🚀 go-pugleaf

In sci.physics, Rich
<someone@someplace.not>
 wrote
on Sun, 27 May 2007 10:06:45 -0700
<kdKdnX5lJ70_J8TbnZ2dnUVZ_vTinZ2d@comcast.com>:
> The Ghost In The Machine wrote:
>> In sci.physics, Phineas T Puddleduck
>> <phineaspuddleduck@gmail.com>
>>  wrote
>> on Sun, 27 May 2007 16:45:09 +0100
>> <phineaspuddleduck-B2278D.16450927052007@news.octanews.com>:
>>> In article <1180239547.283666.73560@z28g2000prd.googlegroups.com>,
>>>  BradGuth <bradguth@gmail.com> wrote:
>>>
>>>> Don't need any stinking big-ass rocket engines, or those impactors
>>>> from our Oort cloud.  As I'd said before, given a good supercomputer
>>>> and of its fully interactive orbital physics software is all that I'll
>>>> need, plus a spare trillion dollars per year for roughly the next
>>>> century.  Got a problem with any of that?
>>>
>>> Yep - its utter nonsense.
>>>
>> 
>> Of course, he is right in that one can move Luna by
>> waving a very small amount of mass in its near vicinity.
>> The catch is that the Moon will move only a very small
>> amount; it's a conservation of momentum calculation.
>> 
>> Take a 1 kg ball on a stick 1 meter in length, sticking
>> straight up from the lunar regolith.  Remove the ball and
>> place it near the base of the stick.  The moon has moved.
>> How much has it moved?  About 1.3605 * 10^-23 m.
>> 
>> It's going to take a little more than that to move the Moon to L1. ;-)
>
> What if we use a 2kg ball?  :^/

2.7210 * 10^-23 m, of course.  Since 1.321 * 10^-15 is the proton's
Compton wavelength, neither movement is all that detectable.

One can also use a longer stick.

>
> I'm remonded of a similar method propsed for changing the orbit or an
> asteroid or comet on path to the earth. My question has always been,
> how much fuel are you gonna need for station keeping and how are you
> going to supply it.

Also propellant -- and that also has mass, which will move
the Moon as well.  (However, most contemporary rockets
use fuel as both a propellant and an energy source.)

It would be mildly interesting -- if very Habshi-like --
to contemplate a very long, extensible rod or truss, with
a few thousand tonnes of mass at its end, projecting from a
framework surrounding the Earth (this framework would allow
the rod to move in any direction, and would compensate for,
among other things, the Earth's rotation).

This is unlikely to ever be built for a very large number
of reasons, among them structural rigidity of the boom,
and the little problem of getting everyone to cooperate
with the building of ugly big iron girders in their field
of view as they're looking for Venus.  :-)  Nor would it
even work, though it might look interesting artwork-wise.

A far surer method would be to build a big mass-driver on
the Moon itself, turning Luna into an ungainly rocket.
However, the energy required would be huge, and the
mass-driver would have to be movable to ensure the thrust
is done in the right direction and from the right point,
lest a torque be implanted to the Moon itself, the Moon
be driven in the wrong direction, or both.

Or one can direct Oort-cloud objects to impact into
the Moon.  That at least has a good chance of working as
well, given sufficient accuracy of the flight path of
said objects, though considering the impactor on Comet
Temple-Tuttle we might be showered with radiation --
not to mention debris -- from the impact.

>
> Cheers,
>
> Rich
>
>


-- 
#191, ewill3@earthlink.net
Linux makes one use one's mind.
Windows just messes with one's head.

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