scottb50":3io1tll2 said:
The biggest problem I see is having the cycler in it's own solar orbit. Timing where it is in relation to the Earth and Mars would limit the orbits it would be close enough to both to be an advantage. What makes more sense is an orbit to orbit cycler, brake into a highly elliptical orbit at both Earth and Mars and accept payloads at parigee and leave orbit nearing apogee. This would allow a wait in orbit until a proper return trajectory is available.
The highly elliptical orbit could use aerobraking and minimum propellant use to reduce costs.
Aerobraking, by it's very nature, cooks a thermal protection system, you would need the ability to inspect, replace, and maintain the TPS system if you use Aerobraking. Even minimum propellant use would be a lot of propellant, considering if you did it that way you would have to slow down twice, and speed back up twice for each cycle.
The solar orbit is not an issue if you place multiple cyclers in the system. Timing is not an issue when orbital mechanics has been understood for generations now. More than likely an Ion thruster would be enough to adjust the orbit of the cycler to keep it in the proper orbit.
I wouldn't think you could do more then three or four round trips without refurbishment, but that would amount to nearly ten years of service. Sitting for extended periods in both Earth and Mars orbits would also allow inspection and needed repair. Considering the cost of getting off Earth even one such cycler would be rather expensive, to put up a constellation needed for Heliocentric orbiters to be effective would be prohibitive.
If every Earth return features an extensive in orbit maintenance cycle even one vehicle would be much better then individual self contained missions with an Orion type system.
Better to have the manned vehicle "catch up" to the cycler, dock, then release, aerobraking, and enter Mars orbit/atmosphere. Minimazation of wear and tear on the cycler would be a priority.
An interesting test for a cycler system would be to contract Bigelow to place a genesis scale inflatable module into a cycler orbit. Use this as a test bed to confirm the radiation levels and prove out the theory.