Easy ways to orbit [was: Cooling technique for Jupiter brains]

From: Robert J. Bradbury (bradbury@aeiveos.wa.com)
Date: Mon Feb 14 2000 - 05:25:49 MST

On Sun, 13 Feb 2000, Spike Jones wrote:

> Kewall! I missed that. Assuming you have a frictionless rail
> or something to ride on, then the tunnel could be anywhere, and
> the oscillation period is 85 minutes on a constant density earth-
> sized sphere. Now that I think it over, if given a frictionless
> tube in which to oscillate, even rotation doesnt spoil the game.

"Frictionless rail"?
Hey buddy, I've got this great perpetual motion machine...

Seriously though, how do you get a "constant density earth-sized sphere"?
One of the problems I've got with dismantling Mercury is what happens
as you peel off the outer crust and the core starts to "spring back"
at you releasing the gravitational energy that is compressing it.

Another problem that you might help with....
Does the orbit of a planet change if you reduce its mass?
As I gradually remove the material from Mercury, I can vector the
direction of the material (within some limits). Can I use that to
alter the orbital plane of the planet (leaving behind solar collectors
as little planetary turds...)?

Then, what happens to the escape velocity if I "grow" a canopy of solar
cells above the planet (suspended on hydraulic lifters). This gradually
converts the planet from a solid sphere into hollow ball. Do my energy
costs to "lift" material to the solar cell canopy level change
significantly as the canopy mass grows (and expands) while the
remaining planetary mass shrinks?

And if you are really ambitious...
Can we build diamondoid (on Venus) or iron (on Mercury) towers into
space? By "space", I presume I mean the point at which at the tower
tip, you are traveling at "orbital" velocity. Hmmmm, now that I think
about this, does this even work for Mercury given its slow rotation?

It would seem there are two solutions to this problem. One would
be to decrease the mass of the planet until the towers can support
themselves. The other would be to increase the rotational rate
of the planet so even the tips of very short towers are at orbital
velocity. (You can probably see where I'm going with this...
How much do I have to drop the mass of Mercury (or increase its
rotational velocity) before I no longer have to "shoot" things
into space, but can simply "walk" them out of the gravity well.

If it helps, Xenology says:
"The maximum height of rocky ranges is therefore proportional to their
weight, the product of the mass and the force of gravity. Higher gravity
planets will have smaller, squatter mountains, because the limits of
compressive strength of rock are reached much sooner. At least down to
about 0.1 M_earth or so, smaller worlds should tend to have taller
formations. As has been discovered with craters on the bodies in our
solar system, the height of mountains should statistically vary inversely
as the force of surface gravity."

On most mountains the rock has a compressive strength of 1500-1800
Atm or 1.52x10^8 N/m^2. The compressive strength of alpha-iron is
~14,900 atm (1.51x10^9 N/m^2) and gamma-iron is ~33,700 atm
(3.41x10^9 N/m^2). Young's modulus for diamond of 1.05x10^12 N/m^2.

> > What a nerd! :-) Amara
Well, Amara, I've got a picture of you sitting at your desk (from
the Proceedings of the '88 Interstellar Dust conference) and I'd
say from the looks of things we can safely say that you and Spike
probably belong to the same stellar class.


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