• Faster than light (FTL) travel is possible, and reasonably common.
• FTL is not instantaneous - it will generally take at least 4 to 5 days to travel between systems.
• FTL travel can only be used a certain distance away from a massive object (the “Zigman Radius”) - about 5 light hours for most stars having habitable planets.
• Objects smaller than an average moon do not have a Zigman Radius, unless made of neutronium.
• Travel from the FTL radius to habitable planets in a solar system generally takes about 12 hours.
• Detection of ships via “ZIDAR” is possible instantaneously within a system (no light speed delay) - subject to line of sight, stealth technologies, and actually looking in the right place.
• FTL communication is possible, and instantaneous, but requires you to know where your target is.

The currently accepted theory underlying space travel, Zigman-Edaakie Dynamics (ZED theory), was first published in the year 723. The full details of the theory will not be presented here, but there are several important consequences.

Firstly, outside of a certain radius from any other massive body (the “Zigman radius”), travel beyond light speed is possible. The Zigman radius of a body increases with its mass - stars have a typical radius of 1 to 20 light hours (4 to 7 light hours for most stars having habitable planets), planets have a typical radius of a few light seconds, and asteroids and smaller bodies do not have a Zigman radius for practical purposes (as it would be smaller than the object itself), with the notable exception of neutronium. An object travelling faster than light which encounters the Zigman radius of another object will decelerate to rest (with no apparent acceleration “felt” by the object), releasing a flash of light in the process.

Secondly, while it is possible to travel faster than the speed of light outside the Zigman radius, there is a further fundamental limit at around 600 times light speed. In fact, due to the particular dynamics of FTL travel, objects travelling FTL will tend to move a speed of 500 times light speed (allowing travel between nearby systems in about four days), since an object travelling at this speed in fact has lower energy than one travelling just above light speed.

Thirdly, information can be sent faster than light anywhere (including within the Zigman radius of an object) - and by similar properties, sensors can be made which can detect objects before the light from those objects has had time to reach the sensor.

Finally, time dilation is much reduced at speeds above around half of light speed - in practice, a ship at normal FTL speed will experience time at about 70% of the rate of a stationary observer, which can be easily compensated for.

When an object travelling faster than light encounters the Zigman radius of another object, it will quickly come to rest (though with little apparent acceleration experienced by the FTL object). Where an FTL object encounters an object too small to have a Zigman radius (i.e. small moon sized or less), the general rule is that the faster object will emerge mostly unscathed, and the slower one will be destroyed - for this reason, any habitats not safely within a Zigman radius of a star tend to have a neutronium core to both provide local gravity, and allow incoming ships to stop safely.

Take a ship travelling in interstellar space. That ship is moving through a very sparse dust containing mostly hydrogen. Stick a scoop on the front, stick a small lump of neutronium at the back (in a carefully constructed chamber, allowing it to be towed along without disrupting the FTL travel), and that dust will hit the neutronium's Zigman radius, and spew out a load of light. Add some cleverness to redirect most of that light backwards, and you have a way to accelerate as fast as you want. Add some more cleverness to allow you to direct it forwards when needed, and you have a way to slow down, too.

Of course, you don't really need to slow down if you just hit the Z-radius of the system you're travelling to - for all inhabited solar systems, this is far enough away from the habitable worlds that the resulting flash is about as bright as a large moon. You don't want to be looking out of a window when a ship stops next to you - but this is easily solved by just not providing ships and space stations with windows (instead, they generally have external sensors connected to internal screens - though some particularly fancy ones may have windows which block the specific wavelengths of Z-radius braking).

That's the basic principle of the ZED drive. As a bonus, this means that every trip gives you a nice store of hydrogen, which you can use to power the ship's fusion reactor, and provide thrust when you are within a solar system.

The ZED drive was invented in the year 743, triggering the Selasi war of independence from Eunomia.

While the ZED drive allows for FTL travel, it is not instant - trips between systems will typically take about a day, with an additional 10 hours on each end for travel between the planet and the Zigman radius of the star.

If you know the route a ZED drive ship will be taking, it is possible (though very difficult) to intercept the ship en-route. Simply putting an object in the way is not sufficient - due to the peculiarities of ZED theory, in a collision between an FTL object and a stationary object, the FTL object will escape unscathed, and the stationary object will be vaporised in the collision. What you need to do is to place a Zigman radius in the way - i.e. a lump of neutronium. To be successful, this requires a lump large enough for the Zigman radius to encompass the whole target ship, which generally means that you need the mass equivalent of a small moon or large asteroid, and you need to construct a ship capable of towing that mass at FTL speeds (possible, but the resulting ship is huge). Onve you've done that, you send your interdiction ship to a point in the target ship's path, drop off the neutronium, move away to prevent your interdiction ship getting destroyed, and make sure you have a lot of weapons pointing at the target location. Then you just wait for the flash which signals their deceleration, and broadcast your threat or fire your weapons, as appropriate.

Smaller ships require less neutronium to intercept than larger ones (because you need a smaller Zigman radius to encompass them), but they are often more manouverable and more able to alter their course to avoid interception in the small time they will have after detecting the blockade.

Faster than light (indeed, effectively instantaneous) communications are possible. These require a line of sight and knowledge of where your target is, as sending a broadcast, or anything other than a direct, point-to-point signal, would require far too much energy. Communication between systems is generally via large hubs in each system, which have permanent, high bandwidth, links to each other.

Any ZED drive ship has a lump of neutronium at its core. This can be detected instantaneously - provided you are looking in the right place. This is because the neutronium will scatter the signal used for FTL communications, and this backscatter can be detected if you are close enough (the same is true for any object large enough to have an external Zigman radius, such as a planet, but they don't tend to move unpredictably). This sensing is known as ZIDAR. As a general rule, a planet can know every ship which is closer than about three times the distance to its moons, will probably detect an approaching ship within the system within a 2 to 3 hours, and will not detect a ship beyond the Zigman radius of the system unless it is specifically looking for it, and knows where it is likely to be.

In the later stages of the war, carrier ships were used which would park well outside the system, before sending in many smaller ships with non-neutronium based drives to avoid detection.