Re: Ages everyone?

On Thu, 07 Sep 2006 22:20:31 +0100, Jim Davies
<jim@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:

On the grave of tussock <scrub@xxxxxxxxxxxx> is inscribed:

Unobtrusive wrote:
Not to mention I'm pretty sure we'll have found a way off this rock in
order to record the final throes of our sun.

That takes more energy than you can imagine. The US, while possibly
an order of magnitude overpriced, spends ten million dollars per
kilogram to put things in orbit.
More like 50 million per kg to get out of our gravity well. More
like 500 million per kg to break out of Sol's well. How do you imagine
anyone's ever going to put the requisite tens of thousands of people
into deep space?

Beanstalk. OK, it's marginal under currently known technology (we need
much better nanotubes with a couple of orders of magnitude fewer
flaws), but it's not completely out. That gets you to GEO, whence you
can get anywhere else in the solar system comparitively cheaply, and
then able to make a Daedalus generation or coldsleep ship.

The trick is surviving the next few hundred years to get to that
point, because I can't see it happening before 2250, probably 2500.

There's a group aiming for a beanstalk in the next decade.

Note that a beanstalk will get you farther than GEO--you have to have
a tail extending far above GEO to balance it. Simply ride farther out
on that tail before you release--you can reach escape velocity from
there.

Or if you want to go farther there's another approach I designed:

A beanstalk will have a release point that will get you to a close
flyby of the moon. Lets build another structure, a track around the
moon. It's a big linear motor/maglev track but it's two-sided: You
can run on it like a normal train but if you get going fast enough
there's another track above your head you can run on. There's a bunch
of solar panels to power it. (Yes, half are in darkness. That only
means you need twice as many. The power cables should be
superconductors anyway--it's the moon, no atmosphere, keeping them
cold is no big deal.)

You want to go somewhere distant? You ride the beanstalk to the lunar
transfer point and let go. You drift to the moon. You'll need some
maneuvering rockets to ensure you're exactly on course but that's all,
no big delta-v requirements. You land on the track--no rockets. If
your destination is the moon, fine, you slow down and get off. If
you're heading somewhere else you speed up instead of slowing down.
Round and round and round building up energy until you have all the
velocity you need and then you leave the track. If you'll accept 5g's
on the track you can build up enough velocity to reach any point in
the solar system.

Any airless body that's a common destination can build such a track
and you can arrive without rockets. Bodies with atmosphere permit
aerobraking. Thus, once the infrastructure is in place you can get
anywhere. I think the airless bodies would be much more common as you
still have to use rockets to get away from the other places with
atmospheres. (Venus: The day is too long for a beanstalk. Mars:
You'll have to do something with the moons before you can build one.
Jupiter/Saturn/Uranus/Neptune: Too big for nanotube-based beanstalks
and there's nothing to anchor the bottom to anyway.)

Note that for getting to the smaller asteroids you can make a transfer
station on a few big ones that allows you to match velocity with the
belt first.
.

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