Say a generation ship arriving at Alpha Centauri A system wants to get into orbit (or land) on an exoplanet there. After decelerating for the 2nd half of the journey, their approach velocity is still too high to land on the surface safely. They need to decelerate more than their ship thrusters can provide.
Can gravity assist slingshots provide enough braking? Say from 40+ kps to 8kps velocities.
I hope ~40kps should be slow enough entry to the system give ample time to calculate the orbits of other exoplanets needed for lining up gravity assists. I see only 1 unconfirmed planet for Alpha Centauri A that is 20-50 M⊕. But, there could be more. Hopefully that planet helps for the calculation though.
Let's also assume that the exoplanet the ship wants to visit is (fictionally) so similar to Earth that we have the same mass and the atmosphere of the Archeaen Earth (lacks the O2. I'm not sure if/how that effects atmos entry). Typical low earth orbit re-entry speeds are near 17,500 mph, or 7823.2 m/s. Let's assume the ship is at least 200,000kg. It is designed for this entry velocity in 1 piece, or breaking up into multiple entry cones with heat shields. Perhaps breaking up into modular smaller masses would help the gravity assist decel as well... I'm only guessing.
I'm curious about figure (g) in: https://upload.wikimedia.org/wikipedia/commons/7/7e/GravPoss.gif As it seems to reverse the vector... perhaps this is a good approach angle to max decel.
Looking on this site and in research, I mostly see gravity assists for accelerating, or minor adjustments for small probes into orbits, not larger deceleration. Thank you!