That is doable for "normal" speeds, not one where you accelerate 1G for twenty years, reach relativistic speeds that make you travel for hundreds of thousands of light-years in merely 20 years ship time
> doable for "normal" speeds, not one where you accelerate 1G for twenty years
It's still a lot of energy you can bleed off, particularly if you're aiming for a system with gas giants. I'm not suggesting one only rely on passive deceleration. But especially given it's fuel saved at the very end of the journey, fuel you no longer need to accelerate and decelerate for the entire duration of the trip, the savings could be sizeable.
the top of this thread is filled with a discussion of the almost unimaginably catastrophic consequences of a ship moving at 0.9C hitting atoms in interstellar space.
trying to decelerate by "braking" anywhere close to a gravitionally significant mass sounds like a guarantee to total destruction from the impact of "stuff" (even individual photons).
You decelerate from 0.9C to 50 km/s conventionally, more if you can aerobrake or line up multiple slingshots, and that last 0.00001% with gravity assist.
It saves you more than that in fuel, because the fuel you'd have used on that last bit of deceleration needed to be accelerated and decelerated the entire way from 0 to 0.9C back to close to zero.
