Mass drivers as spaceship launchers

>

> And then there's always the the other bypass to consider, the
space
> elevator....
>
> Ed
>
> Ah, the space elevator also has been called the space hook.
That
> would be the ideal way to get things into LEO or really close -
take the
> elevator. I think at 40 miles up your steel on the lower floors
would
> get sticky (molten).

OMG no, not steel. And there wouldn't be much of a building at the
bottom; the base structure would be on the scale of an offshore oil
rig. A space elevator would be under tension, not compression.

It will take a few years to develop the materials in sufficient
lengths, but the material used would be Carbon nanotubes, woven into
a ribbon. At the bottom it would only be a meter wide.

>Such a building would take decades of international
> steel production to even start thinking about.

Building with Carbon nanotubes, the total mass of a space elevator
capable of lifting 20 tons to orbit would be 800000 tons; about the
mass of the Empire State Building.

And the first space elevator wouldn't have to be able to lift 20
tons, it would only have to lift a fraction of that - it would lift
additions to itself up, gradually adding mass and capability until
the full elevator is erected.

> Sounds more like fiction
> as apposed to a real idea, but if I remember correctly in
brainstorming
> you don't eliminate ideas. I read a book once about some kind of
tether
> between earth and perhaps the moon - it either guided or the craft
> pulled itself down this cable. I wondered at one time if something
that
> was in orbit could lower a line down to the surface and that
something
> could climb it or be winched up it. Fanciful I know, but if you
wanted
> to move everyone off this planet you would just not have enough
rockets
> to go 'round.

The center of mass of a space elevator would be just barely above
geosynchronous orbit, and it would extend both down to the earth's
surface 35800 km away and up into a high orbit 100000 km up. The
part above GEO acts as counterweight to the part below GEO and
allows for cargo to be released into translunar or transmartian
trajectories. The center of mass is above GEO to maintain tension
when a climber is ascending the lower part of the elevator.

For better information on space elevators check out the NASA
Institute for Advanced Concepts studies page at
http://www.niac.usra.edu/studies/
and click on the two studies by Bradley Carl Edwards.

>
> The way I read the 40 mile long magnetic vacuum rifle - the
> cargo was levitated magnetically the entire length of the barrel.
I say
> barrel and rifle because it has a lot more in common with a SciFi
weapon
> than an accepted way to fire things off planet. Someone should try
to
> get the military to back it as a weapon program seeing as their
budget
> is substantially larger than what NASA ever will get. Mt.
Kilimanjaro
> was sited at a good site, as was Mt. Fuji, but I suppose any
mountain
> would do. The main idea of any new form of spacelift is to leave
as much
> of the launcher on the ground as is physically possible. Any idea
that
> does that is better than the 'bombs with a hole knocked out' we
> currently strap people to, cross our fingers, and launch into
orbit.
>
> - Ted

Yes, and while attaining orbital speed within the earth's atmosphere
isn't a great idea, getting that initial Mach 0.7 would be a big
savings in mass.

Ed