Advanced Spaceship Drive Compendium

## Transcript

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.

### A

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 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.
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.
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.
### B

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.
### C

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 Rocket
Chemical Rocket 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.
### D

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
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
### E

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.
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.
### F

Field Propulsion
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 Drive
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.
### G

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.