Gravity Assist Planning - Is It Really Possible?

[The Flying Kerbal]

OK guys, here's the question: Can anyone truly plan a mission in KSP, using gravity assists to gain velocity from planet to planet?

For years I've tried to find out how to do this, and if I received an answer at all, it was very vague, plenty of words without really saying anything.  Doing a search on Youtube, a few videos do pop up which focus on gravity assists, but again none of those I found explain how to actually plan them.  Even Scott Manley's video fails spectacularly when it comes to this.  it shows him bouncing about but looking at it I have to say it's the only video of his in which I think he's essentially winging it, fiddling about with manoeuvre nodes until he gets an encounter with some planet, and then heading off in that direction.

And then we come to today; I've only just finished Scott's video in which he's showing the Bepicolombo mission being played out in KSP 1.10.  The mission automatically shows the parking orbit required to get a gravity assist from Eve to Moho, and the inclination required is probably around 45 degrees!  Now the obvious question, has any KSP player really got a way or calculation of working this sort of thing out?  I really don't have a clue on this one, but there are many people here who are way better at KSP than me.  So if anyone has a system to actually plan a mission from the ground up which included gravity assists, and not just hitting them by pure luck, I'm sure I can say I wouldn't be the only person who would like to have it explained.

Thanks all!

 

[linuxgurugamer]

Problem with gravity assists is that you have to be extremely accurate. Most people aren't that good.

[The Flying Kerbal]

40 minutes ago, linuxgurugamer said:

Problem with gravity assists is that you have to be extremely accurate. Most people aren't that good.

Well that's a different issue, one which I wouldn't really need to worry about as I don't know how to plan an assist let alone execute it.

[Superfluous J]

With the tools in the stock game, and no outside tools at all?
No. You can't. The game simply doesn't support it.

With tools like (bare minimum) pencil/paper/math or (ideally) a website, mod, or program that can do the math for you?
Sure. No problem. So long as you can perform what the tools tell you is necessary.

Source: None other than common sense. I've never tried any gravity assist more complicated than using Tylo to cheapen both Jool arrival and exit.

Edited June 28, 2020 by Superfluous J

[The Aziz]

I'm still surprised that so many people have no knowledge of this tool here

It's cpu hungry, as it does a frikkin lot of calculations, but if you set it up properly, it will show you the trajectory and required mid burns. Thing is, you have to choose the body for the assist yourself.

[Arrowstar]

7 hours ago, The Aziz said:

I'm still surprised that so many people have no knowledge of this tool here

It's cpu hungry, as it does a frikkin lot of calculations, but if you set it up properly, it will show you the trajectory and required mid burns. Thing is, you have to choose the body for the assist yourself.

KSPTOT author here!  If you have any questions, please post them over on the KSPTOT forum thread and I'll do my best to get back to you. 

And yes, it does use a lot of CPU time for various calculations, but as Elon Musk once said, "space is hard."

[Vanamonde]

There's a difficulty factor, but a bigger problem for me is the delays in waiting for windows. Remember you're not just waiting for one, but for one that will lead to another. 

[Guest]

The Jolian system is terrific for playing with gravity assists.

 

[The Aziz]

2 hours ago, Vanamonde said:

There's a difficulty factor, but a bigger problem for me is the delays in waiting for windows. Remember you're not just waiting for one, but for one that will lead to another. 

True dat, but if you can afford to wait a bit (sometimes QUITE a bit) then you can really save significant amount of fuel. Or you can just be so lucky like Voyager mission was, it made few flybys only because planets were in correct positions at the time.

That said, I used the mentioned tool only once, on my way to Sarnus. Now, the usual transfer would give me a ludicrous speed on approach, but with going nearby Jool first, I was able to get captured by the gravity much cheaper, nearly effortlessly, by using, again, assists from Sarnus' moons. But that maneuver cost me 51 2 years.

2 years more, that is.

[ExtremeSquared]

On 6/28/2020 at 2:16 PM, linuxgurugamer said:

Problem with gravity assists is that you have to be extremely accurate. Most people aren't that good.

Unless you're pretty lucky, floating point errors in the physics engine will ruin complex gravity assists even if you understand the concept and set everything up properly.
Using tylo and ike for crude gravity assists can still be done easily enough though.

[Guest]

4 minutes ago, ExtremeSquared said:

Using tylo and ike for crude gravity assists can still be done easily enough though.

And the other Jolian moons. I've learned to park myself into orbit around any of the big ones from a Hohmann transfer to Jool with only about 200 m/s. Usually takes two passes. With no gravity assists insertion into Jolian orbit costs easily ten times that.

[Laie]

14 hours ago, Brikoleur said:

The Jolian system is terrific for playing with gravity assists.

...wether you want to or not. Sometimes it feels like a pinball machine.

[Guest]

35 minutes ago, Laie said:

...wether you want to or not. Sometimes it feels like a pinball machine.

I once got a World's First notification for escaping the Sun's gravitational influence, and went "wait, what? I didn't do that, must be a bug."

Turns out I had left a bit of interstage debris floating around somewhere in the Jolian system.