How to slingshot?

[Billyk88]

I know if i can slingshot i can save alot more fuel but i have no idea how to do this. I appreciate any help thank you

[rkman]

http://wiki.kerbalspaceprogram.com/wiki/Tutorial:_Gravity_Assist

You won't necessarily save a lot, but a few 100m/s can still be worth it.

[Kasuha]

In general you pass near some planet or moon and that changes your orbital parameters around another body (usually Sun), putting you on higher or lower orbit and/or changing your orbital inclination. I think the best approach is to get experimenting - build a rocket that can reach Eve and watch what happens with your result trajectory around Sun as you change parameters of how you miss Eve.

Eve is about the most useful body for gravity slingshots in the system thanks to its high gravity and orbital speed.

[Poynting]

I reccomend experimenting with maneuver nodes as you approach an encounter with the mun to begin with to get a feel for it. Eve is the most useful target in the game but the mun is easier to reach if you havent got experience with interplanetary travel. Change how you approach the encounter: pass in front of the moon as it moves a long its orbit, behind it, over it or under it. The properties of your approaching orbit will then determine how you leave the muns sphere of influence and therefore your orbit after the encounter.

A gravitational sligshot increases the energy of your orbit has around a primary body after you pass through an encounter with a second body orbiting the primary. After playing around with the maneuver nodes it will become obvious that passing behind the mun (in terms of its orbital direction) accelerates you the most with respect to kerbin.

Also if you havent got a scientific background I reccomend reading about reference frames

Good luck!

[Xiphos]

pass in front of the moon as it moves a long its orbit, behind it, over it or under it.

Be careful setting up an encounter 'behind' the orbit of the mun, because the gravity of the mun can slingshot you into solar orbit very easily. Especially if you accidentally time warp through the encounter....*cough* I speak from experience.

[rkman]

Be careful setting up an encounter 'behind' the orbit of the mun, because the gravity of the mun can slingshot you into solar orbit very easily.

In case of a gravity assist/slingshot that is the purpose of the maneuver.

The advantage is that it saves fuel if you want to get into solar orbit (e.g. to transfer to another planet).

[Kasuha]

In case of a gravity assist/slingshot that is the purpose of the maneuver.

The advantage is that it saves fuel if you want to get into solar orbit (e.g. to transfer to another planet).

I'd call that disputable. When you just want to get to Sun orbit then yes, Mun slingshot can get you there for less dv. But when you actually want to visit some other planet, then Oberth effect from accelerating at low Kerbin orbit is comparable in effect and much easier to implement than Mun slingshot. When passing Mun at speeds necessary for interplanetary transfer, the deflection and whole gravity slingshot effect is very small. And when 'finishing' the maneuver after Mun slingshot, you already lost the advantage of high speed at LKO.

[Claw]

I toyed with a Mun slingshot to Minmus once, it just happened to line up the right way. Usually I find it's also annoying to wait for the timing to line up the Mun with some other body to sling after.

[Supernovy]

Often for interplanetary slingshots, I don't wait for things to line up, I go for it, and just keep waiting until I can find a low Δv manoeuvre to get an intercept with the next planet.

This ends up taking quite a long time, but very little Δv, I once got to Duna with a probe only designed to escape Kerbin.

[Gravitas Shortfall]

Often for interplanetary slingshots, I don't wait for things to line up, I go for it, and just keep waiting until I can find a low ÃŽâ€v manoeuvre to get an intercept with the next planet.

This ends up taking quite a long time, but very little ÃŽâ€v, I once got to Duna with a probe only designed to escape Kerbin.

I recently stumbled upon http://pagmo.sourceforge.net/pagmo/index.html, which comes with implementations of some real-world trajectory optimization problems provided by the ESA. Need to spend some time digging through the code to figure out exactly what it's doing, but at a glance it seems like it could be modified without too much fuss to be used for KSP - then we could actually plan these things prior to launch rather than just hoping for the best. Maybe I'll play around with it a bit this coming weekend.

[SuperBigD60]

I recently stumbled upon http://pagmo.sourceforge.net/pagmo/index.html, which comes with implementations of some real-world trajectory optimization problems provided by the ESA. Need to spend some time digging through the code to figure out exactly what it's doing, but at a glance it seems like it could be modified without too much fuss to be used for KSP - then we could actually plan these things prior to launch rather than just hoping for the best. Maybe I'll play around with it a bit this coming weekend.

You'd be my hero if you did this.

for what its worth.

[rkman]

When passing Mun at speeds necessary for interplanetary transfer, the deflection and whole gravity slingshot effect is very small.

That depends on periapsis altitude. It can be low enough so that deflection and speed gain is significant.

Of course in practice it is very tricky to get everything right for transfer to another planet.

[Billyk88]

Thank u all so much for your help!

[m4rt14n]

Might I suggest some mod like mechjeb that can change conics mode on manuever nodes? I used to be confused on which way prograde and or retrograde the celestial body ur using to slingshot with.

Also check this out. This guy made a whole program to plan the slinghot. Pretty advanced stuff

http://forum.kerbalspaceprogram.com/threads/36476-WIN-KSP-Trajectory-Optimization-Tool-v0-11-2-Mission-Architect-Pre-release-1%21

Edited February 21, 2014 by m4rt14n

[Claw]

Thanks Martian! I'm going to have to check that out.