To my mind, the primary problem is not physics, but politics.
Bring ringing back projects like
Orion would be a great start towards space colonization.
Systems like Orion do not suffer from the high-ISP-but-thrust-measured-in-mouse-farts problems typically encountered in electrical propulsion. This is because, basically, spacecraft like Orion just detonate nuclear bombs and ride the shock wave. A system like Orion is technically achievable now, it's just bloody expensive.
I'd also like to make a point about the thrust/efficiency trade off mentioned in the essay. Nuclear fusion propulsion, particularly pulse detonation models like Orion, are capable of interstellar travel within 'reasonable' amounts of time.
My degrees are in astronautical engineering, and one of my graduate research projects involved doing a constant thrust trajectory analysis from the earth to jupiter using a nuclear fusion propulsion system. The trip took two weeks assuming 50% higher thrust (higher than that and the solution wouldn't converge, and I didn't have time to write a stiff equation solver).
Antimatter has been produced for at least a decade, eventually perhaps at levels sufficient to open up other new doors for us.
Furthermore, I expect major breakthroughs in physics in our lifetime. No one can explain how gravity works or why objects have inertia now: as we learn more about how they work our fundamental assumptions about physical limitations may change as well.
Everyone "knew" that it was impossible to exceed the speed of *sound* at one point in time because mathematical models demonstrated that one's drag became infinite as objects passed through Mach 1. The equation uses the same form as the Lorentz equation that mathematically 'proves' that FTL is impossible.
Mathematical models are just that: models. They can be flawed, particularly around singularities.
-Daniel Pasco
Independent Media Project
Sound. Words. Motion
http://imp.fm/
