This question is really about best possible travel times between celestial bodies. In my current sci-fi setting, the Human race is spaceborne, but incapable of FTL travel. Their thrusters are excellent, fuel is not an object; the real limiters on travel times will therefore be issues (if I'm right) of acceleration - acceleration is bad for us unless its taken in moderation, so speed-up and slow-down times will have to be kept at safe limits; as far as I know, actually going really fast is not, itself, dangerous - as long as you don't stop suddenly.
A little exposition. Humanity is some 4000 years off of Earth, but without FTL, it is largely bound to the solar system, where it resides in thousands of more-or-less self-sustaining habitats and orbitals (Earth is held in preserve by the Ruling Family - think "the King's Forest" but with a whole planet). Several hundred years after we left Earth, constructor ships were sent to Alpha Centauri equipped to construct similar habitats there. A parallel civilization exists around that star, roughly 4.5 lightyears away, one of my biggest questions is how long it takes for a trip from Sol to Alpha Centauri? Even with my rudimentary understanding of the Big Physics involved here, it seems highly unlikely that either group could exert any reasonable political influence over the other, as any threat of force would be at least decades away.
- However, while intra-system flights would likely have flight times that were feasible with 1 Earth-G (our most comfortable level) worth of acceleration, flights to Alpha Centauri would likely want to use much faster acceleration - I know we sometimes put people past 1G (Fighter Pilots for instance, or - go figure - Astronauts), I'm uncertain, however, what kind of effect that would have on the crew after sustained exposure. In any case, suspension or hibernation of one form of another would be necessary for this trip to be feasible; could such a mechanism alleviate the risks of high-G exposure, and if so, how fast could you reasonably accelerate a Human before things started to get... dicey?
More simply, what kind of travel times am I looking at for planet-to-planet intra-system flights, and star-to-star flights utilizing hibernation or suspension (with greater acceleration allowances, acceleration times could be traded for time flying at peak velocity), considering that thrust and fuel are not an issue?