>>11945974I think I see what you are imagining,
1) You would not get any gravity assist from a circular orbit.
2) The effort needed to do so would far outweigh whatever you'd gain from an ecliptic boost, see below.
You can use the planet you are already orbiting to get a boost with some parameter:
- You are already in an orbit with free room below (no atmosphere, no surface)
- You burn so as to make your orbit pass closer near the planet
- Burning at the lowest point of the orbit will give you a boost.
This is what decent players do in the game Kerbal Space Program when they started high or have a low thrust engine.
You can also imagine some very real (if costly) SF method: Building a magnetic accelerator around a planet, accelerate your ship inside as much as structurally possible.
Note that the accelerator-ring itself will loose/gain speed (if in orbit). This is among the way an Orbital ring megastructure could be used.
>>11946000(about Expanse reactionless thruster)
Technically correct but only if it happen to already be on your way which is going to be extremely rare. It's not free if you loose more time setting it up, and time is more costly than a few megawatt.
In the Expanse universe every ship use Brachistochrone transfer, that's the requirement to avoid cruising for years.
