Subspace

Subspace is the extra-dimensional medium our four-dimensional observable universe is embedded in. While weak and strong nuclear forces as well as electromagnetic forces are localized in the observable universe, gravity is not and much of it "leaks" into the subspace - this is why it seems to be weaker than the other three forces. The existence of subspace was first proved during the 21th century but for many centuries it seemed impossible to use it for interstellar travel - getting even atomic particles into subspace required prohibitive amounts of energy and they returned to normal space in a few seconds as their subspace penetration was very shallow and gravity "sucked" them back.

Finally, Tess Van Maan discovered that subspace may be entered through gravitational vortex points located near the L1 Lagrangian point between two astronomical bodies of extremely high mass (typically between binary stars), where spacetime gets more distorted and larger amounts of gravity seep through.

If a ship hits the vortex point with inadequate speed or from a wrong direction, it enters subspace but returns to normal space almost immediately. However, if the ship has the necessary momentum (the breakthrough velocity) and reaches the vortex point from a very specific angle (with arcminute accuracy), it may escape the gravity well of the original star system and get caught by the gravity of another system. Traverse between vortex points is very quick, approximately 90 seconds per lightyear.

Depending on the angle of entry, a ship may reach a number of different stars from any vortex point depending which one pulls it back to normal space. However, the target system must be either very massive or not too far in order to be able to "catch" the ship. Entering the vortex point at a higher speed may allow the ship to reach a number of additional destinations, but this needs a very skilled pilot and often considered a risky move. Lone stars can also catch ships but this results in the ship being trapped in that system since they have no vortex points themselves.

Exiting subspace

The exit point of the ship is somewhat randomized in the target system but a rule of thumb is that it's distance from the centre of mass of the target system is 460 lecs per 1030 kgs of the total mass of the system. For example, the total mass of the Solar System is about 2x 1030 kgs, so the exit point will be 920 lecs away from the Sun, somewhere between the Mars and Asteroid Belt.

Visually, the subspace is an infinite region of absolute darkness as only minimal amount of matter and energy can seep to it through the gate points. Some pilots call it the "backstage", as it is located beyond the boundaries of reality as we know it.