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Re: Langrangian points

In a message dated 1/12/2007 7:22:19 AM GMT Standard Time,  w7lrd@comcast.net 

Hello  Amsat'ers
Is it possible or practical to have a communications satellite at  the L1 or 
L2 points.
73 Bob W7LRD
Hello Bob.
I finally got around to looking at The Langrangian points referred to in  
your mail. - Thanks for that pointer, it's a really interesting piece of  
physics. Good fun looking it all up.
At a first 'pass' it would appear that maintaining a satellite at the  L1 and 
L2 points would require some station keeping, hence fuel. They would give  
excellent coverage from 56,000km / 200,000km  respectively.  Tracking the one 
held between the sun and earth would  give really simple tracking. Start by 
pointing at the sun and then move around a  little to peak the signals. - Of 
course the disadvantage is that instead of  cold sky you would have all the Sun 
noise.  The L2 point is only visible at  night...so may be a bit 'antisocial' for 
practical use. - I wonder how the  eclipse works out there?
The ones I found most interesting were the L4 and L5 points.  Areas of  space 
where satellites are held in a stable position by gravitational forces  alone 
without needing any fuel.  Big problem there is the distance.   At 60 degrees 
ahead and behind the earths orbital position would make the path  loss huge.  
Also, apparently, those areas tend to gather space dust, rocks  etc. Probably 
a bit of a risk for collision albeit at low relative  velocity.
Very thought provoking
David  G0MRF
>From Wikipedia:
The Lagrangian points also Lagrange point, L-point,  or _libration_ 
(http://en.wikipedia.org/wiki/Libration)  point), are the  five positions in 
_interplanetary  space_ (http://en.wikipedia.org/wiki/Interplanetary_space)  where a 
small object affected only by _gravity_ (http://en.wikipedia.org/wiki/Gravity)  
can theoretically be  stationary relative to two larger objects (such as a 
_satellite_ (http://en.wikipedia.org/wiki/Satellite)  with respect to the  _Earth_ 
(http://en.wikipedia.org/wiki/Earth)  and _Moon_ 
(http://en.wikipedia.org/wiki/Moon) ). The Lagrange  Points mark positions where the combined 
gravitational pull of the two large  masses provides precisely the _centripetal_ 
(http://en.wikipedia.org/wiki/Centripetal)  force required  to rotate with them

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