Mun/Kerbin Cycler

[pigletx2]

So my question is, is it possible to set up an orbit which passes between Kerbin and mun SOI(or gets close to the mun, but not in SOI) once every orbit without every using fuel to stop it from leaving the Kerbin system(kerbin/mun/minmus)?

Edited December 31, 2013 by pigletx2

[Taki117]

Not that I am aware ( at least not to that extent) but you can put yourself on a free return trajectory from kerbin, around the mun, and back. (it's what apollo did, in case something went wrong.)

[KvickFlygarn87]

Nope, you can't "yo-yo" between Mun and Kerbin, you'd get flinged into Solar orbit or into a lithobrake maneuver.

[Redjoker]

What you want is called a cycler, it is where every few passes a spaceship encounters a body with little to no fuel use. Here is a proposal for Lunar cycler http://cbboff.org/UCBoulderCourse/documents/LunarCyclerPaper.pdf I believe people have done Duna cyclers using a little rcs for corrections but, a Mun Kerbin one may not be possible without n-body.

[Guest]

Not necessarily n-body, but it would require something better than what we have now. A variation on the limited 3-body problem (bodies are in fixed orbits, so you don't worry about their movement, only the vessel) or a Newtonian approach would both be viable.

[pigletx2]

Darn. Was hoping someone could come up with a solution. I'll leave this for a day as unsolved, and if no-one gets something workings, it's not possible.

[Kasuha]

This is one of things which sound really cool when you talk about them, but are extremely impractical to have.

I think it might be possible to calculate a set of two orbits around Kerbin which intersect Mun's trajectory and each Mun encounter switches the ship from one orbit to the other. It's just not something obvious - you need to take appropriate equations and start crunching numbers.

But even if you find such orbits, they're definitely going to be unstable, meaning any deviation from ideal position and timing will cause the next encounter to deviate even more. Regardless whether in physics mode or on rails, the ship would deviate from ideal orbit gradually more and more without proper upkeep.

Edit: here you have three more ideas which involve putting the ship on the same orbit around Kerbin each pass, but with phase shift. Of course I did not do the math but I'm pretty sure there are enough free parameters to allow a solution.

Edited December 29, 2013 by Kasuha

[Taki117]

snip

Not to blow holes in anything, but wouldn't this result in a lithobrake maneuver at the Mun?

[Kasuha]

Not to blow holes in anything, but wouldn't this result in a lithobrake maneuver at the Mun?

One of the three would, but this is just proof-of-concept graphics. The point is, there's whole range of parameters with which if you enter the Mun SOI, you will exit it with the same parameters. And you just need to pick those which allow you to pass above surface and allow another intercept with the same parameters in an orbit of a few.

It's about doing the math. I can point out there are potential solutions and how do they look like, but I am not willing to do the math because as I wrote above, the thing is cool to talk about but totally impractical to implement.

[pigletx2]

Looks to me like it's solved: It's really, really hard to make a cycler between the mun and kerbin. Oh well.

[Kerbart]

Cyclers are rather pointless in KSP. You'd still need to speed up and slow down to enter/leave the cycler at your origin and destination. In real life there's value in that because you'll need to "pay" for radiation shielding, life support, etcâ€â€heavy gear that only needs to be sped up once between say, Earth and Mars.

But in KSP your cycler doesn't need all that kind of heavy equipment. Unless you can beam your Kerbals up/down to the surfaces of the celestial bodies with disregard for the velocity difference (Larry Niven's stepping discs are not going to work) it won't do you any good.