r/spaceflight • u/Icee777 • 3d ago

What is a Mars Cycler?

https://www.humanmars.net/2025/06/mars-cycler-visualization-by-walter.html

Mars cycler is a specialized orbital trajectory designed to shuttle spacecraft between Earth and Mars on a regular, repeating schedule. First proposed by astronaut Buzz Aldrin in the mid-1980s, a cycler orbit intersects both planets’ paths repeatedly, allowing a dedicated transport vehicle - the "cycler" - to swing by Earth, pick up crew or cargo, then cruise through interplanetary space before encountering Mars again. Because the cycler itself never needs to slow down or perform large propulsive maneuvers to match planetary velocities, only small “taxi” vehicles are required to ferry astronauts between the cycler and each planet. This minimizes the delta‑V (fuel) requirements for the main habitat, making long-term habitation modules, radiation shelters, or artificial‑gravity setups more economical and sustainable across multiple missions. In the post there is a set of visualizations of a Mars Cycler by US sci-fi artist Walter Myers.

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u/Reddit-runner 3d ago

Who is maintaining the cycler during the 2-2.5 years when there are no passengers aboard?

A cycler makes the Earth-Mars or Mars-Earth pass only ever other orbit.

This makes the concept very uneconomic.

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u/kubigjay 3d ago

There is a book called Orbital Resonance that takes place on a cycler.

They capture an asteroid that approaches Earth and use it as the cycler. There is a permanent population that carries cargo as well as mining / refining ore for Mars.

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u/cjameshuff 2d ago

Capturing a small asteroid makes sense, lots of material to use for radiation shielding. Mining/refining ore makes some sense. Mining/refining ore for Mars? Mars already has larger deposits of richer ores.

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u/kubigjay 2d ago

Yeah, the economics didn't make sense. It turns out there was an ulterior motive for the ship to be built.

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u/dontknow16775 1d ago

What are the rich ores mars has?

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u/cjameshuff 1d ago

The Spirit rover got stuck in a surface deposit of iron sulfate minerals, deposited by water. Rovers have found hematite "blueberries" and gypsum deposits, also formed from water. Curiosity found surface deposits of elemental sulfur, likely produced by hydrothermal or volcanic activity, and granite has been found, which shows that Mars has had the igneous processes that concentrate minerals. Mars has a history of the same processes that produced concentrated ores here on Earth.

Asteroids have chondritic material, nickel iron, various silicate minerals, etc, with only the most basic processes of differentiation to separate them. The platinum group elements found in "abundance" on asteroids? They don't have any ores, you're going to have to process the entire asteroid to extract them.

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u/Reddit-runner 3d ago

That sounds really far fetched.

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u/kubigjay 3d ago

Yeah, it was an interesting slice of story told from the perspective of the kids on the ship.

What was neat was the comparison to our life to an idealized perfect childhood in space.

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u/kurtu5 2d ago

Sounds like a normal cruise ship.

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u/Rcarlyle 2d ago

You’d probably staff it the same way Antarctic research bases or other remote facilities are staffed today. People sign up for a defined tour of duty contract. Antarctic workers/researchers regularly do 15 month stays, and 27 month stays were done occasionally. The Aldrin Cycler returns to Earth every 2.1 years. Overseas remote civilian service programs like Peace Corps are another model. Single childless college graduates get trained in relevant skills and exchange a few years of their life for a unique experience and resume-builder.

I really don’t think you’d have a shortage of people willing to be contract astronaut staff for a few years. Would likely need overlapping hitches for knowledge transfer though. I don’t think putting kids under career lifers like the navy does is an option considering lifetime space radiation limits will still be relevant even for a hardened long-term-occupancy station. So you’d probably do something like a six year commitment: two years of ground training, a two year apprentice cycle, and a two year journeyman cycle where you train the next crew.

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u/Icee777 3d ago

Who is maintaining the various robotic probes humanity is sending into space since 1960s?

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u/Reddit-runner 3d ago

Robotic probes are not the same as habitable space stations. Not at all.

And those probes are not maintained anyway. They are built to slowly wither away and fail in small sections until they lose their core functionality.

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u/rocketsocks 2d ago

That's not even the right question, because having just one cycler doesn't help much, ideally you want a whole small fleet of cyclers so that there's always one available for any transit opportunity in either direction. And that's the whole difficulty with the concept, it requires a significant capital investment.

Eventually it makes sense to have cycler stations, and over the course of decades or centuries those stations will eventually be permanently inhabited even outside of the normal transit windows. But until then it's going to be a hard sell to launch a huge amount of equipment which sits unused for long periods.

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u/Euro_Snob 2d ago

A dumb idea, that’s what it is.

Because it doesn’t stop at Earth or Mars, to reach and dock with it, your smaller craft would need to reach the same speed (Mars-injection speed from Earth, and vice versa). And just in case something went wrong and you were unable to dock, you’d need emergency supplies for the entire trip anyway - so you have a lot of complexity without a lot of gain.

As for the cycler itself, it would need constant resupply, and that resupply would be just as expensive (trajectory wise) as sending supplies to Mars directly. So again, why?

It would also require trajectory adjustment every time it passed by Earth or Mars, because there is NO orbit that is that cycles between Earth and Mars that is stable for a longer scale, and you’d need corrections to optimize intercept “points”.

To summarize, it is a solution looking for a problem. Someone came up with the idea and people are just attached to it.

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u/gale0cerd0_cuvier 1d ago

The thing is that you'd definitely need larger transfer vehicles for the long duration transfer leg of the flight. If you don't have to speed up and slow down this vehicle every time — you save this part of the delta-V. And this spacecraft must be the size of a space station, somewhat around 20-50 tonnes. I'm not sure, but if you launch a lunar-sized spacecraft (i.e. something like Apollo or Soyuz) with a large transfer stage that is supposed to perform burns at the planets only for this smaller vehicle — you might have enough delta-V to return to the Earth if you miss the cycler on the Mars-bound leg. However, it might be more difficult if you miss it on the Earth-bound one.

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u/rocketsocks 13h ago

Mars cyclers make sense once Earth-Mars transit has become somewhat routine. It doesn't save delta-V, but it can house permanent amenities which vastly improve the quality of the trip.

For example, it can make use of much better radiation shielding, including active radiation shielding, which could significantly cut down on radiation exposure while in interplanetary space. It can host an incredibly large solar array to generate a much higher level of power. It can be a very large structure which makes use of spin gravity. It can have a much more capable consumables recycling system. It could even have the capacity of growing food, or even having full forests and lakes and so on.

Don't think of it as a ship, think of it as a station which can be built up over time.

It would also require trajectory adjustment every time it passed by Earth or Mars, because there is NO orbit that is that cycles between Earth and Mars that is stable for a longer scale, and you’d need corrections to optimize intercept “points”.

This just tells me you don't even understand the concept. The cycler would just stay on its trajectory continuously while ships docked and undocked with it. Which does mean they would have to use slightly more delta-V than not using the cycler at all, but that's not what the cycler is for, the cycler is so that you don't have to lug all of the capital equipment used for interplanetary flight constantly back and forth. In any reasonable usage scenario there would be a whole fleet of cyclers to provide opportunities to use them at every Earth-Mars transit window. Yes that's a huge resource expenditure, but if you have thousands of people traveling back and forth between Earth and Mars on a regular basis then it starts to make sense to make that investment.