Future technologies

GUT DRIVES

Art (c) Julian De Puma.
Zero Point RocketsTech Level: 21
Inertia DrivesTech Level: 23
GUT stands for Grand Unification Theory. GUT drives have had many different incarnations and names, including vacuum energy engines, casimir drives, zero-point propulsion, and more. GUT drives of one form or another have appeared in a variety of science fiction sources, such as the novel The Songs of Distant Earth by Arthur C. Clarke, many "Xeelee" stories by Stephen Baxter, many "Known Space" stories by Larry Niven, and in driving the ships of the ancient, alien Vorlon and Shadow races in the Babylon 5 TV series.
The search for a Grand Unification Theory has been the holy grail of physics for nearly a century now, a single, eloquent series of equations that would tie together quantum physics and the theories of relativity. It would explain once and for all the origin and behavior of the four fundamental forces of nature (gravity, electrmagnetism, the strong nuclear force, and the weak nuclear force) as well as a number of loose quantum phenomena, most significantly virtual particles and zero-point energy. GUT is also assumed to be a precursor for some other speculative propulsion technologies, such as gravitic propulsion schemes and FTL drives, but those will be discussed in their own sections.
The real life physics that form the basis for the speculation about these propulsion schemes is very involved and not for the uninitiated. The summaries below are very simplified versions. See the "Related Information" section below for references that can much more fully explain the quantum physics involved.
GUT drives rest on the startling fact that a vacuum is not empty--it is actually seething with virtual particles and quantum fluctuations. The particles "borrow" energy from the vacuum via Heisenberg’s Uncertainty Principle and pop into existence in particle/antiparticle pairs. They survive for a few brief microseconds or less, and then annihilate each other again, returning the energy they "borrowed" to the fabric of spacetime. Because the energy is always returned, the net energy of a vacuum is zero, and thus to us appears empty.
The existence of this virtual particle soup and zero-point energy has been confirmed by experimental evidence, as the amount of attraction registered on two closely-suspended electrically charged metal plates, when all other factors were neutralized or accounted for. This force is called the Casimir Effect.
ZERO POINT ROCKETS
Tech Level: 21
GUT drives assume that a way can be found to take advantage of the virtual particle effect for propulsion. As the zero-point vacuum fluctuations are happening in every square centimeter of the universe, a ship that can tap into it would have an essentially endless supply of energy it can use for thrust. It is theorized that black holes can strip away one half of the particle/antiparticle pair before they annihilate and return to the vacuum, so it may be possible to use very powerful artificial gravity fields, or even a captured signularity, to do the same in a GUT drive. Another proposal was to use a supply of neutronium on board a ship to supply the gravitic fields necessary for zero-point energy acquisition.
The energy harnessed from the vacuum can be used in one of several ways. The charged vacuum-derived particles can be accelerated and expelled out a nozzle directly for thrust, very similar to a Beam-Core AntiMatter Rocket. Or, more simply, they can be used to superheat a reactive fluid such as hydrogen, which is in turn expelled for thrust. The particles, if antimatter, can also be used to catalyze fusion reactions.
As the zero-point rocket has an essentially endless supply of energy, it can theoretically accelerate to near lightspeed. How fast it can do so and how much thrust would be available to it would depend on how much energy the drive can liberate from the vacuum at any one time.
INERTIA DRIVES
Tech Level: 23
Inertia drives are often referred to as reactionless thrusters. They’ve been seen in Larry Niven’s "Known Space" stories, and a reactionless engine was seen driving the Rama craft in the novelRendezvous with Rama by Arthur C. Clarke.
Inertial drives reduce or eliminate inertia altogether on some or part of the spacecraft. The idea has been around for a number of decades now, but only with the discovery of quantum fluctuations in vacuum that they have come to be considered more than pure fantasy.
The quantum fluctuations are thought to cause minute planck-scale "ripples" in the fabric of space/time. It has been theorized that the cumulative effect of these ripples all over the volume of an object is what causes inertia, the resistance material objects exert to changes in their state of motion. Inertial drives neutralize or lessen these ripples over some or all of the craft.
If inertia is eliminated or reduced over the entire ship, the craft is accelerated by more mundane means. However, with no or little inertia, it takes far less fuel and engine power to move the vessel at a certain rate of acceleration than it would otherwise.
Inertia can also be eliminated over every part of the ship but the aft, whereupon the ship can use the quantum ripples to propel the ship forward. By shifting the inertial field over the ship’s mass, the vessel can maneuver. Exactly how fast a ship can move by using this method is a matter of some debate. One would think that the thrust provided would be very small, but with nearly all inertia eliminated over the rest of the ship it may be substantially more. Also, if a means exists to eliminate the quantum ripples over an area of space, a means to enhance that effect may also be developed, providing more potential thrusting power.
There’s also the question to what happens inside a ship when all the inertia is reduced or eliminated. Much of our mechanical technology depends certain values of inertia; changing inertia may have to necessitate a serious re-engineering of many systems to keep the ship viable and running. Reduction of inertia would also have disastrous effects on living organisms (what happens, for example, to your blood pumped by your heart if it suddenly loses its inertia and rips through your arteries at hundreds of miles an hour or more?) and unknown effect on electronics as we currently design them. Whether these effects could be mitigated by an inertia drive is unknown. It may be possible to reduce the quantum ripples affecting just the outer hull of the ship, but the ripples would still be affecting the interior volume of the ship, so the effectiveness of a such a technique would seem to be limited at best.

TELEPORT DRIVES
End Teleport Drive
Tech Level: 18
Open Teleport Drive
Tech Level: 19
Teleport Drive Planet Cracker
Tech Level: 20
Stutterwarp
Tech Level: 20
Teleportation was one of the great dreams of science fiction; an incredibly neat idea that once seemed to have little real scientific basis. Recent experiments with quantum teleportation in laboratories has shown this may not be the case, however. Wholesale teleportation of objects larger than an atom still seem extremely unlikely at this point, but cannot be ruled out.
Cheap and easy teleportation would have a number of profound effects on human civilization. Among other things, it would make for a means of space travel, depending exactly on how the technology worked.
The matter-to-energy-and-back-to-matter transfer seen in Star Trek wouldn’t work as a drive; there’s the issue of signal degradation that would almost certainly occur over repeated jumps. It wouldn’t be too fun to have only three-quarters of your original molecules show up at the destination point. The same goes with quantum teleportation currently being investigated in the real world; it is limited to the speed of information exchange, and it isn’t really teleporting the orginal; its destroying the original in order to make an exact quantum copy of it ion the other end.
Instead, the type of teleportation most useful to space travelers would perhaps be based on a well known real-life phenomenon: quantum tunneling, also called the tunnel-diode effect. Thanks to a quirk in the way quantum physics works, it’s entirely possible for a particle to disappear in one spot and appear in another almost instantaneously. Its important to understand that the particle doesn’t actually "go" anywhere in between; it simply fades from existence in one position and fades back to existence in another, as if the universe is using it as a variable in a strange kind of existential bookkeeping. This has been seen in the lab many times, and the effect has been integrated into modern electronic components,
including some of the integrated circuits in the computer you're using to read these words.
Teleportation systems in science fiction have also contemplated "shunting" a mass through a parallel continuum where space and distance have very different meanings than they do here. This continuum might be a level of hyperspace, subspace, a pocket universe, or a parallel dimension of some sort. The mass shunted may precipitate naturally back into our own continuum at its destination, or it may need to be "retrieved" by a teleport system receiver station.
Teleport systems come in two broad types: open and closed. Open systems require only a transmitter, while a closed system requires both a transmitter and receiver. Each gives birth to different types of space drives.
END TELEPORT DRIVE
Tech Level: 18
Closed systems can be used to create an end-teleport drive.
First proposed by Larry Niven in an essay over two decades ago, this consists of a ship with a transmitter built into its aft and a receiver built into its bow. This drive assumes teleportation is near-instantaneous; both transmitter and receiver execute their functions at almost the exact same instant in time. The ship is built in such a way that everything within it, including the teleport machinery and the receiver, is built over the transmitter. When activated, the transmitter teleports the ship to the receiver, which performs its function in the split-second before it too is teleported along with the rest of the vessel. The craft is therefore teleported exactly one ship-length. By doing this over and over, the vessel can fly through space. By cycling through teleports very quickly, on the order of dozens or hundred of times per second, the ship can match the velocity of most other sublight drives.
It is important to remember that it only seems to accelerate that fast. The craft isn’t accelerating at all; its popping up at one point after another without actually moving in a conventional sense. Its momentum can therefore be independent of its direction of travel. For example, the ship can be constantly accelerating using a rocket motor in a direction opposite the one its end-teleport drive is taking it. Once the ship arrives at its destination, it shuts its teleport drive off and shoots back into the direction from which it came, using all the velocity it independently built up while in FTL flight.
OPEN TELEPORT DRIVE
Tech Level: 19
An open teleport drive is similar to the end-teleport drive, but it doesn’t need a receiver in order to work. It simply jumps itself and the surrounding ship to a pre-determined spot. Its range is rather limited, usually somewhere between a few hundred meters and a few kilometers. However, like its cousin, cycling through teleports at many times per second allows it to achieve impressive sublight speeds.
A lot of the characteristics of the end-teleport drive is shared by an open teleport drive with one major difference. An end-teleport drive can only send a ship in one direction: straight ahead. In order to maneuver, it needs to turn off the drive for a few seconds while reorienting itself using conventional sublight thrusters. An open drive has no such limitation. The drive can send the ship anywhere within its range, regardless of direction, with a single jump. Its drive can send it in one direction at apparent translight speed with one jump, then, in a split second, change direction at any angle with no loss of apparent velocity. It can even completely reverse direction instantly.
Needless to say, ships with open teleport drives would be maneuverable on a level most other drives could never match, and might be near impossible to hit in combat.
TELEPORT DRIVE PLANET CRACKER
Tech Level: 20
Teleport drives can be used to build fearsome, planet-cracking weapons. Build a teleport drive around a solid mass, say a small asteroid weighing several hundred tons. Position the weight above a planet so it will fall into the atmosphere, and set the drive to teleport it back into its original position once it falls one teleport-length. The dead weight would constantly fall, as gravity would constantly be affecting it, but wouldn’t move in position. When it achieves the desired velocity, the teleport drive is turned off and the weight shoots at the planet with its new, very deadly speed. After only a few hours of accelerating and teleporting, it would have enough kinetic energy built up to wipe out a county with its impact; after a few days, a medium-sized state. If the attacker were to eventually let it accelerate up to near-light-speed (this could take well over six months) he could blow the entire planet surface to rubble. However, this weapon would need a very rugged and advanced drive system in order to handle the vast kinetic energies constantly being cycled through it.
STUTTERWARP
Tech Level: 20
If an open teleport drive could be made to cycle through its jumps very quickly, say millions of times per second, it could seemingly move faster than a beam of light. Again, its important to note that its not really accelerating in a conventional sense, just teleporting from spot to spot, so by beating a beam of light to its target the ship does not in principle violate general relativity.
This particular kind of open teleport drive is called a Stutterwarp. It was a primary feature in GDW’s late, great hard science fiction RPG 2300 AD. The designers of that game built several limitations into the Stutterwarp, but it should be noted that these were somewhat arbitrary for dramatic and game balance reasons. In the game, the drive wouldn’t work anywhere close to a gravitational mass like a planet or star, and it could only go 7.7 light years before the drive built up a charge of radiation that would be lethal to the crew. In order to discharge the radiation, the ship had to spend a few days in a gravity well, where, of course, the drive couldn’t work, forcing the ship to depend on more conventional sulight drives for maneuvering.
A stutterwarp, if ever made to work, may not have any such limitations, and could prove to be one of the most astoundingly versatile means of getting around interstellar space.

INTERSTELLAR FLIGHT

GENERATION SHIPS

The generation ship Ark, from the 70's TV series The Starlost.
O’Neil-Style Generation ShipTech Level: 13
Hollowed Asteroid Generation ShipTech Level: 14
Converted Moon Generation ShipTech Level: 16
Converted Planet Generation ShipTech Level: 20
Mobile Megastructure Generation ShipTech level: 25
Generation ships are also called space arks or world ships.
The idea of a generation ship has been around since the golden age of science fiction, and has seen many an incarnation down through the decades. The two most famous examples are the short story, "Orphans of the Sky" by Robert Heinlein and the original Star Trek episode, "For the World is Hollow and I Have Touched the Sky." The cheesy 1970s series "The Starlost" was set on board a generation, ship, and a generation ship that used time dilation to reduce a five million year journey into a mere subjective 1000 years was seen in the novel "Ring" by Stephen Baxter. The very first Science Fiction RPG, "Metamorphosis Alpha," was also set aboard a gigantic space ark. "Rendezvous with Rama", by Arthur C. Clarke, features an interstellar craft built very similarly to the vision of an O’Neil-style generation ship.
A generation ship is one of several "low C" options for exploring interstellar space. Low C options assume that achieving significant fractions of lightspeed are impossible or highly impractical for one reason or another, and astronauts must resign themselves to interstellar voyages of centuries or even millennia.
A generation ship is the most straightforward means of dealing with century-long journeys from one star system to the next. The ship is a miniature, self-sustaining world in and of itself, much like an O’Neil colony, and the crew of the ship will live out their natural lifetimes on board, working, playing, building, breeding, etc. Their children and grandchildren and so on will be brought up on board ship as it coasts between the stars, and become the operating crew in their turn.
Generations ships are usually touted as a type of interstellar ship that could be built today, but the truth is many significant advances would still have to be made in propulsion, recycling, and artificial habitat technology to make them possible. The most efficient rocket engine now available to us is the ion drive, and even using a vast array of such devices, it would still take over 10,000 years to reach even the nearby stars. Building an enormously complex, completely autonomous habitat with a self-renewing ecology that could last even a fraction of that time is beyond our current understanding. As structures such as arcologies and space colonies are built and perfected this may change, but for now even this "simple" means of interstellar travel is beyond our means.
Nuclear Pulse Drives, Fusion Rockets, Plasma Rockets and simple Antimatter Rockets could reduce travel time from many millennia to a "mere" few centuries, making a generation ship much more feasible. However, any one of these propulsion options are still decades away.
Extremely efficient resource management would be absolutely essential to the success of a generation ship. Recycling systems would have to work at nearly 100% efficiency to ensure that the ship and its human population will survive the many decades needed to reach its destination. The generation ship could also pick up additional resources by mining comets or asteroids that may be along its way with subcraft, or the world where the ship was launched may have sent unmanned resupply ships ahead of the main spacecraft. The ship would have to rendezvous with these resupply craft en route in the depths of interstellar space.
One of the perils of generation ships that has served as the gristle for a great many science fiction stories is that human societies are dynamic, not static, and the culture on board a generation ship is bound to change in the decades or centuries the vessel will be en route. Sometimes, in these stories, the society which starts the voyage will be torn down in a revolution and something wholly other has taken its place by the time the ship reaches its destination. Democratic societies are replaced by ruthless dictatorships, or carefully engineered but rigid social structures are ripped apart by an unknown element such as a disaster or unacceptable thoughts and ideas. Or, in the most cliched type of societal breakdown aboard a generation ship, the population somehow loses its high-tech knowledge and forgets that it is on a vehicle. It comes to view the ship as the entire universe as generations go by.
These scenarios may not seem very likely, but they do underscore the necessity of taking into account the inevitable changing tides in a human society over the long period of time the ship will be en route. One way of dealing with this may be to start the ship with only a small seed population confined to one small area of the space ark’s artificial habitat, which will then grow and "settle" the rest of the ship’s living space as the decades or centuries go by. This way, all the extra space can serve as a "safety valve" for relieving societal stress by giving disgruntled sections of the culture places they can claim as their own. This can only work as long as there is fallow habitat to settle, but if planned properly the ship should reach its destination long before the population runs out of new living space.
The exact minimum crew needed at the start of a voyage is a matter of some debate. The fewer inhabitants in the beginning, the fewer resources they will consume and the slower the population will grow throughout the voyage. However, if you have too few people, the crew risks inbreeding problems that are sure to arise in succeeding generations. Numbers as large as 10,000 and as small as 25 have all been proposed depending on different sociological and biological assumptions. However, a compromise range of several hundred to a thousand or so initial individuals would probably be a good median strategy.

O’NEIL STYLE GENERATION SHIP
Tech Level: 13 The interior of Rama, an O'Neil-Style generation ship. From the novel Rendezvous With Rama, by Arthur C. Clarke.

This is basically a gigantic rotating cylinder or disk, very similar to the vision of an O’Neil colony, with an interstellar propulsion system attached. The cylinder may be from several hundred meters to several hundred kilometers in diameter, and rotated on its long axis to provide artificial gravity along its inner surface. The interior is sculpted and pressurized to provide an Earth-like environment, complete with forests, hills, streams, lakes, and so on. The inner environment is usually envisioned as being large enough to generate its own weather, supplemented and/or controlled by the ship’s systems. On an orbiting O’Neil colony, light is provided by gimbaled mirrors and enormous transparent sections of the hull. On an interstellar generation ship, illumination would have to be provided by large strips or nodes of lighting equipment recessed into the inner surface.
An O’Neil style generation ship could ultimately hold from 10,000 to several hundred thousand inhabitants, depending on its exact size and design.
HOLLOWED ASTEROID GENERATION SHIP
Tech Level: 14
A hollowed asteroid generation ship basically converts an entire asteroid a mile or more in size into an interstellar craft. The center is hollowed out into either a spherical or cylindrical chamber, and the asteroid itself is set spinning to provide artificial gravity along its inner surface. Usually the inner habitat takes up only a small fraction of the overall volume of the asteroid. However, these are more difficult to build, as gigatons of rock would have to be extracted from the center of the asteroid in addition to building the habitat and drive system.
The hollowed asteroid scheme has two advantages over the O’Neil style space arks. First and foremost, the inner habitat is protected by a thick shell of rock that, depending on the original size of the asteroid, could be kilometers thick. If the ship is expected to pass through hazardous conditions--such as areas of possible meteoroid impact or high radiation--such armor could prove very fortuitous. Secondly, the rock shell can provide megatons additional mineral resources the crew can mine during the long voyage, readily adding to whatever stores they may have packed along at the beginning. A hollowed asteroid generation ship is featured in the novel Eon, by Greg Bear.
A variation on the hollowed asteroid is the hollowed comet. This functions very similarly to an asteroid space ark, except that the outer shell would be comprised of water and methane ice. This could prove advantageous as the crew will have a readily available source of gigatons of water and hydrogen to use for consumables. A variation of the hollowed-comet ship was contemplated in the novel, Heart of the Comet by David Brin and Gregory Benford.
CONVERTED MOON GENERATION SHIP
Tech Level: 16
This is basically the Hollowed Asteroid scheme scaled up enormously to include objects 50 miles or more in diameter. In this case, a gas giant moon is broken out of its orbit from its primary and converted into an enormous generation ship. Larger asteroids such as Vesta or Ceres can also be considered for use, as can large Kuiper Belt objects such as Chiron.
Depending on its exact size and whether it can generate sufficient gravity naturally, the moon may or may not be hollowed out and spun to create an artificial environment. Instead its surface and interior may be interwoven with many interconnected bases and habitats. Like with the converted asteroid, the inhabitants can harvest an enormous amount of mineral resources en route from the interior of the moon.
Propulsion for such an enormous object can be accomplished by several means. Nuclear explosives can be detonated in succession in one hemisphere, the crater they create becoming a sort of crude "nozzle" that can help direct succeeding blasts. The nuclear demolitions would have to carefully calibrated to "nudge" the moon with doing minimal damage to its infrastructure as a whole.
An alternative is a large array of mass drivers, which would continually fling small portions of mass gathered from the moon itself. These would provide only a very gentle nudge for acceleration, but it can build up over time, and the moon has a lot of mass it can work with. Fusion, fission, or simple antimatter rockets could also be used in large numbers, if the moon has enough of the appropriate fuel available.
CONVERTED PLANET GENERATION SHIP
Tech Level: 20
Perhaps the most desirable form of generation ship, this scheme contemplates moving an entire habitable, life-bearing planet from one solar system to the next. Propulsion by necessity would have to be some advanced form of artificial gravity technology, to avoid undo stress on the planet’s fragile surface structure and biosystem. Orbiting electromagnetic radiators would provide heat and warmth.
In the Ringworld novels, an alien race called the Puppeteers moved their homeworld plus four "support" planets via this method to escape from a galactic core explosion.

MOBILE MEGASTRUCTURE GENERATION SHIP
Tech Level: 25 The Magog Worldship, an intergalactic generation ship, from the TV series Andromeda. (c)Tribune Entertainment

Perhaps the ultimate space ark, a megastructure such as a Mech Planet, Ringworld, Dyson Sphere, or Godwheel, can be made mobile by some unfathomably advanced means and sent on a journey across the interstellar depths. These "ships" would give the initial seed population of the ship near-unlimited room to grow and expand en route. While the other types of generation ships discussed in this section would be optimized for voyages of several centuries or millennia, a megastructure ship could conceivably hold enough resources to remain en route for far, far longer.
In the novel Wall Around A Star, by Frederick Pohl and Jack Williamson, a Dyson Sphere was used as a generation ship by an alien race to cross not interstellar but intergalactic distances to settle the Milky Way galaxy, a journey that took them over a million years. On the syndicated TV seriesAndromeda, an alien race called the Magog also used a dyson sphere-like structure to cross intergalactic distances.

SLEEPER SHIPS

The Botany Bay, a sleeper ship from the Star Trek episode "Space Seed." Image (c) Paramount.
Sleeper ShipTech Level: 14
Sleeper ships are a viable means of interplanetary travel, but they are most commonly associated with star ships. Sleeper ships have been seen or mentioned in many science fiction sources, including the original Star Trek episode "Space Seed," the original Planet of the Apes movie, theAlien movies, the early 90’s TV series Earth 2, the novel A Deepness in the Sky by Vernor Vinge, in "Known Space" stories by Larry Niven, and many others.
A sleeper ship is a "low C" option of interstellar travel. Low C (C standing for the speed of light) options assume that obtaining significant fractions of light speed are either impossible or highly impractical, and astronauts must consign themselves to voyages of centuries or millennia.
Basically, the crew of the ship spends most of the many decades in transit in suspended animation, where they age very slowly or not at all. Their physical condition is monitored by computer and they will eventually be awakened at their destination by automated ship’s systems. Exact methods for suspended animation will be discussed in a future article, but include techniques such as cryonics, chemically induced hibernation, fluid replacement, cryogenic suspension, nanotech restructuring, or combinations thereof. The length of a voyage may not be limited by the technology of the stardrive but by how long the human crew can safely remain in suspended animation without risking permanent medical complications.
Sleeper ships are usually associated with low C drive technologies, such as fission rockets, fusion rockets, simple antimatter rockets, and simple lightsails. However, they can be used with just about any form of interplanetary or interstellar propulsion, as the suspended animation process is assumed to consume less shipboard resources than an active human being who will need a constant supply of air, water, food, and other consumables. A good example of this is the ships of the Alienmovies, which use suspended animation as a matter of course despite the presence of FTL drives. Suspended animation may also be used as a "cheap" means of interstellar passage on more sophisticated ships, as per the Traveller universe, where a "Low Passage" in cryogenic suspension is the cheapest means of buying transport on the FTL ships that travel between star systems. Another option is the sleeper ship "lifeboat"--if a larger, more advanced starship runs into trouble deep in the vast voids between the stars, small sleeper ship subcraft can serve as a means of getting the crew to a habitable system despite the vast distances involved.
Depending on circumstances, it may not be wise to have the entire crew in suspended animation for the entire voyage. Individual crewmembers may have to be awakened for rotating ‘watches’ while the rest of the crew sleeps so they can monitor sysetsm and do routine maintenance. For example, on a ten year voyage with a crew of twenty, two crewmembers at a time would spend a year awake to tend to the ship. On very long voyages of centuries or more, the ship would have to run on automatic for most of the time, with the crew being only occasionally awakened for brief periods for routine maintenance or emergencies.

SEED SHIPS

The Terraforming Seed Ship Titan, from the movie Titan A.E. Image (c) Twentieth Century Fox.
Colonizing Seed ShipTech Level: 15
Terraforming Seed ShipTech Level: 18
Seed ships are an intriguing idea for colonizing interstellar space that depends heavily on extremely advanced and reliable artificial intelligence and robotics. It occasionally pops up in various science fiction sources. The novel The Songs of Distant Earth by Arthur C. Clarke, the animated movie Titan A.E., and the "Scorched Earth" episode of the TV series Stargate: SG-1, all used seed ships as major plot points.
Seed ships are a "Low C" option of colonizing interstellar space. "Low C" options assume achieving significant fractions of lightspeed are impossible or highly impractical, and interstellar explorers must resign themselves to voyages of centuries or millennia.
COLONIZING SEED SHIP
Tech Level: 15
No known technique can yet freeze a human being and bring him back to life. However, it is now a decades-old tried and true technology to freeze human zygotes (fertilized ova) for long periods of time, then thaw them and bring them to full term. Since it assumed no human could survive the centuries-long trips between the stars, seed ships are fully automated. When they reach their destination after many deacdes in transit, the ship lands, and the vessel’s mainframe oversees the thawing and bringing to term human zygotes via artificial wombs. When the ship-born children come to term, robots take over rearing them, educating and training them to become the seed population of a new human colony.
Usually this "first round" of humans, from a handful to several dozen in number, is then used to awaken and raise several hundred more humans from the ship’s biological stores. These then form the first human community on planet, which then expands in the usual manner in succeeding generations.
Actually, the most difficult part of creating a seed ship mission wouldn’t be the stardrive or plotting an interstellar trajectory or anything so mundane, but in creating artificial intelligences and robots that could handle and raise human children without causing any undue psychological or physiological damage to their charges. The mission designers would no doubt try to make the parental units and computers as human-like as possible, with true androids being used by advanced enough societies.
An alternative to child-rearing robots would be to keep the children in a total virtual reality environment from birth to maturity, as per the movie The Matrix, with tissue growth, bone density, and muscle tone maintained through electrodynamic stimulation or nanotech restructuring. Within the VR environment, they experience a perfectly normal childhood, then are given "transitional" scenarios that allows them to psychologically ease into their waking lives on an alien planet.
If technology such as memory printing is available, it could also be possible to clone and quick-grow individuals as a seed population, then imprint them with the memories and skills of specialists recorded back on the homeworld.
Besides human zygotes, the ship could also carry frozen genetic material of livestock, crops, and other useful lifeforms.
TERRAFORMING SEED SHIPS
Tech Level: 18
Both Titan A.E. and the "Scorched Earth" episode of Stargate: SG-1 used this type of seed ship.
The Colonizing Seed Ship assumes that the ship will be sent to a previously known planet where the conditions to support its colonists already exist. However, the Terraforming Seed Ship is created with the ability to transform a planet (or, in Titan A.E.’s case, a loose planet-sized mass of ice asteroids) to fit the requirements of its colonists. By necessity, it needs to be much bigger, much more powerful, and much more advanced that its Colonizing cousin.
Besides the zygotes of the colonists, the seed ship would also need to carry the genetic material of all the plants, animals, and microorganisms that will form the ecology of the terraformed planet. It would also have to be smart enough to set up that delicately-balanced ecology while avoiding the many pitfalls that can plague such an undertaking.
Terraforming an entire planet can prove be a long, arduous, and resource-consuming process, one that could take many centuries or millennia. A terraforming seed ship, therefore, would have to be built as tough and as long-enduring as the most rugged generation ship, as it may be a very, very long time running on automatic, between its centuries-long journey and centuries or more terraforming a planet or planet-sized mass.
Once a habitable environment is established, the ship gestates its human crew and raises them as per a colonizing seed ship, above.

STEPPING STONE COLONIZATION

The relative sizes of the solar system, the Kuiper Belt, and the Oort Cloud.
Stepping Stone ColonizationTech Level: 14
This is not so much a particular technology as it is a strategy for using low-C options to eventually colonize other star systems. A low-C option assumes that achieving significant fractions of the speed of light are either impossible or highly impractical, forcing astronauts to resign themselves to voyages of many decades, centuries, or more.
Stepping Stone strategy is mentioned in a number of science fiction sources, such as the novelsHeart of the Comet by David Brin and Gregory Benford, The Gripping Hand by Larry Niven and Jerry Pournelle, and Permanence by Karl Schroeder, but to the best of my knowledge no one has yet done a serious technical study of it.
In most scenarios of interstellar colonization, immense ships of one design or another leave one life-bearing world in the inner system of a star, fly through the void, then brake around another life-bearing world in the inner system of another star. The old assumption was that the outer reaches of a star system, being cold, lifeless, and only sparsely populated with material resources, wasn’t worth the bother.
However, discoveries in the past decade has shown that the outer reaches of a star system may reach much farther, and contain much more in it, than previously thought.
First of all, there’s the Kuiper Belt, which extends from the orbit of Neptune to at least 50 AUs (about 7 billion kilometers) out from the sun in more or less the same orbital plane as the planets. It is estimated that at least 70,000 cometary objects with diameters larger than 100 kilometers exist in this Belt, all primordial remnants from the accretion disk that originally formed the solar system. Pluto, its moon Charon, and a large object near Saturn’s orbit called Chiron are all thought to be unusually large Kuiper Belt objects.
There’s also the Oort Cloud, an even larger and more widely dispersed collection of cometary objects that forms a rough sphere around the solar system, starting roughly from where the Kuiper Belt ends. Comprised of an estimated trillion significantly sized objects, the Oort Cloud is thought to extend to at least 50,000 AUs from the sun, though some estimates put the outer boundary at 2 light years or more. The total mass of all the comets in the cloud are thought to exceed 40 times the mass of Earth, though individual objects may be tens of millions of kilometers apart.
Rogue planets, worlds either ejected from their home star systems or ones that formed along side stars in interstellar nurseries but were never bound to them, are now thought to be far more numerous than previously thought. As are Brown Dwarves, objects too big to be a planet but too small to ignite into a star, which have masses between 15 and 80 times that of Jupiter. Both types of objects are now considered to be more numerous than mainstream stars, and litter the vast interstellar depths.
The Sun itself is thought by some astronomers to have a distant near-interstellar companion that may either be a rogue planet or a brown dwarf. Named Nemesis, it is theorized to have an orbital period measured in the millions of years, periodically sweeping through the Oort Cloud to send comets raining into the inner system, causing mass extinctions such as the one that wiped out the dinosaurs.
The Stepping Stone strategy for colonization takes advantage of all these various objects to very slowly build a ‘step ladder’ out of one solar system and into another. Using both passive astronomical techniques and powerful active radar arrays, most of the major objects in the Kuiper Belt, Oort Cloud, and nearby interstellar space are found and their orbits plotted. One first builds bases and/or colonies on the outer planets to use for building and refueling outbound ships using fission, fusion, antimatter or simple lightsail drives. Then one moves into the Kuiper Belt, mining the objects there for fuel and hollowing out larger comets to use for bases and colonies. One repeats the process once again for the Oort Cloud, then again for any significant objects that may exist in interstellar space.
Once a human presence is established on an interstellar brown dwarf or rogue planet or lonely comet, the process is reversed in a nearby system, moving inward from the interstellar way station to the new system’s Oort Cloud, then to its Kuiper Belt, to its outer planets, and finally to its inner system. If a conveniently-placed interstellar object is absent, a comet can be towed or boosted into place or built up using cyclers.
Needless to say, this is an extremely gradual, multi-generational process. In fact, some think it may not even be done intentionally. As humanity moves out into the solar system, the inner worlds may fill up within a millennium, forcing some elements of its population ever outward looking for new resources and living space.
In all three novels where this concept is mentioned, the people who colonize the worldlets beyond the outer planets end up creating a civilization wholly different and apart from that of their inner system forebears. Sometimes the inner and outer system civilizations maintain contact and relations, and sometimes they don’t. Even when the inner system worlds develop more powerful and faster starships to get them from star to star, the outer system peoples may be content to stick with their slow but inexorable means of colonizing the spaces between.

SELF-REPLICATING PROBES
Self-Replicating Interstellar ProbesTech Level: 15
Self-Replicating Interstellar Nano ProbesTech Level: 19
Self-replicating probes are also sometimes called von Neumann probes or von Neumann machines after the famed mathematician who first created the concept.
Self-replicating probes are usually regarded as a "Low C" option of exploring interstellar space. Low C options assume that achieving significant fractions of lightspeed are impossible or highly impractical, forcing voyages between the stars to take centuries or millennia.
SELF-REPLICATING INTERSTELLAR PROBE
Tech Level: 15
In essence, self replicating probes work as follows: A fully-automated probe with a sophisticated AI is launched toward a nearby star. When it enters that star system decades or centuries later, it exhaustively surveys what lies there. It transmits what it learns back to its homeworld. It then uses the material resources of the star system present in asteroids, comets, moons, and/or planets to construct replicas of itself, which it sends to other nearby star systems to repeat the process. They would be in essence miniature flying factories, designed to use advanced robotic systems to mine and process ore, harvest raw materials, fabricate individual components, and assemble all the varied parts into a whole probe. Depending on the complexity of the probe and the sophistication of the robotic systems involved, the process to produce a single daughter probe can vary from a few days to several years.
The original probe may stay in the system or continue on, depending on its mission parameters. If it stays, it may act as a communication relay between its "children" and its homeworld, or it may begin processing the system’s resources for anticipated follow-up colonization ships from the homeworld, or it may launch said resources back to its point of origin for its building race’s material needs.
Using this method and assuming an average crusing speed of the probes at a few percentage points of light speed, some postulate that the entirety of the Milky Way galaxy could be charted and explored in less than a few million years. More advanced propulsion technology can considerably cut this time.
While self-replicators are ostensibly connected with exploration, they can be used for other purposes, as many science fiction writers have demonstrated in their stories. In the novels Life Probe and Procyon’s Promise by Michael McCollum, an advanced alien race sends out probes to specifically contact other sentient species, to trade all their scientific and cultural knowledge for the secret of a possible FTL drive. In The Ring of Charon and The Shattered Sphere by Roger McBride Allen, probes were sent out armed with wormhole technology to hijack entire worlds for their material and organic resources. And in the most famous example in sci-fi, the many Berserkerstories by Fred Saberhagen, the self-replicators were created to be the ultimate weapon, an ever-growing and adaptable weapon system programmed to seek out and exterminate all organic life it encountered.
Self-replicating probes in many ways resemble living organisms; they consume resources, produce waste, reproduce, and spread out to fill a specific niche. In fact, some would say the distinction is arbitary, and that they would, quite by accident, also inherent the one other distinctive trait of living creatures: evolution.
Small errors in the replication of daughter probes are bound to occur every once in a while; in many ways, these can be considered analogous to mutations. Like mutations in living creatures, most mutations in replicators would be non-viable, and either of no consequence or would reseult in the destruction of the probe. However, every once in a great while, a bit error will carry over into the next generation of daughter probes, who will in turn pass that on to their offspring, and so on. After many millions of years of this, the probes drift away from their original manifestation. Some may just drift into extinction, some may become nothing more than feral organisms focused purely on surviving and reproducing, and some may develop ideas and purposes far beyond what they were originally programmed to do. In fact, in The Ring of Charon and The Shattered Sphere, this is exactly what happened to the Charonians, which started out as Voyager-style exploration probes and ended up after millions of years as immense dyson sphere intelligences who had completely forgotten their origins and treated human-level sentients as microbes.
Both the Charonians and the Berzerkers represent the all-too-easy-to-achieve Frankenstein-like aspect of this scheme. Self-replicating probes can all too easily overwhelm any organic species of lesser technology, and become the dominant form of life, artificial or otherwise, in the galaxy. Though the purposes of the building species may have been benign, their self-replicating probes could, after eons of reproducing and evolution, become a danger without equal to any organic civilization in the galaxy.
In the novels Forge of God and Anvil of Stars, by Greg Bear, the star-faring species of the galaxy consider self-replicating probes to be a menace without equal and formed a very loose alliance called the Law, whose purpose was to hunt down and destroy not only any self-replicating probes it finds but also to punish their building species with extinction.
One method that can be used to avoid the potential explosion of evolved self-replicators is to use a programmed limitation to the number of generations the probes can go through. A dozen or so generations (resulting in a total of a few thousand probes) would be enough to explore a local interstellar neighboorhood without incurring any serious statistical risk of replicator evolution.
SELF-REPLICATING INTERSTELLAR NANO PROBES
Tech Level: 18
I’ve encountered this idea primarily through the novel Assemblers of Infinity by Kevin J. Anderson. Instead of a single, large, factory-like macroscopic probe, the building race instead shoots out many millions of microscopic nanites (nanotech robots) in the direction of a nearby star system. The majority of these probes will most likely be lost, passing through the system without encountering any physical body, or falling into the star or gas giants and meeting their destruction.
However, the trajectories of a small fraction will intersect solid bodies such as moons, planets, and asteroids. The nanites, of course, would be built in such a way as to withstand high-speed impacts with material bodies. After landing, the nanites begin replicating themselves, and when enough of them are present they begin construction of larger-scale structures to complete whatever task their builders meant for them to do at the target system. When this is done, they assemble a nanite launcher to shoot their daughter units at a nearby star system to repeat the process.
The power and versatility of a nanotech-based mineral extraction and fabrication process can be near-unlimited, allowing the nanoprobes to accomplish tasks that are generally considered to be beyond macroscopic probes. In Assemblers of Infinity, for example, the nanite assemblers that had landed on the Moon completed not only a macroscopic launch facility to signal its building race but by the novel’s end had recreated their creators biologically by building them up molecule by molecule.