Rappolee interstellar low energy transfer trajectories
My Hypothesis is that a world ship needs less energy to slow at its destination if the voyage is made as the target star is making a close approach and is veering away from the home star system.
To the world ship it would appear as if we were coming up from behind the stars line of flight and we come up alongside the target star.
http://upload.wikimedia.org/wikipedia/commons/e/e9/Near-stars-past-future-en.svg ***
*** By FrancescoA (File:Near-stars-past-future-de.svg) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)%5D, via Wikimedia Commons
Indeed the Rappolee transfer trajectory could have implications for panspermia in that meteorites with a higher incoming speed would be more likely to destroy life a to an interstellar meteorites incoming at slower speeds from a star moving away from us after lose encounter
EDIT 26 December 2014
A new paper on ballistic Mars capture orbit,fly a ballistic orbit to a future point in space where Mars will be, would apply to my idea for future lose approaches by stars?
EDIT 4 Jan 2015
Click to access 1412.3648v1.pdf
additional paper found on Centauri Dreams
Yellow Dragon, a mission to repurpose existing ideas into new ideas 
Hi Steve. Stars, when they approach the Sun, will reach a minimum distance then recede. This is an illusion of perspective. We measure their radial motion and transverse motion with respect to our point of view over a brief span of time. At minimum distance the radial velocity is zero, but the actual velocity hasn’t changed, as the transverse velocity remains. For example, the current radial velocity of Gliese 710, which will approach the Sun within a light-year in about 1.34 million years, is 13.8 km/s. Presently its tranverse velocity is about 0.23 km/s. At its minimum approach the radial velocity will be 0, but the transverse velocity will be ~13.8 km/s, then the star will begin receding and the two components will change magnitudes. They sum together via Pythagoras’s Law – if Vr and Vt are the radial and transverse velocity, then the star’s space velocity, Vs, relative to the Sun, is Vs^2 = Vr^2 + Vt^2.
This is not to say there’s not some merit to your idea. Meeting a star at its minimum distance of approach to the Sun requires the minimum velocity for any vehicle doing so, but only because the distance is minimised.
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Adam, recently in the news there has been a paper on ballistic orbit to Mars that consumes less propellant then a Hohmann transfer orbit
would this apply to my idea o approaching and receding stars?
I have added a URL for this paper at the bottom of my post
Thanks
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I recently found this http://ralphmoir.com/media/jBIS.pdf that discusse a generation ship clyler that returns to Earth after doing 90 and above degree turns ariound 3 to 4 nearby stars
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Adam,
A thought, if an Ort cloud can form around a close double star system like Alpha Centauri A and B then surely proxima Centauri would have disrupted those into deep space or caused a early bombardment such as in the Nice model
a second thought , a well aimed,well timed worldship could pick up a gravitational slingshot from Proxima and depending on the geometry of A and B sling by both of those stars
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