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General >> Discussion >> L1 , L2 orbit in the moon earth system
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Message started by frankuitaalst on 01/31/14 at 14:25:16

Title: L1 , L2 orbit in the moon earth system
Post by frankuitaalst on 01/31/14 at 14:25:16

Quote from another forum ( Baut ) : "in the latest issue of astronomy magazine there is an article about nasa's plan to capture an asteroid and place it in lunar orbit with it's capturer capsule. it says..... 'the asteroid will shuttle between the first and second lagrangian points of the earth-moon system'. the question is.... why shuttle the asteroid between the two lagrangian points instead of placing it in orbit around one of the lagrangian points as they intend to do with the james webb telescope? "

Anybody  has any idea here why a shuttle should orbit from L1 to L2 ?
I never have simulated this , but I'm sure such an orbit requires fuel .
L1 is the point before the moon , L2 is on the far side .

Title: Re: L1 , L2 orbit in the moon earth system
Post by Tony on 01/31/14 at 17:42:11

Such an asteroid would risk hitting the Moon or Earth, or getting ejected out of the Earth/Moon system.

Title: Re: L1 , L2 orbit in the moon earth system
Post by frankuitaalst on 02/01/14 at 02:39:41

That is my guess also ; if the asteroid has "zero velocity " at that L1 or L2 point .
But I do not know if it is possible for an object to orbit the moon and therby visiting the L1 and L2 point .
Any idea if this can be tackled in GravSim ?

Title: Re: L1 , L2 orbit in the moon earth system
Post by Tony on 02/01/14 at 10:56:43

As a first order approximation, L1 and L2 sit at the edge of the Moon's Hill Sphere.  Nothing can orbit the moon from that distance.  It would be stripped by Earth immediately.

Title: Re: L1 , L2 orbit in the moon earth system
Post by frankuitaalst on 02/01/14 at 14:21:55

Thanks for your input Tony . The distance to the moon is too big to have a regular orbit .
In this case I do not know what the people intend to do with such on orbit .
They might spent a lot of fuel to navigate from L1 to L2 and back .
It's a mystery to me what could be the advantage of doing so .

Title: Re: L1 , L2 orbit in the moon earth system
Post by abyssoft on 02/05/14 at 23:50:38

A L1,2, or 3 halo Orbit is quasi-stable on the order of years, but with stationkeeping maneuvers can be keep for decades

L4 and 5 are stable on the order of millions of years  

Title: Re: L1 , L2 orbit in the moon earth system
Post by frankuitaalst on 02/06/14 at 14:16:49

Thanks , indeed you are right I guess.
The following figure shows the L1 and L2 points are outside the stable orbits around the moon ( equipotential circles around the moon)
http://en.wikipedia.org/wiki/File:Lagrange_points2.svg
Applying some thrust may give the disired orbit .

Title: Re: L1 , L2 orbit in the moon earth system
Post by Tony on 02/06/14 at 18:27:28

I don't like any idea with station-keeping.  Run low on engine oil and everyone on Earth dies.

Title: Re: L1 , L2 orbit in the moon earth system
Post by frankuitaalst on 02/12/14 at 10:23:55

I see , you don't want to get the asteroid on your head if the rocket runs out of fuel  :)
I get involved in the Baut forum about this item .

Is there a possibilty to set up a Gsim in which one positions fi. 100 bodies in the L1 point with various velocities relative to the moon in order to find out if some of them reach the L2 point ( and return to the L1 point afterwards ) ?

Title: Re: L1 , L2 orbit in the moon earth system
Post by frankuitaalst on 02/12/14 at 11:34:04

Here's a Gsim simulation of 100 bodies originally positioned at 50.000 km from the moon .
( the L1 is about 60.000 km from the moon )  
As I expected none of the bodies is in a stable orbit around the moon , perhaps due to the fact that Gsim requires in input of Sma (and thus a relative velocity ) with respect to the moon .
Is there a possibility to arrange 100 bodies at 50.000 km from the moon with "zero" velocity ( in order to simulate the conditions of an L1 or L2 point ?

Title: Re: L1 , L2 orbit in the moon earth system
Post by frankuitaalst on 02/12/14 at 13:11:50

Euh , I'm getting a little bit confused  :-[

( maybe it's too late , ....) , but anyway confused about the Hill Sphere.
According to some articles the Hill Sphere of our moon extends to about 60.000 km .
I've put the particles at 50.000 km and see them wandering away very quickly , so ... why

http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1964SvA.....7..618C&db_key=AST&page_ind=4&plate_select=NO&data_type=GIF&type=SCREEN_GIF&classic=YES

Title: Re: L1 , L2 orbit in the moon earth system
Post by EDG on 02/14/14 at 20:42:44


frankuitaalst wrote:
Euh , I'm getting a little bit confused  :-[

( maybe it's too late , ....) , but anyway confused about the Hill Sphere.
According to some articles the Hill Sphere of our moon extends to about 60.000 km .
I've put the particles at 50.000 km and see them wandering away very quickly , so ... why

http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1964SvA.....7..618C&db_key=AST&page_ind=4&plate_select=NO&data_type=GIF&type=SCREEN_GIF&classic=YES


I seem to recall reading something saying that satellite orbits are only actually stable within about 1/3rd of the hill sphere distance. It was in reference to satellite formation - all the major satellites of planets are within that distance, and all the minor/asteroidal ones are beyond that.

Title: Re: L1 , L2 orbit in the moon earth system
Post by frankuitaalst on 02/15/14 at 05:51:07

You're right EDG , I shoukld have relaized this fact ( stable orbits are within 1/2 ..1/3 of the hill sphere ) , but as i wrote above it was getting too late when I posted . Thanks .

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