Vanakkam. As the founders of the early SETI program (Search for Extra-Terrestrial Intelligence) have pointed out, there are certain basic prerequisites for interstellar communication, the first and most obvious being high powered radio technology.
So too, in Gods of Terra, are there certain basic technologies needed to permit interstellar travel on ordinary human timescales, and those would be:
Helium-3 fusion power:
For power generation of the minimum level and most economically viable reactor size needed to power a useful stardrive, thermonuclear power generation by fusing heavy helium nuclei has both a reasonable level of safety. On many gas giant planets, there’s a plentiful supply of fuel for visiting starships with good aerodynamics, fuel scoops, and purifiers. It’s safer, more efficient, and generates more power and fewer fast neutrons than deuterium-tritium fusion, but requires higher starting energies to achieve.
That’s the bare minimum, and for large spacecraft it’s a prerequisite for the next item, which would be…
The Kurtz-Dunar Effect:
Most famously co-discovered by Ouilette Kurtz of Terra and Ranan Dunar of Sirug, this is a means of generating and manipulating dark energy to expand, twist, fold, contract, and warp the fabric of space-time in useful ways. It allows at the basic level such things as riding a planet’s gravity-well like a bird riding updrafts, or achieving orbit for spacecraft without using large amounts of reaction mass as fuel. This applies for the gravity-well of a stellar system as well, allowing rapid, low reaction-mass interplanetary travel. Carried to the next level in advancement, it also leads to…
Starfold-M and Starfold-S drives:
With these two methods of interstellar flight, the first pre-Shutter, the second post-Shutter, the way to the stars is open to beings with ordinary lifespans who can now settle worlds across the galaxy on reasonable and economically feasible timescales. Both drives use the same principle, the Kurtz-Dunar Effect, but in slightly differing applications during their respective eras of use. It was the cosmological event known as the Shutter that caused the need for Starfold-M to evolve into the more efficient and powerful Starfold-S once the former was rendered ineffective.
Interstellar travel without these technologies is possible, but restricted to sublight-velocity craft, and not the sort allowing human timescale economic or military activity. Some species, like the Broogh, to be dealt with later in this series, are limited to sublight craft, but most of these are sleeper, or in the case of Broogh, generation ships or entire fleets of them.
Rapidly traversing the Local Galaxy requires a very specific set of technologies, those listed above. So for those with short lifespans, or little patience, there’s really no other option.