Ion Tide

The great currents of exotic particles that ebb and flow throughout the galaxy. We called it "Dark Matter" once, in the distance past when Terra was cut off from the Tides.

Flowing through the galaxy like currents on the surface of a vast ocean, vast waves of exotic plasma ripple invisibly across the immense gulf of space, weaving convoluted pathways through stellar clusters and around the great banks of nebulous gas. The true source of this "Ion Tide" is unknown, but is widely believed to be closely associated with the mysterious, almost mythical being known as the Star Dragon, whose constellation spanning wings beat with glacial slowness as it orbits the very centre of the galaxy.

Dynamic And Turbulent

An Astrogator's most difficult task? Trying to predict the damned weather! What? You didn't know the Tides had weather? Boy you're in for a shock.

Traversing the Ion Tides is far from straight forward. The exotic plasma envelopes are far from homogenous across their width, experiencing local variations in density, velocity, and bearing. The flows can unexpectedly shear and reverse, and transient, storm-like vortices meander up and down the flows borne by the Alcubierre-Helmholtz Effect.

The strength and power of the Ion Tide waxes and wanes on a constant, predictable basis like a wave, radiating outwards from the galactic core at a speed that defies reason. Not even this regular ebb and flow remains free from the dynamic chaos of the system, with waves bouncing and reflecting up and down the current pathways, reinforcing and cancelling each other out in ways that ate difficult to predict.
At their lowest, the Tides resemble the glassy surface of a becalmed lake, and at their heights resemble the tempestuous spray of a sea in the midst of a howling gale. It takes many years of experience for an Astrogator to have the skill and intuition required for navigating the Tides safely. Both the galactic core and the very outer boundaries of the spiral arms are ringed by roiling storms that will tear even the sturdiest starship into flotsam, making passage through these regions all but impossible.

Alcubierre-Helmholtz Effect

Main article: Vortex Drive

Interstellar travel had been a dream of humanity long before the currents of the Ion Tide shifted to flow past Sol. Many methods were proposed over the centuries, but alas, none had ever been shown to be viable. Antimatter torches were simply too large and too slow for humanity's needs, and various proposed warp drives always ran into the fundamental impossibility of requiring an object to have a negative mass.

What, sir, would you make a ship sail against the wind and currents by lighting a bonfire under her deck? I pray you, excuse me, I have not the time to listen to such nonsense.

— Napoleon Bonaparte

This reliance on using Tidal Sails has caused humanity immeasurable damage over the countless thousands of years as the Tides periodically shift and leave whole regions of the galaxy becalmed or cut off.
It had been long known that the Tide could to a limited extent be manipulated and followed certain principles analogous to classical fluid dynamics. A major breakthrough was in the study of vortices within the Tide, in which it was shown that a carefully constructed asymmetrical vortex within the tide exhibited properties that were indistinguishable from an object with negative mass.
This virtual negative mass has ignited the development of modern humanity's first practical Alcubierre-Helmholtz Effect Vortex Drives. Slow, inefficient, and unstable, these early devices have so far been met by a near universal mistrust traditionalists who prefer to rely on their millennia of proven experience with Tidal Sails.

Canali

Good news everyone! I know a shortcut!

— An Astrogator's famous last words

On occasion, small, spindly filaments and tubes can extend through the tempests at the edges of the Ion Tides' plasma envelopes and bridge the vast gulfs between otherwise disconnected regions of space.

Known as "Canali", these narrow passages through the void are extremely important to navigating between isolated regions. In many parts of the galaxy, bounties are offered for the discovery and charting of previously unknown Canali. This is a difficult and perilous task, as to locate even a known one, an Astrogator must guide a starship close to the tempests ringing the plasma envelope. Some Canali are known to be stable, while others are transient, opening and closing with the rise and fall of the Tides.
It is rumoured that a stable Canali exists between the edge of the galactic disk and the satellite Nubecula Major. Many have tried to locate it, and few have returned...