In the first part, I talked about going to the stars with lighter ships. Here I will talk about going a bit slower and closer to home. The reason for going lighter or slower is to make the problem over a million times easier. Interstellar travel is very hard. The options for choosing problems that are a million times easier are still hard problems or require money, hard work and the willingness to use nuclear weapons as tools to conquer space.
Going a bit slower or a bit closer
Going at 1-13% of the speed of light instead of 80-90% of the speed of light is a lot easier. Accelerating something to 1% of the speed of light requires 8100 times less energy than accelerating something to 90%. Also, more near term and existing technology can be used to enable the mission. We could use fission power which exists instead of antimatter which is theoretical and requires scaling up antimatter production billions of times. The advanced technology we could use such as antimatter can be done with achievable amounts of antimatter to catalyze nuclear propulsion.
Going up to 3-10% of the speed of light is possible with nuclear pulse propulsion.
A close pass slingshot around the Sun (3 solar radii) with a solar sail allows acceleration to up to 13% the speed of light. Such a close pass allows for someone to just make the solar sail and not have to make a giant laser and lens to accelerate the solar sail to fantastic speed. See page 16 of this pdf for ultralight solar sails Note: you need a really good heat shield to protect you when you go that close to the sun.
Wikipedia has a directory of their own excellent articles about all aspects of space colonization
I believe that we should make orbiting space habitats New designs such as Kalpana One and extensions of the Bigelow space hotels. Note: Bigelow aerospace already launched a one third scale model this year of their inflatable space hotel module.
Buzz Aldrin is a main proponent of turning a space habitat into a cycling transit hub There are many papers that are refining the aldrin cycler or astrotel concept.
Ocean colonization is useful to practice mastering self sufficiency but would not create separate biosphere's to address the survival issue raised by Stephen Hawking.
We should colonize the moon and then the rest of the solar system should be colonized
This can be done far easier and sooner by using nuclear pulsed propulsion whose principles were validated in the 1960's and 70s. Glenn Harlan Reynolds has an article that supports the return to Orion Without Orion (nuclear) technology we will be struggling to get a few dozen people into space but with Orion we can launch 100,000 people at one time.
By more fulling using the resources of the solar system we can easily access one trillion times the power and resources that we currently use Only something that could destroy the sun would be a threat to a civilization that was spread throughout the solar system. Even in that case if the space habitats that orbited the sun had nuclear and antimatter power and propulsion they could being migrations to other star systems when the threat to the sun was identified.
I expect that people will have the sense or courage to go with full nuclear pulse propulsion and super-Orions. The reason is as discussed in the most recent Time magazine. Why We Worry About The Things We Shouldn't...and Ignore The Things We Should Nuclear pulse propulsion is actually not risky. The radiation and fallout issues are not a problem. They would be less than the atmospheric nuclear tests that were performed and did not kill people. Plus we already dump 20,000 tons of uranium and thorium material into the air by burning coal.
If we don't do that then we will have to wait for more advanced nanotechnology and more advanced z-pinch technology for
advanced minimag Orion systems Improved launch systems could reduce the cost of getting into orbit by 200 times or more down to $1-10/kg. Full Orion systems could then be built in orbit or on the moon.
Advanced minimag Orion could use sub-critical nuclear power to make a scaled down Orion system that would still be highly efficient. It could use a lot of smaller explosions. Nanotech could improve the rate of explosions. New materials can lighten the overall system. We could get fusion or highly energy dense power but with absolutely no concerns of any leaked radiation or fallout.
Metamaterials could boost the power and efficiency of the z-pinch I think the system could approach the performance of a fusion power system and could even transition into being a full fledged fusion power system with a post-ignition z-pinch.
New nanostructured (superthread, Carbon nanotube solid and carbon nanotube arrays and nanostructured metals) material is already being produced in small quantities that would be far stronger and lighter which will increase the percentage of payload and overall launch system performance.
Wikipedia has a lot of information about space colonization
Al Globus has interesting writing and plans for space colonization he is focused on orbital and artificial space station colonies.
Space colonization links
A long pdf 170 pages that advocates space colonization Note: I have not read it all but I have scanned it. I think it has some interesting ideas and useful research references. I probably disagree with some of the political views and the timeline and the specific plan.
This site by the same guy as the writer of the pdf has some nice space colonization pictures
magnetically inflated structure
nuclear pulse propulsion