Cycler Ships

[Northstar1989]

This is a thread to discuss Cycler Ships- particularly the "Aldrin Cycler" envisioned by Buzz Aldrin to carry humans between Mars and back, and other Mars cyclers. Although, discussing cycler trajectories to other planetary systems besides Mars is perfectly welcome as well...

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

http://buzzaldrin.com/space-vision/rocket_science/aldrin-mars-cycler/

I'm particularly interested in how this technology could be combined with things like Microwave Beamed Power (what if the Cycler Ship carried a heavy nuclear reactor and a gyrotron that it kept disabled for most of the journey, but activated when in close proximity to Earth or Mars to power the "interceptor" or "taxi" ships as they caught up to the Cycler Ship, for instance? The mass of the reactor and radiation-shielding for crew would be a lot less of an issue on a Cycler Ship since it would only have to be accelerated to a Mars-intercepting orbit once...) or solar sails (free course-corrections, anyone?), or basically any other advanced technology intended to save mass/cost that could be implemented with today's scientific understanding. But discussion of the basic idea is of course more important and just as welcome...

I'll try to improve this explanation in the future- I'm tired, and it's *very* late here...

Regards,

Northstar

[Nuke]

certainly would want a power reactor on board. as i understand it the ship just uses a tiny bit of dv to keep the cycle going. tack on some vasmir engines so that you could operate the thing for extended periods. when not thrusting, you could produce an artificial magnetic shield with surplus power to block out some of the charged particles coming from the sun. i figure the main advantage is you could have all the amenities on board, power, artificial gravity, plenty of room, maybe a green house, of course a long duration life support system (perhaps closed loop).

this means you can pack light. just bring a small capsule, fuel, supplies. a majority of the mission time is spent is on the cycler ship itself. i guess you could save some deltav if the cycler is used frequently enough. and you might be able to depart the cycler early go to mars, spend a few days there and catch up to it before it gets too far away. if your lander has isru gear, it might be a good idea to just leave it on mars for future use. it would be great for colonization efforts too.

[Nibb31]

The only point of an Aldrin cycler is that it allows a large habitable area. For anything else, including crew, supplies, propellant, equipment, and spares, you still need to match the orbit of the cycler and leave that orbit when you arrive at your destination, which requires at least the same amount of dV as if you were going direct. The cycler itself also needs to readjust it's trajectory at each end, which is going to cost extra dV, for which the supply ship needs to bring the propellant.

All in all, it's not worth it.

[Kibble]

Don't forget radiation shielding! Apollo or Orion's aluminum walls might be good enough for a journey to the Moon, but in interplanetary space subjected to SEPs, GCRs, and sometimes violent CMEs, you need a bunch of (heavy!) shielding. Accelerating it around all the time is probably not practical. Also IIRC, on (some?) cycler trajectories, the delta vee required for course corrections is small enough that you can use like an ion thruster. If you keep the ECLSS mostly closed-cycle with a Sabatier, all the taxi needs to bring is the crew, some hydrogen gas, and the food for the trip. Maybe.

EDIT : And plastic for the onboard 3D printer! :3

Edited December 9, 2014 by Kibble
3d printing is best printing

[shynung]

The only point of an Aldrin cycler is that it allows a large habitable area. For anything else, including crew, supplies, propellant, equipment, and spares, you still need to match the orbit of the cycler and leave that orbit when you arrive at your destination, which requires at least the same amount of dV as if you were going direct. The cycler itself also needs to readjust it's trajectory at each end, which is going to cost extra dV, for which the supply ship needs to bring the propellant.

All in all, it's not worth it.

Oh, we're not saving on dV here. We're saving on propellant. In other words, rather than dV-ing an entire habitation module, along with all the hardware associated with it, we're just dV-ing a smaller spacecraft carrying only crew and supplies, but no habitation hardware. Other than the first time the cycler is set off, the fuel requirements for each subsequent trip is lowered because we're sending less mass on transfer orbit, despite the dV requirements being almost the same.

Whether it's worth the trouble of sending the cycler ship off in the first place depends on how often trips to Mars are undertaken. A yearly voyage between Mars-Terra would certainly be a solid reason for such a ship. Since there are no such thing as of today... well, you get the idea.

[Kibble]

Regular exchange of astronauts to a Mars or Venus base with a cycler is tantalizingly reminiscent of the 6-month expeditions to Space Station!

[Nibb31]

Oh, we're not saving on dV here. We're saving on propellant. In other words, rather than dV-ing an entire habitation module, along with all the hardware associated with it, we're just dV-ing a smaller spacecraft carrying only crew and supplies, but no habitation hardware. Other than the first time the cycler is set off, the fuel requirements for each subsequent trip is lowered because we're sending less mass on transfer orbit, despite the dV requirements being almost the same.

Not necessarily, because the cycler needs its own propellant to adjust its orbit on each pass. A cycler between Mars and Earth is effectively in an excentric solar orbit. This orbit will only line up perfectly between both planets on vary rare occasions, so you are going to have to adjust the cycler's orbit on each trip. Those manoeuvers are going to be very expensive in propellant due to the mass of the cycler. And the propellant for those manoeuvers is going to have to come on a supply ship, which in turn is going to need more propellant to carry that propellant.

So basically, unless the cost in propellant to adjust the cycler's orbit on each pass is lower than the cost in propellant to simply add a proper hab module to your supply ship, it's not worth it. I suspect it isn't.

[Kibble]

Not necessarily, because the cycler needs its own propellant to adjust its orbit on each pass. A cycler between Mars and Earth is effectively in an excentric solar orbit. This orbit will only line up perfectly between both planets on vary rare occasions, so you are going to have to adjust the cycler's orbit on each trip.

You're overestimating how much ballistic correction is required. Using Venus as an example, the Earth-Venus synodic period is almost exactly 8/5 of a year. An Earth-Venus Hohmann period is about 4/5 of a year. Every eight years a cycler will encounter Earth, and 5 months later encounter Venus. With a system of 5 cyclers, one will encounter Earth every 1.6 years. The cyclers will also have beautiful, almost perfect 5-way symmetry! The orbits do not require any major corrections, outside of the gravity assist occurring when the cycler encounters either destination. Minor corrections can be done with low-thrust, high-efficiency ion drives which could function without refueling for decades.

[shynung]

Not necessarily, because the cycler needs its own propellant to adjust its orbit on each pass. A cycler between Mars and Earth is effectively in an excentric solar orbit. This orbit will only line up perfectly between both planets on vary rare occasions, so you are going to have to adjust the cycler's orbit on each trip. Those manoeuvers are going to be very expensive in propellant due to the mass of the cycler. And the propellant for those manoeuvers is going to have to come on a supply ship, which in turn is going to need more propellant to carry that propellant.

So basically, unless the cost in propellant to adjust the cycler's orbit on each pass is lower than the cost in propellant to simply add a proper hab module to your supply ship, it's not worth it. I suspect it isn't.

I suspect it is. The cycler is a strictly orbit-to-orbit ship, with plenty of time for maneuvering burns. We can fit it with more efficient engines than typical chemical engines, like nuclear thermal or nuclear electric engines that, despite being ultimately heavier, can lower the propellant needs for maneuvering burns at each pass.

Though, I think that ultimately our suspicions on whether the cycler scheme is worth the trouble compared to an integrated hab module depends entirely on how massive the hab module actually is, compared to the supply/crew ship.

[Tex_NL]

All cyclers do have a serious flaw. In order to transfer fuel, crew, cargo and whatever you'll need to dock. And to dock you'll have to match velocities. If you match velocities with a cycler to for example Mars you will be on a trajectory to Mars. Since you've already spend a lot of fuel to get into that trajectory it makes a lot more sense to stay on that orbit and actually go to Mars yourself. Why would you waste another great amount of fuel to stay in Earth orbit?

[Kibble]

Why would you waste another great amount of fuel to stay in Earth orbit?

I actually pictured the taxi as being an expendable capsule. Like it gets launched up (Soyuz-Block D on Proton could probably do it!) rendezvous and docks with Cycler, and stays docked until arrival, where it undocks and makes a minor course correction to enter the planets atmosphere.

[Tex_NL]

I actually pictured the taxi as being an expendable capsule. Like it gets launched up (Soyuz-Block D on Proton could probably do it!) rendezvous and docks with Cycler, and stays docked until arrival, where it undocks and makes a minor course correction to enter the planets atmosphere.

That could work. But if you plan to do that, why do you need the cycler?

[Kibble]

That could work. But if you plan to do that, why do you need the cycler?

Radiation shielding, living space, power (if your capsule doesn't have solar panels, like Apollo), and an advanced, closed-cycle ECLSS. But mostly radiation shielding, because it is so heavy. AFAIK the other stuff isn't that heavy and if you really need extra living space you could just use inflatables or something.

[shynung]

One could, say, limit the radiation shielding to some sort of 'storm cellar' for the astronauts to hunker in whenever the Sun spits out a nasty flare. The rest of the living space can be inflatables, or otherwise built out of lighter materials, shielded just enough to block background cosmic radiation, with additional rad-shielding in the form of water bags. A lot of them would be needed on such a long trip anyway, might as well use them as shields.

[Sandworm]

This line from the wikipedia entry kills it for me "Taxi and cargo vehicles would attach to the cycler at one planet and detach upon reaching the other." That suggests that the cargo pods will have to accelerate up to match that if the Cycler ship. If they are already up to that speed, why bother attaching? If they are already on the same trajectory, they can make the journey on their own. Maybe the cycler could be a living space, a hotel, but you would sill need to accelerate all the consumables.

[Hannu]

Maybe the cycler could be a living space, a hotel, but you would sill need to accelerate all the consumables.

That is cycler's idea. It can be large and massive and have redundant live support equipment. Maybe even some kind of resource recycling (greenhouses for example). Then you do not have to make and accelerate such a large and expensive system for every mission. But that kind of system is reasonable after we have regular manned traffic between the planets. On other words, somewhere on unforeseeable future. It is so long away that we can not say anything about do we really need them. If, for example, some exotic nuclear powered electromagnetic engine gives tens of km/s delta-v, we clearly do not need slow and massive ship on minimum energy orbit.

[sndrtj]

One could, say, limit the radiation shielding to some sort of 'storm cellar' for the astronauts to hunker in whenever the Sun spits out a nasty flare. The rest of the living space can be inflatables, or otherwise built out of lighter materials, shielded just enough to block background cosmic radiation, with additional rad-shielding in the form of water bags. A lot of them would be needed on such a long trip anyway, might as well use them as shields.

Not sufficient if you rely on a greenhouse. Just like you, the plants and animals in your greenhouse are sensitive to radiation. You might save yourself by temporarily hiding in a bunker, but if that means you're going to starve later on, it's not much use.

[Kibble]

Plus coronal mass ejections are the only thing to worry about with radiation - you'll also be exposed to galactic cosmic rays, which aren't just isolated events.

[Sandworm]

Not sufficient if you rely on a greenhouse. Just like you, the plants and animals in your greenhouse are sensitive to radiation. You might save yourself by temporarily hiding in a bunker, but if that means you're going to starve later on, it's not much use.

I assume that plants have a greater radiation tolerance than large animals like us. Trees don't get skin cancer after decades, centuries, in the sun. Also, a seed vault in the protected area could mitigate against the risk of total loss. But I also assume that any radiation, ionizing radiation, sufficient to kill off plants in a greenhouse may also render that greenhouse so contaminated that people might not be able to return to it for a while.

[sndrtj]

I assume that plants have a greater radiation tolerance than large animals like us. Trees don't get skin cancer after decades, centuries, in the sun. Also, a seed vault in the protected area could mitigate against the risk of total loss. But I also assume that any radiation, ionizing radiation, sufficient to kill off plants in a greenhouse may also render that greenhouse so contaminated that people might not be able to return to it for a while.

Mwa, that's unfortunately not really true. Plants can get tumors, and for any given moment just a tiny fraction of a tree is actually alive.

[Rakaydos]

It might be interesting to try somethink like this for a Kerbal Grand tour- put your mothership in a hoffman orbit, but dont circulrize it- instead, wait for the next enounter before recovering your lander.

[Fuzzy Dunlop]

The other big thing about the cycler orbit is the return to Earth. Lets ignore any hab vehicle or radiation shielding for a second. With a normal Mars mission profile all the consumables for the return flight have to be:

1) Accelerated to the Mars transfer orbit

2) Deccelerated into Mars orbit

3) Accelerated into Earth transfer orbit

With a cycler all you have to do is boost all this air, water and food into the cycler orbit and the crew can just rendezvous with it after leaving mars. That's a big fuel saving. When you consider you'll probably want a larger living space than the mars launch vehicle and some radiation shielding - well it doesn't make sense to waste fuel powering that into and out of an orbit around mars where it won't be used.

[m4rt14n]

Has someone made this yet in KSP? I assume you can just stick Mechjeb and KAC in the craft to stop warp on every SOI transfer.

[Northstar1989]

Not necessarily, because the cycler needs its own propellant to adjust its orbit on each pass. A cycler between Mars and Earth is effectively in an excentric solar orbit. This orbit will only line up perfectly between both planets on vary rare occasions, so you are going to have to adjust the cycler's orbit on each trip. Those manoeuvers are going to be very expensive in propellant due to the mass of the cycler. And the propellant for those manoeuvers is going to have to come on a supply ship, which in turn is going to need more propellant to carry that propellant.

So basically, unless the cost in propellant to adjust the cycler's orbit on each pass is lower than the cost in propellant to simply add a proper hab module to your supply ship, it's not worth it. I suspect it isn't.

Nibb31, I don't say this to be mean or brash, but clearly you don't understand how a Cycler Ship works at all. I suggest you read the material I linked to in the OP (I'll try and add a better explanation later on what a Cycler actually is to avoid issues where people don't bother reading it)

A Cycler Ship (such as an Aldrin Cycler) is set on an orbit that intercepts two planets (such as Earth and Mars) regularly. Virtually no velocity-change is required to adjust the orbit at either end. This is comparable to how a free-return trajectory to the Moon only requires a one-way burn, except instead of getting a free return from the Moon, you're getting a free return from Mars- and back again and again and again.

This is for a "full-cycler". There are also "semi-cycler" designs which depart from LEO or Low Mars Orbit, and enter into a trajectory that will EVENTUALLY (slowly) take them back to Earth or Mars for free. In these designs, like with the full cycler, the crew only rides the cycler one way because the return-voyage is extremely slow. The advantage of a semi-cycler is that it's MUCH easier to intercept with an "interceptor" vessel as the velocity-difference is much smaller.

With either version of cycler (full or semi), there are two possible variants of the orbit- one that travels from Earth to Mars quickly (5-6 months), but takes a long time (15+ months) to return, and one that travels from Mars to Earth quickly (5-6 months), but takes a long time to return to Mars (15+ months). Thus, with any manned round-trip mission, you would normally want at least two cyclers in operation- so the crew takes the short leg of a journey each way.

Ultimately, with a Aldrin Cycler or other design of Cycler Ship, you only need to accelerate the Hab Module (which can include rotational/centrifugal "artificial gravity"), Life Support Systems (which can include heavy things like greenhouses), heavy radiation shielding, and solar panels or nuclear reactor to the cycle-trajectory ONCE. It costs less than twice as much Delta-V as sending these directly to Mars for a full-cycler, yet doesn't require any fuel for a return-voyage, and can be re-used an unlimited number of times.

The components you re-use are some of the heaviest components for a Mars-Mission (especially the radiation shielding), and don't have to be accelerated quickly. In fact, if you were patient enough you could literally launch the cycler ship to LEO and accelerate it to the cycle-trajectory using ion engines or however many square kilometers of solar sail over the course of several YEARS (you would only launch crew to it later, on its next cycle around). These same ion engines/ solar sails could be re-used for the minor course corrections (only a few dozen m/s or so every couple years!) necessary to maintain the cycle orbit against the solar wind and repeated Mars/Earth gravity-assists (to minimize these, the taxi/lander would detach while the Cycler Ship was still a few days out from Earth/Mars, and move onto a closer approach trajectory- whereas the Cycler Ship would just skirt the edge of the Sphere of Influence),

With solar sails, ZERO propellant would be required for course-corrections (all course-corrections would be made by constantly trimming the solar sails during the entire voyage). With ion engines, only a VERY small amount of propellant would have to be carried to Cycler Ship on each interceptor ship.

And, of course, if you equipped the Cycler Ship with a heavy nuclear reactor and a laser or gyrotron to beam that power as microwaves, you could use that nuclear reactor to accelerate the Cycler to its cycle trajectory in the first place via nuclear-electric propulsion, and then re-use that same reactor an unlimited number of times to accelerate interceptor ships via Microwave Thermal Rocketry (the higher TWR of thermal rocketry vs. electric propulsion would be necessary for the interceptor ships) to meet up with the Cycler Ship, and landers/crew capsules to reach the surface of Earth/Mars...

Microwave Thermal Rocketry has around a 1/4th efficiency at these large distances (1/3rd efficiency when beaming power *through the atmosphere* to a craft ascending to LEO)- meaning if you placed a 800 MW reactor on the Cycler Ship, the tiny interceptor-ship would have around 200 MW of beamed-power available, which would allow for a MASSIVE TWR (in fact, with a reactor this powerful, and a typically tiny interceptor ship, maybe you would want to use a high-powered microwave-electric propulsion scheme just so you didn't kill your crew with g-forces... Or, you could just use a much smaller nuclear reactor and take longer to accelerate the Cycler Ship in the first place...)

Regards,

Northstar

Edited December 10, 2014 by Northstar1989

[m4rt14n]

Why not then make multiple cyclers going both ways like trains. Then you can have regular train lije schedule to hop on a ride to mars and other planets.