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Old November 17th 03, 10:52 PM
Brad Guth
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Default Is the moon leaving, or are we shrinking by 38 mm/year

Marvin wrote in message ...
So again, how much kinetic energy, and/or in terms of thrust (ISP
or kg/s in terms of fuel/energy consumption), would it take for a
satellite the size and mass of our moon, to be accelerated so as to
escape Earth by a rate of 38 mm/year?


Thanks so much for all the feedback. I'll try a little more input into
my three remaining brain cells and see if the amount of recession
energy can be realized.


The amount of energy needed to raise the moon's orbit by that 3.8cm/year is
easy.. Just plug into basic orbital mechanics, out pops an answer of some
1.25 * 10^20 joules per year, easier to visualise as a constant power input
of some 4 terawatt (4 * 10^12 watt)

The problem is that this is indeed the *resultant* of all forces
applicable. Just how big are the other forces working on the moon,like
frictional drag against the not-quite-empty vacuum of local space.(keep in
mind the moon orbits earth at about 1km/sec, and the earth whizzes around
the sun at about 30km/sec)?


Terrific feed back, at least 4 terawatts plus something for drag,
thanks much.

BTW; here's something I picked up off the net:

http://www.europhysicsnews.com/full/.../article3.html
Hydrodynamics of planetary nebulae: 10e10 atoms per m3.
and of much lower density, typically 10e7 atoms per m3.

Perhaps the friction aspect can be roughly derived, as there's got to
be some worth in that much surface being driven through at the 1.025
km/s.

The part about keeping up with Earth I'd think is a given, as pushing
ahead (into the solar wind) should be fully counteracted by the exact
opposit of traveling down-wind while being taken along by the momentum
of Earth's traveling about the sun.