A Discussion of a Mars Cycler Transit System

[cjameshuff]

How does any ofn this add up asd an advantage over sending people and cargo directly to Mars.

I have to wonder if you read my post...
"...aside from comfort and health beyond simple survival, there would be greater safety margins and more options in case of trouble with access to cycler-based supplies and equipment."

Rescue craft from the cycler? How big do you want to make this thing?

Huge, eventually, with large living spaces, stockpiles of food, fuel, tools and emergency equipment, recycling systems, even eventually automated gardens and those rescue craft. It can be huge because only minor amounts of delta-v are ever applied to it to maintain its orbit. The bigger it is the more sense it makes, the benefits add over time, and the rate at which the benefits add over time increases over time as the size and capabilities of the cycler grow.

If you don't have a cycler you don't need any rescue craft.

If you don't have a cycler you can't have a rescue craft, because your Mars ship's at a high delta-v to both Earth and Mars and heading into the gulf between them, and may not approach either again for many years to come. If a transfer vehicle falls short, there's a possibility for rescue, distance and delta-v may leave it within reach. If a Mars ship falls short, its passengers are as good as dead.

Cyclers are still a slower, more expensive in propellant*, and require more in space infrastructure and operations than any other way of getting to Mars. What's the point?

They're safer (having more radiation and micrometeorite shielding, more emergency supplies, more reliable and redundant equipment built to less stringent mass requirements), more comfortable, and cheaper in propellant.

*Even if you you tethers for momentum transfer it is still more efficient to go directly to Mars. And tethers are just a concept.

Self-contained manned Mars-ships are just a concept.

[Ara Pacis]

Nothing about cyclers is neccessary. They are the hard way to do things. IMHO.

How does any ofn this add up asd an advantage over sending people and cargo directly to Mars.

Rescue craft from the cycler? How big do you want to make this thing? If you don't have a cycler you don't need any rescue craft.

Cyclers are still a slower, more expensive in propellant*, and require more in space infrastructure and operations than any other way of getting to Mars. What's the point?

If you want to go to Mars, send stuff to Mars, keep the space infrastructure needed to go there to a safe minimum.

Jon

The main advantage is not having to spend delta-v accelerating and then decelerating the entire mass of a vehicle that is capable of life support for months at a time. Think of it this way: It's just like having any other space station, like the ISS, instead of launching a rocket with the same mass, shape, and capabilities of the ISS each time we want to go do something in space. Consider the analogy of the aircraft carrier, we use small planes to go back and forth to targets instead of flying the aircraft carrier over the target.

Oh, and cyclers are not slower, not where it counts, in the trans-planetary segments of their trajectories. Indeed, one of the major quibble-points about cyclers is the necessity of a taxi to shed excess speed.

[ravens_cry]

How about using aerocapture to slow down the taxi?

[loglo]

From reading all the above it seems a cycler only makes sense if your Mars missions have immense spaceships like those proposed in NASA's 90-Day Study from the 1980's. With the newer, slimmed down, Zubrin-esque DRM mission plans I think they have become totally useless for exploration missions and impractical for colonisation transport.

So would they be useful at any stage of human habitation of Mars? The only use I can think of is as luxury cruise liners cruising. The population of potential Martian tourists with the wealth to economically support that kind of activity would be immense. The benefits that cyclers offer just don't seem to be substantial enough to make them economical and I doubt they ever will be.

A Mars space elevator seems a more practical way to reduce transport costs - as impractical as it is.

[Ara Pacis]

How about using aerocapture to slow down the taxi?

You can. It's not what I envision, but it's certainly one possibility. When you add more modes to a vehicle, you generally have to increase it's mass. An interorbital taxi meant for short-duration vacuum mode between cyclers or cycler-station, can be a basic tin-can with a small engine (or none) and a few hours of air supply and maybe a lavatory. If you intend to interface with the atmosphere you may need to increase the vehicle's mass with the addition of heat shields of some sort and control surfaces and longer duration life support and perhaps more radiation shielding. Of course, you could exchange that mass for the rocket motor and fuel/propellant.

Howeover, the general idea of a taxi, in my opinion, is a reusable vehicle that can be used to decelerate from the cycler and accelerate to another cycler eventually. I had planned on space taxis to be interorbital affairs only and leave landing to another class of aeospace taxis altogether.

[Ara Pacis]

From reading all the above it seems a cycler only makes sense if your Mars missions have immense spaceships like those proposed in NASA's 90-Day Study from the 1980's. With the newer, slimmed down, Zubrin-esque DRM mission plans I think they have become totally useless for exploration missions and impractical for colonisation transport.

The Zubrin-esque plans call for small missions of what, half a dozen people? How would you get 100 people to Mars in one pass? I'm thinking 20-50 years farther down the road.

So would they be useful at any stage of human habitation of Mars? The only use I can think of is as luxury cruise liners cruising. The population of potential Martian tourists with the wealth to economically support that kind of activity would be immense. The benefits that cyclers offer just don't seem to be substantial enough to make them economical and I doubt they ever will be.

Actually, I think of cyclers as more of a cheap fare than a luxury fare. Fast direct rockets would seem more expensive in terms of everything to be measured. More delta-v over the short-term mission profile, more propellant for that delta-v due to increased total mass that needs to be accelerated and then decelerated for each segment of the mission, more mass in disposable consumables per person. Meanwhile, in order to reduce the impact of the aforementioned considerations, you'd suffer more mass compromises in radiation shielding, artificial gravity or its lack, and additional material and equipment for additional profitable enterprises that might be undertaken during the same mission. JonClarke makes some good points, but he's talking apples v. oranges when the idea I'm promoting is more along the lines of apples v. grapefruit & grapes. Yes, the basic Aldrin idea is barely competitive, if at all, but I plan to increase the capabilities of the cycler idea by an order of magnitude.

Volume discounts makes it more affordable. Due to fewer limitations, a cycler would be able to accomodate more people in more comfort and more safety for less money. When you factor in the amount of propellant and consumables necessary to support people for the same duration trip, a vehicle that doesn't have to stop expends that much less propellant. A vehicle that is large enough to produce its own food doesn't require as much mass per fare in terms of pre-packaged food or additional nutrients for maintenance of the aeroponics system as human waste is recycled, and the balance of imported foodstuffs is maintained aboard as a nutrient reserve. Where else would it go? A person who masses 75kg upon boarding and who brings and eats 1000kg of food over the course of a trip will not exit the craft massing 1075kg. That argument is a bit of a red herring as a nominal taxi won't need to pack all that food mass per person. It would be a startup and maintenance consideration but it would not dramatically affect standard flight operations.

Moreover, additional missions of the cycler to pick-up and drop-off probes, personnel, material and equipment at an apoapsis in the asteroid belt would profit from those services. Other astronomical services, such as radio and optical telescopes for interferometry and radar surveys for skywatch can also help fund the cycler and subsidize fares. All of these services can be better performed on a cycler since it is a longer-ranging platform that requires dramatically less delta-v over the course of its cycle and is, therefore, less hindered by the increased mass of these extensions.

A Mars space elevator seems a more practical way to reduce transport costs - as impractical as it is.

It can help get things away from Mars and into a trajectory for Earth (or rendezvous with a cycler) but isn't as helpful in the Earth-to-Mars leg of the trip, though I suppose it could conceivably help with capture and landing of taxis.

[loglo]

The Zubrin-esque plans call for small missions of what, half a dozen people? How would you get 100 people to Mars in one pass? I'm thinking 20-50 years farther down the road.

Hence my reference to the 90-day study. If you need to take 100 people at a time, you will need very large spacecraft and maybe the cycler would make sense, if they are going to return at some point.

JonClarke makes some good points, but he's talking apples v. oranges when the idea I'm promoting is more along the lines of apples v. grapefruit & grapes. Yes, the basic Aldrin idea is barely competitive, if at all, but I plan to increase the capabilities of the cycler idea by an order of magnitude.

More like watermelon than a grapefruit!

Do the economics still make sense if the traffic is mostly one way though? (Hence my colony reference.) Or are you wanting to cycle 100 people back and forth each trip? (Hence my huge population reference.) I only see this being economical if there are millions on Mars.

Moreover, additional missions of the cycler to pick-up and drop-off probes, personnel, material and equipment at an apoapsis in the asteroid belt would profit from those services. Other astronomical services, such as radio and optical telescopes for interferometry and radar surveys for skywatch can also help fund the cycler and subsidize fares. All of these services can be better performed on a cycler since it is a longer-ranging platform that requires dramatically less delta-v over the course of its cycle and is, therefore, less hindered by the increased mass of these extensions.

Some type of cycler is definitely a good possibility for an advanced space-faring civilisation, I think. There are, it seems, a lot of potential technologies we can take advantage of once we have a large amount of people and infrastructure in place in space. I should have read the OP closer, I didn't think you were looking so far ahead. What I don't see clearly is any technology that will allow us to get to that stage. A question for another thread though.

[JonClarke]

The main advantage is not having to spend delta-v accelerating and then decelerating the entire mass of a vehicle that is capable of life support for months at a time.

Yes, I am aware of the rationale. The problem is that the actual spacecraft mass savings are small the as transit time from planet to cycler is still weeks and your spacecraft will still be fairly large in consequence. Plus it will still have to carry all the consumables for the trip to Mars anyway, to resupply the cycler.

Then the cycler orbit is not the optimum one for the oppounity. You have to expend more propellant matching orbit with the cycler and then un-matching than if you went direct. And propellant will be the biggest part of your mass It is always takes less mass overall to take the direct route than use the cycler.

Plus if you fail to rendezvous with the cycler you die. Windows for rendezvous will be very tight. You wan't have enough propellant to get home again. The only way to survive if you miss the rendezvous is to have a spacecraft that will enable you to each your destination anyway - which defeats the point of the cycler.

And you don't need just one cycler, you need at least two and perhaps up to five, as no one cycler can cover all opportunities.

Think of it this way: It's just like having any other space station, like the ISS, instead of launching a rocket with the same mass, shape, and capabilities of the ISS each time we want to go do something in space. Consider the analogy of the aircraft carrier, we use small planes to go back and forth to targets instead of flying the aircraft carrier over the target.

That is not a good analogy. A better one would be where you have two choices. You can fly your aircraft directly too and from the carrier, or you can rotate them through a second carrier which is off the direct route. This requires more fule and exposes the aircrafdt to additional hazardous take off and landings. Which do you prefer?

Oh, and cyclers are not slower, not where it counts, in the trans-planetary segments of their trajectories. Indeed, one of the major quibble-points about cyclers is the necessity of a taxi to shed excess speed.

What counts is time, not absolute velocity. It takes longer to get to and from Mars with a cycler than any other method. It is surely better to maximise time at Mars than in transit (which is also the most dangerous part of the mission).

Jon

[JonClarke]

How about using aerocapture to slow down the taxi?

Aerocapture is a great idea whatever method you use to get to and from Mars.

Jon

[JonClarke]

So would they be useful at any stage of human habitation of Mars? The only use I can think of is as luxury cruise liners cruising. The population of potential Martian tourists with the wealth to economically support that kind of activity would be immense. The benefits that cyclers offer just don't seem to be substantial enough to make them economical and I doubt they ever will be.

That is a very interesting idea. I can imagine this at some stage in the future.

Jon

[ravens_cry]

Yes, I am aware of the rationale. The problem is that the actual spacecraft mass savings are small the as transit time from planet to cycler is still weeks and your spacecraft will still be fairly large in consequence. Plus it will still have to carry all the consumables for the trip to Mars anyway, to resupply the cycler.

With more efficient then we have now, but done quite satisfactorily by our own planet, recycling onboard, one would only take as much they would take away, which isn't that much, as well as consumables such as medicines that it couldn't manufacture. Things like air and even food could be grown onboard. I say 'grown', because I envision some form plant based recycling.

Then the cycler orbit is not the optimum one for the oppounity. You have to expend more propellant matching orbit with the cycler and then un-matching than if you went direct. And propellant will be the biggest part of your mass It is always takes less mass overall to take the direct route than use the cycler.

Unless you had several, I admit this would be even more expensive, but this is dreaming big.

Plus if you fail to rendezvous with the cycler you die. Windows for rendezvous will be very tight. You wan't have enough propellant to get home again. The only way to survive if you miss the rendezvous is to have a spacecraft that will enable you to each your destination anyway - which defeats the point of the cycler.

That is rather a linchpin, no engineer likes a single point of failure. At this time I admit I have no answer.

And you don't need just one cycler, you need at least two and perhaps up to five, as no one cycler can cover all opportunities.

What counts is time, not absolute velocity. It takes longer to get to and from Mars with a cycler than any other method. It is surely better to maximise time at Mars than in transit (which is also the most dangerous part of the mission).

Jon

I see the cyclers as infrastructure, like highways and railways. Expensive, but open up new opportunities. By the time a cycler becomes viable it won't be about exploration admittedly, it will be about colonization or something else that requires lots of to and fro traffic. I admit we need to blaze the trail before we can start paving it. And alas, we haven't even done that yet.

[cjameshuff]

From reading all the above it seems a cycler only makes sense if your Mars missions have immense spaceships like those proposed in NASA's 90-Day Study from the 1980's. With the newer, slimmed down, Zubrin-esque DRM mission plans I think they have become totally useless for exploration missions and impractical for colonisation transport.

Are you planning on colonizing Mars by peppering it with thousands of little independent prefab apartments, each shipped as a unit, occupants included, from Earth?

This actually illustrates the need for cyclers pretty well. The Direct plan makes major compromises in crew comfort, health, and science on the ground to save mass. The only part of the Mars Habitat Unit with heavy radiation shielding is the airlock, in the event of increased solar particle radiation, everybody needs to cram into that small space. Even with the small volume enclosed, the radiation shelter is a significant fraction of the fully loaded vehicle's mass.

Even with that minimal shielding, most of the total Mars-bound payload is structure and equipment that would be a candidate for leaving on a cycler, where it could be given the Earth-Mars transfer delta-v once, and be used on both legs of multiple trips without having to push it in and out of orbit.

When you consider the mass costs of more extensive radiation shielding and life support systems with greater capacity, cyclers start to look extremely attractive for transporting colonists. When you consider the potential for production of consumables (one of the larger single items of mass in the Mars Direct plan) on the cyclers themselves, they look even better. The same propulsion system could land a larger crew and more equipment next to an existing habitat on the ground, the mass of all the MHU-like equipment they were using on the trip from Earth remaining in its cycler orbit. Or a far smaller propulsion system could deliver just the people to an existing colony, with all that radiation shielding, structure, and life support continuing on to be re-used.

Failure to rendezvous is still an item of discussion? If you fail to reach Mars, you die. In the case of a cycler, a failure could still leave the transport within reach of a vehicle based from the cycler it was attempting to rendezvous with. Failure to rendezvous isn't a new failure mode, it's a less severe form of a failure mode that exists for the direct to Mars option.

Time in transit is dangerous largely because of the lack of radiation shielding and other thin margins resulting from the high cost of mass. These are characteristics of bare-minimum direct Mars craft, not of cyclers.

[JonClarke]

Are you planning on colonizing Mars by peppering it with thousands of little independent prefab apartments, each shipped as a unit, occupants included, from Earth?

If we settle Mars then thousands of shipments will be needed over many years. They probably won't be little, however.

This actually illustrates the need for cyclers pretty well. The Direct plan makes major compromises in crew comfort, health, and science on the ground to save mass.

Wrong on all counts. if you wish to discuss, it would be best to start another thread. You brought up Mars Direct, not me. I said going directly to Mars, as opposed to using a cycler. This is not the same as Mars Direct.

The only part of the Mars Habitat Unit with heavy radiation shielding is the airlock, in the event of increased solar particle radiation, everybody needs to cram into that small space.

As conceived the hull would provide about half the protection needed against even the most intense storms. Strategic location of equipment and conmsumables on the margins would provide the other half. The inner airlock provides additional shelter if required.

Even with the small volume enclosed, the radiation shelter is a significant fraction of the fully loaded vehicle's mass.

What fraction over and above what is needed for other purposes?

Even with that minimal shielding, most of the total Mars-bound payload is structure and equipment that would be a candidate for leaving on a cycler, where it could be given the Earth-Mars transfer delta-v once, and be used on both legs of multiple trips without having to push it in and out of orbit.

The prupose of the mission is to explore Mars, not build giant cyclers in interplanetary space. That mass you want to be used for cyclers is best used on Mars.

When you consider the mass costs of more extensive radiation shielding and life support systems with greater capacity, cyclers start to look extremely attractive for transporting colonists.

By the time we want to settle Mars I would hope we have better ways of transporting people than cyclers.

When you consider the potential for production of consumables (one of the larger single items of mass in the Mars Direct plan) on the cyclers themselves, they look even better.

The biggest mass of consumable in Mars Direct is propellant, followed by water and breathing gases. These manufactured on Mars from mostly martian resources. What resources will consumables be manufactured from in your cycler?

The same propulsion system could land a larger crew and more equipment next to an existing habitat on the ground...

The same propulsion system as what? A larger crew and more equipment compared to what?

...the mass of all the MHU-like equipment they were using on the trip from Earth remaining in its cycler orbit.

What's the MHU?

Or a far smaller propulsion system could deliver just the people to an existing colony, with all that radiation shielding, structure, and life support continuing on to be re-used.

Payload sent to directly Mars is reused, on the surface, not just for building a giant station in space.

Failure to rendezvous is still an item of discussion? If you fail to reach Mars, you die.

This applies to all Mars missions.

In the case of a cycler, a failure could still leave the transport within reach of a vehicle based from the cycler it was attempting to rendezvous with.

And how many such vehicles would the cycleer carry? What's their capability? How are they supplied? This all adds up. All mass that does not help get people to Mars.

Failure to rendezvous isn't a new failure mode, it's a less severe form of a failure mode that exists for the direct to Mars option.

How is failure to rendezvous in deep space with the very large velocity change requirements, very narrow windows, and very few backup options less risky than going directly to Mars?

Time in transit is dangerous largely because of the lack of radiation shielding and other thin margins resulting from the high cost of mass. These are characteristics of bare-minimum direct Mars craft, not of cyclers.

Even cyclers will be mass constrained. Every gram sent to the cycler to improve its radiation protection is mass that could be sent to Mars to improve the mission there.

There has never been a detailed mission study using cyclers. All the studies have basically involved the orbital mechanics, which are appealing because of their elegance. None have looked in detail at what the requirments actually are, and comapred them to the alternatives.

You are proposing cyclers, that is fine. Do the sums, calculate the mission masses, and show how they are superior overal to more direct routes. By superior I mean parameters like savings in overall mission mass, increases in payload to Mars, better safety. etc.

Good luck.

[Ara Pacis]

Hence my reference to the 90-day study. If you need to take 100 people at a time, you will need very large spacecraft and maybe the cycler would make sense, if they are going to return at some point.

I have to admit that I don't think I've read that study. At least, I don't recall. Was it about Mars or cyclers?

More like watermelon than a grapefruit!

Do the economics still make sense if the traffic is mostly one way though? (Hence my colony reference.) Or are you wanting to cycle 100 people back and forth each trip? (Hence my huge population reference.) I only see this being economical if there are millions on Mars.

Yeah, I guess watermelon is probably a better size analogy.

Well, I would see it doing both ways. There doesn't have to be a million inhabitants for 100 to want to transit at any particular opposition. In the beginning, a lot of the people will be temporarily assigned to Mars for scientific expeditions and surveys. They would probably leave their families on earth for the time being as they look for areas to construct habitats and begin construction. Over time, the reasons may change and instead of just commuting, it will be a route of migration. And it's not necessary that people always make the trip, it could be profitable to transfer small masses to and from Mars as well. A large fraction of the return mass alottment at first might be Mars rocks for geological and horticultural study on earth. The population base on Mars for an full cycler mission of 100 pax or equivalent mass is probably only a few thousand, maybe less.

Some type of cycler is definitely a good possibility for an advanced space-faring civilisation, I think. There are, it seems, a lot of potential technologies we can take advantage of once we have a large amount of people and infrastructure in place in space. I should have read the OP closer, I didn't think you were looking so far ahead. What I don't see clearly is any technology that will allow us to get to that stage. A question for another thread though.

When I said I was looking 20-50 years into the future, I was not referring to technological development so much as simple project engineering and plausible requirements based on a generous scenario for space exploration that commences in the near future. Obviously, if we all decide to turn inward and get lost watching TV then there won't be much impetus to go do anything in space. We have the basic technology to start on it today.

The confusion may be in the comparative design goals. The cycler I have planned isn't just a cycler for the sake of being a mars transit vehicle. It's a space station that just happens to have an interplanetary orbit. Thus, it's not a "mission vehicle" but instead an "infrastructure asset". The design would be based on a standard long-duration space station template. Thus, the construction would be part of a mass-production line. The goal is to develop a space infrastructure using these basic modular systems and that means generating orders for many of them. These stations would be just as at home in Low Planetary Orbit as they would in solar orbit or an interplanetary cyclical trajectory.

If we design small craft for one-off shoe-string missions that are build on earth, then we won't have much of a need to develop space mining and manufacturing or or much in the way of human exploration and colonization. This is meant to be raison d'être for space construction in general more than a sene qua non for mars transit in particular. Howeover, since the mass savings in propellant are there and there are bonus rewards as well we might as well make something of it. But keep in mind that this is an "infrastructure asset" and would be subsidized and amortized over the long term. The savings would be on individual fare costs.

[Ara Pacis]

Yes, I am aware of the rationale. The problem is that the actual spacecraft mass savings are small the as transit time from planet to cycler is still weeks and your spacecraft will still be fairly large in consequence.

I suppose that would depend on the trajectory of the cycler and the starting trajectory of the taxi and the delta-v capabilities of the taxi.

Plus it will still have to carry all the consumables for the trip to Mars anyway, to resupply the cycler.

No, it won't. The cycler as envisioned in my plan will not require resupply by passenger taxi.

Then the cycler orbit is not the optimum one for the oppounity. You have to expend more propellant matching orbit with the cycler and then un-matching than if you went direct. And propellant will be the biggest part of your mass It is always takes less mass overall to take the direct route than use the cycler.

It might require more propellant per kg of loaded taxi, howeover the taxi masses much less than a direct transit vessel of equal capability as the cycler-taxi combination. Thus, that should be less than the total required propellant for a direct transit, the savings being dependent upon the energy of that comparison direct transit.

Plus if you fail to rendezvous with the cycler you die. Windows for rendezvous will be very tight. You wan't have enough propellant to get home again. The only way to survive if you miss the rendezvous is to have a spacecraft that will enable you to each your destination anyway - which defeats the point of the cycler.

And your direct flight vehicle's engine could blow up when you start it up while attempting to brake into Mars orbit so that it overshoots Mars and people die as it drifts around the sun, derelict, a ghost ship. Poo happens. "You pays your money and you takes your chances."

How tight of a rendezvous are you thinking? Using high-strength tethers with rocket tips and winches, or rocket tugs depoloyed from the cycler, a taxi could miss by a few hundred km and be rescued. If the taxi's engine were to fail to fire, then it wouldn't be lost in interplanetary space but remain in earth orbit.

Perhaps it would be illustrative to examine rocket failure modes. My understanding is that most failures, in mechanics in general, seem to occur during a transition, like starting and stopping. How reliable are rockets once lit? How often does a rocket engine start and fail to make it's delta-v goal?

And you don't need just one cycler, you need at least two and perhaps up to five, as no one cycler can cover all opportunities.

So far as I know, the minimum seems to be two, if we limit ourselves to ballistic or semi-ballistic cyclers. With the right delta-v you could use only one cycler, but it would cease to be a classical cycler and essentially be a direct flight that doesn't stop at Mars but only at Earth. It would still save propellant mass by not stopping at the red planet.

That is not a good analogy. A better one would be where you have two choices. You can fly your aircraft directly too and from the carrier, or you can rotate them through a second carrier which is off the direct route. This requires more fule and exposes the aircrafdt to additional hazardous take off and landings. Which do you prefer?

No, you fail to understand my analogy. The carrier is the cycler and the target is Mars. The aircraft are the taxis that fly from the cycler to Mars and others that fly up to it as it floats past the target. You would have the ship park right over the target, mars.

What counts is time, not absolute velocity. It takes longer to get to and from Mars with a cycler than any other method. It is surely better to maximise time at Mars than in transit (which is also the most dangerous part of the mission).

That depends on the cycler trajectory. Some trajectories have shorter segments between the Earth and Mars, but require more energy for a taxi rendezvous (ignoring operation startup costs). These may also require a more numerous constellation of cyclers if they are required to provide this high-speed service at every opposition. These may come online further down the road as premium routes if they are competitive with high-speed direct routes. Or, they may simply not have a full constellation and only be used for transit intermittently, perhaps serving other roles in astronomy and life sciences research between passenger routes.

Oh, and thank you for making my point. Transit is the most dangerous part of the mission, and a cycler will generally be safer in all particulars. Cyclers can be over-engineered since the mass of a cycler is not really an issue like it is with an interplanetary class vehicle that needs to make high energy delta-v maneuvers.

Of course, you could just strap a powerful enough rocket system to my cycler design and make it a direct-transit vehicle. I have no problem with that myself, but we may have to consider more speculative propulsion technologies. My advanced cycler idea is basically a capitulation to the idea that we may not be able to discover the technology or permission to use high thrust nuclear rockets necessary to move vehicles that mass thousands of metric tons.

[ravens_cry]

You can. It's not what I envision, but it's certainly one possibility. When you add more modes to a vehicle, you generally have to increase it's mass.

Howeover, the general idea of a taxi, in my opinion, is a reusable vehicle that can be used to decelerate from the cycler and accelerate to another cycler eventually. I had planned on space taxis to be interorbital affairs only and leave landing to another class of aeospace taxis altogether.

But wouldn't the taxi need to slow down to dock with some form of hub station?
Heres how I imgine it. Small craft docks with cycler when it approaches Earth. Time passes. Upon reaching mars orbit, crew undocks to dock with a bub station in mars orbit that has a reusable lander, that is refueled by ISRU. However, won't it have a velocity that needs to be shed somehow to enter Martian orbit? The question being of course would the weight required for a reusable taxis shielding that can shed velocity by aerocapture instead of using fuel be less then the weight of the infrastructure and fuel of a rocket to slow down to enter orbit more traditionally?

[Starfury]

I read the article, and while I think it could work, I also think it has a lot of moving parts to it (figuratively and literally). Personally, I favor an approach more like that of Robert Zubrin's Mars Direct. However, I could see Aldrin's plan being employed once we've got a few missions to Mars under our belts.

[cjameshuff]

Wrong on all counts.

Incorrect.

You brought up Mars Direct, not me.

Are you reading my posts? The very first thing in the post you're responding to is the quote where loglo brought up the Zubrin-style missions.

What fraction over and above what is needed for other purposes?

Going by Wikipedia's numbers, 4% of the fully loaded vehicle's mass. Yes, much of that doubles as an airlock, but that wouldn't be true for a more completely shielded vehicle.

The prupose of the mission is to explore Mars, not build giant cyclers in interplanetary space. That mass you want to be used for cyclers is best used on Mars.

Only for the establishment of the initial bases. Once they are established, you're shipping huge quantities of structure and life support equipment to a place that doesn't have any particular use for it.

The biggest mass of consumable in Mars Direct is propellant, followed by water and breathing gases. These manufactured on Mars from mostly martian resources. What resources will consumables be manufactured from in your cycler?

Exhaled air and other human waste.

The same propulsion system as what? A larger crew and more equipment compared to what?

The Mars Direct missions that loglo referenced.

What's the MHU?

The Mars Direct Mars Habitat Unit. I figured spelling it out in the second paragraph would be clear enough.

Payload sent to directly Mars is reused, on the surface, not just for building a giant station in space.

It's significantly less valuable on the surface, with inflatable structures and locally produced construction material, and very expensive in fuel to get it there.

This applies to all Mars missions.

Exactly. You can't use it as a point against cyclers.

And how many such vehicles would the cycleer carry? What's their capability? How are they supplied? This all adds up. All mass that does not help get people to Mars.

No, it helps keep them from dying if something goes wrong. A single vehicle could mean the lives of the crew. Their capabilities depend on how much of a safety net you desire. They could be little more than a fuel tank, engines, and fittings to attach to a removable crew module of a transfer vehicle, with somewhere on the order of a km/s delta-v (including the burden of return carrying the crew module).

How is failure to rendezvous in deep space with the very large velocity change requirements, very narrow windows, and very few backup options less risky than going directly to Mars?

I believe this is the third time I've said this...if the craft falls short of rendezvous but comes close enough, rescue is practical. This is not the case for a direct transfer to Mars, unless they fall so far short that they don't even leave Earth orbit.

Even cyclers will be mass constrained. Every gram sent to the cycler to improve its radiation protection is mass that could be sent to Mars to improve the mission there.

No. A ton of unneeded equipment sent to the surface of Mars is two that could be used on a cycler, going by the mass fractions of the Mars Direct missions. Or for a given payload to ground capacity, for either a cycler or a direct plan, every ton of surplus structure, shielding, and life support left behind is a ton of useful equipment and supplies landed.

If you're sending passengers somewhere that already exists and not using a cycler, the most economical thing to do is to brake just a small landing capsule and throw away the majority of the vehicle. The cycler just reuses all that mass you're throwing away.

Hence my reference to the 90-day study. If you need to take 100 people at a time, you will need very large spacecraft and maybe the cycler would make sense, if they are going to return at some point.

Just the opposite, actually. Cyclers make more sense if you use them for many trips. If you're going to send giant spacecraft on a handful of trips, there is much less to gain.

[Ara Pacis]

But wouldn't the taxi need to slow down to dock with some form of hub station?
Heres how I imgine it. Small craft docks with cycler when it approaches Earth. Time passes. Upon reaching mars orbit, crew undocks to dock with a bub station in mars orbit that has a reusable lander, that is refueled by ISRU. However, won't it have a velocity that needs to be shed somehow to enter Martian orbit? The question being of course would the weight required for a reusable taxis shielding that can shed velocity by aerocapture instead of using fuel be less then the weight of the infrastructure and fuel of a rocket to slow down to enter orbit more traditionally?

Yes, but how much it needs to decelerate will depend on the orbit of the Mars Station.

In his Case for Venus (second image) David Hollister suggests using Highly Elliptical [planetary] Orbits that reach to near escape velocity at periapsis. Part of his idea is for that vehicle to then rendezvous with a station in a circular High [planetary] Orbit near apoapsis. I think it's a possibility for Mars too, though there seem to be different goals at work (I think his idea assumes these are the only habitats in Venus vicinity (which also has higher gravity that might make a difference), whereas Mars can have habitats on the planetary surface). With a high speed habitat or mini-cycler in a high-speed segment of it's orbit at the time of transfer, the taxi can expend less delta-v to match velocity and make a quicker transfer between more heavily shielded vehicles, reducing the total mass necessary for the taxi (in terms of structure, fuel/propellant, and life support requirements).

Or the taxi could simply pack enough juice to brake into orbit and rendenzvous with a station in lower orbit.

Or it could interface with a some sort of tether system, like a space elevator or rotovator.

Or maybe you're right and they'll use aerocapture and either have to add on some sort of shield while enroute if necessary or use a different set of taxis. Or maybe they'll just use disposable taxis and then recycle the taxi into something else.

[JonClarke]

I have gone through the responses to my most recent posts above and addressed the points but was not satisfied with the results. So I thought I would try a different approach.

The difficulty we are having is, I suggest, due to comparing the general claim about cyclers in the OP: that it reduces the amount of material needed to be accelerated for each transit by limiting it to a small passenger craft that travels to or from the planet to the cycler and vice-versa. relevant to transportation once Mars stations are established, against a very specific exploration phase Mars mission, Mars Direct. We need to compare like and like. This is challenging as mission studies are always done under different assumptions, making comparison difficult. But we can try.

Cycler trajectories

A good paper on trajectories is McConaghy et al. (2006) http://www.troymcconaghy.com/storage/AIAA_2002-4420.pdf . To summarise, a wide range of cycler orbits are available, unfortunately as a rule those that repeat frequently (e.g. every 2 and 1/7th years requiring only 2 cyclers) and have comparable or shorter flight times to semi-Hohmann flight have ugly excess velocities (more than 12 km/s in the worst case) and those that have friendly excess velocities (only marginally more than Hohmann transfers), repeat rarely (once every 7 cycles requiring 12 cyclers), and long flight times.

Cycler spacecraft

Few cylcer studies look at the actual spacecraft, One study that gives some details of the spacecraft is Nock et al. (2002) http://www.gaerospace.com/projects/A..._2003_ICES.pdf . This looks at supporting a Mars station of 10 people using two 60 tonne Aldrin cyclers they call astrotels. These are supported by two structurally similar spaceports, one in Earth orbit and one Mars orbit. The Earth port changes orbit to seek the most favourable location. Two 16 tonne taxis provide transport two and from the cyclers, propellant requirements vary drastically according to the cycle, but average 308 tonnes per mission. There is also a low thrust cargo craft that resupplies the astrotels with 9 tonnes of consumables each mission, but unfortunately no mass breakdown is given. A reusable Mars shuttle carries people to and from Mars orbit. ISPP is assumed at Phobos and on the Mars surface. Heavy cargo delivery to Mars is not discussed.

Direct spacecraft

An alternative approach is the Mars Transfer Vehicle (MTV) approach that forms part of the study of Willson and Clarke (2007) http://www.marssociety.org.au/library/willson-et-al.pdf. The MTV ferries 4 people from Earth orbit to Mars orbit during exploration phase missions using a direct trajectory. It uses a semi-Hohmann trajectory. The MTV masses 130 tonnes of which 74 tonnes is propellant. In the paper it releases a descent capsule for Earth orbit and is not intended for reuse.

Adapting the design to aerocapture in LEO and reused would be straight forward. It can also be scaled up to 10 people to give an indication of the masses required for direct trajectories in support of Mars stations. Scaling the MTV to carry 10 people gives a mass of 325 tonnes. This equates to 140 tonnes dry and 185 tonnes of propellant.

Comparison

Common infrastructure (not counted): Mars station, Phobos port, Mars shuttle

Cycler: two cyclers 138 tonnes (including consumables), two taxis 32 tonnes (dry), one Earth port (60 tonnes) 230 tonnes, 308 tonnes average propellant each mission

MTV 140 tonnes (dry) 185 tonnes propellant used each mission (Earth port not needed as MTV leaves from LEO)

Thus the cyclers require investment in 71% more spacecraft structure than the MTV. It is actually worse than this as the mass of the cargo craft used to resupply them. A round trip using the cycler uses 66% more propellant than the MTV.

The taxis are high risk spacecraft, they have only 7 days life support, near instantaneous launch windows, have average excess velocities at Earth and Mars of 3.5 and 7.1 km/s respectively, and must carry out two deep space rendezvous each mission. By comparison the MTV has the same life support as the cycler, extended launch windows, and needs no deep space rendezvous.

Given these numbers I really cannot see why justification for cyclers for primary transportation. Tourism perhaps, science platforms maybe, but not transport.

Jon

Edit: note that the comparison between the cyler of Nock et al. and a MTV based on Willson and Clarke is biased towards the cycler. The cycler mass allocation does not include the cargo freighter, which would mass at least 15 tonnes, the spacecraft mass allocations not not include a margin, the consumable allowanceis very optimistic (I suspect it assumes very high efficiencies), and the taxis use hydrogen for fuel. The MTV masses include a 20% margin, it is propelled by methane fuel, and its much more conservative with the consumable allocation. Recalculating everything to the same rules would shift things even further towards the MTV.

[mugaliens]

Even if you you tethers for momentum transfer it is still more efficient to go directly to Mars. And tethers are just a concept.

Jon

More efficient "how?" Merely saying it doesn't make it so. Would you please describe, in detail, how direct shuttles are more efficient? At what point of repetition do tethers become more efficient? (there is such a point)

As far as tethers being "just a concept," various tethers have been in use in many situations requiring sound engineering solutions for many, many years, from mountain climbing, to Fulton recovery systems and other air/ground transfer systems. Space tethers are nothing new, either - astronauts have been using tethers for space walks for decades.

As for mass-transfer systems, however, tethers in space are indeed "just concept." That in no way undermines their viability, however.

[ravens_cry]

I am no scientist, and my math sucks. However,what would the calculations be for a cycler, that was also a recycler? That is to say, when your on board, everything was reprocessed, in a Biosphere like concept? Oh, there would still likely be some things still needed to be stocked up, things that an internal environment couldn't reprocess, like medicine and (initially at least) meat, as well as things that break down, and spare parts.

[JonClarke]

More efficient "how?" Merely saying it doesn't make it so. Would you please describe, in detail, how direct shuttles are more efficient? At what point of repetition do tethers become more efficient? (there is such a point)

As my earlier post pointed out travelling to Mars via will aways require more dV than going using a Hohmann orbit. Sometimes considerably more *worst case is almost double). Regardless of whether this dV is supplied by rockets of tethers in terms of energy efficiency it is ways more efficient to go direct.

Also you always need more than one cycler. The minimum is two, the maximum is 12 (not 5 as I incorrectly said earlier). Plus the taxis to go to and from them. It will always more mass efficient to travel directly to Mars in a single spacecraft.

So why use cyclers?

As for mass-transfer systems, however, tethers in space are indeed "just concept." That in no way undermines their viability, however.

This is the sense I meant. I never said they were not viable, but I suggest that using existing technology where possible to go to Mars is much more desirable.

[JonClarke]

I am no scientist, and my math sucks. However,what would the calculations be for a cycler, that was also a recycler? That is to say, when your on board, everything was reprocessed, in a Biosphere like concept? Oh, there would still likely be some things still needed to be stocked up, things that an internal environment couldn't reprocess, like medicine and (initially at least) meat, as well as things that break down, and spare parts.

Some sort of recycling will be neccessary regardless of how you go to Mars. And as I far as I can tell any recycling technology (short of actual food production) that can be applied to a cycler can also be applied to a MTV.

But no recyling is 100% efficient. There are losses, which will need to be made up. Propellant will need to be replenished. There will be things that the cycler cannot replace, like spares and medicines. Solid waste that cannot be be recycled onboard will need to be disposed of. Unless we want to turn the cycledr orbit into a meteor stream of space junk, this means returning it to Earth (or maybe Mars)

Jon

[ravens_cry]

Some sort of recycling will be neccessary regardless of how you go to Mars. And as I far as I can tell any recycling technology (short of actual food production) that can be applied to a cycler can also be applied to a MTV.

But no recyling is 100% efficient. There are losses, which will need to be made up. Propellant will need to be replenished. There will be things that the cycler cannot replace, like spares and medicines. Solid waste that cannot be be recycled onboard will need to be disposed of. Unless we want to turn the cycledr orbit into a meteor stream of space junk, this means returning it to Earth (or maybe Mars)

Jon

None at present. However, Starship Earth does it quite handily, with only the energy of the sun. Can this be reproducible on a smaller scale? I think it could be done. Also, any kilogram of matter that is reprocessed back into breathable air, water, and foodstuffs, is a kilogram that doesn't have to be rocketed out of a gravity well. In theory, ultimately the only thing that can't be recycled is propellant for orbital corrections. That, as well as anything else needed could be brought by the taxis themselves, as a form of payment for the service. Of course, recycling technology is useful for a Mars direct, it would significantly reduce the mass, and hence the cost.
But Cycler's are for a society that has lots of interplanetary traffic, because the more they are used, the more they make sense. We aren't at that stage yet, but we may someday, and it's a good idea to look at how we will do things for when we do do them.

[JonClarke]

None at present. However, Starship Earth does it quite handily, with only the energy of the sun. Can this be reproducible on a smaller scale? I think it could be done. Also, any kilogram of matter that is reprocessed back into breathable air, water, and foodstuffs, is a kilogram that doesn't have to be rocketed out of a gravity well. In theory, ultimately the only thing that can't be recycled is propellant for orbital corrections.

This is true. But recycling isn't free. It has a price in terms of mass, volume, power, complexity, and labour. The longer the mission the more attractive it becomes. The space shuttle does not recycle anything because it is not worth it. The ISS recycles much of its water and some of its oxygen. The greater the efficiency the greater the cost. So there are trade offs between mass of systems, consumables, start up costs, ongoing costs etc.

Nor is recycling ever 100% efficient and there are always leakages. So there will always be some replenishment.

That, as well as anything else needed could be brought by the taxis themselves, as a form of payment for the service. Of course, recycling technology is useful for a Mars direct, it would significantly reduce the mass, and hence the cost.

Recycling of water and to a lesser degree oxygen is a given I suggest regardless of mission profile.

But Cycler's are for a society that has lots of interplanetary traffic, because the more they are used, the more they make sense. We aren't at that stage yet, but we may someday, and it's a good idea to look at how we will do things for when we do do them.

Certainly it is worth looking at all possibilities. And cycler orbits may well be useful for something, just not transport. But I suspect that a society with extensive interplanetary society might well prefer to spend the extra propellant getting between planets faster than to use slow cyclers.

Jon

[mugaliens]

As my earlier post pointed out travelling to Mars via will aways require more dV than going using a Hohmann orbit. Sometimes considerably more *worst case is almost double). Regardless of whether this dV is supplied by rockets of tethers in terms of energy efficiency it is ways more efficient to go direct.

Also you always need more than one cycler. The minimum is two, the maximum is 12 (not 5 as I incorrectly said earlier). Plus the taxis to go to and from them. It will always more mass efficient to travel directly to Mars in a single spacecraft.

So why use cyclers?


This is the sense I meant. I never said they were not viable, but I suggest that using existing technology where possible to go to Mars is much more desirable.

Ok. My question was, "Would you please describe, in detail, how direct shuttles are more efficient? At what point of repetition do tethers become more efficient? (there is such a point)"

So far, it's interesting verbage, but no details.

How's this for an idea? Shuttles going back and forth between Mars and Earth, using mere gravity for the turnarounds. If the Earth's gravity isn't enough, perhaps an Earth-Moon combination.

In the meantime, rotovators would provide the local acceleration-deceleration, either from LOE, or, if we work out the through-the-atmosphere trick, directly from the planet's surface. Only the initial cadre of shuttles would require propulsion. After that, it would simply require tethered energy exchanges between the returning and outgoing shuttles.

[Ara Pacis]

JonClarke, I appreciate the links and will read them later. I wonder if it would be instructive to do an even simpler set of comparisons of Dv and propulsion and determine where a breakeven point in mass may be, if that makes sense. I understand your points, but I am assuming that at some point in size the disparity in the size of a smallish taxi/shuttle versus both a larger cycler and larger mars transit vehicle will make it more economical.

Of course, even then, propulsion technologies will change the balance. A tether system would reduce the amount of propellant mass needed by flinging taxis for rendezvous, but it could also fling propellant tanks to an MTV for rendezvous too. (BTW, this brings up a side note, would it be possible for a rotovator to have a highly eccentric orbit for increasing velocity in a fling?) The same goes for an electromagnetic catapult in orbit. These systems along with orbital stations would be useful as infrastructure for multiple mission profiles and not just appended to the mass requirement of a cycler, which may be another source of disagreement in comparisons.

Since a year ago when I first started this thread, my ideas have changed a little. Instead of a direct comparison, like in some of the links, I started thinking of these as infrastructure assets. Make them big and robust and adaptable and multipurpose. My idea is not to choose between MTVs and cyclers, but to have both options for different purposes. Unlike a statement above that cyclers would be luxury affairs, I suspect the latter would be true. Large and capable of carrying a lot of people, these would be cheap fares that may take longer in certain trajectories, while people who feel time is more important would spend more for a faster direct transit.

Maybe it would be useful to describe the basics of the cycler of which I'm thinking. When I say it would be an order of magnitude larger, I'm not exaggerating. I think a basis would be to obtain mars gravity through rotation. Assuming 3RPM we'd need a deck at a radius of around 37m, plus an engineering deck below making the rotating hab section about 40m in radius or 80m in diameter. Add some room between this and a stationary pressure hull and between that and the external shield-hull of a meter or more and the total diameter of the vehicle is about 90m, excluding appendages like radiators, solar panels, antennae and dishes. The Mars gravity deck would be about 20m wide and with a circumference of about 233m it would have an area of ~4,650m² (50,000+sqft). After subtracting engineering walls, a 2m wide plant-lined corridor, and 8 elevator/stairway sections of several square meters in area it would have 48 pressure compartments divisible into different sized rooms, with the densest capacity (288 rooms with 12 bunks) of 3,456 passengers and personnel, more if you hot bunk. Howeover, I'd expect a much looser standard civilian capacity with larger rooms and fewer occupants with some of those compartments being used for other purposes such as: meeting, office, cafeteria, retail shop and community lavatories and sports areas. That's all on one level. With a tolerance for lower gravity, there might be several habitable upper decks, then the decks above that can be used for lower-g stowage that require atmosphere. Depending on the needs for a co-axial spinning engineering section for energy systems that require bouyancy (nuclear reactor or solar steam system or such) and then non-spinning compartments for zero-g non-atmospheric stowage and a hangar compartment for docking with the taxis (if not complete envelopment) and you have ~100m or more in length. I was thinking that a cycler might also has a electromagnetic cat on one end for launching taxis backwards, to reduce their velocity. This would further extend the length to several hundred meters if not a km or more.

Now, if we use vessels of this size and mass class for interplanetary transits, it might make the cycler-taxi idea more palatable from a propulsion point of view. I know it seems ridiculously large at present. Howeover, once we get real space manufacturing started (like Al from lunar regolith) then minimum production quantities of basic materials will make such vessels quite obtainable (unless we go out of our way to limit efficiencies of scale by forcing cottage industry-scale techniques).

[JonClarke]

Ok. My question was, "Would you please describe, in detail, how direct shuttles are more efficient? At what point of repetition do tethers become more efficient? (there is such a point)"

So far, it's interesting verbage, but no details..

More than verbiage I hope! Transfers from planetary orbit always require more dV than into a Hohmann orbit. The excess varies between 0.7-9.4 km/s for Mars and 0.1-9.3 km/s for Earth. The variance depends cycler orbit type. For further details see the McConaghy et al. paper in post #50. Even within a single orbit class the amount of energy needed varies on encounter, for example the taxis to and nfrom the Aldrin cycler in the Nock et al. paper (again see post #50) need from t24 to 284 tonnes of propellant.

How's this for an idea? Shuttles going back and forth between Mars and Earth, using mere gravity for the turnarounds. If the Earth's gravity isn't enough, perhaps an Earth-Moon combination.

Most cycler orbits use some gravity assist. It minmises the propellant the cycler needs to stabilise the orbit. It does not effect the propellant needed to get to and from the cycler though.

In the meantime, rotovators would provide the local acceleration-deceleration, either from LOE, or, if we work out the through-the-atmosphere trick, directly from the planet's surface. Only the initial cadre of shuttles would require propulsion. After that, it would simply require tethered energy exchanges between the returning and outgoing shuttles.

This is technology well beyond what can be realised for the immediate future, or even the medium term. But even so it would still take less energy to send the payloads direct to Mars on an MTV than via a cycler. And how massive is the rotavator compared to the propellant it saves?

Jon

[JonClarke]

JonClarke, I appreciate the links and will read them later.

Glad you like it. This is an interesting discussion! There has been almost no real comparison that I know of. I too have wondered if there is some kind of break even point.

I wonder if it would be instructive to do an even simpler set of comparisons of Dv and propulsion and determine where a breakeven point in mass may be, if that makes sense. I understand your points, but I am assuming that at some point in size the disparity in the size of a smallish taxi/shuttle versus both a larger cycler and larger mars transit vehicle will make it more economical.

Of course, even then, propulsion technologies will change the balance. A tether system would reduce the amount of propellant mass needed by flinging taxis for rendezvous, but it could also fling propellant tanks to an MTV for rendezvous too. (BTW, this brings up a side note, would it be possible for a rotovator to have a highly eccentric orbit for increasing velocity in a fling?) The same goes for an electromagnetic catapult in orbit. These systems along with orbital stations would be useful as infrastructure for multiple mission profiles and not just appended to the mass requirement of a cycler, which may be another source of disagreement in comparisons.

I see several possibilities that might lead to a break even point which relate to this:

1) Highly efficient propulsion greatly reduces (or eliminates) the mass required for transfers. Momentum transfers and solar sails would be extreme examples of this.

2) Launch costs become trivial, making propellant costs a smaller fraction of the whole.

3) Off planet source of bulk propellants developed.

4) The operational life of the cycler grealy exceeds the life of the MTVs. If a cycler is good (say) for 20 round trips (44 years) and an MTV only (say) three (7 years) then the upkeep costs of the cycle system may become attractive.

I suspect that 1) and 4) are the more likely to be realised in the shorter term, and 4) would have the biggest impact. It might need a combination of several or all opf these to achieve a tipping point Of course 1) may lead to MTVs capable of very fast transit times and make cyclers less attactive.

Since a year ago when I first started this thread, my ideas have changed a little. Instead of a direct comparison, like in some of the links, I started thinking of these as infrastructure assets. Make them big and robust and adaptable and multipurpose. My idea is not to choose between MTVs and cyclers, but to have both options for different purposes. Unlike a statement above that cyclers would be luxury affairs, I suspect the latter would be true. Large and capable of carrying a lot of people, these would be cheap fares that may take longer in certain trajectories, while people who feel time is more important would spend more for a faster direct transit.

Maybe it would be useful to describe the basics of the cycler of which I'm thinking. When I say it would be an order of magnitude larger, I'm not exaggerating. I think a basis would be to obtain mars gravity through rotation. Assuming 3RPM we'd need a deck at a radius of around 37m, plus an engineering deck below making the rotating hab section about 40m in radius or 80m in diameter. Add some room between this and a stationary pressure hull and between that and the external shield-hull of a meter or more and the total diameter of the vehicle is about 90m, excluding appendages like radiators, solar panels, antennae and dishes. The Mars gravity deck would be about 20m wide and with a circumference of about 233m it would have an area of ~4,650m² (50,000+sqft). After subtracting engineering walls, a 2m wide plant-lined corridor, and 8 elevator/stairway sections of several square meters in area it would have 48 pressure compartments divisible into different sized rooms, with the densest capacity (288 rooms with 12 bunks) of 3,456 passengers and personnel, more if you hot bunk. Howeover, I'd expect a much looser standard civilian capacity with larger rooms and fewer occupants with some of those compartments being used for other purposes such as: meeting, office, cafeteria, retail shop and community lavatories and sports areas. That's all on one level. With a tolerance for lower gravity, there might be several habitable upper decks, then the decks above that can be used for lower-g stowage that require atmosphere. Depending on the needs for a co-axial spinning engineering section for energy systems that require bouyancy (nuclear reactor or solar steam system or such) and then non-spinning compartments for zero-g non-atmospheric stowage and a hangar compartment for docking with the taxis (if not complete envelopment) and you have ~100m or more in length. I was thinking that a cycler might also has a electromagnetic cat on one end for launching taxis backwards, to reduce their velocity. This would further extend the length to several hundred meters if not a km or more.

Now, if we use vessels of this size and mass class for interplanetary transits, it might make the cycler-taxi idea more palatable from a propulsion point of view. I know it seems ridiculously large at present. Howeover, once we get real space manufacturing started (like Al from lunar regolith) then minimum production quantities of basic materials will make such vessels quite obtainable (unless we go out of our way to limit efficiencies of scale by forcing cottage industry-scale techniques).

I think you have a good point here. It might be better not to think of such platforms as transportation, but space settlements in their own right (what you describe is not far short of the smaller O'Neill settlements).

Maybe such platforms would be the best places for some kinds of research or industries. Maybe luxury tax havens or casinos. People might even use them for travel, but for the luxury cruise market where the journey, rather than the destination becomes an end in itself. I recall this was loglo's point some days back.


The could be a lot of transfer at each end of the cycler orbit of passengers and craw materials. But primarily with the cyler as the destination, rather than as a form of transport. However I suspect bulk transport will still go by Hohmann and interplanet mass passangers by fast transfer.

I think exploring the type of science and commerce that could be better done on a cycler than elsewhere would be something worth pursuing. Suggestions? Cycler orbits are so elegant they must be good for something!

Jon