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Xavier-Ryu, Ion, and Reaction Drives: Motive Technologies
The nature of interstellar warfare demands powerful drive systems. As in most other areas, the wilderzone features an eclectic variety of technologies to propel ships between stars.
Xavier-Ryu Warp Drive
The Xavier-Ryu gravity-warping drive is the primary method of transportation in the wilderzone. The X-R was humanity’s first “stardrive,” and has been used ever since the days of the Chase. These warp drives are powerful tools, but bulky and large. The smallest X-R drives mass about fifty metric tons, with mass and volume increasing geometrically with the amount of force the drive will be required to produce in sub-light mode. Modern X-R drives have three settings.
This was the original setting for the Xavier-Ryu drive, and allows faster than light travel in the absence of a jumpgate. The drive traps a pocket of normal space in a powerful bubble-shaped gravity field. The ship lies at rest in this pocket. The gravitational force created by an X-R drive in FTL mode is so strong that the bubble is essentially a pocket of non-Einsteinian space. This means that the pocket can be accelerated nearly instantly to velocities faster than light. The field harmonics of tribal X-R drives allow them to produce FTL velocities from 56c to 169c - that is, a maximum velocity of one parsec per week. It is important to note that an X-R drive can only produce a given range of velocities. It is impossible, for instance, for a tribal X-R to produce a velocity of twice light-speed. Doing so would rip the generator - and the ship along with it - to shreds.
FTL mode is only used between star systems, for several reasons. First, the enormously powerful gravitational bubble blinds all sensor systems and makes fire into and out of the bubble impossible. A ship under FTL drive has no connection with the outside world. While this effect has enormous tactical potential in theory, practically speaking it is more of a liability than an asset in combat. Interference between the X-R drive and the local star’s gravity well would blow the drive nanoseconds after activation in FTL mode, leaving the ship crippled and helpless. It becomes safe to use an X-R drive in FTL mode about forty light minutes from a system, depending on the mass of the local sun. While such “microjumps” are used occasionally as evasive maneuvers, tribal skippers generally consider the cost of destroying their ship’s primary mode of locomotion great enough that the microjump escape is used only as an absolute last resort. Moreover, FTL jumps only take place along straight lines - FTL navigation consists of dropping out of warp and re-entering along a different vector. A moderately skilled tactical officer can thus predict the terminus of a microjump fairly accurately; the maneuver is successful as an escape only if the enemy skipper is unwilling to subject his vessel to the same stress as the fleeing one.
A peculiar side effect of FTL travel with X-R drives is the so-called “FTL boom.” As a ship travels between stars its grav envelope encounters radiation and particles that get trapped on the surface of the bubble by the gravitational forces. When the ship drops its bubble and drops to sublight speeds, these cosmic rays and particles are released at light-speed along a cone centered on the path of the ship. This advance warning of a ship finishing an FTL journey is a serious tactical consideration, since the boom is quite distinctive and can easily ruin a clever skipper’s attempt to enter a system undetected. Astrogators generally try to end their FTL journeys on a vector that will direct the boom away from the areas of a system where enemy ships are expected to be, but it is of course impossible to predict where enemy vessels will be with absolute certainty.
This is the most common setting for X-R drives in the modern era. Miniature X-R drives only capable of sub-light settings are referred to as “grav drives” instead of “warp drives.” As Xavier and Ryu’s work was improved upon by successive generations of scientists, it became feasible to manufacture warp drives that could operate in a range of harmonics that allowed for sub-light travel.
In sublight mode the drive operates very similarly to a spinfusor. The drive produces a powerful gravity source along the desired axis of travel, accelerating the ship towards the source like an animal chasing a carrot attached to a rod tied to its back. The ship is continually “falling” in the desired direction. This means that X-R drives in sublight mode are essentially very powerful thrusters. X-R drives offer several advantages over conventional thrusters, however. Compared to reaction thrusters they are very fuel efficient, although not quite as efficient as ion thrusters. Unlike ion thrusters, however, X-R drives can produce their thrust at any angle. Finally, they are capable of producing far more raw force than either ion or reaction thrusters. Depending on the size, mass, and make of the drive, an X-R in sublight mode can produce accelerations of anywhere from 300 to 600 gees for a typical starship.
The amount of thrust a warp drive can produce in sub-light mode varies inversely with the square of the distance to local gravity wells. That is, the closer a ship gets to a planet or star, the less power its drive can provide without tearing itself apart due to interference with other gravity wells. By the time a ship is in orbit, its X-R drive is all but useless.
A jumpgate normally exists in space as a small aperture; large jumpgates have realspace apertures only a few microns across. This is far too small for a ship to pass through. Xavier-Ryu drives can be set to “pulse” a jumpgate with a powerful gravitic wave that opens the gate to a blazing disk up to hundreds of kilometers across. The gate will remain open for approximately ten minutes between pulses.
While this means that any warp-capable ship can enter a jumpgate, it is important to note that X-R drives in jump mode have severe limitations. First, the range of the warp drive in jump mode is very short. The most powerful tribal warp drives cannot open a gate at ranges longer than 100 kilometers. This means that careful timing of the warp drive is necessary if a jumpgate is to be entered at high velocity. Second, a warp drive in jump mode cannot select threads. The jumpgate may be opened, but any object passing through it will travel down the same thread as the last object. To change a jumpgate’s active thread requires a spindle array.
Spindle Arrays and Hyperweb Travel
Spindle arrays are not, strictly speaking, drive technologies. These long, finger-like projections from a ship’s hull are used to switch the active thread of a jumpgate. Spindle arrays are massive, bulky, and fragile. They are by far the most delicate part of a ship’s hull. Unfortunately, the arrays can be sheltered only so much, because they must physically enter the disk of an open jumpgate to accomplish their work. Retractable spindle arrays are possible, but rare. Spindle array size increases with the length of the thread they will be switching. Spindle arrays are expensive to manufacture even in small forms, so most tribes have a policy of creating spindle arrays capable of handling large threads; the marginal cost for increasing a spindle’s size is small compared to the initial cost of building a spindle in the first place. The standard benchmark is for a spindle array to be able to handle a thread of 20,000 light years - resulting in a spindle of about 400 meters in length. The size of each individual spindle can be reduced by adding more spindles to the array; a “standard” (20,000 LY) array requires 1600 meters of spindle, but if the array includes eight spindles each need only be 200 meters long. Because size is only loosely related to the expense of producing a spindle array, most arrays consist of four or less spindles. Having large numbers of spindles makes the most sense on warcraft, who naturally wish to minimize the size of these delicate components to shield them as much as possible from enemy fire.
For a spindle array to be active, it must be in free contact with the thread and within one hundred kilometers of the terminus. A ship can switch threads only during the first and last one hundred kilometers of its journey; this tactic is sometimes used by spindleships to avoid an ambush or evade pursuit. A spindle array that is retracted or folded against a hull will not work, because the hull is in contact with the array. The area of spindle that must contact the thread depends on the size of the thread - for a 20,000 light year thread, for instance, requires 1600 meters of spindle in unobstructed contact with the thread.
Technically speaking, a thread requires a certain area of spindle in contact with it. However, spindle arrays must be manufactured to exacting specifications; spindles are shaped like a trapezoidal prisms with a fixed relationship between dimensions. For this reason, thread requirements are given in length instead of area as a matter of course.
The mechanics of hyperweb travel are not thoroughly understood, since the method of the web’s manufacture remains a mystery. What is known is that a thread compresses the distance between two points into a much smaller distance. Thus a ship traveling a thread experiences a much smaller distance than the thread appears to span in normal space.
It is important to note that ships traveling a thread observe themselves as moving at sublight velocities. Maximum velocity in a thread for a ship is .8c, while electromagnetic waves can still move at lightspeed. This is why hypercast is a faster mode of communication than couriers - the radio waves simply move through the hyperweb faster. The time it takes for a ship to move through a thread, however, is relatively low, and given by Laschetecher’s First Law: time is equal to the “length” of the thread (that is, the distance between entrance and exit points in real time) divided by the square of the velocity of the ship in the thread. Thus, a ship traveling a 10,000 light-year thread at .8c will arrive at its destination in a mere twenty-two minutes. A radio message would arrive in eighteen.
Needless to say, most skippers feel that the faster a ship can move through a thread, the better. Skilled warp drive and spindle array crews, working as a team, can coordinate their efforts to pulse a jumpgate and select the proper thread moving at breakneck speeds. This maneuver is generally considered risky, however, since if the ship overshoots the jumpgate before it is fully opened, or the spindle array techs are a just a little slow in selecting the wrong thread, much valuable time can be lost as the ship turns around to correct its error. In a combat situation such bungled jumps can have disastrous consequences. Most skippers make hyperweb translations at much lower speeds because of this.
Unfortunately, ships without spindle arrays cannot accelerate inside a thread. That means that ships with X-R drives who make jumpgate translations travel the thread at the same speed they enter it - and that warp capable ships must either attempt a high-speed jump or settle for much longer transit times than a spindleship. Spindle arrays allow acceleration by Laschetecher’s Second Law: spindle acceleration is equal to the maximum acceleration of the ship’s warp drive in sub-light mode squared. It is important to note that Laschetecher’s laws describe the effects of jumpgate travel, rather than the actual mechanics. A ship capable of accelerating at 600 gees in normal space does not actually accelerate at 360,000 gees in a thread; that would override even Imperial acceleration compensators and turn the crew of a spindleship into unrecognizable goo from the gee forces. However, relative to an observer outside the thread, the ship behaves as if it is accelerating at 360,000 gees. This makes web capable ships much more convenient to use in jumpgate transits, since they can accelerate to the maximum thread velocity of .8c in mere minutes and travel the thread essentially instantaneously even if they enter it at close to a dead stop. The ability to vary one’s acceleration with a spindle array also allows warships to lay in wait in a thread, awaiting information from advance scouts before committing to exiting the thread.
Hazards of the Hyperweb
Though space travel is fraught with peril because of the sheer number of components aboard a starship, there are two dangers spindleship skippers must be especially wary of. The first of these are fluxstorms, energetic discharges that occasionally inhabit threads. The causes of fluxstorms are unknown, and little definitive research has been done on the phenomena because they are so dangerous. When a ship encounters a fluxstorm in a thread the results can be spectacular. The faster a ship is moving, the more havoc a fluxstorm tends to wreak - at best, a spindle or two may be blown; at worst, the ship can be ripped to shreds. If a craft is equipped with spindle arrays, it has limited steering capability within the confines of the thread. The average thread is a mere thousand kilometers in diameter, however, so it is not uncommon for fluxstorms to span the entire thread. If a ship cannot avoid a storm, it is best to pass through it at low velocity. Fluxstorms are another hazard that make stringers wary of using merely warp-capable ships in threads, since a ship without a spindle array cannot even slow down to avoid a fluxstorm.
The other hazard peculiar to the hyperweb is collisions. On the scale of space a thread is a very narrow tunnel, and spindleships tend to travel them at very high speeds. Usually collisions can be avoided, since most spindleships are civilian transports and travel threads at an agreed-upon standard velocity of .65c. If all traffic moving through a thread is moving at the same velocity the odds of a collision are very low, especially since spindleships can steer to avoid oncoming traffic. The odds of collision are slightly greater at the realspace termini of a thread, but since exiting ships must pulse a jumpgate to open a sufficiently wide exit point the traveling ship usually has plenty of warning that traffic is waiting to enter the gate. Because of Laschetecher’s Second and Third Laws, a web capable ship in a thread has far more maneuvering power than it would normally have. According to stringer custom, the onus for avoiding a collision is always on the ship exiting the thread rather than the ships waiting to enter the thread.
Ion thrusters (or “ion-grav drives”) are a hybrid technology similar to tribal battle armor jets. Thrust is accomplished by expelling heavy-element ions through a charged grating, and a gravitic inertial enhancer is used to amplify the thrust far beyond that of a pure ion drive. Sometimes a magnetic sail is added to further augment the drive’s effectiveness, essentially allowing the ship to surf its own drive.
Ion thrusters are by far the most fuel efficient drive system in the wilderzone, making them popular for use on fighters. They do not offer the maneuverability of a grav drive, since the thrust ports must be physically moved to alter the direction of thrust. To make up for this, most ships with ion drives mount secondary “maneuvering thrusters” at various angles and places along the ship’s hull. Ion maneuvering thrusters are also common with small and medium warcraft as station-keeping and maneuvering-thrusters. Delicate maneuvers like docking require a level of finesse that grav drives cannot provide close to a gravity well, so a secondary set of thrusters is necessary.
Unlike warp drives, ion thruster systems are small enough to be mounted on starfighters. They cannot produce the raw power of a warp drive, but because the ships they propel are usually much smaller than warp-capable vessels they are capable of producing higher accelerations. A typical ion thruster vessel is capable of anywhere from 450 to 800 gravities of acceleration.
Despite these impressive figures, a grav drive would be capable of even greater accelerations on a fighter-sized craft. The reason that most fighters mount ion drives instead of grav drives is related to the interference problems grav drives experience in the presence of gravity wells. The performance of an ion drive is degraded somewhat by the proximity of other gravity wells, but not by much. Since most fighters are designed to operate close to planets by astronomical distances, ion drives allow them to remain nimble when grav-drive ships have become sluggish and lumbering. Moreover, ion drives are cheaper than grav drives, which is always considered a plus from the standpoint of tribes’ fragile economies.
Reaction thrusters are the most primitive drives in the wilderzone, or indeed all of human-inhabited space. These systems are simply refined versions of rocket engines, which expel exhaust through a nozzle of some sort to produce thrust by equal and opposite reactions. They are extremely fuel inefficient, and far weaker than either ion or grav drives.
On very large warcraft reaction thrusters are sometimes used as maneuvering thrusters. Very large cruisers or transports require too much force from ion-grav systems to use those as maneuvering thrusters, since the size of the thrusters would render their gravitic inertial enhancers clumsy and imprecise in the presence of a nearby gravity well. This leaves reaction thrusters become the only viable alternative for such vessels. This makes very large craft particularly unwieldy as range to a planet or star decreases.
The only real benefit to reaction thrusters is that they are cheap. Purely atmospheric fighters can often get away with reaction thrusters and still claim a quite satisfactory 400 gees of acceleration, although they have very short legs at such high thrust settings. More often, reaction thrusters are used on missiles. The primary virtue of missiles as a propelled weapon is their low cost, so it makes sense to provide them with cheap reaction thrusters for steering purposes only.