Kerbin-Kerbin Slingshot?

[Aubri]

On 5/6/2016 at 10:08 AM, eddiew said:

That's interesting, cheers. I hadn't found an example of Earth-Earth slingshotting before! 

The MESSENGER probe did this too -- before it settled into Mercury's orbit, it got gravity assists from Earth, Venus, Venus, Mercury, Mercury, and Mercury. 

[Epox75]

The best tool you can use to plan such kind of mission is KSP Trajectory Optimization Tool. I'm using it since a year and I've been able to redo missions like Messenger, Cassini, Juno and Voyager 2  all thanks to this tool. In my career I use Outer Planets Mod and Trans Keptunian Objects and I never go to this planets without having a gravitational assist from Jool.  Using this tool in combination with the node editor of Mechjeb makes you able to plan these mission with absolute precision. 

Here's a screenshot of KSP Tot while i'm planning a Juno-like mission:

Spoiler

 

 

[herbal space program]

OK, so I finally finished my Kerbin/Mun assist-only route to Jool. Please see the linked album for images. The bottom line is it required 1297.6m/s total dV for me to get to a Jool encounter, which saves almost 700 m/s relative to the 1987 m/s ejection burn required for a direct transfer. Total transit time is 8 years, 200 days.

http://imgur.com/a/XQSnn

The whole principle of doing this is to climb a ladder of resonant orbits through successive gravity assists. The course I chose was based on a 3:4 followed by a 2:1 resonant orbit, using deep space maneuvers near my solar apoapsis to create an angle of incidence between my orbit and Kerbin's for gravity assist. I started with Kerbin a bit less than 30 degrees ahead of Jool. Next time, I would probably try a bit more than 30 degrees. I ejected Kerbin-prograde with a 950 m/s burn that went low around Mun, as pictured. This gave me an initial solar orbit with a 20.18 MKm apoapsis and a period of 596.7 days. this is 28 days longer than the 568d period of a 4:3 resonant orbit, which seems to be sort of a sweet spot to shoot for wrt any resonant orbit. From a bit after the Ap of that orbit, I burned retrograde for 169.5 m/s (DSM1), lowering my period to 564d and setting up a Kerbin encounter after 3 orbits, at the far intersection. Setting a periapsis of ~1000km at this encounter, I was boosted into a new orbit with Ap 30.1 Mkm and a period of 882d. This again is 30d longer than the 2:1 resonant period of 852d. From near the Ap of that orbit, I pulled back for another 173.1 m/s (DSM2), resulting in another Kerbin encounter on the very next go-round, from which I was able to get catapulted to a Jool encounter from an 88km periapsis. Another 70 m/s of plane correction and a tiny in-plane maneuver got me captured via a retrograde Tylo encounter. Anyway, this route is not quite as efficient as the PLAD route (1000m/s), but that route only has one window in 17 years while this one can be taken as often as the direct Hohman transfer window comes around. Anyway, I'd be interested to see how much this can be improved upon, but I think I'm done with it for my own part.

Edited May 26, 2016 by herbal space program