Creating (semi?)stable multi-body orbits.

[Pbhead]

Since this thread: http://forum.kerbalspaceprogram.com/showthread.php/49803-the-cyclers-difficulty-inane

Never quite got off the ground, due to the usual single post newbie thing...

It would be quite something to create a object that gravity assists itself between two bodies. We cant expect such something to maintain such a orbit for very long, but... I would be very interested in what some of the smarter maths people on these boards have to say about how we might create such orbits.

I think If you could tell your ship while in kerbin's SOI to encounter duna, then encounter kerbin again, We could call that close enough. (Maybe start -> destination -> start -> destination encounter if you want to get super fancy)

Even a kerbin -> moon > kerbin > moon free return trajectory like thing would be fancy.

Edited September 13, 2013 by Pbhead

[Meltro]

Unfortunately, it's not that simple. Although you could, in theory, do this with two intercept calculations it would end up looking something like a rotosketch drawing. What is really needed to do this is a frame of reference between the two bodies to be orbited that has zero angular velocity between the two. To my knowledge, such a frame of reference is unavailable.

[Captain Sierra]

Unfortunately, it's not that simple. Although you could, in theory, do this with two intercept calculations it would end up looking something like a rotosketch drawing. What is really needed to do this is a frame of reference between the two bodies to be orbited that has zero angular velocity between the two. To my knowledge, such a frame of reference is unavailable.

Such mechanics would effecively require the creation of a planet that has no mass, no volume, no visual appearance, but instead a virtual mass relative to the two masses. Basically a barycenter. Devs said no. Why? nobody knows. Was that a mistake? Probably given the number of people that ask for it. Barycenters and lagrange points significantly complicate the orbital mechanics and would likely require a switch from patched conics to Newtonian orbital mechanics on the physics and potentially even taking planets off rails, which complicates stuff . . . a lot. That leads to more intense physics calculations and thus more CPU power required (not that we don't have that problem already or anything, NO!).

[TheDarkStar]

Such mechanics would effecively require the creation of a planet that has no mass, no volume, no visual appearance, but instead a virtual mass relative to the two masses. Basically a barycenter. Devs said no. Why? nobody knows. Was that a mistake? Probably given the number of people that ask for it. Barycenters and lagrange points significantly complicate the orbital mechanics and would likely require a switch from patched conics to Newtonian orbital mechanics on the physics and potentially even taking planets off rails, which complicates stuff . . . a lot. That leads to more intense physics calculations and thus more CPU power required (not that we don't have that problem already or anything, NO!).

When I asked about it several months ago, I was also told that there were some engine limitations: Massless barycenters would exert no gravity, because they are massless, so planets would not be held. Giving them mass would allow odd things like getting close enough to be ejected faster than light like the old surfaceless sun. You'd also be orbiting empty space.

Edited September 13, 2013 by TheDarkStar

[Burninate]

While yes, there are a lot of changes the devs might be able to make to the engines at some point in the future, let's not focus on that.

*WITHIN THE CURRENT* perfect patched-conic system, are there free return trajectories with sharper ends inside another SOI than a normal parabola? What do the minimum-thrust return trajectories look like?

Is it possible to do a 180 grav-assist on one end, and a 180 turnaround on the other end, and adjust them to balance out using minimal aerobraking & small maneuvering burns?

This is not a well-explored system, because we do not live in a solar system where patched-conic equations rule.

The kerbals do.

What's possible *there*?

[antiquark]

You might be looking for something like this:

http://en.wikipedia.org/wiki/Mars_cycler

http://en.wikipedia.org/wiki/Lunar_cycler

"A Mars cycler (or Earth-Mars cycler) is a special kind of spacecraft trajectory that encounters Earth and Mars on a regular basis. "

"Cyclers are potentially useful for transporting people or materials using little propellant. Instead, they rely on gravity assist manoeuvres to keep them going[1] with occasional powered corrections to maintain the trajectory.[2]"

[CaptainArchmage]

I found this video of an Aldrin cycler between Earth and Mars:

It looks like there are two intercepts for the inner body. The cycler leaves the first intercept, passes by the outer body, and then returns, passing by the inner body at the second intercept on a gravitational slingshot that alters the orbit so the cycle repeats.

In Kerbal Space Program, you probably don't need the cycler to enter Duna's SOI, just pass by with a close enough encounter that you can release a lander or orbiter and launch it towards Duna. You do need the cycler to enter the SOI of Kerbin on return, because you need the gravitational slingshot to alter your trajectory.