Interstellar

Each of the current starfaring Races uses its own variant of Gravity Wave Manipulation (colloquially: grav diving - gravity well diving) to circumvent the Einsteinian Space "speed of light" restrictions. Exactly why the drive works is not understood during the period of the history and it is not obvious during the Terran's early exploration that the mass of the star is more important than the density (white dwarves)

Historical All known evidence suggests {wave 1 race} did not use gravity wave manipulation and instead relied on near C ramjets (the maximum modern races have achieved is just under 30% of C). It has been confirmed that Bats used Gravity Wave Manipulation on a small scale but relied heavily on various sub-lightspeed technologies for their interstellar travel including lightsails, anti-matter and ramjets. No confirmation is available for Crickets due to the limited amount of technological artifacts discovered. The other Wave 2 Races all utilised gravity wave manipulation at some point for interstellar travel.

Gravity Wave Manipulation
Initially discovered in 2053 by Terrans due to cascading power failure in an Indian solar probe caused it to accelerate towards sun and overload its electromagnetic particle shielding, triggering a microjump from the edge of the corona into the photosphere. It was the exit flare that confirmed the event as the probe itself disintegrated during transit Range of jump determined by the strength of the magnetic field (created by the drive not the rad screen !) and gravity well size – this means that jumping in gas giant likely to be local solar system only. Later tuning of magnetic field allows more efficient jumping. The reliance on gravity well size also means that travel is not strictly two way ..... typical efficiency 11 liners working the Sol to ?? route usually pass through Sirius first then ??? but can make the return jump directly from ??? to Sol because of ??? massive gravity well. The strength (efficiency) of the drive field means interstellar jumps initially required huge power sources (and thus large ships) until tuning improves efficiency Speed of transit determined by velocity at jump, 5000x increase is typical. Transit time does not exist subjectively. Direction of jump determined by vector during entry to gravity well - the vessel maintains this vector during transit (aim at the destination in normal space). "Exit flare" a result of change in local velocity compared to rest of galaxy so it is minimal during local jumps but post-interstellar transits can be huge – the exact cause not discovered initially because incoming charge (solar wind) against the electromagnetic field also has a flaring effect. Exit velocity is always zero compared to the local star

Planetary Drives
There are no magic "reactionless" drives in use. Gravity Wave manipulation drives do not affect local travel times (until drives become strong enough to allow jumping in planetary mass gravity wells). With this in mind, many neophyte space travellers are suprised that they travel to orbit using a high-G thruster equipped craft and then their starship dodders in towards the star for the jump using a low-G ion drive. Thrusters pass huge quantities of atmospheric gases through their engines for an hour or two to reach orbit. If their craft had to carry that atmosphere aboard to serve as reaction mass, it would look more like the early space age rockets ! The starship's ion drives on the other hand use minute quantities of reaction mass expelled at very high velocities to generate a fairly low but constant acceleration. Because this acceleration compounds for the entire trip it can potentially reach a significant percentage of C. The difference this compounding acceleration makes can be best understood by comparing the 120 days typically required by an early space age rocket (equivalent of a few hours under thruster) to travel between Terra/Sol and Mars/Sol using an unpowered "Holmann transfer" orbit against the 15 days typical of ion drive ships travelling under constant 0.1G acceleration. The benefits of higher constant acceleration are not linear. Increasing the thrust to a full 1G would only reduce the transit time for such a short transit distance to around 4 days (note that 10 times the acceleration/power only creates a 75% time saving not 90%) while halving the acceleration to the 0.05G of a typical ore freighter only increases the transit time to 19 days