On 2008-02-27, IsaacKuo <mechdan@[EMAIL PROTECTED]
> wrote:
> The original concept didn't specify the target was Earth, but
> that's not really the main issue.
I think you've forgotten what the original concept was:
"Suppose the First Marshen Republick launches an expedition to visit
various uninhabited asteroids, a-to-b-to-c-to-d. The carefully
selected crew (who all happen to have high security clearances and
tight lips) visit the asteroids and publish their papers and all is
right with the worlds. Ten years later, an unmapped giant asteroid
wipes out the Terran Pacific Rim with giant tsunamis and earthquakes,
and severely inconveniences the rest of the earth with several nuclear
winters."
> Naturally, you need to time it well, so it will fall onto the
> target as it passes by. It'll take decades for the object to fall
> onto the target, but that's compatible with the original scenario.
Not as originally written. The whole thing took place within ten
years, from beginning emplacement to devastation.
> In principle, at least, a mass driver rocket can be pretty efficient
> (also specified in the original scenario). With a mission delta-v
> of only 5km/s, an average exhaust velocity of 3-4km/s is fine.
If your payload is only a quarter of the original asteroid, sure.
> But since the mass driver can be pretty efficient, you'll only be
> contending with a fraction of that energy.
Not just the mass driver: every step of the conversion from potential
energy to kinetic. With near-future technology I'd be dubious of any
claims of more than 30% total efficiency, though I'd accept up to 50%
or so for improvements in the more distant future. I'd be especially
critical of something rigged while plausibly pretending to be mapping.
With a 3-4 km/s exhaust for 5 km/s total delta-V, the minimum energy
required is on the order of 25 MJ/kg of payload. That's easily enough
to vaporise any common asteroid materials even neglecting the fact
that the efficiency will drop as the environmental temperature rises.
> So, for example, let's suppose the asteroid is a million ton Kuiper
> belt iceball. Roughly 3/4 of the mass is consumed by the mass
> launcher rocket, leaving a 250,000 ton payload and a mission delta-v
> of 4km/s.
That's multiple orders of magnitude too small for "wip[ing] out the
Terran Pacific Rim", and too slow to get there in ten years.
> And no, I still don't find this method of attack any more plausible
> than in my first reply.
At least we're agreed in that. We just disagree in some of the
details.
- Tim
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