FTL travel is possible via *skip drives*, which as their name suggests, allow you to skip normal space. (The implied failure of strong causality leaves the door open to time travel stories, but they shouldn't be the focus of a campaign, and it's still impossible to travel into your own past.)

Skip travel involves creating a local hole in space-time. Energy requirements to create a hole are proportional to r^2 * (perimeter length of hole), which in ideal conditions means O(r^4). Ships therefore tend to be long and thin, with circular cross-sections.

Travel time is linear to the distance in real-space, with routine trips travelling approximately 2ly/d (~500c), and cutting edge TL10 technology allowing travel at about 2000c. However, energy expenditure climbs as the swept volume in skip space+time; hence, shorter and faster trips are much more efficient than longer and slower ones. (Since the area and speed of the ship in skip space tends to be constant, it's easiest to think of the energy as proportional to d^2.)

In practice, energy to punch the hole dominates in jumps under about 2 ly for normal interstellar ship sizes, and energy to travel dominates in longer trips. A standard jump is about 10 ly; some fast ships may make 20ly trips, but more than that is unusually extravagant.

Note that the proper distance must be used, which includes relatavistic contraction based on the relative speed of the ship and its target. Human ships utilize Lorenzian contraction to slightly reduce travel times by first accelerating strongly in the direction of their destination. However, this requires enormous outlay of resources before entering skip space; it made the most sense when leaving an energy-rich starting point (Sol) for a distant target. It is also strongly advisable to have some way to decelerate when reaching your destination!

Skip space requires a skp space generator (SSG), a 5D hypersphere manipulated in 3D-space via esoteric field-binding. Each SSG generates a spherical bubble of protection from the rigors of skip-space, which is incompatible with real matter. Because spheres do not pack 3-space, ships necessarily must have a densely-packed array of SSGs; however, overlap of fields causes dissonance in the generators, causing even more wasted energy than that implied by simple overlap.

SSG power draw is (unsurprisingly) proportional to the cube of the radius, or proportional to the volume enclosed. There is no net win over many smaller generators vs. a few larger ones, but in practice, generators displace ship space that could be used for other purposes. The generators themselves can be quite small–the smallest being those found on needlecraft, which are about 1cm in radius for the generator, and produce bubbles of about 4cm in radius.

The entirety of the ship must be covered by an SSG field, not merely its surface. This naturally leads to a lot of innovation in the size and arrangement of SSGs within a craft. On top of this, it is critical to avoid SSG failures while in skip space, lest the uncovered region of the ship simply vanish into realspace.

(Diversion: spherical packing of an infinite volume (probably) maxes out at π / (3 √2), or about 74%. Packing a cylinder with spheres tops out around 55%. But filling a space with uniform spheres requires an orthogonal packing, with overdensity of about (4π/3) / (√3 / 2 )^3 = ~6.5x.)

In practice ships tend to use SSGs of two or three different radii to enhance coverage and reduce overdensity. The net effect is that for a large ship, SSG overportioning tends to be ~6-10x the volume of the ship, with a consequential energy demands.

Some races (notably the Odocon) ascribe to the “spherical ship” philosophy, eschewing the efficiency of hole creation for efficiency of SSG powering: a single SSG (with redundant backups) covers the entirety of the craft. Their ships are therefore significally more efficient at longer trips, but significantly less so at short distances.

Needle-casting involves sending extremely compact ships through jump space for the purposes of communication. Needleships are centimeters across and meters long; they generally are launched from a disposable/reusable shell which contains fuel to accelerate and send the cargo. The needle itself contains a string of small SSGs surrounded by a minimal hull, which contains fuel and computational resources.

The needle is “caught” at the far side, as it possesses no means to navigate in real-space, copied, refueled and re-imaged, and then sent on to the next point or back to its origin.

Needles can carry informational cargo equivalent to that of a comparably-sized computer for the appropriate TL; e.g. at TL9, a petabyte of storage is reasonable.

As alluded above, skip mishapes tend to be messy and final. If an SSG fails, the portion of the ship no longer covered is immediately returned to normal space, causing a burst of Cherenkov radiation as it immediately slows down to less than light speed. The resulting matter quickly sublimates into a plasma and generally ablates against itself, causing a harmless lightshow. (The Sinin briefly experimented with attempting to use forced-deskipping of matter as a weapon, but found that, except in the case of extremely precise aiming, the shockwave generated by the plasma was insufficiently effective to be worth pursuing.)

For this reason, SSG engineers generally recommend over-apportioning SSG coverage, but economic demands sometimes intrude. A skilled engineer can also recognize signs of incipient generator failure, and expand adjacent SSGs to cover the space, but depending on the geometry this may canse significant energy drain and drastically reduce the ship's skip range.

Some races (eventually, the Bavorans) have begun to experiment with “skip trains”, extremely long craft made of a number of modular, connected “cars” with the same destination. Each car has its own SSG network, with couplings also protected to prevent disconnection during travel. This saves on wormhole-opening energy while not requiring a enormous synchronized SSG network.