I spent all my time this weekend doing calculations involving acceleration and deceleration times, distances, masses, energy collection and generation capabilities, etc., etc., etc., etc....
... just to arrive at the determinations of what I can do straight, and what I have to handwave, in order to let the story play out as we generally want it to.
The overall conclusion: What happens in Threshold is theoretically possible. In practical terms I think I'm going to be being, shall we say, extremely optimistic in the timeframes available in terms of how much power generation capacity will be able to be created for certain things to work out. Then again, as Dr. Nordley (who has been kind enough to advise me in certain areas) said, "Interstellar propulsion is no game for those with macronumerophobia." This is true even for fast interplanetary.
Fast, I say? Yes. How about from Earth to Jupiter in about 70 days, with good conditions? Or about 21 days Earth-Mars?
Yeah, that's getting pretty fast. I can actually GET there faster, but then I start having REAL problems *STOPPING*. (I'm pushing "stop" limits pretty far, as I understand them, but they're POSSIBLE. Anything much beyond where I'm taking things, though, and I suspect it becomes impossible)