Interstellar Travel

> "What is the very backbone of a civilisation? Laws? Money? An army? Roads. Before laws and armies, and after food, a society cannot exist without connections. Spacetime compression drives, simply put, have done for space travel what combustion engines do for sea travel."
>
> To the Stars: In Building the Future With Epiphanies of the Past.

When travelling between planets, stars, or even galaxies, the distances involved are vast, vast enough that light itself can spend years, centuries and even millennia crossing the void. And so for a timely journey, speeds must be equally colossal. To accelerate a ship to near light-speed and then to decelerate it again would necessarily require a huge quantity of energy, and render even the tiniest speck of dust an extreme collision hazard.

Travelling between the worlds and stars of the galaxy, however, has been conquered by many various civilisations within Dravanmus and beyond, by a variety of conceptually related, but distinct methods. Despite this, interstellar travel is by no means casual for the vast majority of the population of the known universe. The distances and times involved are still lengthy, and even at faster-than-light speeds, journeys between destinations can take months, if not years, dependent on the technologies used, their sophistication, and the unfathomable distances involved.

## Sublight Travel

### Reaction Engines

> In terms of complicated. You can’t get much simpler than a long controlled explosion out the back of a vacuum-safe crate.
>
> Unknown

One of the simplest forms of space travel in the universe. Reaction engines are ejection nozzles that ignites a high-energy fuel to push a solid mass, such as a starship, forward. Reaction engines are capable of high acceleration, at the cost of a proportionately high energy cost, and the energy required means an energy-conservative journey can spend as much time slowing down as speeding up when travelling through the interplanetary medium.

Reaction engines become impractical for interstellar distances. For a ship using one to reach its destination, it must slow down as much as it had sped up in order to reach its destination. To get to another planet “faster” requires burning far more fuel only to burn even more fuel just to slow down on approach to the destination.

Reaction engines are still a reliable source of fast propulsion even for advanced societies, particularly in stellar orbits or for surface-to-orbit transit. with more established civilisations using deuterium plasma for thrust over a hydrocarbon-oxidiser burn for the higher energy-to-mass ratios offered.

### Solar Sails

A low-tech alternative to reaction engines, the humble solar sail is a cheap alternative method of spacecraft propulsion using radiation pressure exerted by the stars themselves to propel a vessel through the void. Comparable to ancient fishing vessels using sails and the wind to navigate ocean currents;  the light exerting a force on the mirrors of the sail is akin to the fabric sails of a boat being blown by the wind.

Despite being extraordinarily slow compared to reaction engines, solar sails offer a significant advantage in fuel costs and lifespan. No fuel is necessary for a vessel operating via solar sails once it is on-course for its destination, and a lack of moving parts renders wear and tear a far slower process.

Solar sails instead utilize a phenomenon that has a proven, measured effect on astrodynamics; Solar pressure. The total force exerted on an 800 by 800 meter solar sail is about 5 newtons at a distance of 150 Million km from a typical G2V-class stellar body. This force, although small, allows a sail-based vessel to exploit what would otherwise be a navigational hindrance to cheaply navigate into the edges of a star system and beyond. Unfortunately, like with a reaction engine, any momentum must be bled to reach a stable orbit around whatever location the vessel hoped to reach, thus typically necessitating a “solar net” to use the same processes to slow down when arriving in a new star system. Alternatively, reaction engines can slow a vessel down much faster, while solar sails bring the vessel to its destination cheaply.

### Slow-Warp

A civilisation’s first step into developing a true interstellar drive is often to create a version that works at sublight speeds. It is common for sublight warp or “slow-warp” to be used to cross interplanetary distances. Journeys that could take many months even by the fastest of reaction engines can be done in just days or hours using the same principles for moving as interstellar warp.

Slow-warp’s advantages over reaction engines when energy costs are not taken into account make it an attractive alternative for sublight movement for civilisations which have the resources. And are particularly useful for larger vessels which may suffer structural strains from a reaction engine pushing at the rest of the vessel.

## Faster-Than-Light

> When talking about space travel always remember: Anything with mass cannot travel faster than a photon. Interstellar space is so big, photons can take years to travel between stars. Except for space because space has no mass. The solution to travelling faster than light? Travel at the speed of space!
>
> - Tarnus' Ellyron's Easy-Peasy Guide To Starflight

### Fast-Warp

“In principle the physics are straightforward. bend space around the ship, the ship rides that bending like a board on a wave. You go faster than light without actually going faster than light.“

Interstellar (“fast-warp” or "true-warp") travel involves compressing the space-time fabric into a “bubble” around the vessel. The enclosed vessel rides the bubble of warped space-time, which can move at velocities greater than the speed of light. The power requirements for effectively warping space the same way an object like a black hole would require very high energy fuel sources such as deuterium or antihydrogen to produce enough power. It remains one of the slower methods of interstellar travel even if it holds as one of the most reliable and straightforward available to a majority of the galaxy.

Because of the immense amounts of energy required to maintain these warping fields, Most drives require time to gradually biuld up to their maximum rate of compression. In order to regulate fuel flow and minimise component stress, instantaneous warp acceleration is ill-advised save for certain drive models found only in the Crown Circuit,

An Imperial dreadnought, fitted with the most modern capital-class warp drive, can manage a maximum travel speed of 100 light years a day.

### Hyperspatial Breaching

Hyperspace, also known as Slipspace, Warpspace, Subspace, 11D Space and Otherspace, is a secondary plane of the universe’s topology, on which the dimension known as “realspace” uses as a foundation. It is speculated that without the existence of hyperspace, the entire universe would be fundamentally inconsistent with its current self; both in terms of politics and topology.

As a reflection of 11th-dimensional reality, hyperspace exists as a seemingly paradoxical tangle of intertwined higher-spatial dimensions and the natural home of supersymmetric partner particles to everyday ones. It can be best described as - though in a vastly inaccurate oversimplification - as the results of taking the classical "flat sheet" model used to represent the dimensions of spacetime and crumpling it up into a dense, melting ball, thereby creating shorter spaces between points in a method comparably similar to a tightly wadded up piece of paper.

Entry into hyperspace itself also has a considerable effect on hyperspatial travel. While less advanced Hyperdrives will typically “ram” or punch their way into Hyperspace, more elegant and advanced drives will be more precise. Analogous to cutting with a scalpel as opposed to a hammer or a dull knife. These differences in entry and exit can have considerable effects on the safety and accuracy of travel within hyperspace, and can severely affect travel times as a result.

### Hyperlanes

The unpredictable intricacies of Hyperspace make it almost impossible to reliably use without knowing an exact route though the extra-dimensional topology. Hyperlanes are analogous to the roads of hyperspace; not a natural construct, but a concept. Given hyperspace’s topology, the knowledge of the position of a location in realspace will almost be useless to reach it in Hyperspace. Consequently, hyperspatial coordinates (an entirely different coordinate system that factors in the extra topology) must be used. Even the most advanced of computers struggle to navigate the topology of Hyperspace, leading to the use of Hyperlanes; exact navigational instructions from one location to another that, if followed exactly, will allow a ship to exit Hyperspace at the intended destination.

New hyperlane routes are always being logged and recorded in navigational databases by automated drones and Hyperspatial navigators, allowing a ship to travel from any planet in the galaxy to any other with complete confidence. Vessels that do not adhere to hyperlanes are typically expected to end up completely stranded or lost.

### Psi-Drives

A more exotic method of travel. Using Psi-tech to link several minds at once, colloquially-named “Psi-drives” use The Aether to travel space in accompanyment with space-time warp. The precise workings of a Psi-Drive varies wildly. Some require only a single pilot, tethered to a network. Others require the entire navigational crew to imagine their destination or a specific caste of hypersensitive navigators. Whatever the method, the journey is instantaneous. The ship effectively teleported to its destination.

Travelling with a Psi-Drive exposes the navigator(s) to the unfiltered Aether. A dreadful experience comparable to experiencing the world without any unconscious filters to make sense of the input. Navigators can spend months or even years in extended recovery from their visions. Some drives can handle switching out navigators while others will map themselves to one specific individual. Thus a ship with a Psi-Drive will often have the device as an auxiliary to another form of FTL on board.

### Gateway Networks

The ancient gateway network is older than many species and civilisations, having been constructed during the mythical Era of Diamonds by a more ancient draknir civilisation from which the modern Imperium claims descendance. Hailed as one of the greatest achievements of technological engineering within the history of the galaxy, these gateways form an enormous network allowing interstellar, and intergalactic, travel. By compressing hyperspatial tunnels one-thousand-fold, Gateways are portals capable of near-instantaneously transporting starships to another gateway within the network tens or even hundreds of thousands of light years away. Allowing for journeys that would otherwise take years or even centuries with only FTL drives to be made in moments. The distances travelled still incur travel times, though this is only noticeable when crossing the entire length of the galaxy in a single jump, or when attempting to travel intergalactic distances using the network.

The strategic and economic advantages Gateways offer make them extremely important wayports for cross-galactic travel. The more used gateways doubling as starports for interstellar travel and military checkpoints.

#### Railshots

An older technology, likely long predating the Gateways but simpler in their sophistication, are devices colloquially referred to as FTL railshots. Railshots differ significantly from Gateways in that instead of creating a permanent wormhole between two points, a railshot creates a very narrow tunnel of super-compressed space. Capable of launching their users many thousands of lightyears in a very short space of time. The downside however is they require exact precision.

A miscalculation can extend the funnel significantly, and a vessel can easily become a high-velocity projectile. Although useful for crossing over large distances of interstellar space, they pose an enormous risk of slamming the user into a planet, a star or an asteroid that was not accounted for.

## Mega-Carriers

FTL Drives can be prohibitively expensive for common use in the galaxy, the expenses in technology and fuel making the purchase of an FTL-capable vessel simply untenable for mass private use. For other vessels, there is simply not the space for bulky FTL drives within the hull, leaving the ship simply unable to operate at faster-than-light speeds. The solution for these vessels in crossing the great distances of the galaxy is the extraordinary Mega-Carrier class of starship. Titanic vessels working as dual-purpose cargo carriers and starfaring cities.

Usually operated by powerful companies, guilds, or individuals of extreme wealth, these behemoth vessels - some of the largest being above a hundred kilometres long - are so utterly immense that mile-long cruisers can comfortably fit inside of them. Each and every Mega-Carrier is a feat of engineering in its own right; flying cities capable of interstellar travel that compare to small planetoids in size. The gravity of such vessels is even strong enough for smaller vessels to comfortably orbit within their spheres of influence.

Even smaller mega-carriers, which might measure tens of kilometres long instead of several hundred, hold services for docking corvettes and frigates. Large-scale cargo carriers, with space in their holds for millions of tonnes of goods special and mundane, are an important lifeline for interstellar commerce.

Ubiquitous for long-distance travel by corvette or cruiser-sized vessels, it is not uncommon for battleships and freighters to use these colossal ships to cross the galaxy in practical amounts of time. With the largest FTL drives in the galaxy available to them, even a large battleship can benefit from the FTL-speeds and distances Mega-carriers are capable of with their titan-sized cores. Their enormous fuel stores giving them a much greater range than most capital vessels as their drives can run for for many weeks without needing to refuel.

Mega-carriers are not easy to decommission. Comparable to dismantling a mountain, many will be maintained by their holders to operate for as long as possible. Operational lifetimes spanning millennia with refurbishments so thorough that the oldest Mega-carriers can be completely unrecognizable to when they were first built. Even for the Mega-carriers that date back to the Era of Diamonds, plenty have been so thoroughly refurbished they have lost the lustre that might come from a construction of that mythical age.