The possiblility of a Mars Cycler in KSP

[Geo793]

I was reading Cracked.com when I came across something very intresting called a Mars Cycler. A Mars Cycler is basicly a craft that has a special kind of trajectory that encounters Earth and Mars on a regular basis with out any fuel, using just gravity to sling shot it from each body (heres the wiki article for more details: http://en.wikipedia.org/wiki/Mars_cycler). I was wondering if this is possible in the game with Duna and Kerbin and if there is a possiblility to use this for cool looking ships!

[Richy teh space man]

It might be possible if you could calculate the orbit precisely, but I'm not sure of what advantage it would have since by the time you intercepted it and docked you'd already have a transfer to Duna set up.

[rodion]

I'd applaud you if you could set this up with any two bodies in the Kerbol system, but my guess is that over the course of a few cycles the game engine's accuracy across large distances, or lack of it, would fail it and an encounter would no longer be made as predicted.

[Vlk]

"It might be possible if you could calculate the orbit precisely, but I'm not sure of what advantage it would have since by the time you intercepted it and docked you'd already have a transfer to Duna set up."

Exactly my thoughts. The only advantages i can think of may be that it would be easier to calculate the route to mars/duna, because you would only have to intercept the cycler. The other is that it may have a good and reliable life support system, and more space for the travelers to hang out. Well actually, one is good for playing ksp, the other would be good for real life. Oh except: in KSP, i think you would have a really hard time constructing a stable path. And if you have to correct it in every cycle... that would not worth the time.

[Matt56]

The advantage in real life of having a Mars Cycler (or any craft on an Aldrin Cycle) I think would be to have a large craft making regular encounters between two bodies, while a smaller craft serves as a shuttle to and from the large craft. That way the shuttles could have minimal life support and other supplies, using less fuel to manoeuvre between orbits while the passengers spend the bulk of the journey in the larger craft. That advantage is largely lost in KSP due to the lack of life support. The other interesting thing about an Aldrin Cycle is that the Cycler's orbit would have to be in resonance with the orbits of both of the destination planets, so it wouldn't be a simple Hohmann Transfer. In at least one direction the journey would be significantly shorter than in a Hohmann transfer, but the orbital period of the cycler would have to be at least twice that of the inner planet I think. I've thought about trying to set one up in KSP, but then I think that it would be largely useless. Maybe I'm just lazy

[Dkmdlb]

Link to Cracked article?

[lincourtl]

Link to Cracked article?

I think the OP is possibly referring to this one: 5 Retarded Space Travel Ideas (That Might Actually Work)

[Exclipse]

It might be possible if you could calculate the orbit precisely, but I'm not sure of what advantage it would have since by the time you intercepted it and docked you'd already have a transfer to Duna set up.

It would have application in the case of holding massive life support or other facilities, something big enough that it would have a massive Dv cost to transfer. So it is cheaper to use small vehicles to simply transfer people on and off. Small vehicles that might not have all the life support and accommodations for the long journey.

[Richy teh space man]

It would have application in the case of holding massive life support or other facilities, something big enough that it would have a massive Dv cost to transfer. So it is cheaper to use small vehicles to simply transfer people on and off. Small vehicles that might not have all the life support and accommodations for the long journey.

For the real world I understand how housing life support features could be useful, and if they did add this to KSP then I could see a use for it, especially if finances come into play.

[rottielover]

Scott Manley can do it.

[Blackstar]

It might be theoretically possible to set the orbit up once in KSP (maybe, if it doesn't depend on n-body interactions), but it wouldn't hold for more than a few cycles because it's impossible to get the trajectory completely perfect.

In real life, you'd need some kind of navigational computer to make tiny course corrections as necessary to keep it on the cycle. Unfortunately in KSP that isn't really doable since ships on rails can't take any action to modify their orbit.

[RoboRay]

I'm not sure of what advantage it would have since by the time you intercepted it and docked you'd already have a transfer to Duna set up.

The advantage is that you only need to accelerate/decelerate your cargo/passengers/supplies, not the entire structure of the ship, at each end of the journey. You end up saving a lot of propellant mass by making your transfer and capture burns with small shuttles that normally wouldn't be suitable for a long interplanetary journey.

[Starwhip]

Scott Manley can do it.

Yes he can. Any new KSP fans out there need to drop everything and watch his tutorials if you already haven't, because he can do everything.

[meyst]

Cyclers can and do work in KSP, I know this because I have been testing them out for use in an architecture challenge.

The common perception of cyclers is that of the ballistic cycler that requires no propulsion. While these exist in the literature and should be possible in KSP they have a significant disadvantage. Most Earth - Mars ballistic cycler set ups require at least 12 cycler vehicles to cover all the conjunction opportunities, unless your willing to wait 15 years before missions. In addition those that utilize gravity assist (all of them that use under 14 vehicles) require precise control, this is a challenge in the real world (esp when solar winds can be pushing a cycler off course). In KSP navigation is skewed by floating point errors during SOI changes that require course correction maneuvers as well.

As 12 to 14 cycling vehicles would be expensive to build, put up to speed and maintain most plans looking at cyclers in the literature for Earth -Mars transit have at least intermittent propulsive requirements. As an example, the trajectory of the Aldrin cycler using only gravity assists on it's fly bys would take it 100's of KM's below the earth surface, this is mathematically correct but challenging for space craft. This makes propulsion to make up the difference favorable. Electric propulsion (ion drive) has favorable mention in many papers. Of course that creates the challenge of calculating, "optimum non-impulsive propulsive gravity assist maneuvers". apparently the computer used in the testing of that took up to 20 minutes to find a solution to a single maneuver.

I was not aware of this when I attempted my first Kerbin - Duna cycler probe by following an Aldrin cycler style trajectory of one orbit every synodic period while attempting to use gravity assists. Initial test probe encountered excessive atmospheric drag and broke upon entering the Kerbin lithosphere.

[samstarman5]

Yes he can. Any new KSP fans out there need to drop everything and watch his tutorials if you already haven't, because he can do everything.

Considering he uses the same stuff we do, it should be argued that we can, too. We just have to be willing to be more like Bob and less like Jeb and actually crunch the numbers.

Even with Cracked's apparent enthusiasm about a lot of things, I figure I would post the wiki link to the Mars Cycler, with links to further material: http://en.wikipedia.org/wiki/Mars_cycler

[NASAFanboy]

I might be able to build a Mun cycler, equipped with landers, equipment, and RCS/small engines to help it adjust it's course every time a little

Will post on spaceport once done. Launcher may not be included. Docking ports may not be included. You will be responsible for launching/subbing it into parts that can be launched.

[lazarus1024]

It is, to a degree, less about the life support/supplies and more about "space" and ancillary systems.

You are going to have to find a way to replenish the life support and supplies that each person would consume whether it is a shuttle, ship or the transfer ship.

So you'll have to carry it on the shuttle anyway. The perks are that you can have a much larger ship, for more personal space (don't knock the merits of having more than 5m^3 to yourself for months on end). You can also build in more efficient systems, such as more efficient CO2 scrubbers, waste water reclamation, laundry facilities, etc.

You could also have hydroponics/aeroponics bays which could help out significantly with both the life support and food supply issues (as well as waste water treatment/disposal). These likely wouldn't be particularly feasible in a small ship, but if mass is less of a concern because you can add on to the ship on each cycle, then you can end up with a largely self sufficient ship, even including what it takes to support passengers.

It would take a huge amount of resources to do though and it would still need resupply, but there are perks (like thicker radiation shielding, because again, overtime the cost per dV goes way down since you pay once for a launch and then you get many, many, many trips out of it).

[lazarus1024]

Oh, and either whoever writes their articles has little background in science or else not good at math.

One of their other articles talking about "sci fi weapons" when mentioning rail guns, talks about how the naval rail gun demonstrator used 10.6 million joules! Or enough electricity to power the average home for a year!

Uh...except 10.6 million joules works out to about a quart of gasoline, or enough energy to power the average american home for about 3 hours. Its still a lot of energy when you consider it is being discharged in a fraction of a second, but by comparison an M60 105mm cannon has a muzzle energy on the order of 11-14MJ...or actually more than the naval rail gun demonstrator.

IIRC the Navy is looking at, its either, 20MJ or 40MJ as the basic "first installation" rail gun as a future weapon system. Something about on the level of the M1A1 120mm gun up to closer to 155mm gun. Of course firing a much smaller projectile and vastly higher velocities, so that it can strike targets a hundred+ miles away.

I digress. Math/science errors that bad just annoy the piss out of me.

[rosenkranz]

I'm not sure I understand. Conservation of momentum would kind of invalidate this wouldn't it?

I mean, if a shuttle has to accelerate up to speed to dock with the cycler, then it's already on the same ballistic path and wouldn't need to dock making the cycler itself redundant?

[Nikolai]

I mean, if a shuttle has to accelerate up to speed to dock with the cycler, then it's already on the same ballistic path and wouldn't need to dock making the cycler itself redundant?

Yes, except that the shuttle only has to carry enough consumables for the trip to the cycler. The rocket equation shows you that mass is very, very important in terms of total delta-v gained from a given amount of fuel. Saving the considerable mass needed to carry all the consumables needed from start to finish at each launch is no small thing.

[rosenkranz]

So where are the consumables for the trip coming from? Or are you just referring to fuel?

If fuel, then you didn't need anymore fuel than that anyways as you're on the same course. Once you've matched trajectories with the cycler, you're going where ever it was going whether you dock with it or not.

If you're not referring to fuel, I'd assume you're referring to human consumables such as food and water. These things have to get to the cycler somehow.

The function I'm seeing for such a thing is like a mobile hotel with sufficient space and facilities for long trips. However, something like that would need a crew of its own. Thus each shuttle would have to bring up not only supplies for itself for the trip but extra supplies to restock the cycler. Double that actually as the crew on the cycler would also be on the return leg.

All of that is still likely more efficient than launching or accelerating a large interplanetary ship but not by a whole lot me thinks.

[Kromey]

...the trajectory...would take it 100's of KM's below the earth surface, this is...challenging for space craft.

LMAO! This cracked me up!!!

Real-world lithobreaking!!

[nadreck]

Actually it is partly about the consumables, but not because the cycler is magically stocked by the space ice-cream faeries and tang sprites, but because the infrastructure to recycle consumables (hydroponic gardens etc.) would not need to be accelerated each trip. The same is true for the large extra mass required to make an effective centripetal habitation unit. Oh and active course management would be needed, in the Solarian and Kerbol systems.

In KSP one option for dealing with a cycler, and one needed to plan two or more simultaneous interplanetary expeditions (or even simultaneous flights to Mun and orbital launches), is keeping a future manoeuvre timeline on paper or spread sheet and note each time you are considering a physics warp as to whether it would cross one of those points. If it does, then that is the time to go out to the Space Centre, switch to the cycler (or other vehicle) and do the manoeuvre. As a general rule you might want to avoid having certain types of manoevres overlap (landing, aerobraking, rendezvous/docking, etc)

[Nikolai]

So where are the consumables for the trip coming from? Or are you just referring to fuel?

Some of them can be recycled. If you've got enough know-how to make your cycler out of a hollowed-out asteroid, they can even be made out of the materials in your ship; you could hollow it out more and more as you go.

If fuel, then you didn't need anymore fuel than that anyways as you're on the same course. Once you've matched trajectories with the cycler, you're going where ever it was going whether you dock with it or not.

True. But if you only had to accelerate, say, 200 metric tons to your new velocity, that's going to cost you a lot less than accelerating that mass and the mass of everything you need for the trip to your new velocity.

Note that asteroids need not be diverted with lots of fuel. If you have time, you can use a gravitational tug to move it and keep it in the right trajectory, for example. Or you could use solar-powered lasers to vaporize parts of it and divert it into a new course without any fuel expenditure at all (assuming the asteroid has enough gravity to keep dragging you along for the ride).

If you're not referring to fuel, I'd assume you're referring to human consumables such as food and water. These things have to get to the cycler somehow.

Intially, sure. But if they're recycled or refined on-site, you don't have to change the velocity of enough stuff to take you on the entire trip and back every time you go. That's what's key.

However, something like that would need a crew of its own. Thus each shuttle would have to bring up not only supplies for itself for the trip but extra supplies to restock the cycler. Double that actually as the crew on the cycler would also be on the return leg.

You're also assuming that the crew would be returning each trip, and that each new trip would have a new crew. If you have a sufficiently large cycler, why wouldn't they live and work on it in a more permanent way?

Edited November 1, 2013 by Nikolai
Changed "Not" to "Note"

[wilt57]

How much delta-v would one need to establish one of these cycler orbits? Hypothesize with Duna. 1060 to Hohmann transfer. Will a cycler orbit take 1100? 1500? 5000? No matter, it will be a less efficient orbit than a Hohmann, that'll be for the initial burn for the cycler, for each rendezvous orbit for the crew module, and each circularization/de-orbit burn at Duna. Then to rendezvous back up with it and circularize back at Kerbin (or aerocapture, either way it'll take another burn). How much extra d-v it takes to establish that cycler orbit would determine how many Duna missions would be necessary to economize. Or I really don't have a clue what I'm talking about...