Star Drives
Interplanetary travel is not only possible, but practical, given technology that we already know how to build. Interstellar travel is a very different matter.
The fundamental problem faced by anyone planning interstellar travel is Einstein's theory of relativity. Einstein's model of the physical universe – one of the most successful scientific theories of all time – assumes that the speed of light is an absolute limit (see Relativity Effects). All objects with mass must travel at lower speeds, unable to accelerate to lightspeed no matter how much energy they apply. This means that starships will always take years to travel even between neighboring stars.
Ever since it became obvious that there are no other habitable worlds (or alien civilizations) within our own solar system, science fiction writers have turned to other stars as settings for adventure. This almost demands that the heroes of the story to have some method for traveling faster than light! Thus, many writers who are otherwise quite rigorous with their scientific content have invented some form of "FTL" travel.
Scientific speculation and science fiction have considered a bewildering variety of FTL drives. All of them should be considered superscience, although a few might have some justification in cutting-edge physics. Most science-fiction universes only permit one form of FTL, although a few use multiple forms, each with its own advantages and problems. Some of the most common forms are as follows.
Hyperdrive
Einstein's model applies to the physical universe that we live in. But what if there’s another universe where different laws apply, a universe that can be reached from ours? A starship could drop into that "hyperspace," travel there according to its own laws, and then shift back into our own universe at a new location – reaching its destination much faster than Einstein would normally allow.
When thinking about a hyperdrive for a space setting, some of the things to consider are:
How fast is the drive? Does a starship take weeks or months to travel through hyperspace between two stars? Or does the trip take a fraction of a second? The GM will want to consider how quickly a ship can cross known space.
How quickly can the drive be used? This is important for dramatic reasons – if a hyperdrive can be used quickly and easily, a starship can always escape from trouble. Perhaps the drive requires a great deal of energy to make the shift into hyperspace, requiring long periods of charging the ship's engines from its power plant. Perhaps planning a trip through hyperspace requires a lot of computer power and time. Or perhaps hyperspace needs to "relax" after the stress of being crossed, ensuring that a new hyperspace transition can't be made too quickly after emerging into normal space.
How finely can the drive be controlled? Unless a hyperdrive ship can choose any point of emergence it wants, it will still need a maneuver drive to reach nearby planets or engage in space battles. Maybe hyperdrives can't be used within a certain distance of a large mass, requiring a starship to travel out to "flat space" before entering hyperspace.
What is hyperspace like? Perhaps ships in hyperspace are cut off from verything, including each other and the normal universe. A trip through hyperspace would be a good time to do shipboard maintenance, and have locked-room adventures in which none of the characters can get away from each other. Perhaps ships in hyperspace can communicate with each other or with planetary facilities. Or perhaps hyperspace is a real place, with its own geography and even its own natives – ships can explore it using special sensors, hover or change directions in hyperspace, or even fight battles there!
Can a ship in hyperspace be detected? If a ship can't interact with the normal universe, then nothing in normal space can detect them until they emerge. That means that battle "lines" won't exist in a universe with hyperspace – invasion fleets won't be detected until they emerge, already close to their targets. On the other hand, if special sensors can reach into hyperspace, invaders will be detected in advance, and can possibly be met in hyperspace itself.
What happens if the hyperdrive fails? If a ship in hyperspace is damaged, does it return to its starting point? Does it drop back into normal space at an unpredictable point? Or is it stranded in hyperspace until the drives can be repaired? This can be particularly critical if ships can fight battles in hyperspace...
Hypersails
What if hyperspace is like an ocean, with energy currents (and reefs, and storms) on which a starship can ride? Such a starship might need hypersails – more likely to be energy fields rather than physical sails – to take advantage of the ether's flow. David Weber's "Honor Harrington" novels use this model for hyperspace, deliberately mimicking the flavor of sea-adventure fiction set in the Napoleonic era.
Tachyon Drive
Physics predicts the existence of tachyons, fundamental particles that can't travel at less than the speed of light. A tachyon drive turns the starship into a beam of tachyons that then hurtles across space. A ship that is converted into tachyons might require a receiving station to restore it to its original condition.
Jump Drive
It's not possible for a physical object to accelerate to speeds faster than that of light. But what if it's posible for a ship to move from point A to point B in space, without accelerating and without crossing the space in between? A jump drive permits a starship to teleport from one location to another, usually in no more than a tiny fraction of a second. The ship never leaves the normal universe or enters any form of hyperspace.
Some of the things to consider when choosing a jump drive include:
Where can the drive be used? Many jump drives can only be used at "jump points," specific locations in space. Jump points may occur naturally, they may be relics of a prior civilization, or it may be necessary to build them in order to use FTL travel. If jump points are necessary, they may be located far away from planets or other interesting places, requiring long trips through normal space to reach them. A jump drive that can be used anywhere can be a plot-breaking convenience, making travel or escape too easy for drama.
If there are jump points, how are they arranged? Perhaps a starship can jump to any number of different places, so long as it starts at a jump point. If a starship jumps to a region of space with no jump points, it may be stranded! Or possibly jump points are always connected in pairs, so that when a ship triggers its drive at one end, it always moves to the other end. Paired jump points can create a network of "jumplines" in known space, in which the real distances between stars are less important than the convenience of their jump-point links. Stars without jump points are inaccessible, while jumplines without stars at each end are not useful. Stars with several jump points become important crossroads, even if they don't have habitable or useful planets.
How are jump points created? If jump points are a natural phenomenon, or were built by a prior civilization, then starships will need to search for them – and the first trip through one will be a major voyage of discovery! If a jump point must be created with special equipment, then that equipment might be located on a stationary facility, a stargate that can send starships to their destination without itself moving.
How is the jump drive triggered? Does it simply take the application of energy? Or does it require the use of special computer programs, psionic powers, or other rare items? Those who control the ability to trigger a jump will control interstellar travel!
What happens if a jump fails? A jump ship may be stranded if it appears in a place without jump points, or if some jumplines are only one-way. Perhaps planning a jump requires a great deal of computation, and bad aim can send a ship anywhere.
Do jump points only cross space, or do they permit time travel? Some jumpdrive schemes permit travel through time as well as space. Starships can visit the distant past or the distant future of the universe. A ship that curves back through time can end up changing its own past, or dropping into an alternate universe where events turned out differently. Jump navigation errors can be even more dangerous in such a setting...
Wormhole or Keyhole Drive
Wormhole-based drives are effectively jump drives, in which the "jump points" are artificial. Wormholes are predicted by modern physics; they are "tunnels" through space that connect distant points. Some quantum-mechanical models of space claim that tiny wormholes are constantly appearing and disappearing at the smallest scales. With a great deal of power, it might be possible to catch a wormhole that would connect to a desired destination, and then force it to open widely enough to accommodate a starship.
Current theory suggests that wormholes are likely to collapse catastrophically when an object tries to enter them. It might take a great deal of power to hold one open. Perhaps a stargate installation is needed at one or both ends, both to create and to hold open a wormhole. In this case, a starship doesn't need any special drives at all – it can use a maneuver drive to reach and then pass through the wormhole.
Alternatively, a starship may have the equipment and power needed to find, expand, and hold open a wormhole as needed. Such a "keyhole drive" is likely to be very expensive and dangerous. If the wormhole collapses while the ship is in transit, the result is likely to be catastrophic destruction! Some serious suggestions have been made for manufacturing and using wormholes, falling into the realm of fairly rigorous SF. One proposal requires each end to be held open by a ring of superdense matter, massing about as much as the solar system, and spinning at nearly the speed of light. These requirements would seem to be beyond any but the most powerful and advanced civilizations – but perhaps as-yet-unknown science will find shortcuts that make the idea feasible.
Probability Drive
This variant on the jump drive relies on the inherent uncertainty of quantum mechanics. Even an object as massive as a starship can be treated as a quantum-level entity, its location and velocity uncertain. When the probability drive is engaged, the ship is no longer likely to be at its origin point, and instead becomes very likely to be located at the destination...
The drive may be controlled by psionic talents, using the "observer effect" of quantum physics to trigger the drive. Probability drives in fiction tend to be very dangerous, especially since they can't always be controlled. A ship suffering a drive mishap may end up anywhere, nowhere, or everywhere at once...
Interstellar Teleport Gates
If teleportation is available (see Teleporters) and has interplanetary or interstellar range, then it can be used to move people and cargo through space.
The details of the teleportation system have a profound effect on the flavor of the setting. If teleportation requires massive facilities, and can't be used near a star or world, then it becomes a stargate system and spaceships are still necessary. Cheaper and more flexible teleportation makes spaceships less likely. At its extreme, teleportation "portals" can be part of everyday life – a single house can have rooms on different planets!
Warp Drive
Another way to get around Einstein is to warp the geometry of normal space, so that two points that are usually vast distances apart are (at least temporarily) much closer together. A ship can then move from origin to destination through normal space, and still reach the destination without ever approaching the speed of light. In practice, this means that the starship surrounds itself with some kind of energy field that lets it move at FTL speeds with respect to unwarped space. If the drive malfunctions, the ship loses its FTL speed, but it keeps the normal-space velocity it had before the warp drive was activated.
When choosing a warp drive for a space setting, some of the things to consider are:
How fast is the drive? As with a hyperdrive, the GM should consider how long it will take a warp drive ship to make a typical journey between stars.
Where can the drive be used? Perhaps a warp drive can only reach FTL speeds in deep space; close to a world or other large mass, the warp drive drops to STL speeds or stops working altogether. Perhaps the ship must accelerate to close to lightspeed using normal-space drives before engaging the warp engines. Or possibly the warp drive is dangerous to use except in uncrowded space. A warp drive ship that can't use its drive close to a planet or star will need a maneuver drive as well.
How well can a warp drive ship interact with normal space? Some varistions on the warp drive permit full interaction: sensors can scan nearby space, ships can maneuver at will, and battles can be fought in warp. Other variations (including at least one proposed in real-world physics) call for the ship in warp to be almost completely cut off from the rest of the universe. Such a warp drive means that the ship can't see out of its warp bubble, can't steer, and may not even be able to turn off the drive without aid! A warp drive like this may be much like a hyperdrive that permits sensor in normal space to detect the moving ship, but in which the ship is otherwise out of contact until it leaves the warp state.
Inertialess Drive
This variation on the warp drive was first invented by E. E. "Doc" Smith. A device negates the inertia of the ship's matter, thereby abolishing Newton's laws of motion. The ship's speed is now limited only by the strength of its maneuver drive and the friction of the medium it's flying through. Ships are highly streamlined in order to reduce friction. In a planet's atmosphere, the ship is extremely fast. In the high vacuum of interstellar space, speeds many times that of light are possible (assuming, of course, that an inertialess ship isn't subject to Einstein's laws either).
The ship can instantly stop or change direction, "turning on a dime" in the manner some UFOs reportedly can. Inertialess ships are also immune to collision or explosion damage; a collision stops the ship dead at the point of impact, and an explosion simply bats the ship aside like a piece of thistledown.
In reality, there's no reason to believe that an inertialess object could break Einstein's laws. An inertialess object may be equivalent to a massless object, required to move at exactly the speed of light like other objects with no rest mass.
Blink-Warp Drive
This variation on the hyperdrive or jump drive permits a starship to make instantaneous leaps, but only over relatively short distances. To cross interstellar space, the ship makes a lot of jumps very quickly. The effect is like a warp drive, in that the ship remains in normal space, may be detectable at a distance, and may be able to interact with other normal-space objects.
If blink-warping is possible, a ship's ability to interact with other ships may depend on its ability to synchronize its "blinking." A ship wanting to attack another may have to struggle to coordinate jumps – if the two ships aren’t in phase, a normal-space weapon fired by one will always miss the other by microseconds in either direction! This may be a situation in which human intuition and guesswork are as powerful as computer prediction, giving human pilots a chance to be effective.
Space Highways
Some real-world science suggests that warp drives may actually be possible, although the power requirements would be extremely high. One proposal suggests that specific paths through space could be treated to permit FTL travel. While staying on this "space highway," a ship can move at FTL speeds in the normal universe; the drawback is that it can't reverse course or leave the highway until it reaches its destination. A space-highway system is rather like a jumpline system, in which the ships take measurable time to complete each jump.
Ships on a highway may or may not be able to detect one another or to interact. If a highway is very narrow, then the probability of collision may be high enough to worry about...
Designing a Stardrive
Once the GM has chosen a general type for his FTL drive, he can customize it with a variety of options. These decisions are important; they provide much of the campaign's flavor.
Drive Reliability
Decide how much attention the drives need. They may be so reliable that a yacht owner only needs to order a checkup every few years. Or they may be so finicky that a specialist has to roll against Engineer (Starships) at -4 after every use just to get them working again! Decide what skills are needed to maintain the FTL drive in good condition, how often the skill rolls are needed, and how difficult the task of maintenance normally is.
FTL Astrogation
Decide how difficult it is to control the FTL drive. It may be as simple as "point the ship and turn on the engines." Or astrogators may need high levels of Navigation (Hyperspace) skill and lots of computer power. Astrogators might also need unusual advantages - psionic powers, special mental abilities, or access to a rare and addictive drug. Decide what skills are needed, what modifiers might apply to skill in different circumstances, and any special abilities astrogators will need.
Drive Speed
Decide how fast the drive will go. This will depend on how large a region the campaign covers, and how fast you want the ships to get where they're going.
Hyperdrives and warp drives can be given a speed in parsecs per day (or hour, or second, or some other convenient unit). For hyperdrives, there may also be a limit to the time or distance a ship can travel in hyperspace without emerging into normal space. Each separate trip is called a "skip," and the ship must wait a GM-set time between skips. For instance, if the maximum skip is one parsec, and the skip is almost instantaneous, but the ship must wait a day before making another skip, then the effective speed is one parsec per day.
For jump drives, "speed" depends entirely on how far a ship usually needs to travel to reach a chosen jump point. The important factors are the endurance of the drive (how often a ship can jump, with respect to refueling or maintenance) and normal-space time from one jump exit to the destination world or the next jump entrance.
The scale of the campaign setting is determined by the assumptions the GM wishes to make about his campaign map. See Mapping the Galaxy for some suggestions.
Comparative Speed
Starships may have different speeds, especially when using hyperdrives or warp drives. Alternatively, a ship always moves at the same speed, and the drive simply either is or is not powerful enough to boost the ship's mass into an FTL state. With jump drives, the instantaneous jump is likely to be the same for every ship, although some ships may have better maneuver drives than others.
Maximum Range
How far can a ship go at a time? Ships that have to refuel often, or that need lengthy calculations before entering FTL travel, may have limits on the distance they can go before needing more fuel or new computations. Decide what limits may exist on a ship's range. If ships can travel long distances in FTL, then interstellar borders become harder to defend – especially if ships are undetectable while in hyperspace or in some other FTL state! If ships can travel only short distances without a stop, or if jump points are required and are easy to defend, then interstellar borders become possible.
Fuel Consumption
If an FTL drive makes use of some consumable material, then ships will need to stop and restock from time to time. Even a ship whose FTL drives run on internal power may need fuel to run the power plant. Or the drive may need some unusual material to work: a rare crystal, expensive transuranic elements, or antimatter. In general, if fuel is expensive or rare, then exploration and travel will focus on fuel sources. Ships that refuel often will need to stop frequently, and may be dependent on civilized ports to travel far. Ships that are fuel-efficient, or can scavenge fuel as they travel, will be able to travel longer distances without stopping. The availability of fuel will help control how cheap and commonplace interstellar travel will be.
Side Effects
Any FTL drive may have undesirable side effects. These can be an interesting balancing factor in a setting with multiple FTL drives; the faster drive may be more unpleasant or more risky. These effects may vary from one civilization to the next – some races may make excellent space navigators, or use certain drives that no one else can use.
Mechanical effects: The use of an FTL drive may affect mechanical devices, plaguing engineers. Perhaps the activation of the star drive is equivalent to violent maneuvers in normal space, forcing equipment and people to be secured to avoid damage. More subtly, FTL travel may cause certain devices (electronics, computers, even astrogational equipment) to fail or to function unreliably.
Physical effects: FTL may do harm to living creatures on board a starship! Perhaps everyone must roll vs. HT when the ship enters FTL (or at intervals while it is in FTL) to avoid nausea and spacesickness. Crew and passengers may suffer pain or disorientation, taking a penalty to DX or IQ. Or they may suffer illness or death in FTL, requiring that they take drugs or go into suspended animation!
Mental effects: Crew and passengers may suffer psychic distress, delusions or manic impulses that require medication or suspended animation to avoid. If psionics exist, FTL travel may interfere with their use (or may boost psionic talents). Or possibly FTL travel is psychically pleasurable, inviting an Addiction among frequent passengers or navigators! If drugs are required to navigate FTL space or to avoid physical harm, this may represent addiction to those drugs instead.
What happens when a starship goes off-course? STL starships, and those using a warp drive, are unlikely to get lost since they can always see where they are going. Jump drive and hyperdrive ships can go wildly off course, especially if a power plant or stardrive malfunctions in mid-journey.
In general, an astrogator should roll against the appropriate Navigation specialty, modified as the GM sees fit to reflect the difficulty of interstellar astrogation. A hurriedly set course, relative to the time usually required, gives a penalty to the roll (according to Time Spent). A successful roll means that there was no error. The consequences of a failure depend on its magnitude.
The GM should custom-build his own failure table, appropriate for the drive he has designed. Players should not be allowed to see this table, although they may know what the general results of a minor error will be. If the penalties for miscalculating are low, then starships escaping from danger will always use quick-and-dirty computations. As consequences become more severe, "snap astrogation" becomes more of an emergency measure.
Some possibilities include:
Nothing happens: Literally. If your calculations are wrong, you use up a lot of energy – and go nowhere. This is especially appropriate for jump drives.
Off-position: This is more appropriate for hyperdrives than for jump drives. Deviation from the intended destination depends on the amount by which the skill roll was missed, and may be minor (AUs) or major (parsecs). A ship might go in the correct direction but the wrong distance, or it could go the correct distance in the wrong direction. Lost: The ship is sent to a wholly unexpected location – the worse the roll, the more lost it is. The actual destination may be a reasonable number of parsecs from the departure or destination point, or it might be random on a galactic or intergalactic scale. Astronomy or Navigation rolls will be required just to figure out where the ship is.
Time-Lost: Along with one of the previous results, the ship also moves a random distance forward or backward in time. Small time-movements are an interesting nuisance. Big ones can be catastrophic, and may be appropriate only if the GM is ready to start a new campaign. If ships can become "time-lost" predictably, the GM may find himself running a time-travel campaign.
Damage: The ship (or the drive) takes a certain amount of damage. For example, the drive may burn out, or the ship may lose a percentage of total hit points.
Total Disaster: The ship is destroyed, or thrown into another universe with no possibility of return. Not a good result for play balance, although as a final consequence for very stupid escape plans it may have some merit.