Aldrin Cyclers

[shynung]

I just found this in Project Rho:http://www.projectrho.com/public_html/rocket/infrastructure.php#id--Aldrin_Cyclers

Take the habitat module, the hydroponics, and the storm cellar and make it into a space station. Spend enough propellant to delta-V it up into an orbit that passes by Mars and eventually returns to Earth. It will regularly pass by Earth and Mars for the rest of eternity, with a little mid-course correction now and then. So you now have a habitat module delta-Ved for a Mars mission that can be re-used. It is a Cycler.

My question is, how do I set up a space station on a cycler orbit, say, between Kerbin and Duna?

Edited August 27, 2014 by shynung

[Sirine]

Further explain what is Aldrin Cyclers.

Possible answer:-
http://forum.kerbalspaceprogram.com/threads/51227-The-possiblility-of-a-Mars-Cycler-in-KSP
http://www.reddit.com/r/KerbalAcademy/comments/1x06wa/how_to_make_a_kerbinduna_aldrin_cycler/
http://www.reddit.com/r/KerbalSpaceProgram/comments/2ar0ix/building_an_aldrin_cycler_system_is_it_possible/
http://www.reddit.com/r/KerbalSpaceProgram/comments/1sspoy/aldrin_duna_cycler_launched_and_in_position_for/

ANSWER:- http://forum.kerbalspaceprogram.com/threads/49803-the-cyclers-difficulty-inane?p=650160&viewfull=1#post650160 Edited August 26, 2014 by Sirine

[Kasuha]

The matter with cyclers is, they're not on optimized transfer routes. That wouldn't be a problem since they can stay on that trajectory for long time without spending any substantial dv, but to get on the cycler, you need to spend that inefficient dv on your ship - and you can get to Duna significantly cheaper. Kerbals don't really need to spend the travel on large space station, having stations on Duna and Kerbin orbits is much more useful and flexible.

And most importantly, the cycler orbit is extremely unstable. You need to make corrections after each pass or you're not going to meet the planet anymore.

[Red Iron Crown]

There's not really a good reason to make a cycler in KSP as Kerbals don't require living space or other equipment for extended journeys, but don't let that stop you; there's not much use for space stations or rovers either but they're still fun to make. If I were attempting this I would set the cycler's orbit so it never enters the SoI of either planet and instead just comes fairly close to it, it should be much more stable that way. Have low mass shuttles to do the actual SoI entry and exit, but remember that these ships will need more dV than for a more conventional transfer to the planet. The savings are in not having to carry all the extra equipment that your particular role play requires.

[Kasuha]

If I were attempting this I would set the cycler's orbit so it never enters the SoI of either planet and instead just comes fairly close to it, it should be much more stable that way.

You cannot build a cycler that way. Each time you're at Kerbin or Duna, you need Kerbin and Duna to be in specific phase angle. But they get to this phase angle at different points of their orbits each time so no body on stable orbit can be at each of them. You need to make a gravity assist every time you pass Kerbin, Duna, or either, and shift your trajectory by appropriate angle to make the next visit at the right place.

[Red Iron Crown]

That's a good point, I just ran some numbers and it technically is possible but not practical, the orbits will realign to the second after, oh, 34 million Kerbin years. They'll probably have a few windows much sooner that aren't down to the second, but it's still a long, long time before they get close (assuming we don't overflow the time counter first). Thanks for the correction.

Probably only feasible to use the non-SoI entering cycler among Laythe, Vall and Tylo, with their convenient resonance.

[Kasuha]

I ran a few numbers as well and my result is that the cycler should be possible as long as the gravity assist is possible.

Point 1: execute ejection from Kerbin which meets Kerbin again on descending leg in 801 Kerbin days (801d 3h 50m 1s, 17315401 s, including the pass-through). At intercept, you need to get gravity assist that will deflect you by 42.7 degrees, sending you for another intercept in 801 days.

Point 2: execute such ejection in phase where you will make a near miss of Duna SOI on either leg of your trajectory.

The gravity assist is pretty strong, though. I'm not sure if it is possible. Of course two-phase trajectories should be possible as well (i.e. shorter trajectory to meet Duna and return in slightly under a year, then gravity assist for shorter trajectory to meet up again after 801 days. Two Kerbin intercepts per one Duna visit.

Edit: on second thought, the deflection is not by 42.7 degrees. The position of intercept moves by 42.7 degrees but the deflection should send the ship from descending leg to another ascending leg so the angle difference is smaller because both intercept and ejection angles subtract from the phase shift.

Edited August 26, 2014 by Kasuha

[psyper]

Cyclers would be useful if you use lifesupport mods - have a large ship with crew quarters, large lifesupport supplies and a means to recycle them (hydroponics?) then all you need to do is get the crew launched from kerbin and meet the cycler as its passes through the system - you spend the same amount of dv but because your ship doesn't have any lifesupport on it then it can be smaller than a ship required for the journey - the crew spend their time and the resources on their trip out to duna - course correct the cycler at duna and then eject their small craft and do an aerobreak. meanwhile the cycler is on its way back to kerbin recharging its lifesupport. Wouldn't be too much hassle to set up maneuver nodes once a year-ish with kerbal alarm clock.

Interesting idea. I'm guessing it would work for Jool too?

[cantab]

I've been wanting to try one of these for a while, good to see they're possible in KSP.

I can see refuelling from a cycler depot being useful, since you wouldn't need to carry your fuel for your insertion burn on your ejection burn. Not such an issue for Kerbin-Duna in stock when you can freely aerocapture either way, but in a FAR+DRE setting it might help, or maybe a Kerbin-Dres cycler if you fancy doing stuff there.

Of course the big issue is whether the benefit from that offsets the extra dV needed for the non-optimal transfer. (And you have to get the fuel on the cycler in the first place, so it might be best suited to resource mod settings where you could mine it from Ike or even an asteroid.)

[shynung]

Thanks for the answer, I really appreciate it.