The benefit of using a cycler rather than a ship that travels orbit-to-orbit is that there is no need to accelerate/decelerate the mass of the ship, just the perishables (people and provisions for the voyage)

You would accelerate a small vessel (like a crew dragon or orion), intercept and dock with the much larger cycler, then enter the ship for your x-month trip.

When you near mars, you get back into your dragon, and burn away from the cycler, entering into martian approach.

7 people in a Crew Dragon for 18-24 months would not be pleasant. 7 people in a flying space hotel would be far nicer.

You could presumably look at using a small asteroid to provide the bulk of the "cycler", offering plenty of shielding for the trip, you'd only have to get it into position once - far less fuel requirement.

My understanding though is Musk is planning on using BFR to go surface-to-surface, with maybe a refuel in earth orbit. I believe this is because of the amount of material that needs transporting to Mars for the first 20 years or so, and that mass can be used as useful shielding. Even if Mars becomes self sustaining and doesn't require a large amount of cargo:people ratio, I believe Musk is aiming for a much shorter transit time than 2 years.

> You could presumably look at using a small asteroid to provide the bulk of the "cycler", offering plenty of shielding for the trip, you'd only have to get it into position once - far less fuel requirement.

Or maybe even something like, as some have suggested (not me!), Phobos:

http://enterprisemission.com/Phobos.html

Warning: it's kind of out there. At the very least, it's perhaps interesting as speculative sci-fi.

Grand theft moon? That's as crazy as Space 1999.

Not as crazy as claiming Phobos is an alien spaceship though, with highly places ESA sources due to announce it soon (article date 2010)