Re: emissionless drive?
- From: IsaacKuo <mechdan@xxxxxxxxx>
- Date: Tue, 18 Sep 2007 14:04:19 -0700
On Sep 17, 9:06 am, "Peter Webb"
<webbfam...@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
Lets imagine that I have a spaceship consisting of two one ton weights, at
opposite ends of a 100 km rod. This in orbit round the earth - with one end
pointing down and the other up.
Now lets make that orbit elliptical.
The two one ton masses will fall at slightly different rates, as the gravity
is slightly different at the two ends. This sets up a slight force between
the two masses. When the force tends to separate the masses (as when the
spaceship is approaching the earth), you use a motor to pull them together.
When the force tends to bring the masses together (when the spaceship is
receding), you use the motor to push them apart.
The energy you put into the motor pushing the masses in the opposite
direction to the tidal force comes out as increased speed, with 100%
efficiency. On each orbit you pick up a little more speed, until you end up
at escape velocity.
Theoretically possible?
Okay, I've figured it out. It doesn't work. Consider conservation of
angular momentum, with the center of Earth as the origin. Since
the rod and masses are all lined up with the center of Earth, no
torque acts on Earth. Thus, Earth's angular momentum remains
the same.
That just leaves the angular momentum of the masses and rod.
That will remain the same. You can do a tiny bit of trading
angular momentum between the rotation of the rod itself and
the spacecraft's orbit, but this is insignificant.
With the Moon, a different sort of effect is going on. The tides
are never actually "lined up" with the Moon, but always lag behind
by a little bit. It's this assymetric mass distribution of the Earth
which gives the Moon some "traction" with which to leech
angular momentum from Earth.
Isaac Kuo
.
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- From: Peter Webb
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