Originally Posted by gyldenlove
This may sound defeatist, but we as a species have nothing to fear from the sun. By the time the sun kills off all life on earth we will either have moved elsewhere or destroyed every opportunity of ever going anywhere ourselves. We have all the resources we need.
Fusion would definitely be a good power source. Magnetic fields are not the only option for radiation protection, electronically charged shielding may be a lot better. Fake gravity can be done by making a rotating vessel, protection against debris, you are probably going to have to go low-tech with a Titanic like solution, compartmentalize and accept that if there is an impact you may take casualties, so make sure you have very high redundancy. Water generation is trickier, you would need to bring a lot of water from the outset and you would need to recycle like crazy, so you would need to purify urine and bathing would be a thing of the past. Food is a bit easier, it is much more compactable than water and diets that are very high nutrients can be devised.
I think the best option of going far (out of solar system) would be to create either flotillas of smaller ships or a few bigger ships so groups of 50.000 to 100.000 can go together, that would leave room for redundancy and provide enough genetic variance to avoid inbreeding problems among descendants.
I think our best option for long term space travel would be capturing a couple nice sized asteroids, get them rotating fast enough for gravity, hollow them out for living space. An ideal one would have lots of ice on/in it already. Use the excavated material to manufacture tools and possibly even metal/mud sheets that form bulkheads. I would capture a couple asteroids and get them rotating around the main "ship". Attach Fission and ION propulsion to the main asteroid and smaller chemical based engines to the "resource" asteroids to keep them orbiting properly etc... Get everything spinning the right way, allow gravity to keep it all together then propel the whole mass using the main ships engines. You could have chemical engines to alter course and get the mass moving, then use a combo of Fission and ION engines to get fast over time. Not sure how big the main asteroid would need to be to keep the other smaller resource asteroids in tow as it gains speed. That would be a lot of math for people smarter than me.
As far as radition shielding the rock and ice from the asteroid would be the major protection and we could store the liquid water (both clean and dirty tanks) around the sleeping and or living quarters, places where the crew would spend the majority of their time. I have read that water is the best or one of the better shields for cosmic radiation, at least that is what they are looking to do for a trip to Mars.
I think for long term manned missions and habitations we need to look at inflatable fabrics that are extremely strong, stuff made of Kelvar that can be lifted into space then expanded to provide working/living space. A hollowed out asteroid that has a blown up Kevlar type shell. Think pop up camper type stuff but more reliable.
Just a quick thought in response to what Glynden said.