Cycler Orbits (Mun, Duna and Jool)

[Swifty]

Hi,

I've just read about cycler orbits in Buzz Aldrin's book Mission to Mars and was wondering:

a) Does anyone know if it is possible to set up Cylcer Orbits in KSP?

Has anyone done it before?

c) Does anyone have a handy simple maths article on how to calculate them?

Done a few searches for this and other than technical papers for real world physics not found anything conclusive for KSP. All the threads I've found finished without a conclusive answer.

[PakledHostage]

I've just read about cycler orbits in Buzz Aldrin's book Mission to Mars and was wondering:

a) Does anyone know if it is possible to set up Cylcer Orbits in KSP?

Has anyone done it before?

c) Does anyone have a handy simple maths article on how to calculate them?

a) I think it should be possible, but you'd need to be very precise with your trim manoeuvres.

I did a "proof of concept cycler" trajectory about 9 months ago. It wasn't a true cycler trajectory because it wouldn't have continued to cycle, but it did originate at Kerbin then intercept Duna before returning to Kerbin on the same orbit. I would have had to move my Duna flyby periapsis closer to Duna to set up a true cycler.

c) Unlikely. I did it by patching together the orbital conics in a MathCAD spreadsheet (we didn't have manoeuvre nodes yet at that time). I can't think of an easier way than that other than to try using the manoeuvre nodes. I'll see if I can find my notes for that mission but it might take a few days.

Edit:

Here's a video showing the trajectory intercepting both Duna and Kerbin. The trajectory in the map view was flicking back and forth between them.

Edited August 2, 2013 by PakledHostage

[Swifty]

Thanks for the answer PakledHostage. Yeah I'd read your thread before posting. What I wasn't clear on the phrases " it wouldn't have continued to cycle". Does this mean that it on the next pass it would be so far away from Duna that course correction burns to force an intercept would exceed the that of a standard Hoffman Transfer?

[PakledHostage]

What I wasn't clear on the phrases " it wouldn't have continued to cycle". Does this mean that it on the next pass it would be so far away from Duna that course correction burns to force an intercept would exceed the that of a standard Hoffman Transfer?

Yes. It would not have intercepted Duna at all on the next pass. Depending on the type of cycler trajectory that you're trying to set up, an intercept may not occur every orbit. I think only an Aldrin Cycler trajectory will intercept every orbit.

In this case, the trajectory merely demonstrated that it was possible to set up a transfer with sufficient accuracy to intercept Duna and Kerbin on the same orbit, with very little in the way of orbital trim manoeuvres required to return to Kerbin. A true cycler would have to use a gravitational assist from Duna to set up the next intercept with Kerbin, and the gravitational assist from Kerbin would then set up the next intercept with Duna. Your craft may have to orbit for several years between each set of intercepts, however.

[Swifty]

I've been trying to under stand this Aldrin Cycler orbit. My understanding is that a Cycler orbit intercepts both bodies every orbit with transfer leg times that varie from short hops to really long ones going all the way round the sun and back.

I'm going to crack out my rust math skills and try and set up a solver for calculating these orbits. To bad I no longer have acces to MATLAB going to have to use sci lab or numpy I guess.

Now the only advantage of using a Cycler orbit is so you don't need to expend fuel accelerating life support, radiation shielding, accommodation etc up to transfer velocities. However, it still requires what ever is being ferried onto the Cycler craft to be accelerated up to this speed. Thus Cycler orbits are not very useful for heavy unmanned cargo as a Hoffman transfer would be more cost effective?

Is this the correct understanding of the Cycler system, it's basically like an ocean liner that never stops. Only useful because of the overhead sustaining life requires.

[PakledHostage]

Sounds like you're well on your way... Have a look at the orbital characteristics in the Wiki. They should get you started with planning your intercepts.

And I think the ocean liner analogy is quite apt. A cycler only saves resources if you maintain it for long enough to offset the cost of building it/maintaining it against the cost of flying all of your life support and habitation infrastructure on every mission.

[metaphor]

shows how Aldrin cyclers work. Basically you're trying to arrive back at Kerbin when Kerbin and Duna are at the same relative positions as when you first launched. Then with the right gravity assist from Kerbin, you will be going along the same trajectory but rotated. So the cycler orbit should have the same period as the Kerbin-Duna synodic period, which is about 227.4 days.

There is no easy math way to calculate the exact trajectory since Duna's orbit is elliptical so you'll have slightly different orbits each time.