Hyperspace

"We live on a ship powered by energies that sunder cause and effect, beginning and end&hellip; hyperspace is a mystery more profound than gods and demons."

- Micha Evon

Hyperspace was an alternate dimension that could only be reached by traveling at or faster than the speed of light. Hyperdrives enabled starships to travel through hyperspace lanes across great distances, enabling travel and exploration throughout the galaxy.

Nature
Hyperspace was a dimension of space-time alternative to that of realspace. It could only be accessed through molecular displacement, which was achieved by breaking the speed of light. It was coterminous with realspace, meaning that each point in realspace was associated with a unique point in hyperspace, and all adjacent points in realspace were adjacent in hyperspace as well. Additionally, every object in realspace (such as stars, planets, and asteroids) had its "shadow" counterpart in hyperspace. Aside from those well-established facts acknowledged by all competent astrophysicists and astrogation experts, other aspects of hyperspace admittedly remained a mystery.

Hyperspace usage
"Traveling through hyperspace ain't like dusting crops, boy! Without precise calculations we could fly right through a star or bounce too close to a supernova, and that'd end your trip real quick, wouldn't it?"

- Han Solo, to Luke Skywalker

Hyperdrives manipulated hypermatter particles in order to thrust a starship into hyperspace whilst still preserving the ship's mass/energy profile. This shortened journeying distance significantly, allowing the vessel to "jump" from a specific point to another without having to travel directly between them, therefore reducing journey time by an extraordinarily large margin. However, large objects in realspace cast "mass shadows" in hyperspace, so hyperspace jumps necessitated very precise calculations. Without those, a vessel could fly right through a star or another celestial body. Because of the danger, there existed predetermined hyperspace routes which interstellar travelers could take. The discovery of a new, safe hyperspace route could play a pivotal role in war, as it would allow naval forces to move faster unbeknownst to their adversaries. A vessel's ability to travel through hyperspace depended on its being equipped with a hyperdrive engine. Quick jumps into hyperspace could be unsettling to even experienced pilots, but those with the proper stamina and training could overcome this. The Galactic Empire employed Interdictor vessels to disable hyperspace capabilities in other vessels, both to pull them from hyperspace and to prevent them from making the jump to it.

Upon entering hyperspace, a ship appeared to accelerate dramatically&mdash;a phenomenon known as pseudomotion&mdash; and emitted Cronau radiation, which made their jump detectable by specialized sensors.

It was technically possible for a vessel, such as a shuttle, to disembark from another vessel while in hyperspace, but the procedure carried extreme risk. Such a move would tear the disembarking vessel violently out of hyperspace.

Safely entering hyperspace from a standing start while docked or exiting hyperspace directly into the atmosphere of a planet were both feats that were generally considered impossible, even for an experienced pilot. Despite this, Han Solo managed to accomplish both with the Millennium Falcon after being drawn into the First Order-Resistance conflict. In fact, starships had safety protocols that prevented hyperdrive engines from firing within the gravitational pull of a planet. Although it was possible to turn those protocols off, such a move was highly dangerous, and any a ship doing so had a high chance of blowing up or falling apart in hyperspace. Successful jumps near a planet were possible, though: during the Clone Wars, a cruiser carrying an injured Anakin Skywalker had its hyperdrive accidentally triggered while still in a planet's atmosphere due to damage from droid fighters, and despite the proximity to the planet the ship successfully jumped to hyperspace without being destroyed. Jyn Erso and her company managed to jump into hyperspace from inside the atmosphere of Jedha after the Death Star destroyed the moon's Holy city. Hera Syndulla while fleeing Lothal in a U-wing, jumped to hyperspace right in front of an Imperial construction module and flew through the hangar, successfully getting out the other side and making the jump. Desperate to save the remaining Resistance escape ships, Vice Admiral Amilyn Holdo engaged the hyperdrive of the Resistance cruiser, Raddus directly into the path of the First Order Mega-class Star Dreadnought, the Supremacy, heavily damaging it and effectively vaporizing all traces of her ship.

History
"When I was young, I was told amazing stories of creatures that lived in the stars, traveled between the worlds. Old pilots said it was the purrgil who inspired us to jump from system to system. But I don't believe it."

- Hera Syndulla

The ability to travel through hyperspace occurred in nature. The space-based species known as the purrgil could naturally travel through hyperspace. At some point in the ancient past of the galaxy, an ancestral species unlocked the secrets of traveling through hyperspace and opened the galaxy up to exploration. Hyperspace travel was mastered as early as four millennia before the Cold war, as demonstrated by the existence of hyperspace sextants from that era. In the early days of the Galactic Republic, hyperspace travel between the Greater Seswenna and the Core Worlds required astrogating by hyperwave beacons, with numerous reversions to realspace necessary to ensure safe passage. At the time of the First Order–Resistance conflict, the First Order discovered sub-hyperspace, which they utilized with their superweapon, Starkiller Base. The firing of Starkiller Base during the Hosnian Cataclysm in 34 ABY released enough energy to create a temporary rip in sub-hyperspace. This allowed the disaster to become visible from across the galaxy instantaneously, for a short time.

Non-canon appearances

 * Rogue One: Recon A Star Wars 360 Experience
 * LEGO Star Wars: The Freemaker Adventures