It's not the WRITING that's hard...

[seawasp]

.... it's the darn research. I posted this on the more private beta-reading list, but realized it probably belonged here as well.

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)

Comments

[ninjarat.livejournal.com]

I think it is more a matter of how much g stress the crew and passengers can handle.

No, actually...

[seawasp]

... it's a matter of power.

If you're playing "Hard SF" and "reasonably near-term tech", which is where we are, the limits aren't how much human beings can take. You cannot MAKE a constant-boost drive in the range of 3G and consume power that makes sense to build in a relatively short time (say, a few years). While disposable boosters and so on have their place (especially in stopping, using the sort of inverse of the slingshot effect), *NO* ordinary reaction-mass limited approach (which includes standard rockets, NERVA, and electric/ion drives) can in the long run (and that "long run" is actually pretty short) match any constant-thrust drive, even if that constant thrust is very low. I'm playing with constant accelerations in the range of 0.01g. And those are requiring, depending on method, many gigawatts of power. Getting g+ accelerations with similar methods would require many, many terawatts.

Re: No, actually...

[ninjarat.livejournal.com]

I see where you're going but that isn't what I got out of the last bit, that you're having problems stopping once you've achieved the acceleration/velocity you want/need in the time and distance allowed. Atmospheric drogues could bleed off the energy very quickly (assuming you don't slingshot yourself out of orbit again). It's hypothetically, maybe theoretically, possible to get your 3g+ delta-v. Ships can be designed to withstand that. Humans cannot.

Outside of the context of using some external braking mechanism, yes, you're stuck with energy problems.

Re: No, actually...

[seawasp]

Yes, you're correct, and in fact I'm using disposable boosters and possibly atmospheric drag for slowing one of the vessels. If you use the boosters at the right point in a planetary approach you can get a LOT more delta-V (either positive or negative) than from the straight booster alone. Which is a good thing, given the velocities I'm having some of these things go at.