Star Travel

Direct Drive

This is the simplest known method of interstellar travel: launch a self-contained capsule which accelerates from its origin, travels through space and eventually decelerates to its destination.

Even that simple explanation omits several significant steps. In its earliest stages, there was a brief period where human technology could only devise engines capable of reaching planets within a star system. That level of technology also allowed the launch of "generation" and "sleeper" ships which travelled through space for hundreds of years to reach other star systems, which might be only a few light-years away. Only fourteen of these were known to have been built, and of those only two succeeded. Most of the rest remain unaccounted for.

Such attempts were few because the technology was soon superceded; after a few generations of experience and improvements, engineers developed reliable high-impulse engines capable of accelerating ships at rates approximating normal gravity. These increased travel within the Terran Union and allowed for large-scale industrial development and greater exploitation of its resources. This in turn was important because the chief limit on using the new high-impulse spaceships was the amount of fuel they could carry; accelerating fast was of little advantage in reaching other stars unless one could sustain it for a long time. With ships that had both the engines and fuel to accelerate constantly between stars, travel time dropped from hundreds of years to a couple dozen. Not only that, the new ships could approach relativistic speeds.

For the first time in human history, it was practical for people to live long enough both to travel to other stars and return, through the combination of faster travel and suspended animation. Few did so, though, because of the difficulty of fueling a ship for the return voyage. The standard mode of travel was to build "colony" ships intended for a one-way voyage, which would be partly disassembled and used for materials at the other end, generally leaving some core parts of the ship in orbit. However, on several occasions ships arrived in systems where it was impractical to settle on-planet, forcing the colonists to build on moons or asteroids, and sometimes to live permanently on their ship and what other stations and ships they could construct.

That this was possible was due in large part to additional life support technology that had been developed along with the new starships. High-velocity direct-drive ships have a common problem; as they near the speed of light they are subject to increasingly destructive radiation from collisions between the ship and interstellar particles. Without protection this radiation would sterilize the ships before arrival. The ships protected themselves in part by travelling behind the great mass of fuel they carried, cutting radiation levels. However, they also made extensive use of biotechnology and simple nanotechnology to repair damage to their bodies and ship systems.

Further improvements in direct drive technology made it even easier and allowed for limited co-operation and commerce between systems, making the Terran Sphere possible. However, historically, direct drive travel was only found practical for distances on the order of 10 ly, and even at its height the Terran Sphere was thought to be only about 30 ly in radius, limited chiefly by the political difficulties inherent in managing such widespread territories.

C-tunnels

Black holes (more properly known as "collapsars") have been theorized since ancient times, and people have speculated on possible connections between them for just as long. The first real examples were found in the outer reaches of the Terran Sphere, not long before the Great War. Although their fine structure remains little understood even now, scientists studying them soon noticed that matter seemed to appear and disappear in the volumes of space around the collapsars. Probes were launched into these regions in great numbers to attempt to investigate and map them out. Most were simply destroyed but a few appeared at distant points in space and, to great surprise, their signals were received years later. Collapsar tunnels (c-tunnels for short) had been discovered.

Soon after, manned starships followed the probes. In the early days of c-tunnel travel the losses were horrific and interstellar colonization attempts were little better than suicide. With time the method was improved and the risks cut, until at the peak of c-tunnel technology the death rate per transit was estimated to be between 0.1 and 5 percent. (Exact statistics are hard to estimate since this period coincided with the Great War and many such transits were made under fire.)

With the technology tamed for all practical purposes, human civilization changed shape. Although c-tunnels made it possible to travel long distances between stars, they in no way solved the supply problems inherent in direct-drive travel. Ships which arrived at a c-tunnel would be out of fuel and, after making their transit, would be unable to carry on without acquiring new stocks of fuel somehow. To satisfy this need, c-tunnel systems became settlement zones themselves, serving no other purpose than as industrial bases to supply ships (and later, military bases to ward off Crucian attacks).

Much of the benefit of c-tunnels came not from their direct use but from the technology developed to exploit them. Collapsars provided the first practical laboratories for studying higher-order "n-forces", and one of the few solid results of these early studies was the discovery of crude ways to harness them. Our understanding of such forces at the time was probably comparable to the level at which humans understood electricity when they first learned to harness fire but, as with fire, it nevertheless had considerable practical benefits. Even our simple level of understanding let us make simple gravity-control devices and a new form of direct-drive engine which exploited vacuum energy. This sped up direct-drive travel greatly, as well as making it practical to transit c-tunnels.

C-tunnels are still used for travel, in a few areas not connected by any charted spacefold. Although in theory they could connect any point in the universe (or possibly another universe) in practice most extend distances less than a few hundred light years. C-tunnels are known to often be bundled together so that a collapsar with a connecting tunnel is often close to another collapsar with a tunnel that connects in the reverse direction. A common misunderstanding is that c-tunnels are "wormholes" which connect black holes to each other or to some sort of "white hole". This is not true; c-tunnel travel in fact does not involve entering the collapsar at all.

Spacefold Drive

Much like the case with collapsars, theories of higher-order "n-spaces" have been known since ancient times. The discovery of C-tunnels led research in a new direction, though, by conclusively disproving the physical principle of locality. This forced us to rebuild theoretical physics, working largely beyond the realm of possible experiments - an exceptionally difficult task. Scientists across the Human Federation worked on the problem for thousands of years, making little progress until finally an experimental collaboration on Safe Harbour produced definitive experimental results confirming one of the myriad theories which had been proposed (or, more accurately, disproving its competitors). C-tunnel travel was put in its proper place as a special case of a much broader phenomenon, in which space warped upon itself in higher dimensions that could occasionally be traversed with the use of n-forces operating in those dimensions. The collapsars provided these "tears" in space naturally, but the Safe Harbour group were the first to do so artificially.

The practical implications of this discovery are universally known; Magnus Freyr backed further research into this new theory with all his family's considerable resources, eventually succeeding with the development of the spacefold drive — which allowed humans to win the Great War and propelled Freyr on to become the first emperor.

Although our knowledge of n-space and n-forces is still limited even now, practical progress at exploiting it has been made. Spacefolds of size large enough to be useful are known never to be found in volumes of space with significant mass (excepting the special case of collapsars). They are regions of space rather than exact points, and the likelihood of their potential existence can be predicted, but with only limited certainty, so surveying them remains a difficult and uncertain task. To traverse a spacefold, a starship must be travelling within a narrow cone of velocities. Spacefolds can in theory connect any two points in the universe, but there are particular "resonant" distances at which they are known to be far more likely. We also know that the longer-reaching spacefolds require a narrower range of velocities for transit. Scientists maintain an ongoing debate as to whether some potential spacefolds simply do not exist, or whether they all connect somewhere but we have not yet found the correct velocity to unlock them.

No spacefold has ever been found to link to more than one other spacefold but there are many examples of two different spacefolds found close to each other. Starhub is the best-known example of a star system with more than one spacefold, hosting 17 known folds, although there are other systems known to have more. The longest known distance connected by a space fold is the traversal from Starhub to Springboard, a distance of some thirty-one thousand light years. It is often theorized that the Imperial Navy knows of longer folds but keeps them secret, and occasional leaks have forced them to admit to the previously-disclaimed existence of spacefolds with particular strategic value.

Other methods?

Our current understanding of n-space theory leaves open an infinite range of possibilities by which we might better exploit n-space. One popular approach is to examine if it might be possible to transit n-space not only at points where space folds upon itself, but between points where it is [i]close[/i] (in n-distance) to itself. However, research into the field has continually failed to produce results.

Perhaps the greatest possibility of all comes from the Disappearance. Although its mechanisms are unknown, the most common theory is that the disappeared travelled somewhere else by unknown means. If true, this would be by far the most efficient form of star travel ever discovered.