From: Robert J. Bradbury (bradbury@aeiveos.com)
Date: Wed Dec 13 2000 - 12:01:30 MST
Amara wrote:
> The mechanisms are fascinating though. I would love to have it as
> my thesis topic, if I didn't already have a thesis topic (below).
Well gee, I always thought women with 2 PhDs were tres tres chic.
Spike wrote:
> WOW cooool, Drexler, Bradbury, spike. There are three names I
> like to see mentioned in the same sentence.
> ...
> Today I was doing some back of the envelope calcs and I think
> I know why the other two wanted to know.
Spike, you only get *temporary* membership in the club unless
you take those "back of the envelope" calcs, format them, put
them on the net *linked* to the references and respond to
questions that people ask about them!
Think of all of the times someone else will repeat all of that
work because you threw away those envolopes (remember, I've
been to your house and I didn't see any envelopes, so I assuming
you throw them away. Or perhaps they are *virtual* envelopes...
We trust you enough that we would only occasionally suspect
they are "imaginary" envelopes).
As I recall Amara was right and I was investigating the dust
from the point of view of missing baryonic matter, esp. carbon.
For those who are unaware of it the recent surveys of the cosmic
background radiation are suggesting that there is more baryonic
matter in the universe than current nucleosynthesis theories would
suggest. So the theorists are having a very difficult time
reconciling things with the experimental physicists. Its *very*
interesting though that Eric was asking about it. Perhaps IMM may
be working on some NASA grants into the impact of nanotechnology
on various NASA agendas (such as interstellar travel). Just as
a historical tidbit, Eric many years ago did look at the astronomy
plates at MIT to see if there were galaxies that had "dark regions"
that could be interpreted as signs of expanding (colonizing)
civilizations. He didn't discover any.
The way the problem of interstellar dust (and to a lesser extent
cosmic rays) was handled by the British Project Daedalus study
was to put an ablative shield on the front of the spacecraft.
I believe they were using boron, presumably because of its
light weight and high melting point. Spike, you might want
to redo the calculations with Tungsten. If anyone wants it,
I've got the entire study converted to MS-Word. It hasn't
been proofed or converted to hypertext yet unfortunately.
I don't believe the shield they used was that thick,
certainly not the km that Spike has suggested.
Of course it depends on what speed they were going
(I don't think it was as high as 0.1c) and what dust
density they used. Other methods that might be useful
would be magnetic shielding. The question is does
the dust carry a charge?
I also can't believe you are talking about interstellar
travel with short-lived individuals (though I haven't
followed the thread to its origin). That makes no sense
at all. Any civilization that has the energy to waste
on interstellar travel, certainly will have engineered
itself so as to be "non-aging". You also have to have some
interesting entertainment on those long voyages or preferably
put the individuals in "biostasis". But longer biostasis periods
will either require periodic reactivation to repair the accumulated
radiation damage or a *really* hefty shield around the stasis chamber.
An interesting comparison would be the energy requirements to
accelerate and decelerate the ship vis-a-vis the energy requirements
to maintain 100W individuals over the duration of the trip.
Now the interesting thing to my mind is the fact that you don't
need the massive fusion propulsion system envisioned by the
Project Daedalus folks. You construct big mass drivers and/or
laser systems in the local star system to launch lightweight
ships. You can slow down on the far end using magnetic braking
or the leading light sail reflecting back at the ship powered
by long distance laser power transmission.
Of course, much better is to send Spike's maaany km of ice
arranged as a cylinder a few mm in diameter with a solar-system
engineering nanobot attached to the back end. If the nanobot
survives the cosmic radiation (still an unresolved question
in my mind), then it can pre-engineer the target solar system
to provide you with a nice safe happy landing when you arrive
on the slow boat and pop out of your biostasis chamber.
Keep this in mind, 1% of the power available to us in our solar
system allows us to power ~10 billion 100 TW laser beams.
If you want to do some interesting calculations Spike,
see what the mass limits and times required would be on
what you can accelerate to 0.01, 0.05 and 0.1 c with that
kind of power at your disposal.
Oh, yes, and as one final tidbit, courtesy of the All Sky
Automated Survey data, I now have definitive candidates for
stars going "dark". They may be nothing more than long
term variable stars, or they might just be....
Robert
This archive was generated by hypermail 2.1.5 : Fri Nov 01 2002 - 15:32:22 MST