-core NTR and potentially attractive enough (at least for some missions) to outweigh the above issues, but the "open" gas-core NTR (where the fuel gas is held in the reaction chamber purely by hydrodynamic means), which is required in order to get the fuel hot enough for the maximum theoretical performance, has seemingly-insurmountable problems (keeping the fuel from escaping is practically impossible [and gets progressively harder still under even very gentle acceleration], efficiently transferring all that heat to the hydrogen propellant rather than the reactor walls is extremely difficult, and, even if you do manage to get most of the heat from the fuel gas into the propellant, the fuel is so darn hot [in the tens-to-hundreds of thousands of Kelvin in the highest-performance designs] that even the small leftover amount of thermal radiation absorbed by the engine itself is still enough to cause hideous thermal issues) which we aren't much closer to solving than we were in the 70s, and the "closed" gas-core NTR (a.k.a. "nuclear lightbulb", as it holds the fuel gas in a number of fused-quartz bulbs which the hydrogen flows over the outsides of) has a lower maximum performance while still having issues (albeit not nearly as insurmountable as the open gas-core NTR has).
• Theoretical designs purport to use fusion reactors with a hole in the Containment Field leading to a rocket nozzle made of superconducting wire, which works to stretch the field so that the plasma doesn't actually touch any of the physical components. The fusion reaction can be squeezed very tightly (something called a "Zeta Pinch"), and then allowed to flow through the hole and into the nozzle. This method would be capable of flying a spaceship at about 2G's of acceleration, and would have the power to obliterate Rhode Island if it got caught in the exhaust plume.
  Another method merely uses the fusion reactor as a combustion chamber, similar to the nuclear thermal rocket concept, and can be built to have a Ram Scoop for free remass.
• One nuclear reactor-free method currently within the grasp of modern science involves uranium salt dissolved in water. This salt would reach critical mass as the water is squirted out of the rocket nozzle, causing a sustained nuclear explosion at the ship's tailpipe. They would need special fuel tanks honeycombed with neutron-absorbing materials to keep the fuel from exploding early, and rocket nozzles protected from their exhaust's heat somehow. It has the unfortunate downside of vaporizing the ship if the fuel tanks are punctured. For obvious reasons it would only be usable in space, since the rocket is essentially a flying Chernobyl.
• An offshoot of particle accelerator experiments known as a "macron gun" utilizes charged particles about the size of a bacterium, rather than an ion, allowing them to hold a much greater charge. These can be filled with fissile materials, which explode like eeny-weeny nukes when they hit something. Harnessed as an engine, they are projected to rival The Expanse's Epstein Drive in top acceleration. They would also make dandy weapons.

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