In order to reach the stars, we’ll need space ship drives of titanic output, even those powered by the stars themselves… So, over the years, we’ve reviewed a lot of spaceship designs in our overall discussions of humanity’s future and of space colonization in general, some in-depth, and some only in-passing, and some in episodes that were made so long ago that they’re buried in search engine results, and since our Megastructure Compendium episode from last summer was well received, I thought we might follow that up today with a list of all the various advanced spacecraft propulsion methods that are either on the drawing board, represent popular theories, or are even just things that are regularly and seriously discussed in science fiction. Each will have its own alphabetical entry, and those on youtube should see a chapterized version available, and we’ll have a time index of topics in the description on all of our platforms. If you review those, you’ll note that some aren’t very advanced drives at all, or even propulsion methods, as I felt that certain critical topics like the Rocket Equation or what Specific Impulse is; should be in the episode, especially as while you can listen to this episode all the way through, it’s not necessarily intended to be observed in that way like most of our episodes incline towards. It is also going to be a long one, so a drink and a snack is advised, and my wife Sarah will be calling off the titles and references between episodes to help distinguish the break up of the individual entries. Also, at the end of every entry there will be a list of other entries related to the topic or mentioned in the entry, and we will sometimes reference relevant episodes, and for viewers the cover art of that episode will appear as thumbnail on screen, to help you find that episode, as Youtube limits us to 5 in-video links, and also 100 chapters, which we discovered with the previous compendium episode, and is part of the reason why some of our topics are merged. One of the others being that some are very similar, especially without getting into technical details that most casual watchers wouldn’t follow.
Indeed, being a physicist rather than an aerospace engineer, there are a few I’m not sure I do either, and there is a reason why rocket scientist is synonymous with being very smart. I would also like to note that virtually all of these ideas are someone’s brainchild, whether it was a scientist or scifi writer or both, and for brevity’s sake we’re not delving into the full backgrounds and bios of the device and their designers, especially when the device is named for them. Though that means folks like Mark Millis, who proposed or expanded on tons of hypothetical drives like the Bias Drive, Diametric Drive, Disjunction Drive, Pitch Drive and more, are not getting anything like the credit they deserve. I can only say that for as long as this episode is, much is being left out, and there is mind-bending science, fascinating development backgrounds, and amazing science fiction out there for those who choose to go beyond these short entries and explore these topics more.
If you are looking for good places to continue finding out more on these drives, I’d definitely recommend the National Space Society, Tau Zero Foundation, Atomic Rockets, Centauri Dreams, Orion’s Arm, and of course NASA’s Eagleworks Lab. With all that said and without further ado, let’s get started. Alcubierre drive The Alcubierre Warp Drive is a well known example of a type of warp drive that uses hypothetical negative matter or negative energy to warp spacetime in front of a ship to contract, and behind a ship to expand. Because the ship itself is not accelerating, this not only allows high speeds but bypasses normal limits on the speed of light in the same way dark energy and Hubble expansion do. Because of it requiring an exotic matter not currently known to exist in nature and permitting faster than light, or FTL travel, this technology is an example of Clarketech - technologies so advanced they are indistinguishable from magic and to which we have no clear scientific path to produce - and is very similar to an Induction Ring Drive, as it is creating a bubble of warped space around the ship.
See our episode on Warp Drives for more on the Alcubierre Drive. See also: Bias Drive, Clarketech, Diametric Drive, Disjunction Drive, Pitch Drive, Warp Drive Antimatter Rocket Antimatter is matter with opposite characteristics of normal matter, and when particles of antimatter such as the anti-proton or anti-electron, better known as a positron, come into contact with a proton or electron respectively, they typically turn into a pair of photons containing the total mass energy of those particles. By itself this is not explosive and occurs often enough in nature, as many particles emit positrons during decay, including inside your own body, and rapidly find an electron to mutually annihilate with. In large quantities antimatter makes a nuclear bomb look weak, as a single kilogram of antimatter would combine with a kilogram of mundane matter to release the equivalent of a 43 megaton hydrogen bomb, equal to the Tsar Bomba which was the largest thermonuclear device ever tested, which also weighed 27,000 kilograms, not just 1. Antimatter has the second advantage that it doesn’t require any other hardware to do its job, other than presumably magnetic containment. The difficulty of making it and storing it are the two main limitations, and the basic theory and techniques for producing antimatter are discussed in our episode Antimatter Factories.
Assuming you can make and store it, antimatter, along with an equal amount of mundane matter, can be easily magnetically sprayed into your equivalent of a rocket nozzle and form a photon rocket with an exhaust velocity of light speed. An antimatter rocket such as the theoretical Valkyrie spacecraft was expected to be able to reach 92% of light speed, at which speed the crew of the ship would be experiencing less than 10 hours for every day here on Earth, or 40 years for every century. For this reason antimatter is generally considered the most powerful rocket fuel available under known science. However, due to its incredible rarity in nature and difficulty to produce and store, more frugal uses of antimatter are often considered, such as the Antimatter Ablated Light Sail & Antimatter Catalyzed Fusion. See also: Antimatter Ablated Light Sail, Antimatter Catalyzed Fusion, Photon Rocket.
Antimatter Ablated Light Sail As antimatter is thought to be hard to produce and store, various rationing ways to use it in tandem with other materials have been contemplated, and this includes the Antimatter Ablated Light Sail. This technique involves a small supply of anti-hydrogen, maybe just a few grams for smaller ships. This uses anti-hydrogen slowly released toward a forward plate or dish, akin to the Medusa Drive, made of Uranium-238, which might be as small as a few meters, allowing a relatively small ship.
The antimatter reaction with the U-238 should produce neutrons and other secondary products which would leave the sail at very high speeds, and produce a power rate of a couple megawatts per kilogram of sail. Such ships may be able to gather the necessary antimatter from natural sources, such as gas giants. See also: Antimatter Rocket, Antimatter Catalyzed Fusion, Medusa Drive Antimatter Catalyzed Fusion We have been pursuing artificial fusion with varying but improving degrees of success for decades, but one of the most promising methods is antimatter catalyzed fusion.
Using small amounts of antimatter we can catalyze far larger bursts of fusion, releasing far more energy than that bit of antimatter held, and it is believed to be a fairly simple process. This could either run a fusion reactor, to power ion drives, or simply be used for micro-fusion bombs right behind the ship as an effective fusion rocket. Unfortunately it requires a small supply of antimatter, which is barely existent naturally and hard to make and store.
Should we find a way to make and store antimatter, but not in sufficient quantities for a full antimatter rocket, antimatter catalyzed fusion could allow a Fusion Torch Drive behind a ship allowing it to travel at very high speeds, possibly in excess of 10% of light speed. See also: Antimatter Rocket, Antimatter Ablated Light Sail, Fusion Torch Drive, Nuclear Pulse Drive, Orion Drive Arcjet Rocket The Arcjet Rocket or Thruster is an electric spacecraft propulsion method commonly used in small spacecraft as it is simple and small. An Arcject that uses a pair of electrodes to generate an electric arc, the same as a conventional arc welder, that in turn vaporizes the propellant and pushes it back. The arc and propellant, now plasma, then continue backward through the thruster gaining speed from the anode and cathode. This is an example of a low-thrust, high-efficiency rocket, as very little thrust is produced at any given moment, but the exhaust velocity is very high. Ammonia, a popular Arcjet rocket propellant, typically has an exhaust velocity of 9000 meters per second, more than double that of a typical chemical rocket.
The arcjet is generally more efficient than its cousin, the Resistojet, but both suffer from some durability and longevity issues, particularly of its electrode, which electrodeless designs such as Pulsed Inductive Thrusters seek to circumvent. See also: Pulsed Inductive Thruster, Resistojet Bias Drive A Bias Drive is an example of a Clarketech engine that works not by warping space or time, but by locally altering physical constants of the Universe, in this case the Gravitational Constant, in front of and behind the ship, letting it essentially fall to its destination. Beyond having no method to alter physical constants at this time, it is likely that a bias drive would produce a singularity in the center of the ship. If functional however, such a ship would not need to expend any fuel to move from point A to B, and a bias drive would appear to allow perpetual motion machines, for producing electricity and power, though it is entirely possible that techniques for changing physical constants might still conserve quantities such as energy and momentum.
See also: Clarketech, Pitch Drive Black Hole Drive Black Hole Drives are a group of hypothetical spacecraft propulsion methods that can range from using a naturally occurring one to accelerate and redirect a spaceship to co-opting one to move an entire star system, as discussed in our episode Fleet of Stars. The most well known version relies on using micro black holes in the sub-megaton range to generate Hawking Radiation, and Hawking radiation drives are covered in their own section. Other methods include using the Penrose Mechanism or similar methods to dump matter into a black hole, presumably a micro black hole larger than a megaton, and get 20-40% of its mass energy released as radiation during the descent.
Gaining power from black holes this way is not technically complex, it’s simply absorbing high energy photons coming off it as with any nuclear process, and such black holes may be tethered to spaceships or stations with magnetic fields, which black holes both produce and interact with. Additional uses, which are discussed in our episode Black Hole Ships, would also involve using them as the power plants of ships running photon rockets, using them to power giant laser pushing beams such as we contemplate for Laser Sail and pushing relay stations, or even using them in pairs for accelerating ships around them in a loop to achieve high speeds. See also: Hawking Radiation Drive, Laser Sail, Matter Beaming, Photon Rocket. Bussard Ramjet The core concept of the Bussard ramjet is that most of space is full of ionized gas particles, most of which are hydrogen, a ready source of fusion fuel, and if you can grab these magnetically and suck them down into your ship, you can use them as fuel. The ramjet part comes from parallels to how an air-breathing ramjet works, sucking air in and superheating it, then shooting it out the back, but here the power source for heating that gas up is the gas itself by fusion, and that fusion is ignited by sucking in interstellar gas at relativistic speeds and jamming them tightly down the throat of the ship to ram into other gas particles at high speeds, temperatures, and pressures.
This seemed like a possible way to give ships an infinite power supply, simply grabbing it out of space as they flew by, like a ship sailing on a sea of diesel fuel. Indeed it was contemplated for a while as a way to keep accelerating indefinitely, something we see in the scifi classic novel Tau-Zero, or with other drives likes the Gravitic Dipole or Laser Sail, but the math turned out not to work. Indeed some argue the method would actually require more energy than the reaction released and result in the ship slowing. Which ironically makes this drive handy for decelerating for free, which would make it function very well with a laser sail and relay system on the front end of the journey, to push the ship up to speed, and the ramjet to slow on arrival, while also powering other ship functions.
Additionally, this technique of sucking in ionized particles magnetically; works perfectly fine if you have otherwise functional fusion reactors and are not planning to move in excess of what that ship’s normal exhaust velocity is, and thus works just fine for giant ships with conventional fusion reactors who only plan to move a few percent of light speed. This might include freighters, deep space miners, monitors or patrols, or giant beaming stations, be it laser, energy, or matter beams, needing to do station-keeping and to resupply their fuel. It also works just fine if you have a refuelable black hole in the throat of your ship, into which you’re stuffing in the matter you sucked in, though only to whatever speed your effective exhaust velocity of that system would be, since otherwise, you’re sucking in matter that you have to absorb the momentum of to use for power and propellant which would exceed what you were getting out of it. That makes it handy for big carrier ships wanting to turn directions or launch higher speed vanguards out of, since it can supply power to those too, by laser or energy beaming.
So the bussard ramjet wouldn’t work as planned but they do have some variations and alternative applications worthy of note. See also: Black Hole Ships, Gravity Dipole Drive, Laser Sail, Matter Beaming. Caplan Thruster A Caplan Thruster is a method for moving stars proposed by Matthew Caplan in 2019 for using statites to concentrate solar energy and erupt solar wind in a beam out from a star, which would then pass through an enormous Bussard Ramjet Assembly and jets of Oxygen-14 to push a star at a faster rate than a traditional Shkadov Thruster would allow.
See our episode: Fleet of Stars, for more discussion of potential methods of moving stars. See also: Bussard Ramjet, Helios Drive, Nova Drive, Quasar Drive, Shkadov Thruster Chemical Rockets Chemical Rockets is the ballpark term for any rocket running on chemical interactions but generally refers to those running on combustion and producing the classic high-intensity rocket flame seen in countless rocket launches. In such cases the fuel is typically burned with an oxidizer to emit a propellant that, because of its high temperature, also has a high exhaust velocity, allowing it to exit the rocket nozzle with a high momentum, while pushing the ship in the opposite direction with that same momentum. Chemical rockets typically have far higher exhaust velocities and specific impulse than alternatives such as compressed gas, as is used in CO2 cartridge guns, pumped water rocket toys, or other alternatives such as the elasticity that traditional catapults or bows use for firing a projectile.
Because combustion occurs very quickly, it permits a spacecraft to have enough thrust to escape from a planetary gravity well, whereas more efficient ion drives could never get off the ground or clear an atmosphere, even though they will ultimately push a ship to a far higher speed. However, as a result, chemical rockets are most efficient at high temperatures and so we run their combustion as hot as the rocket body and nozzle can withstand. The most efficient known chemical rocket fuel is molecular hydrogen burned with oxygen, though it is difficult to handle compared to its more commonly used counterpart rocket fuel, which is essentially kerosene.
Many other fuels have advantages in certain conditions or environments, or are easier or safer to work with, or easier to obtain, which becomes critical in wanting to source your fuel from your destination for a return trip, in-situ production of fuel from whatever is available on the Moon or Mars or elsewhere. See also: Ion Drive, Propellant, Oxidizer, Rocket Equation Clarketech Clarketech is not a propulsion system itself but a category applying to many possible propulsion methods suggested in hypothetical science or science fiction. The name is derived from Arthur C. Clarke’s famous quote that “any sufficiently advanced technology is indistinguishable from magic”, and is the name for various technologies that folks have suggested that would not seem possible under currently-known physics and can include negative matter or other exotic matter types, as well as faster than light systems and perpetual motion machines.
It would also include propulsion technologies that operated by altering physical constants, such as the speed of light or force of gravity, or the electromagnetic or strong and weak nuclear forces. Or bending spacetime in strange fashions, like creating a circle with only 359 degrees inside, or portals to other dimensions with different properties. See our episode: Clarketech, for more discussion of these near-magical technologies. See also: Alcubierre Drive, Bias Drive, Diametric Drive, FTL drive, Inertia Reduction Drive, Krasnikov Tube, Pitch Drive, Negative Matter Propulsion, Warp Drive, Wormhole Drive Diametric Drive The Diametric Drive is a Hypothetical Clarketech reactionless drive typically envisioned as running on negative mass, but may work on any field or force which can be used to create an effective pressure difference on the ship to push it along, much as an airfoil in the atmosphere works. A property of negative mass particles is that they are believed to gravitationally repel both positive and negative mass, unlike positive mass which is believed to pull on both positive and negative mass. Therefore, two positive mass particles pull toward each other, two negative mass particles repel each other, and a positive and negative mass particle will actually shove the positive mass away from the negative mass, while pulling the negative mass toward the positive mass, resulting in the positive mass particle being chased by the negative one.
This technology is akin and equivalent to a gravitational dipole drive where gravity is the force or field being used for propulsion. Diametric Drives are a subcategory of Pitch Drives, and again may use negative energy to achieve this push, or other effects, and is very similar to a tractor beam, which might also be used for spaceship propulsion. See also: Bias Drive, Clarketech, Gravitational Dipole Drive, Pitch Drive, Negative Matter Propulsion, Reactionless Drive Disjunction Drive The concept behind the disjunction drive is that a field might be disjoined from the object that created it. Conceptually, we might imagine a ship built near a large gravity well, which was then disjoined from the mass creating it and potentially reattached to the front of the ship so it constantly fell forward. We might also disjoin something’s inertial mass while leaving its gravitic mass in place, or disjoin an electrostatic or magnetic field from their generator.
This could also be a disjunction from a Higgs boson field. Needless to say, such technology would be Clarketech. See also: Bias Drive, Clarketech, Pitch Drive, Reactionless Drive Electric Solar Wind Sail Our Sun has a surface temperature of thousands of degrees constantly being stirred around by the Sun’s immense magnetic field, and this results in emission of particles, principally ionized hydrogen, from our Sun’s surface, moving at hundreds of kilometers per second. It is possible to create a large thin sail that would take these particles and be shoved by them, same as a ship sails the winds here on Earth, but as solar wind is very diffuse, such a sail would need to be very large and potentially impractical, even if made from graphene. Instead though we might run out conductive cables or wires as thin as a hair, like spokes on a wheel and kept in a circle by slow rotation of the main body, allowing the equivalent of square kilometers of sail from tiny threads. As these particles are mostly ionized, they can interact with electric and magnetic fields, and in this case electrically to push the ship along.
This method only works inside solar systems, and thus is a good method for accelerating ships to speed or decelerating them once they reach another star, to save fuel, if used in tandem with other drive systems. It should be noted that, while all stars have solar wind, the quantity and speed of those particles will vary immensely as the difference in brightness from the dimmest red dwarfs to the largest supergiants is a factor of over a billion. Stellar remnants may also have more polar particle stream, such as we might expect from pulsars, which interstellar ships might use for both gravitational assist, to gain speed and direction, and to ride away on that jet, gaining more speed. So too, technologies such as Starlifting, see that episode, which are normally intended for mining a star of its materials, also allow for increasing solar wind and directed streams of denser and higher speed wind, similar to what we might use for matter beaming.
See also: Magnetic Solar Wind Sail, Matter Beaming, Solar Sail Electrodynamic Tethering Electrodynamic tethering is an electric propulsion technique available around large magnetic fields, such as many planets like earth have. By having a satellite with an anode hanging below it attached by an insulated tether, we can run electric current through that system and push away from Earth, shoving on the magnetic field, or de-boost by having the tether above instead of below. Due to the size of these magnetic fields, in a physical sense, the tethers must be long to function, typically on an order of kilometers of wire, and this technique may be reversed to generate power rather than turn power into thrust. Electrodynamic tethering is often considered an option for regenerating momentum in Skyhooks and Rotovators, which lose momentum while helping spaceships move from air to orbit, though vastly reducing their own fuel needs with the boost, see our episode: Skyhooks for details, but a skyhook which lost some momentum and altitude by lifting a spaceship to orbit could slowly regenerate that over some hours by gathering sunlight from solar power and using that electricity to run an electrodynamic tether, as skyhooks are already very long tethers themselves. Such technology is also good for stationkeeping of satellites, space stations, or high orbital variations of a rotavator meant to slingshot a ship into deep space at high speed, and could also be employed near superpowerful magnetic fields like those of gas giants, stars, and stellar remnants like white dwarfs, neutron stars, pulsars, and black holes.
See aso: Rocket Equation EM Drive The EM Drive is a spacecraft thruster that gained popularity, or notoriety, early this century as a potential reactionless drive or perpetual motion machine, as it seemed to exhibit properties violating conservation of momentum. It was catapulted into fame when NASA Eaglework’s Lab built and tested one in 2016 and it seemed to exhibit the purported physics-breaking properties but those were later blamed on measurement errors and no other experiments have since replicated the desired results. As it appears to be a falsified technology, rather than a still hypothetical one, we will not classify it as Clarketech, and we will also not give it further discussion today, other than to say the basic principle is to supply power to a magnetron into a resonant cavity that is roughly cylindrical but narrows a bit, thus has one side with a slightly smaller diameter than the other, which the microwaves will now bounce between. This is said to produce a larger force on the slightly wider side and a smaller force on the narrower side, for a net force on the object pushing it toward the narrow side, which would be fine from a conservation of momentum standpoint except the claim is that it is producing more thrust than a photon rocket under similar power input would achieve.
See also: Clarketech, Quantum Vacuum Thruster, Reactionless Drive Exhaust Velocity Exhaust velocity is a critical term to rocketry and spaceship propulsion, and represents the speed at which particles of propellant are being exhausted out of the back of a rocket or ship drive. That velocity, times the mass of the exhausted particle, is its momentum. As conservation of momentum requires a ship to gain the same momentum in the opposite direction as the propellant being exhausted, a fuel with twice the exhaust velocity lets a ship travel twice as fast, or the same speed but on far less fuel. Most chemical rocket fuels have an exhaust velocity on an order of a few kilometers or miles per second, and it is typically impractical for a spaceship subject to the rocket equation to go much more than thrice the exhaust speed, thus we seek propellants with higher exhaust speeds, or drives which circumvent the rocket equation. Fundamentally, all particles moving around as a hot gas do so at a certain average speed based on their temperature and mass, low mass particles like hydrogen move much faster at the same temperature as higher mass particles like carbon dioxide do and thus are generally preferable propellants, where a simple thermal rocket is involed. Most objects - including rocket nozzles - will melt at temperatures of thousands of degrees, so this is often our limit on exhaust velocity as well, though options like magnetic containment and ion drives circumvent this issue, and can work better with heavier ions.
A propellant’s exhaust velocity divided by the gravitic acceleration of Earth, 32 feet or 9.8 meters per second per second, will give the approximate Specific Impulse of a propellant, or essentially how many seconds a rocket running on it could hover the ship in Earth’s gravity. See also: Propellant, Rocket Equation, Specific Impulse Field Propulsion Field Propulsion refers to any type of spacecraft whose momentum is exchanged by interaction with external force fields, such as we see in Electrodynamic Tethering, or any spaceship being launched from an electromagnetic space catapult, such as those discussed in our episode Mass Drivers. This also includes more hypothetical or fictional examples, such as most gravitic drives, or various other hypothetical external fields, possibly including Vacuum Energy.
See also: Electrodynamic Tethering, Gravitic Propulsion FTL or Faster Than Light Drives This category includes any method of moving a spacecraft at superluminal speeds or faster than the speed of light, which can range from Tachyons to Wormholes to Hyperspace and Warp Drives. As known science generally considers this impossible, it is classified as Clarketech, and methods for doing it usually require exotic matter such as negative matter or imaginary mass, and generally result in time travel and violations of casualty. See our FTL series for more discussion of techniques proposed and their strengths and flaws.
See also: Alcubierre Warp Drive, Hyperspace Jump Drive, Krasnikov Tube, Warp Drive, Wormhole Drive. Fuel Fuel is what keeps a ship speeding up or slowing down, or runs its onboard power plant to keep the crew alive and the equipment running. Most often with modern spacecraft the main fuel is burned up with an oxidizer and the byproduct of that combustion is expelled out of the rocket as a propellant, pushing the ship along.
Not all ships would have conventional fuels, and might rely on nuclear reactors, solar panels, energy beamed in from afar, or exotic materials like antimatter. We also contemplate ships needing no fuel or propellant, a reactionless drive. See also: Oxidizer, Propellant, Reactionless Drive, Rocket Equation, Thrust Fusion Torch Drive While the term torchship originally referred to a ship that converted matter completely into energy, a fusion torch drive is one that achieves very high speeds by being able to turn fusion fuel, potentially even basic hydrogen, into energy and the fused remainder into its propellant heated by that energy. Since fusion occurs at millions of degrees, this is not something that takes place inside a normal chamber, and generally needs magnetic confinement and involves lots of equipment for conversion of released radiation and heat into electricity and then into accelerating propellant, typically by some form of ion drive or plasma thruster. In practice this would really limit how fast a fusion-powered ship could reach and how fast it could accelerate up to that speed. This is where the torch ship comes into play as it is assuming the reaction is taking place at the rear of the ship and basically acting like a rocket flame rather than a reactor or engine burning gas.
A ship able to do this is one which can reach high speed quickly by high thrust, rather than requiring low thrust from a reaction inside the ship designed not to melt the ship or blow it to bits or erode it all under the intense gamma and neutron radiation. There are many basic if still theoretical designs, Atomic Rockets has the best collection of them I know of, and many examples in science fiction, but probably the best known, The Epstein Drive from the Expanse series, is a fusion torch ship design. Fusion Torch Ships are beloved by space enthusiasts as often being considered the most near-future technology which definitely makes space travel practical for regular human transport, including interstellar travel and ground-to-space travel. Though as we’ve discussed elsewhere, there are lower tech or parallel tech options that should allow interstellar colonization, many of which we’ll review today.
See our episode: Fusion Propulsion for a more in depth look on the topic. See also: Antimatter Catalyzed Fusion, Ion Drive, Photon Rocket, Torch Drive or Torch Ship Gravitational Dipole A type of negative mass reactionless drive, using a dumbbell-shaped ship with a sphere of negative mass on one end, and positive mass on the other, able to accelerate due to the suspected properties of negative matter, that it is attracted to positive matter but exerts a push on it, thus two particles, one negative mass and one positive, will result in the positive mass fleeing the negative which is pulled behind it in a perpetual and accelerating chase. This is a parallel concept to the Diametric Drive. A ship utilizing this technique is described by Robert L. Forward. He proposed a simple dumbbell-shaped spacecraft design using a ball of regular positive mass on one side, the front side, and negative mass on the back or stern of the ship.
Such a ship in theory can accelerate eternally, though likely would experience drag force on its prow, from interstellar gas and radiation, giving it a maximum speed at 99.9-something percent of light speed, making it what is sometimes called a lighthugger, a ship that moves at within a tiny fraction of light speed. Such a ship could slow down by flipping over and would accelerate or decelerate based on its ratio of drive mass to payload, and could likely physically anchor itself to any larger object. Such a ship may or may not violate conservation of energy or momentum, though would appear to do so on first glance. See also: Diametric Drive, Negative Mass Propulsion, Reactionless Drive Gravitic Propulsion Gravitic Propulsion is a blanket term for any ship drive manipulating artificial gravity or using anti-gravity, directed gravity waves, graviton beams, certain types of tractor beams, or insulating itself from gravity to move. While we typically classify this as Clarketech, and indeed have an episode on the topic, Clarketech: Anti-Gravity, it does seem plausible that gravity may be able to be manipulated or produced by means other than raw mass.
In theory a gravity drive might also circumvent normal inertial problems of rapid acceleration, as discussed in Isaac Asimov’s 4th Foundation novel, Foundation’s Edge, which features a ship using this sort of drive. Normally, rapid acceleration causes damage as not everything is accelerating simultaneously at the same rate, but when falling into a gravity well, this is not an issue, as the force applies to every particle equally, no matter how strong or fast the acceleration, and ignoring tidal effects. A gravitic engine with this property would permit safe super-rapid acceleration of people and cargo, which is of inestimable value for short space journeys especially, or those on interstellar ships able to reach ultra-relativistic speeds. See also: Clarketech, Diametric Drive, Field Propulsion, Gravitational Dipole, Inertia Reduction Drive, Negative Mass Propulsion, Reactionless Drive Hall Effect Thruster A type of ion drive, the Hall Effect Thruster, is named for Edwin Hall and the Hall Effect, and is recognizable for its rather lovely plasma jet colors that it emits, based on the propellant it uses. The Hall Effect results in a potential difference perpendicular to a magnetic field, so we can create a cylindrical chamber with a large magnetic solenoid in it, and any ionized particles will accelerate down the axis of that chamber as with a normal ion drive. The magnetic field itself is responsible for ionizing the propellant and shoving it and the electrons out the back to neutralize the ions as they emerge.
Hall Effect Thrusters have been around since before we went to the Moon and have seen continual improvement, and come in multiple varieties, as well as achieving exhaust velocities as high as ten times our best chemical rocket fuels. As is often the case, we have to choose between high thrust or high efficiency, and Hall Effect Thrusters are very low thrust. The highest power one yet produced is the University of Michigan’s, which is a 100 kilowatt thruster massing 230 Kilograms and producing just 5.4 Newtons of thrust.
Force being equal to mass times acceleration, this thruster, without any additional equipment including a power source, would only accelerate at about 0.0022 meters per second per second, about 4,500 times slower than something falling in Earth’s gravity. So, by itself, it could not be used to leave Earth, however one accelerating constantly for an entire day would reach a speed of 190 meters per second, for an entire month, nearly 6 kilometers per second, and if its fuel held for an entire year, 70 kilometers per second. See also: Ion Drive, VASIMR Hawking Radiation Drive A Hawking Radiation Drive is one that utilizes a small black hole to create a photon rocket, as it is believed that black holes evaporate over time, releasing mostly photons, and do so faster as they get lower in mass.
A one megaton black hole is believed to evaporate at a rate that would release 356 Trillion Watts of Power, and would do so at a slowly rising rate for a lifetime of 1474 years, while one at a tenth of the mass, 100 kilotons, would emit 100 times more power and live just a thousandth as long, 1.47 years, and it is usually assumed Hawking Radiation Drives would use black holes in this mass range of 100 to 1000 kilotons for operation. Bigger ships would use multiple black holes, not a bigger one, as bigger is lower power for black holes, albeit vastly longer lived and with higher ultimate energy output. Smaller is better but smaller is harder to make, and even harder to refuel, and we have looked at methods of using them as ships, power sources, and weapons, in our Black Hole Series, including hypothetical ways of creating them.
This does appear possible under known physics, so we do not necessarily classify it as Clarketech, though it is at the hazy edge of that category, especially as it is also difficult to chain the black hole magnetically to the ship and to make the emissions, mostly gamma rays, to leave the ship non-omnidirectional, as we have no gamma-reflective materials. In their absence you have to absorb those and re-emit it as heat at a lower frequency that existing materials could then reflect. For Hawking Radiation drives, bigger is not better, and again for a bigger ship you just add more black holes.
This is not the only way to use black holes as spaceship drives or to move ships. See also: Black Hole Ships, Clarketech, Photon Rocket. Helicon Double-Layer Thruster A type of Plasma Thruster, the Helicon Double Layer Thruster, or HDLT for short, excites its propellant to high velocity by using radio waves to break it down into a plasma. It is similar concept to the better-known VASIMR thruster, and is not subject to building up a charge and needing a neutralizer, as an ion drive is by default, nor does it have any moving parts or anything particularly susceptible to erosion for it to function, which makes it a low maintenance design as long as you have a power supply and remaining propellant. See also: Ion Drive, VASIMR Helios Drive The Helios Drive is a variation of the Shkadov Thruster that incorporates Starlifting Technology to move stars and can accelerate a star faster than a Shkadov Thruster but achieves a slower maximum velocity, because it uses accelerated plasma as the drive, lowering the stars mass in the process. By turning mirrors towards a star instead of reflecting its light in a single direction like the Shkadov Thruster does, we can cause a stream of hot matter to come off that star like a rocket flame.
This technique works well for moving dangerously large stars which might go supernova out of a region of space, as it takes far less time to get that star moving at interstellar speeds and also reduces the mass of that star, potentially extending its lifetime. A variation of this using Bussard Ramjets to fuse the plasma as it comes off that star to provide more thrust is called a Caplan Thruster. This technology can also be used to boost the surface temperature of a star, by statite mirrors over its polar regions such as a red dwarf, to produce a hotter star with a spectrum more like our own, for its equatorial region where the planets and space habitats might be at, and is known as Starboosting.
See our episodes: Starliftng and Fleet of Stars for more discussion. See also: Caplan Thruster, Shkadov Thruster, Statite Hyperspace Jump Engine or Hyperdrive Hyperspace drives are a blanket term for any number of FTL drives that operate by having a spaceship leave this Universe to enter into another congruent to our own, that allows for faster travel by either being smaller or having a higher speed of light. As a conceptual example, imagine you wanted to travel from The Western United States to the Eastern US, and could leap from the real world onto where you are on a map of Earth the size of a normal piece of paper in an atlas, and just step from where you were to where you want to be, as that map is congruent to the US, and teleport back to the real world, as opposed to walking the whole way.
Popular scifi examples of hyperspace would be Star Wars, Babylon 5, Event Horizon, Warhammer 40,000, and many more. It is more or less interchangeable with the terms subspace, superspace, overspace, underspace, or Nulspace, though these are different concepts in mathematics. While many modern cosmological models permit various possible hyperspaces or similar, we have yet to document any, nor a means to transfer between them or survive in such a hyperspace, and for this reason we would classify this as Clarketech. This topic is discussed in greater detail in our episodes: Cheating Reality, the Edge of the Universe, and Folding Space. See Also: Clarketech, FTL Drive Inertia Reduction Drive Inertia reduction works on the assumption that all objects have an inertia or momentum that must be conserved, and which is based on their speed and mass.
Specifically their inertial mass, which is seen as different from the mass which generates or interacts with gravity. Inertial mass is how much an object resists being shoved on, by something like a rocket attached to it. A ship which massed 100 tons, and was able to shift its inertial mass down to 10 tons while in flight, should be able to move like an object with the same momentum or kinetic energy but a tenth the mass, thus far faster. It would also do far less damage on a collision with an object, which means it would represent a safer form of space traffic.
So too, it could slow down very suddenly, like we often see spaceships in science fiction do, braking speed by rapidly restoring its true inertial mass or raising it even higher. Such Technology is generally considered Clarketech, and may violate conservation of momentum or energy. Inertia Reduction Technology may also imply access to Inertial Dampening Technology, such as we see in science fiction for explaining how ships can rapidly jump to high speeds or down from them without painting the ship's interior with the jellified remains of the crew, a feature we might also see with Gravitic Propulsion, which might be considered as a twin technology. See also: Clarketech, Field Propulsion, Gravitic Propulsion Ion Drive Ion Drives, also known as ion thrusters or ion engines, represent a large category of electric spaceship propulsion, generally any situation where ionized particles, being those with some electric charge, are accelerated in an electric or magnetic field powered by an electric supply. The ion is typically propelled out the back of the ship by the electric or magnetic field at a far higher speed than combustion of a rocket fuel allows.
They require an electricity supply which can be anything from batteries to radioisotope thermal generators, or RTGS, to onboard reactors, solar panels, or energy delivered by a laser or energy beam. These are typically low-thrust, high-efficiency engines which cannot be used for take off from a planet, but allow for much higher speeds, as they typically could operate for many hours or even weeks in comparison to a chemical rocket, which will usually run for mere minutes at most, but can provide a high enough thrust during that period to escape a planet. For this reason ion drives are a popular option for situations where power can be provided but haste is not needed, such as an interplanetary voyage or a satellite needing to counter minor orbital perturbations, or station-keeping.
There is no real limit on ion drive exhaust velocity, as fundamentally it is a particle accelerator, and those have achieved velocities as high as 0.999,999,999,988c, but they are likely to have practical limits on what is most effective. See also: Hall Effect Thruster, VASIMR Krasnikov Tube The Krasnikov Tube is an example of a Warp Drive for FTL travel, and like other warp drives relies on the existence of exotic matter not yet experimentally shown to exist in nature, and thus is classified as Clarketech. Under standard special relativity, a ship moving at near-light-speed will experience far less time on a journey than those outside it will have experienced. A ship moving at 99.5% of light speed will have only one day pass for every 10 experienced by those outside, and thus could travel to Epsilon Eridani, a star System 10 light years away, in roughly 10 years, but only experience one year on board the ship.
In simplified terms, S.V Krasnikov argues that in the wake of that ship is a tube that allows a shortcut through time, where someone could make that 10 light year journey in just one year. This allows a fast ship to make the journey as normal, but for someone to depart 9 years later in its wake and arrive at the destination when the ship does. This means a ship could depart in the year 2090 to Epsilon Eridani and a person could leave here in the year 2099 and both arrive at Epsilon Eridani in the year 2100. One should be able to keep a constant stream of ships to a given destination, say one departing the first day of each month, to provide a tube of constant FTL travel between two star systems. However, a two-tube system, one going each way to allow return trips, is generally considered to violate causality.
See also: Alcubierre Warp Drive, Clarktech, FTL Drive, Warp Drive Laser Sails A Laser Sail is very much like a solar sail, bouncing light or other EM radiation off a thin reflective sail to impart momentum and thrust on the ship the sail is connected to, except it allows us four options: First, to push on a spaceship by sending a concentrated supply of photons to be absorbed or bounce off the back, like a solar sail, only vastly more powerful and thus allowing a smaller sail to achieve the same thrust. Second, by concentrating a beam we can also keep it focused on the sail far from its origin source. Third, its origin source need not be a star, but can also be a power planet or relay station, such as a deep space comet converted into a fusion reactor and laser, allowing us to extend range indefinitely. And Fourth, it allows us to transfer energy to the ship, be it by solar panels absorbing a laser beam far from the Sun or giant rectennas absorbing microwaves. Depending on circumstances, a ship might take advantage of one or more of these options, even if it had another drive system and power plant. Transmitting energy to a spaceship allows us to run ship operations, but can also allow us to achieve higher thrust by using that energy to superheat a propellant or ionize it and fire it out the back as with an ion drive.
Doing this will usually sacrifice a higher final speed in favor of faster acceleration, though such technology can be employed in tandem with a matter beam to potentially refuel the ship's propellant. That propellant can also be used to fire forward, and thus slow the ship even though a beam is hitting it from the otherside, which is a good way of moving comets, by beaming energy to them from in-system that they use to vaporize ice as propellant to push back against the beam and bring them into a system. So too, if your destination system has a laser beaming array in place, it can slow a ship on arrival without fuel.
And we have discussed how to forward deploy these beamers to use them to slow each other on arrival in a new system to help a fleet slow down. Use of Laser Sails is heavily discussed in the show, particularly in our Episodes Exodus Fleet, Interstellar Laser Highways, and Interstellar Colonization Strategies, where we discuss using relay chains of them between star systems to allow cheap relativistic travel to near light speed. See also: Electric Solar Wind Sail, Magnetic Solar Wind Sail, Matter Beam, Solar Moth, Solar Sail Magnetic Solar Wind Sail A Magnetic Solar Wind Sail, also called a Winglee or just a Magsail, is very much like an Electric Solar Wind Sail, using the stream of ionized matter emitted from the Sun to drive it to speed, but can take advantage of superconductors, especially high temperature superconductors, to speed or slow or maneuver inside a star system by using the solar wind.
It should also be noted that the galaxy has many pockets of high speed ionized gas that might be ridden around the galaxy or out toward the rim, and that it may also be used for slowing from higher but still modest interstellar speeds by spiraling into a solar system. See also: Electric Solar Wind Sail, Solar Sail Magnetoplasmadynamic Thruster The Magnetoplasmadynamic Thruster, or MPDT, or MPD Arcjet, or Lorentz Force Accelerator, is another example of electric propulsion, but a potentially very high speed one compared to your basic ion drive or Resistojet. The MPDT is fed on ionized gas, with everything from hydrogen to neon, argon, or xenon being good but lithium having the best known performance to date. The acceleration chamber is acting on the principles of the Lorentz force or Electromagnetic force, as opposed to electrostatic or magnetic forces alone, and that is what is accelerating our plasma, and as with similar designs we have a lot of erosion of our cathodes. This combined with it being a power hog, needing hundreds of kilowatts to run efficiently, often make it of low interest for satellites and small probes.
That is no bar to usage for larger ships and manned interplanetary missions, however, and it is a popular candidate for those options, where you would expect to have lots of power and a crew able to do some maintenance. In theory a MPDT could achieve an exhaust velocity of over 100 kilometers per second, though just over half that is more common in tests, but that would be sufficient for interplanetary travel and at the lower edge of viable interstellar travel, as we discussed in our episode Crawlonizing the Galaxy. It also has a very high thrust compared to most other electric propulsion techniques, permitting not just a high final speed but an acceleration rate to it that is not superslow. See also: Arcjet, Ion Drive, Resistojet, VASIMR Matter Beam Matter Beaming is an example of how we can circumvent the rocket equation by accelerating matter at some stationary facility to push on a ship, much like a laser sail, but such matter beams in theory could also refuel a ship. A beam of oxygen could provide air to breathe and shove on a ship from behind, as a simple conceptual example. This is typically thought of as a stream of ionized atoms fired out of a long linear particle accelerator, and has the problem that they will tend to shove off each other being ionized and like particles of the same electric charge repelling each other, causing the beam to spread out too fast.
Numerous workarounds have been proposed, though it should be noted this could also include actual cargo pods rather than microscopic particles, as a ship might catch such a pod in its own net, a long decelerator, or a pod might be designed to vaporize near a ship so that its scattered atoms spread to push on the sail or pusher plate, and such a pod can have limited guidance and transmission packages on it. Regardless of focusing methods and their effectiveness, matter beams are far more useful than laser sails for pushing ships up to speed while they are moving up to or at interplanetary velocities. Matter beaming is a parallel concept to energy beaming, though there it is assumed we would be using photons and electromagnetic waves, and principally to transfer power, which we discuss more in the laser sails entry.
See also: Laser Sail, Magnetic Solar Wind Sail Medusa Drive The Medusa Drive is a variation of Pulsed Nuclear Drives that replaces the pusher plate behind the ship with the equivalent of a parachute in front of the ship. A large sail assembly connected to the ship by a very long tether is shoved forward by detonating nuclear bombs inside the sail, and much like the normal Orion Drive’s pusher plate, this shoves the sail forward, which then drags the ship along by the tether, rather than shoving the plate forward to push the ship from behind. This potentially lets you use nukes for leaving low orbit, as the detonation might be in safer higher orbits and drag the ship along. See Also: Nuclear Pulse Drive, Orion Drive Microwave Electrothermal Thruster Whether generated by an internal power source or beamed in as microwave energy beam, it is possible to use microwaves inside a spaceship much as we use them in our kitchens, to heat matter up. The Microwave Electrothermal Thruster or MET does this, and much like the arcjet rocket, igniting a plasma in a propellant gas. Electrothermal Thrusters all work on the concept of using electricity to heat the propellant, and as mentioned, this electricity might be supplied internally, by reactor, RTG, or battery, or by solar panels, or beamed in.
As electrothermal propulsion goes, the MET is usually considered superior to the Resistojet, due to its higher specific impulse, but inferior, or at best roughly equal, to the arcjet. Electrothermal thrusters in general are popular mostly for their simplicity as an electric propulsion system, as they are generally neither efficient nor high thrust, even for electric propulsion. One advantage they do have is fuel, as a MET can run using water as its propellant, which is super abundant throughout the cosmos. See also: Arcjet Rocket, Laser Sail, Resistojets, Solar Moth Negative Mass Propulsion Negative Mass Propulsion is a catch-all term for any drive that relies on the properties of negative mass, generally how it should warp space to expand around it, opposite of normal matter contracting space around it, or be pushed toward you if you shove on it.
As no negative mass has ever been detected, any negative mass technology currently qualifies as Clarketech, and this includes most warp drive and wormhole proposals. There are multiple versions of how negative mass should operate, depending on if it is negative inertial mass or gravitational mass, active or passive, or some combination thereof. In the most commonly discussed version it is generally assumed that positive mass will attract both positive and negative masses, and negative mass particles would repel both positive and negative masses. As a result, two positive mass particles pull toward each other, two negative mass particles repel each other, and a positive and negative mass particle will actually shove the positive mass away from the negative mass, while pulling the negative mass toward the positive mass, resulting in the positive mass particle being chased by the negative one. This is the basis of reactionless spaceship propulsion concepts like the diametric drive, and we discuss variations of negative matter in our episode Clarketech: Anti-Gravity See also: Alcubierre Warp Drive, Bias Drive, Clarketech, Diametric Drive, Pitch Drive, Warp Drive, Wormhole Drive. Neutrino Rocket Neutrinos are very low mass high speed particles that normally do not interact with regular matter, being more likely than not to pass through an entire planet without being absorbed.
If you could manipulate them they would be very handy as a rocket propellant, as they would not superheat air or structures around them or shake the ground, allowing for quieter propulsion. A Neutrino Rocket currently would qualify as Clarketech, as it would require technology that either allowed for the near total reflection or absorption of neutrinos or their production in a directed fashion. Such technology or materials generally imply the ability to have far more efficient fusion reactors. While a rocket beam made of neutrinos is useful for stealth purposes, as neutrinos are hard for us to detect,this probably only assists in stealth against lower-tech targets, as it might be assumed that anyone possessing this ability also has a very good neutrino detector too.
It would remain a valuable propellant for its low heat transfer rate to objects around it. It potentially would represent a Quiet Aliens technology for the Fermi Paradox as well, as the implied technologies of stealthy neutrino drives that emitted little heat or noise would also have advantages being used in other energy and industrial applications. See also: Clarktech, Photon Rocket. Nova Drive Nova Drives, along with their big brother, the supernova drive, are a method of moving dead stars such as white dwarfs, by delivering a stream of hydrogen to them to cause a small nova. This is a parallel technology to the Orion Drive, which propels a ship with nuclear bombs, only vastly bigger.
See our episode: Fleet of Stars, for more details. See Also: Helios Drive, Pulsed Nuclear Drive, Orion Drive Nuclear Electric Ion Drive A Nuclear Electric Ion Drive, also called a nuclear electric rocket, or nuclear electric propulsion, refers to any type of drive where a nuclear reactor, fission or fusion, is being used to generate heat to convert into electricity, which in turn is used for electric propulsion, such as an ion drive, where charged particles are accelerated by electrodes or electromagnets to serve as a high-speed propellant. This would apply to a ship that was running a nuclear reactor as its main way to heat the ship, run the lights, life support, and other equipment, and use excess power to run the ion drive propelling the ship.
As there is always some significant loss in converting energy at each step, as well as additional equipment to buy, carry, wear down, and maintain, many nuclear designs seek to circumvent the normal heat engine producing electricity for options like the Nuclear Light Bulb, Nuclear Thermal Propulsion, or Nuclear Pulse Approaches. See also: Ion Drive, Fusion Torch Drive, Nuclear Lightbulb, Nuclear Pulse Drive, Nuclear Thermal Propulsion Nuclear Lightbulb While a nuclear lightbulb drive might seem like a photon rocket at first glance, and indeed could be modified to act as one, the purpose of a nuclear lightbulb is to take a gas core fission reactor rocket, run it at roughly 22000 Kelvin, and give it a quartz wall, which is transparent to photon emissions at that temperature, which are mostly hard ultraviolet. Again, that light could be allowed to move out the back, making for a weak but reasonable photon rocket, since the power source is nuclear and energy dense. Instead though, we run it into a propellant that absorbs those ultraviolet photons and which we would expect to provide an exhaust velocity possibly as high as 30,000 meters per second, far better than our best chemical fuels and quite reasonable for interplanetary spacecraft. For details, see our episode: The Nuclear Option.
See also: Nuclear Electric Ion Drive, Nuclear Pulse Drive, Nuclear Thermal Propulsion, Photon Rocket Nuclear Pulse Drive The Nuclear Pulse Drive, also called external pulsed plasma propulsion, is best known for its Orion Drive variation, which uses nuclear bombs detonated behind the ship and pushing it to higher speed, relying on the vast amounts of energy proportional to mass that nuclear detonations have. These are not always large bombs or at a very high rate of explosion. Ideally we would like many very small nukes to detonate almost continuously, to produce the equivalent of a nuclear rocket flame, but generally, bombs are both cheaper and more efficient the bigger you make them, and we must resort to ultra-rare artificial elements or antimatter catalyzed fusion to contemplate very small nuclear explosions more equivalent to a typical bomb or even less than a hand grenade. Your basic design calls for a large and sturdy plate behind the ship, called the pusher plate, which can absorb or reflect the photons released by the blast, and this shoves it forward where it slams into a layer of immense springs, which slowly push the plate back into place to await the next detonation, while moving the ship forward at a more modest acceleration, translating the rapid shove of the plate into a protracted push on the ship.
The Medusa variation uses a forward
2023-04-04