> takes the same amount of time to slow down as it did to speed up
Assuming you're going somewhere, you can use atmospheres and gravity to slow down. Decelerating should take less time than accelerating in practical contexts.
Assuming you're going somewhere, you can use atmospheres and gravity to slow down. Decelerating should take less time than accelerating in practical contexts.
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.
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.
The places people talk about travelling to tend to have atmospheres and gravity, yes.
You can tolerate 2G for hours, particularly if everyone's oriented eyeballs in. That said, both aerobraking and gravity assists are intermittent accleerations.