In a message dated 1/12/2007 7:22:19 AM GMT Standard Time, w7lrd@comcast.net writes:
Hello Amsat'ers Is it possible or practical to have a communications satellite at the L1 or L2 points. 73 Bob W7LRD Seattle
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
73
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
Hi David,
Wikipedia also has a nice description of the SOHO satellite which sits near but not exactly at LI ( for the reasons you mention) watching the Sun
http://en.wikipedia.org/wiki/Solar_and_Heliospheric_Observatory
73
Graham G3VZV
At 09:09 AM 1/14/2007, G0MRF@aol.com wrote:
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?
Umm, there seems to be a lot of confusion here. Firstly, there are 2 sets of Lagrange points - those of the Earth - Moon system and those of the Earth - Sun system. You seem to be mixing the two.
First, the Earth - Sun system. L1 is around 1 million miles away, 4x the distance of the Moon, so in addition to Sun noise, you have the extra 12dB path loss to the satellite.
L2 is on the night side, as you stated. You still have the million mile distance to contend with.
L3 is on the far side of the Sun - 'nuff said ;)
L4 and L5 are at the +/- 60 degree points along Earth's orbit, with extreme practical considerations due to distance from Earth.
Now on to the Earth - Moon system.
L1 is between Earth and the Moon, but much closer to the moon end (due to the lesser gravity of the Moon). There would be some advantages of putting a satellite there (slightly less distance, full time availability of solar power, except during brief eclipses, no wild temperature swings), but these would be offset by the requirement of fuel for station keeping (L1 is unstable).
L2 is on the far side of the Moon - again, not going to work too well. L1 and L2 would be good points for satellites to service the Moon though. :)
L3 is on the far side of the Earth from the Moon. Comms considerations as per a lunar outpost apply, and station keeping as per L1 applies.
L4 and L5, being stable would be potential places to park a satellite, though some fuel would still be required for attitude control. Distance would be same as for a station on the Moon.
73 de VK3JED http://vkradio.com
participants (3)
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G0MRF＠aol.com -
Graham Shirville -
Tony Langdon