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This thread is for the discussion of Aldrin Cycler Ships.

First of all, an introduction to the topic- since most readers on this forum are undoubtedly unfamiliar with the concept, and the last time I wrote about it (many months ago) I received a lot of responses from people who clearly had no idea what they were talking about...

Please read ALL of the following first, before commenting, I would really appreciate it.  None of these are that long, and are only meant to provide a preliminary introduction to the topic:

https://en.m.wikipedia.org/wiki/Mars_cycler

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

https://space.stackexchange.com/questions/3880/what-uses-would-the-aldrin-cycler-have

And, for more context I HIGHLY RECOMMEND reading these articles:

http://www.popularmechanics.com/space/moon-mars/a333/2076326/

https://www.damninteresting.com/the-martian-express/

Please read through at least the first three links, and the fourth and fifth ones if you can, and let me know your thoughts on the concept: advantages or disadvantages, synergies with other approaches/technologies, etc.

 

Regards,

Northstar

Edited by Northstar1989
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The benefit of aerocapture at Mars (and at Earth) is substantial. In order to use aerocapture, the crew vehicle would have to break away from the Cycler well before the flyby (on both ends) in order to gently modify its trajectory for atmospheric intercept. However, this means the crew vehicle would have to have extended on-orbit life support compared to a shorter-persistence shuttle intended to ferry the crew from an orbiting mothership. This additional requirement somewhat obviates the value of the high-velocity Cycler, since you have to duplicate life support systems and crew space.

Then there's the problem of getting back to the Cycler from Mars. Surface ISRU and a reusable crew shuttle is definitely the best option.

Supplies and surface hardware would still all have to be sent via conventional Hohmann transfer to aerocapture in unmanned vehicle.

One of the advantages of a persistent orbital mothership is that you can put not only life support and crew/cargo space on it, but you can also put your heavy transfer engines on it, to boost the mass of your actual cargo and crew up to speed for the transfer. But you can't do that here.

9 minutes ago, kerbiloid said:

If I don't miss something, when such thing orbits around the Earth, they call it "space station". Just it orbits around the Sun.

Yes, an Aldrin Cycler is a space station orbiting the Sun in such a way that it maintains periodic flybys of both Mars and Earth on a repeating pattern, using gravity assists each time.

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28 minutes ago, sevenperforce said:

The benefit of aerocapture at Mars (and at Earth) is substantial. In order to use aerocapture, the crew vehicle would have to break away from the Cycler well before the flyby (on both ends) in order to gently modify its trajectory for atmospheric intercept. However, this means the crew vehicle would have to have extended on-orbit life support compared to a shorter-persistence shuttle intended to ferry the crew from an orbiting mothership. This additional requirement somewhat obviates the value of the high-velocity Cycler, since you have to duplicate life support systems and crew space

The benefit of an Aldrin cycler station is reducing the propellant requirements of both the incoming and outgoing transfer burns from both planets. DeltaV requirements are still the same - catching up to the station means doing a transfer burn - but instead of imparting that deltaV to long-term hab module, one would impart it into a much smaller ship, on both ends of the transfer burn. The cycler station only need enough deltaV for mid-course corrections to ensure its next flyby, and this can be much less than that needed for an orbital insertion/escape burn.

The drawback is that a cycler station that is optimized for quick trip time of the Earth-Mars leg would take much more time for the return trip, and vice versa for the Mars-Earth leg. That means for reasonable trip times in both directions, one would need a bunch of them operating at any moment.

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It requires:

  • At least 2 extraplanetary rendezvous per flight.
  • Up to several weeks long taxi flight duration (twice: near the Earth and near the Mars). So, a full-featured life support in the ferry boat, not just snacks and diapers.
  • Additional fuel (and longer taxi flight) because Earth and Mars orbits are not coplanar, so the ferry boat should undock and turn its orbit plane before the cycler reaches a planet.
  • Same amount of supplies (as mentioned above) and fuel to send them to Mars through the cycler.

From my amateurish pov, this scheme makes sense only if the cycler is a monumental-looking space station with artificial gravity and meter-thick protection layer around the habitat.
Then of course, they don't have to launch these several thousand tonnes again and again. Just several hundred tonnes of a ferry spaceship.
Unlikely an asteroid, as: 1) why need one, when all required goodies can be placed in a station built on a desired orbit; 2) is a heap of frozen stones (so-called "asteroids") enough stable to be sure that it will not deform and bury the hotel.

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The Popular Mechanics article was certainly interesting, especially the Semi-Cycler concept. However I was struck by the logistics of getting a crew to the Cycler which (as proposed in the article) required two launches to assemble the crew vehicle-lander-Earth departure stage stack,   followed by a third tanker vessel to top off the tanks before trans-Mars injection.

My honest opinion - the SpaceX ITS proposal looks much more straightforward , at least from a mission architecture viewpoint.

In terms of hardware, the Semi Cycler vs ITS seems to be a trade off between one, complicated ship that's a big step beyond any currently flying (or slated to fly) vehicle, vs multiple, smaller ships that are closer to current technology).

In terms of risk and cost - I'm going to wimp out here and claim too many variables for useful discussion.

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Delta v is still the same, obviously, as others have stated. The point is to have a more substantial crew transfer vehicle for the transit parts of the missions. as @kerbiloid says, unless the transfer vehicle is spinning, and radiation neutral (heavy shielding), I see little reason to prefer this method as it requires multiple such vehicles to even achieve the same synodic transfer rates. The abort architecture is also somewhat troublesome I think in combination with the number of cyclers in play.

I think it makes more sense to deploy a Mars orbital habitat within reach of any designed MAVs as a backup. Such a facility can be delivered via the most economical method possible as it is uncrewed. You then have pre-deployed habs, etc on the surface (Mars Direct and current DRA style). Then you mitigate radiation via shorter transfer times (good orbital mechanics, or higher DV budgets---mess around on https://trajbrowser.arc.nasa.gov and see what this can look like).

The transit radiation environment is clearly a check in the "pro" column for a cycler assuming any such vehicle is very well shielded. By this I mean a vehicle that ideally has a lower radiation exposure for the crew than ISS does. Remember that ISS has a 50% reduction in all radiation as a default due to the fact that the Earth blocks half the sky at all times for GCRs, and half the time for solar radiation (not to mention the magnetic field of the Earth into the bargain).

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We should also take into account possible lifespan of an orbital station (tens of years) and frequency of its orbital turns. According to the first link, at least 2 years per cycle.
This means, a cycler can support just 10-20 interplanetary flights before it becomes too old to use.
Then Mir/ISS/Skylab-type cycler will be just dangerous to visit. While a huge, thick, and spinning wheel-shaped station will be a museum of outdated technologies (and probably also worn).

So, for me a (heavy, thick, spinning) cycler makes sense if you are going to perform an agressive 20-years lasting assault to Mars.
It doesn't make sense if you are going to send ships from time to time or if you are going to use it longer.

Also, to build such heavy station in heliocentric orbit you need high-ISP ships to deliver its components.
This means that when the cycler  creation will be completed, very likely your current ships will get to Mars directly in weeks.

P.S.
Of course a cycler unlikely makes any sense for anything beyond Mars (due to enormous flight durations).
So it is by definition a technological dead end.

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2 hours ago, shynung said:

The benefit of an Aldrin cycler station is reducing the propellant requirements of both the incoming and outgoing transfer burns from both planets. DeltaV requirements are still the same - catching up to the station means doing a transfer burn - but instead of imparting that deltaV to long-term hab module, one would impart it into a much smaller ship, on both ends of the transfer burn. The cycler station only need enough deltaV for mid-course corrections to ensure its next flyby, and this can be much less than that needed for an orbital insertion/escape burn.

The drawback is that a cycler station that is optimized for quick trip time of the Earth-Mars leg would take much more time for the return trip, and vice versa for the Mars-Earth leg. That means for reasonable trip times in both directions, one would need a bunch of them operating at any moment.

From memory, the delta-v requirements to Mars only become a problem when you have to apply them to a multiple-month habitat.  Sending kerbals (or deeply sleeping astronauts) is pretty cheap.

Perhaps some nuclear-powered ion engine could move your asteroid into position over the course of a decade or two.  Assuming the cycler-station looked a lot like the ISS (since that is how we know how to build space-stations), it would only have to have an asteroid at one end, which would point at the Sun and block the radiation (presumably the solar panels would be either in front or beside the asteroid).

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57 minutes ago, wumpus said:

it would only have to have an asteroid at one end, which would point at the Sun and block the radiation

Solar wind is just one of deadly radiations. Galactic high-energy gamma-rays are omnidirectional.

6 m of reinforced heavy concrete (with boron and lead admixtures) around a nuclear reactor active zone is enough to protect personnel around it.
1-2 m of ground over a vault protects from nuclear explosion fallout.
As estimated doze for Martian expedition is about several Sieverts (much less than in both mentioned cases), you don't have to move a whole asteroid to feel safe. About a meter thick protective layer looks enough.
So, instead of redirecting an asteroid, it's much easier to bring several hundred tons of boron-lead mixture and pour it in hollows around the orbital station habitat.

Edited by kerbiloid
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These "cycler" ships are not terribly useful when talking about 10 or 100 people at a time. If they make sense at all, they need to be big, self-contained, space habitats that just happen to go between planets and can carry along people and supplies. They have to be amortized over a LOT of trips before they start making sense.

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The advantage of aerobraking cannot be understated. In particular, since the required dV for the outgoing trip is much higher than the dV for the homeward journey, aerobraking can be used in unconventional ways.

My preferred mission architecture for long-term Mars exploration uses a combination of propellant transfer, aggressive aerobraking, reusable shuttles at both ends, and partial ISRU. The core is a ship similar to an Aldrin Cycler, with power and habitation but only small propulsion systems. The main difference is that the whole thing a) carries extra propellant tanks, and b) is structured such that it can point in a single direction and successfully, repeatedly aerocapture at both Earth and at Mars.

The cycler is assembled in low earth orbit, and Earth-based shuttles (presumably the second stage of a beefy two-stage launch vehicle like New Glenn or ITSy) gradually fill the ship's propellant tanks, then re-enter for reuse. The cycler carries substantially more fuel tankage than oxidizer tankage.

The final shuttle takes the crew/passengers up, docks with the cycler, then uses the fuel that has already been placed in orbit (along with its own engines) to execute 95% of the transfer burn to Mars. Immediately after a Mars intercept is reached, the shuttle decouples, flips to retrograde, and uses a short burst of fuel to bring itself back to an eccentric Earth orbit, from which it can aerobrake in multiple passes back down to a safe re-entry. 

The cycler uses its smaller engines to complete the transfer burn and make any necessary midcourse corrections. It aerocaptures at Mars, circularizes, then executes a rendezvous with the already-orbiting Mars-side shuttle. The crew transfers to the Martian shuttle and the cycler transfers all its oxidizer and a large portion of its liquid fuel, and then undocks. The Martian shuttle heads for the settlement or research station on the Martian surface.

Once on the surface, the Martian shuttle deploys a solar array and begins cracking Martian atmosphere (CO2) into liquid oxygen. This can be done without the need for any drills, reprocessing, or access to Martian ice reservoirs. 

At the conclusion of a given mission, when the Martian shuttle's LOX tanks are full, it returns to Martian orbit using all but the last of its fuel reserves, and does a rendezvous with the waiting orbital station. The orbiter takes on a small amount of LOX and transfers most of its remaining liquid fuel to the shuttle, which uses its engines to execute 95% of the transfer burn back to Earth. Like its counterpart at Earth, it then flips, burns retrograde into eccentric Martian orbit, and uses aerobraking to return to a low Martian orbit, ready for the next mission.

The orbiter aerocaptures at Earth, circularizes, and meets up with a waiting shuttle. 

8 minutes ago, wumpus said:

From memory, the delta-v requirements to Mars only become a problem when you have to apply them to a multiple-month habitat.  Sending kerbals (or deeply sleeping astronauts) is pretty cheap.

Perhaps some nuclear-powered ion engine could move your asteroid into position over the course of a decade or two.  Assuming the cycler-station looked a lot like the ISS (since that is how we know how to build space-stations), it would only have to have an asteroid at one end, which would point at the Sun and block the radiation (presumably the solar panels would be either in front or beside the asteroid).

Contrary to common assumption, the biggest dose of background radiation in space is omnidirectional. Blocking the sun only protects from high, sudden doses due to unanticipated solar flares/storms; it doesn't protect from the majority of the radiation.

24 minutes ago, mikegarrison said:

These "cycler" ships are not terribly useful when talking about 10 or 100 people at a time. If they make sense at all, they need to be big, self-contained, space habitats that just happen to go between planets and can carry along people and supplies. They have to be amortized over a LOT of trips before they start making sense.

Cylers are not-so-useful for the same reason that you can't just "hitch a ride on a comet".

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2 hours ago, kerbiloid said:

Solar wind is just one of deadly radiations. Galactic high-energy gamma-rays are omnidirectional.

6 m of reinforced heavy concrete (with boron and lead admixtures) around a nuclear reactor active zone is enough to protect personnel around it.
1-2 m of ground over a vault protects from nuclear explosion fallout.
As estimated doze for Martian expedition is about several Sieverts (much less than in both mentioned cases), you don't have to move a whole asteroid to feel safe. About a meter thick protective layer looks enough.
So, instead of redirecting an asteroid, it's much easier to bring several hundred tons of boron-lead mixture and pour it in hollows around the orbital station habitat.

So the background 3K energy is just in really nasty short bursts?  I'd never guess it was ionizing.  Or is that just between galaxies and things don't go that low in the Milky Way?

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Solar radiation actually moves in a spiral, making pointing somewhat counterintuitive. GCRs are the bigger concern (past acute solar radiation from solar events).

Galactic Cosmic Rays are isotropic, and with lesser shielding particle spalling actually increases radiation exposures (parent gcr hits a hull atom nucleus, and a shower of daughter particles results).

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2 hours ago, mikegarrison said:

They have to be amortized over a LOT of trips before they start making sense.


That's the basic problem with many schemes for making things in space 'cheaper' - they fudge the accounting to hide the enormous up front costs and feature the much smaller marginal costs instead.

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3 hours ago, mikegarrison said:

These "cycler" ships are not terribly useful when talking about 10 or 100 people at a time. If they make sense at all, they need to be big, self-contained, space habitats that just happen to go between planets and can carry along people and supplies. They have to be amortized over a LOT of trips before they start making sense.

And... if you can build these in the first place, why go to Mars with them? It's a dead rock with inconvenient gravity, icky dust getting everywhere, and which is just as complicated to carve out a living on as the vacuum of space itself. Might as well stay in your awesome, self-sustained space habitats until the robot colony has made the planet somewhat habitable.

Edited by Codraroll
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18 minutes ago, tater said:

The trick is that you need the hab for the return trip as well. 3-5 months is a long time, lol.

Not sure if you were referencing my preferred architecture or not, but if you read closely, I definitely have the hab on the return trip. The whole system is fully-reusable and cyclic.

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Also when something goes wrong in ISS or Mir, they just send supplies (sometimes - a repair team) and fix it.

If something happens with a cycler - you can do this only in the same short periods when you send the Martian ship.
So,
either they should work fast and return before the cycler gets  too far from the Earth,
or the Martian expedition should be repairing the cycler themselves (though, a nice way to make their journey not so dull),
or you have to have all cycler systems redundant, so in fact build two-three cyclers in one, but use only one (a ship lifespan is only two years, while cycler should float for decades without major repairing and with no fast escape option).

***

Also what if by some reason (ballistic, technical) the ferry ship docking failed?
The ferry ship misses, it unlikely can return to the Earth due to delta-V requirements.
So, it should perform a Martian flyby and 1.5 years later return to home (like Apollo-13).
To keep the crew alive it anyway needs protection and supplies for a full Martian trip.

(Also this means that simple Hohmann trajectories are risky: their orbital period doesn't match the Earth year.
If possible, better use something like 2-year orbit, exactly matching the Earth orbital movement.
Yes, this needs more delta-V, but you can get inspired by Apollo-13.)

So, if a ship anyway requires a full-scale life support (and anti-rad protection), why bother with extraplanetary rendezvous and docking?
The only reason - artificial gravity. If they fly there under normal gravity, they don't spend their health, get to Mars healthy and you can pay them less.

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8 hours ago, Codraroll said:

And... if you can build these in the first place, why go to Mars with them? It's a dead rock with inconvenient gravity, icky dust getting everywhere, and which is just as complicated to carve out a living on as the vacuum of space itself. Might as well stay in your awesome, self-sustained space habitats until the robot colony has made the planet somewhat habitable.

Actually ... the "inconvenient gravity" is one of the attractions. Obviously people can live for months in microgravity, because they do on the ISS. But there are still a lot of suspicions that living years without gravity will cause health issues. Nobody knows for sure, of course.

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20 minutes ago, mikegarrison said:

Actually ... the "inconvenient gravity" is one of the attractions. Obviously people can live for months in microgravity, because they do on the ISS. But there are still a lot of suspicions that living years without gravity will cause health issues. Nobody knows for sure, of course.

Yes, but I think that can be found out easier - well, everything is relative - by making a spinning station somewhere close to Earth. Or just in Mars orbit, if one is so adamant to make a colony there. You need roughly the same measures to survive on Mars as you need to survive in space (air tightness; radiation shielding; food production; recycling of everything organic, breathable, or drinkable; emergency contingency plans since Earth is months away at best...), and the only benefit offered by the planet surface is access to raw materials and water.

Frankly, I think any eventual Mars colony would be situated in its orbit, in a large, spinning space station. It saves any supply ships and visitors from the hassle of landing and eventually getting back to orbit. There would be mining outposts on the surface, possibly some refineries too, but the bulk of the colony itself would enjoy 1 G and a dust-free environment high above it. Working on the surface would be like working on an oil platform today: Two weeks on site, four weeks off, the site only has quarters for temporary living, while the workers have their home and family on the orbital station. Same would go for Mercury and the Jovian moons. Except on Earth, life isn't any easier down the gravity well, so you might as well stay out of it.

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Cyclers are basically a way of overcomplicating the whole thing into the realm of sci-fi. Let's start from the beginning... what are Cyclers for? Well, theoretically, they lower the mass necessary to launch from Earth for a Mars mission... once you have launched a bigger mass to build it in the first place.

And yeah, they make a ~6 month travel a bit more comfortable... but then why do we have crews of humans living in a tin can for longer stretches at a time in ISS.

Bottom line? They sure are a way to overcomplicate your architecture and increase the cost of the first mission. They add complexity and failure points (what happens if the transfer ship fudges up the rendezvous/docking? How do you send a menteinance crew to the cycler without committing them to a whole mission?). They add to the total R&D cost, because they imply a separate vehicle to be developed and launched (and a big vehicle at that).

And all of those compromises, all of those additional costs, for what? To make 'easier' a trip that can be done in a single lousy chemical stage. Yes, I said that. Mars is very much not far away, the dV to land on Mars is lower than to do the same thing on the Moon. And if you ain't landing, a slightly more sophisticated chemical stage can actually do a roundtrip to Mars if you design the architecture smartly (aerocapture into a high orbit on both ends of the journey).

 

Rune. TL,DR: I see no real benefit, and a whole lot of added difficulties.

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8 hours ago, kerbiloid said:

So, if a ship anyway requires a full-scale life support (and anti-rad protection), why bother with extraplanetary rendezvous and docking?
The only reason - artificial gravity. If they fly there under normal gravity, they don't spend their health, get to Mars healthy and you can pay them less.

This is the biggie. The shuttle/taxi has nearly all the requirements of the cycler itself. And if you must have gravity, just make your shuttle/taxi a tumbling pigeon and call it a day.

3 hours ago, Rune said:

Cyclers are basically a way of overcomplicating the whole thing into the realm of sci-fi. Let's start from the beginning... what are Cyclers for? Well, theoretically, they lower the mass necessary to launch from Earth for a Mars mission... once you have launched a bigger mass to build it in the first place.

And yeah, they make a ~6 month travel a bit more comfortable... but then why do we have crews of humans living in a tin can for longer stretches at a time in ISS.

Bottom line? They sure are a way to overcomplicate your architecture and increase the cost of the first mission. They add complexity and failure points (what happens if the transfer ship fudges up the rendezvous/docking? How do you send a menteinance crew to the cycler without committing them to a whole mission?). They add to the total R&D cost, because they imply a separate vehicle to be developed and launched (and a big vehicle at that).

The only thing Cyclers are good for is ensuring a commitment to extended Mars missions.

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4 minutes ago, sevenperforce said:

The only thing Cyclers are good for is ensuring a commitment to extended Mars missions.

That is a point for them, yeah. But even then, if you think about it,  they need the commitment beforehand, right? I mean, they ain't going to be cheap toys to put together.

14 hours ago, Codraroll said:

And... if you can build these in the first place, why go to Mars with them? It's a dead rock with inconvenient gravity, icky dust getting everywhere, and which is just as complicated to carve out a living on as the vacuum of space itself. Might as well stay in your awesome, self-sustained space habitats until the robot colony has made the planet somewhat habitable.

You know, I am usually the one to bring up the "you guys are all a bunch of planetary chauvinists" spin to the conversation, but I had never though about using Aldrin cyclers as an argument and/or intermediate step. That could almost work, right, the two things justifying each other? But nah, on second thought, if you want to learn to live in space for realsies, you don't really want to go to Mars, and one thing distracts you from the other.

 

Rune. Just to clarify, I truly believe that in, say, 2,000 years, living in a planet's surface full-time will be for the eccentric few.

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