Disclaimer: The Internet is rife with "fantasy aerospace engineers", who imagine that it's trivial to bolt together disparate components Lego(tm)-style and have them work first time, who think that a pretty Photoshop magics away the need for aerodynamic loading, vibration and thermal analysis, who wouldn't know a trade study if it leapt up and bit them in the ass. I am not an engineer, and I know just barely enough about the subject to realise how little I know. If you're a professional engineer reading this, please forgive my presumption.
The concept I'm about to discuss arose out of my previous suggestion for 'Island Zero', a British space station based on a Bigelow module, and employing spin gravity to enable bioscience research on the effects of partial gravity on humans. I wondered what would be a suitable smaller-scale precursor mission to Island Zero which would give useful engineering validation for that and other technologies on Jonathan Goff's "Laundry List" of essential systems for space infrastructure.
The Cycler-A spacecraft would be unmanned. It would consist of a small-scale, inflatable Bigelow habitat comparable in size to the Genesis-I and II test modules, coupled to a boost stage of Blok-DM class by an extensible tether. The tether allows the hab and boost-stage counterweight to rotate around a common centre of mass. The tether is conductive, and able to function in an electrodynamic mode. After the coupled spacecraft reaches orbit, the boost stage ignites and injects the combined payload into a 14-day cislunar cycling orbit. The tether between the hab and spent boost stage can be extended or retracted as desired once the cycling orbit has been established. Continue reading 'Thinking aloud: Cycler-A'...
Science and engineering goals for Cycler-A include:-
* Structural performance of a subscale inflatable habitat under spin gravity
* Bioscience payloads in partial gravity and deep space (an advanced 'Biobox')
* Materials science payloads in partial gravity, including fluids handling (e.g. how much spin is required to 'settle' fluid for stable pumping, useful for orbital propellant depots)
* Radiation shielding performance of Bigelow habitat material in deep space, including repeated passages through the Van Allen Belts, and response to solar particle events
* Testing of supplementary advanced radiation shielding techniques, including active electromagnetic shielding
* Stability of cislunar cycling orbit to natural perturbation
* Performance of structural tether in deep space
* Performance of electrodynamic tether in near-Earth and deep space
* Use of electrodynamic tether propulsion to 'trim' cislunar cycling orbit
* Remote sensing of lunar surface during perilune passages
* Nanosatellite subpayloads jettisoned during perilune passages
* Externally-mounted astronomical payloads (e.g. the Lobster X-ray camera) perform all-sky 'sweeps' when spacecraft is under spin, or pointed observations when not.
Engineering validation of Cycler-A would facilitate the design of Cycler-B, an upscaled version which would consist of a Sundancer habitat and associated boost stage. Cycler-B would operate in both unmanned and manned modes -- a SpaceX Dragon would rendezvous and dock with the cycler at perigee and transfer 2-3 astronauts for a 2-week voyage to perilunar space and back. Cycler-B astronauts would not disembark at the Moon -- they would primarily be performing human bioscience research and engineering tests on the performance of the cycler habitat systems. See also thesediscussions on using the Dragon directly on a circumlunar free-return trajectory (I'm ShimaKatase in comments).
Cycler-C would be a still larger system based around a Nautilus habitat, with the capability to attach both Dragons and reusable lunar landers, and inflatable fuel tankage to function as a cislunar refuelling depot. This would be essentially similar to the "Nautilus Moon Cruiser" concept already suggested by Bigelow. This would form the very first part of a truly reusable manned cislunar infrastructure.