Buzz Aldrin's Cycler Orbits - Are they useful in KSP?

[Goddess Bhavani]

Yes, there is a type of orbit named after Buzz Aldrin of Apollo fame!

The Aldrin Cycler orbit proposes placing a transit vehicle in an orbit that periodically encounters 2 or more bodies - potentially unstable due to being thrown off by successive gravity assists, a Cycler Orbit could nevertheless be setup to ferry crew, supplies, and taxi vehicles attached to a long endurance interplanetary vessel.

Fascinated, I thought to repurpose an old Tech I "primitive orbital station" into a Kerbin - Minmus - Mun cycler tug only to realize it's not as efficient as I hoped; while it was certainly entertaining to catch the speeding tug as it passed Kerbin periapsis, I realized the ascending Minmus surface lab module required quite a lot of delta V to chase the racing tug swooping out beyond the Mun; the requirement to conduct a high speed orbital interception meant the same dV could be used to send the lab on a conventional or direct ascent trajectory to Minmus with equal or greater haste.

In the end, sending the POS-1 orbital tug / habitation / lander carrier module directly from Mun to Minmus while the bodies are in the right phase would have 'cost' just 150m/s. Sending the POS-1 down to Minmus to pick up the OS-4 Minmus Lab cost 220m/s to exit Munar SOI, then another 220m/s (this time towing a 30 ton lab/tanker station!) to send the resulting gargantuan assembly to Minmus transfer.

Still, with plenty of fuel to waste from no less than 2 20 ton tanker flights in LKO and 1 to POS-1 while it was attached to the OS-3 Munar Orbital Lab, it was very welcome mission experience for multi-vessel interplanetary operations that no doubt I will greatly enjoy being utterly inefficient at. The decision to launch POS-1 on a cycler orbit from the Mun was due to the fact I would have waited a long time for Mun and Minmus to be in the correct position for a conventional transfer, and thought a gravity assist from Kerbin would be a fun thing to try. Then I thought - hey, why not pick up a new station module?

The result is this rather graceful and relaxing 4 minute video depicting the SpaceSheep and the tiny POS-1 shepherding it to Minmus.

Try not to fall asleep!

In the end, I concluded the only plausible utility of setting up the cycler orbit system was that it certainly gave a purpose to an obsolete orbital module and the fuel and veteran crew it carried; Jeb, Bill, Bob and Val easily kept the 50-ton POS-1 / OS-4 assembly under tight control from rendezvous, reboost and Minmus orbital insertion; and if their trajectory was unchanged, they can drop off OS-4 in Minmus SOI and continue onwards on their cycler orbit to encounter Mun and return to LKO in 30 days with no further dV expenditure.

All in all, pretty good re-cycling (no pun intended) of an old 10 ton Primitive Orbital Station! The crew of the OS-4 mission was actually drawn from one of the major Facebook KSP groups, giving new life to my Primitive Orbital Station series that sat long dormant while I messed with huge, impractical rotary-winged flying machines!

ps. Spacesheep!

[Hotaru]

I don't think cyclers are meant to save delta-v per se, it's more like they allow you to have a big, comfortable ship for the interplanetary transfer while only having to launch a small shuttle craft to get to it--which translates to a smaller launch vehicle, less on-orbit assembly, etc. per transfer, once the cycler is set up.

Also, cool video! I did not fall asleep.

[cantab]

The "gotcha" is that in order to catch the cycler you need just as much delta-V as it takes to make the transfer directly. With no need for life support and the relative ease of aerocapturing at either end of the trip there's not much point using a cycler ship.

[GarrisonChisholm]

Beautifully entertaining, and thank you for including the engineering specifics for the transfer- I had wondered personally if this were at all a reasonable proposition.

[Rocket Farmer]

As stock KSP stands its of very little value. Getting an intercept with the cycler means your landing ship has enough DV to get to Kerbal by itself.

In stock the only use I could see was if you were running an ultra efficient science mission and kept the science lab and your kerbin deorbitor on the cycler while just landing a very small lander once (any more than 1 planned landing and the gains are offset by the lost science from no science lab in orbit around the target body). That way you don't have to pay the DV cost to decelerate and reaccelerate the science lab and deorbitor.

If you use a mod for life support it becomes more reasonable. If you had to deal with the heavy shielding from cosmic radiation when between planets (like NASA does) it becomes a good idea.

My question is more the physics of it. Can you get an orbit that on every loop intercepts kerbin on one end and Duna on the other without burning tonnes of DV in course corrections?

[Zephram Kerman]

Can you get an orbit that on every loop intercepts kerbin on one end and Duna on the other without burning tonnes of DV in course corrections?

I gather the Cycler orbit only works for a single point of reference, such as Kerbin - Mun, or Duna - Ike, etc. The varying phases and distances of two planetary bodies would mess it up. Correct me if I'm wrong?

On the bright side, I can see this making sense IRL. Something like Bigelow's space hotels would certainly take advantage of such a setup. Take a station full of tourists from LEO to the Moon and back, in style, with low operating cost.

A space plane is much less massive than a hotel. So it makes sense to do the transfer orbit burns in the smaller vehicle.

To make it even cheaper, the space plane could accompany the hotel through the whole tour. That saves the cost of undoing the transfer orbit burn. Then, a few hours before Earth periapsis, everyone gets in the plane which then does a small course correction to set up for aerobrake and landing.

[cantab]

The whole idea is it works for things like Earth-Mars, and by implication Kerbin-Duna. In theory it needs no course corrections but in practice you'll never get your path perfect, I reckon you'll need at least one correction per cycle.

[gavman420SSJ]

I gather the Cycler orbit only works for a single point of reference, such as Kerbin - Mun, or Duna - Ike, etc. The varying phases and distances of two planetary bodies would mess it up. Correct me if I'm wrong?

On the bright side, I can see this making sense IRL. Something like Bigelow's space hotels would certainly take advantage of such a setup. Take a station full of tourists from LEO to the Moon and back, in style, with low operating cost.

A space plane is much less massive than a hotel. So it makes sense to do the transfer orbit burns in the smaller vehicle.

To make it even cheaper, the space plane could accompany the hotel through the whole tour. That saves the cost of undoing the transfer orbit burn. Then, a few hours before Earth periapsis, everyone gets in the plane which then does a small course correction to set up for aerobrake and landing.

the intended benefit of a cycler isn't dv (fuel savings), it's time savings for each payload. you set up one cycle ship going out and another coming back. each full orbit may take years, but the time to target is much less. with multiple cycling ships you could have incoming and outgoing ships at regular intervals, like airplanes. so the space hotel guests would be switching hotels at the moon, while their outbound "flight" continued out on the long leg of its orbit.

[Rocket Farmer]

I'm hearing you say that while the perapsis would be around kerbin the aopsis would be well past the mun so that the time it took for the ship to complete one orbit would be the same time as it takes for the mun to complete one orbit around Kerbal in (one munar month). That would be feasible even with the requirement for a encounter both when outbound and inbound (just have to match the wide angle of your orbit). Also this may not be possible in Kerbin as your apoasis might lie outside of kerbins sphere of influence.

The other problem with that is that it's intensely DV inefficient. Not only would you have a very large DV burn to catch the cycler (because you are catching a much faster orbit than otherwise required) but instead of efficiently being at your aopsis (and thus slowest speed) when you hit the mun you would still be moving very fast meaning you would have to burn a bnch more DV to catch orbit around the mun.

So I don't think it's speed they ar after with the cycler.

[GoSlash27]

The "gotcha" is that in order to catch the cycler you need just as much delta-V as it takes to make the transfer directly. With no need for life support and the relative ease of aerocapturing at either end of the trip there's not much point using a cycler ship.

^ This. In fact, a direct transfer takes *less* DV and less time. The really short answer is "no"; cyclers have no practical advantage in KSP.

Best,

-Slashy

Edited September 18, 2015 by GoSlash27

[BagelRabbit]

ps. Spacesheep!

After minutes upon minutes of careful construction, I present to you the newest in Kerbal technology:

It amiably wanders around the KSC with its rover wheels! It eats scrap metal! And if you keep it well-oiled, it's a reliable source of steel wool!

Yeah, this thing is a terrible rover and it isn't even a very good representation of a sheep. But hey, I had fun making it.

Now what were we talking about again? ...oh, that's right.

Even though cyclers don't have a true practical advantage in KSP, it's still a very satisfying challenge to get one set up! I would strongly recommend trying it as a challenge if you don't have anything better to do. It's possible with any ship with enough delta-V, but it ain't easy.

I will also mention, as always, that your ships are absolutely beautiful. I definitely think this one could benefit from a few tomato slices/beef patties/hamburger buns, though. Then again, in my opinion, everything could benefit from some tomato slices and hamburger buns...

-Upsilon

[GarrisonChisholm]

After minutes upon minutes of careful construction, I present to you the newest in Kerbal technology:

http://i.imgur.com/sTKWmKy.jpg

It amiably wanders around the KSC with its rover wheels! It eats scrap metal! And if you keep it well-oiled, it's a reliable source of steel wool!

Yeah, this thing is a terrible rover and it isn't even a very good representation of a sheep. But hey, I had fun making it.

Now what were we talking about again? ...oh, that's right.

Even though cyclers don't have a true practical advantage in KSP, it's still a very satisfying challenge to get one set up! I would strongly recommend trying it as a challenge if you don't have anything better to do. It's possible with any ship with enough delta-V, but it ain't easy.

I will also mention, as always, that your ships are absolutely beautiful. I definitely think this one could benefit from a few tomato slices/beef patties/hamburger buns, though. Then again, in my opinion, everything could benefit from some tomato slices and hamburger buns...

-Upsilon

You have some fairly non-sheepish competition Kitt!

[selfish_meme]

I saw a video of a guy set up a cycler mod once, it only required 80ms correction each end he was having trouble detaching it from the timeline to self maintain.

- - - Updated - - -

So if its 2150ms for a Duna transfer (non efficient) and 2400ms into LKO, would it cost the full 2150ms to catch the cycler briefly? Or would it be a much smaller amount?

[Goddess Bhavani]

I gather the Cycler orbit only works for a single point of reference, such as Kerbin - Mun, or Duna - Ike, etc. The varying phases and distances of two planetary bodies would mess it up. Correct me if I'm wrong?

On the bright side, I can see this making sense IRL. Something like Bigelow's space hotels would certainly take advantage of such a setup. Take a station full of tourists from LEO to the Moon and back, in style, with low operating cost.

A space plane is much less massive than a hotel. So it makes sense to do the transfer orbit burns in the smaller vehicle.

To make it even cheaper, the space plane could accompany the hotel through the whole tour. That saves the cost of undoing the transfer orbit burn. Then, a few hours before Earth periapsis, everyone gets in the plane which then does a small course correction to set up for aerobrake and landing.

I think I am going to definitely try this - the next step forward from Minmus / Mun station ops would be to send one out to interplanetary space to test the sort of logistics I need for a Duna or Eve mission. I haven't actually attempted to go that far out first so if I spend a while to work out the orbital characteristics of a Duna Cycler it would be very educational indeed (I mainly mess with plane and helicopter replicas in KSP).

Having tourist contracts to fund station construction and operation partway would certainly make having such a large endeavour fruitful. You're definitely right about keeping the shuttle on the cycler too - it's going to come back around eventually anyway, and realistically NASA / Roscosmos likes to keep an escape vehicle on hand at all times.

Something tells me I'm going to have some sort of space-Titanic incident though, kraken threat and all

After minutes upon minutes of careful construction, I present to you the newest in Kerbal technology:

http://i.imgur.com/sTKWmKy.jpg

It amiably wanders around the KSC with its rover wheels! It eats scrap metal! And if you keep it well-oiled, it's a reliable source of steel wool!

Yeah, this thing is a terrible rover and it isn't even a very good representation of a sheep. But hey, I had fun making it.

-Upsilon

Wow! I will definitely want to keep a small herd of those steel-wool producing rover sheep around the base! Would you be posting / PMing the craft file anywhere?

Lol! Thanks for the compliment. I'll think of a way to add burger patties to my station program... maybe an orbital diner? The burger mod parts act as batteries and fuel tanks, they have an uncanny practical side too.

I saw a video of a guy set up a cycler mod once, it only required 80ms correction each end he was having trouble detaching it from the timeline to self maintain.

- - - Updated - - -

So if its 2150ms for a Duna transfer (non efficient) and 2400ms into LKO, would it cost the full 2150ms to catch the cycler briefly? Or would it be a much smaller amount?

In my video example it took 1,200m/s for the "spacesheep" lab to launch out from LKO and then intercept the cycler: 700+ m/s for the initial intercept solution and 500m/s to match velocity with the tug. I could not schedule a more 'graceful' intercept solution due to time constraints. So it's practically Duna levels of dV for an MKO intercept.

POS-1 did a reboost to get back to Minmus transfer 2 hours after the lab arrived, taking another 200+ m/s of dV and about 13 tons of fuel carried in wet lab storage (the cones of the spacesheep are stock cone tanks).

So it's quite an insanely inefficient first attempt by moi, although I guess experience would offset the inefficiency somewhat with less clumsy vehicles and better/cheaper refuelling infrastructure.

The spacesheep was flown to the tug using its second stage; there is no third stage and was loaded on the pad with just enough fuel to reach LKO, then rendezvous with a pair of 20 ton tankers to fuel it completely for both the cycler intercept, docking and long duration operations on Minmus.

When I reached the cycler / tug I realized there was no purpose keeping a second Poodle engine, offloaded fuel to POS-1 and spacesheep tanks, sent someone out on EVA to detach support struts and ditched the stage.

Edited September 19, 2015 by pandoras kitten

[selfish_meme]

Theres a scifi book with tethered cans in a cycler orbit, maybe ion propulsion core with winches for the cans

[MalfunctionM1Ke]

This is awesome! I didnt know that such a concept existed allthough I am not sure how to put it to use

[Captain H@dock]

This is awesome! I didnt know that such a concept existed allthough I am not sure how to put it to use

The key is that dV is a uniform measurement of your craft capability to change speed. It is therefore taking into account the mass of your craft. Saying "it saves no dV" doesn't really make sense if you're comparing two chips of widely different masses, because dV isn't a mesure of cost. dV*Mass is the real mesure of cost.

So you only accelerate once that huge ship (the cycler) which will contains all the nice systems required for long duration space travel, and when it swings by the body you are at, you take a smaller ship to accelerate to the cycler speed (same dV, much lower fuel/engines requirements. Also, not intended for long period of use, so reduced life support systems and crew accomodation). You dock to the cycler, transfer the crew and the supplies. The smaller ship undocks and slows back down to orbit. You sit in the cycler until you reach destination with all the luxury of an interplanetary cruise boat.

Once there you repeat the process with another smaller chip.

SOI probably render the concept very un-efficient since cycler trajectories rely on n-body. You would need to compensate with big correction burn, make it pointless. Also, cost doesn't really limit you in KSP... If you're going to duna several times, you have millions

Edited September 19, 2015 by Captain H@dock

[MalfunctionM1Ke]

The key is that dV is a uniform measurement of your craft capability to change speed. It is therefore taking into account the mass of your craft. Saying "it saves no dV" doesn't really make sense if you're comparing two chips of widely different masses, because dV isn't a mesure of cost. dV*Mass is the real mesure of cost.

So you only accelerate once that huge ship (the cycler) which will contains all the nice systems required for long duration space travel, and when it swings by the body you are at, you take a smaller ship to accelerate to the cycler speed (same dV, much lower fuel/engines requirements. Also, not intended for long period of use, so reduced life support systems and crew accomodation). You dock to the cycler, transfer the crew and the supplies. The smaller ship undocks and slows back down to orbit. You sit in the cycler until you reach destination with all the luxury of an interplanetary cruise boat.

Once there you repeat the process with another smaller chip.

SOI probably render the concept very un-efficient since cycler trajectories rely on n-body. You would need to compensate with big correction burn, make it pointless. Also, cost doesn't really limit you in KSP... If you're going to duna several times, you have millions

Anyway, thats pretty interesting and you would have a fast and regular route to Mars and back if you do it with 2 or more cyclers.

I am glad you guys brought this Thread up

[Kegereneku]

Cycler's DO save deltaV... indirectly.

Their point is to avoid accelerating-decelerating each time an important mass : the live-support infrastructure.

ex : Rather than needing to spend (say) 100tons of propellant to accelerate (then decelerate) a large ship containing both Engine, fuel, A LARGE LIFE-SUPPORT INSTALLATION (and the fuel to propel that mass) it would allow to just use a shuttle which can be kept more versatile later.

So they are to be useful if :

- You need Life-support (space farm, centrifuge gravity...etc)

- You already have comfortable habitat and life-support at your destination

Also, it can allow tremendous economies of scales. If we ever were to colonize a close by planet, a Cycler would over a few years save as much dV as its life-support would have added for the same number of colonist.

Though, just saying : I don't believe we will ever have a need for them. Colonizing a planet is less efficient that simply living in asteroid belt (though you could use an asteroid-cycler).

[Skorpychan]

Cyclers don't save dV. They can't; you still need to get into their orbit to dock with them.

They DO, however, save resources. You don't need to put up all that mass every time you want to take a big ship to your desired location.

However, since Kerbals will happily spend decades crammed into their seats, it's irrelevant unless you're using it for something else, such as a battery charger, refinery, or fuel storage.

I gather the Cycler orbit only works for a single point of reference, such as Kerbin - Mun, or Duna - Ike, etc. The varying phases and distances of two planetary bodies would mess it up. Correct me if I'm wrong?

On the bright side, I can see this making sense IRL. Something like Bigelow's space hotels would certainly take advantage of such a setup. Take a station full of tourists from LEO to the Moon and back, in style, with low operating cost.

A space plane is much less massive than a hotel. So it makes sense to do the transfer orbit burns in the smaller vehicle.

To make it even cheaper, the space plane could accompany the hotel through the whole tour. That saves the cost of undoing the transfer orbit burn. Then, a few hours before Earth periapsis, everyone gets in the plane which then does a small course correction to set up for aerobrake and landing.

Your Wikipedia link put me onto reading about space stuff again. Great. There goes my weekend.

It did, however, lead me to this: http://settlement.arc.nasa.gov/70sArt/art.html - 1970s space colony artwork.

Edited September 19, 2015 by Skorpychan

[selfish_meme]

I think this is the one I saw previously

https://m.reddit.com/r/KerbalSpaceProgram/comments/2xd3u4/kerbal_aldrin_cycler_i_did_the_math/

[Goddess Bhavani]

Cyclers don't save dV. They can't; you still need to get into their orbit to dock with them.

They DO, however, save resources. You don't need to put up all that mass every time you want to take a big ship to your desired location.

Great posts guys, thanks for pointing out the key point -> Big well equipped ship launches once on cycler duty, small fast boats hitch a ride on it from both ends; possibly I haven't realized the true value of the cycler yet as I was doing it "backwards", having a large laboratory lander hitch onto a tug with 1/3 the mass.

I might follow up on this with a follow on cycler habitation station, perhaps for tourist use or long enduance spaceflight training, that, would have a large multi-module station on a Mun/Minmus/Kerbin cycler orbit aimed well outside Mun / Minmus SOI to reduce the orbital corrections needed for sustained operations. I was thinking I could also use cargo supply ships as a means to 'top up' the cycler complex dV by firing engines whist being attached to the station.

We'll call this a 30-day limited duration cycler just to test competency of designing and operating regular shuttle services from Kerbin, and as a means for future payloads and crew to hitch a ride to Minmus for resource exploitation (whenever I get that far in the career tech tree!).

Then once I'm done with that, perhaps then would be a good time to see if I can send out interplanetary probes to see how a proper Duna cycler orbit looks like - can't wait to try it!

I think this is the one I saw previously

https://m.reddit.com/r/KerbalSpaceProgram/comments/2xd3u4/kerbal_aldrin_cycler_i_did_the_math/

Saving this for reference - I saw the key points; the challenge of intercepting a very fast inbound cycler, and 450m/s dV needed for corrections on each cycle.. let's see, if I make the periapsis somewhere around Munar orbital distance, it would be much easier to intercept the inbound cycler due to the reduced velocity differential.

Edited September 19, 2015 by pandoras kitten

[waterlubber]

That explains the accidental cycler orbit that I set up on Sarnus. Nailed 3 flybys.

[GoSlash27]

Cycler's DO save deltaV... indirectly.

Their point is to avoid accelerating-decelerating each time an important mass : the live-support infrastructure.

ex : Rather than needing to spend (say) 100tons of propellant to accelerate (then decelerate) a large ship containing both Engine, fuel, A LARGE LIFE-SUPPORT INSTALLATION (and the fuel to propel that mass) it would allow to just use a shuttle which can be kept more versatile later.

So they are to be useful if :

- You need Life-support (space farm, centrifuge gravity...etc)

- You already have comfortable habitat and life-support at your destination

Also, it can allow tremendous economies of scales. If we ever were to colonize a close by planet, a Cycler would over a few years save as much dV as its life-support would have added for the same number of colonist.

Though, just saying : I don't believe we will ever have a need for them. Colonizing a planet is less efficient that simply living in asteroid belt (though you could use an asteroid-cycler).

Kegereneku,

The original question was about cyclers in KSP, not RL. Kerbals do not need life support or comfortable habitat, so cyclers aren't useful at all *in- game*. In addition, the transfer shuttles burn more fuel to match a cycler orbit than they would need to establish a Hohmann transfer and the trip is longer.

Best,

-Slashy

[Der Kosmos]

If you are using a life support mod, it might be interesting to have a cycler that was a closed loop habitat to cut down on life support requirements on interplanetary trips.