How big is a LaGrange Spot?

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brellis

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With all the planning for telescopes and stations destined for L-spots, will it get crowded? <div class="Discussion_UserSignature"> <p><font size="2" color="#ff0000"><em><strong>I'm a recovering optimist - things could be better.</strong></em></font> </p> </div>
 
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agnau

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I would suspect the spot to have the same volume as the planet in whose orbit it resides based on lightly reading related materials... unfortunately, since that was some time ago, I do not have the references for you. <br />After reading Calli's post, I believe that I was referencing the halo orbits.
 
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CalliArcale

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Technically, the Lagrange point is just that -- a point. Spacecraft don't actually occupy the true Lagrange points. Instead, they orbit them in what's referred to as a "halo orbit". If I recall correctly, SOHO takes almost a month to go around the Sun-Earth L1 point.<br /><br />Crowding could eventually become an issue, although in the forseeable future there aren't enough Lagrange spacecraft planned to be a real problem. All spacecraft at L1 and L2 have to have propulsion systems (the points are unstable, so they have to fine tune their orbits on a regular basis). So when they reach the ends of their missions, I would hope that mission planners would move them into a long-term storage orbit. Even if they don't, though, the dead spacecraft will drift away from the Lagrange point over time, which helps a bit with the problem.<br /><br />L4 and L5 are a different matter. These are stable points. In fact, there are natural satellites in other L4 and L5 points, such as the Sun-Jupiter ones. They're called Trojan companions (named for the class of asteroids orbiting in the vicinity of the Sun-Jupiter L4 and L5 positions). Spacecraft should be moved off of them somehow at the ends of their operational lives, although given the nature of L4 and L5, this may require a substantial investment of delta-vee. There are no spacecraft currently planned for these positions anyway, though. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>
 
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agnau

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Could we actually build an asteroid station there (L4 & L5) and setup a sort of colony in the next 40 or 50 years?
 
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toothferry

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even at the L4 and L5 positions wouldn't they eventually drift away from their LaGrange point locations? ..even if took thousands of years. I'm imaginining that finding that perfect point, "forever", would be equivilent to trying to balance a pencil on its tip.
 
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willpittenger

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<blockquote><font class="small">In reply to:</font><hr /><p>If I recall correctly, SOHO takes almost a month to go around the Sun-Earth L1 point. <p><hr /></p></p></blockquote><br />I was under the impression that SOHO views the Sun from the side. That would require an L4 or L5 point. If you looked at the Sun from L1, you could not see any particles (like a Coronal Mass Ejection) headed towards Earth (behind you). This is because your glare shield would be in the way.<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>There are no spacecraft currently planned for these positions anyway, though.<p><hr /></p></p></blockquote><br />Actually, L4 and L5 would make great places to put a planet finder telescope (most concepts involve a constellation of satellites) or a really large (as in moon-sized) colony. I thought up one of the later years ago. It would have been HUGE. The radius would be over 300 miles. At the center would be a large asteroid that had been moved near the Sun to melt it and allow for compaction (I never specified how). You do anything you can to boost the station's mass so it can provide a weak gravitational field -- without rotating. Down would appear normal. You would look "up" and see stars if there was a window. I provided a hole in the surface for ships to come and go. I do not know how I would support them, but they would dock inside the structure above what was left of the asteroid.<br /><br />Before you point out all of the things that would not work with that, please remember this was set even farther into the future than my orbiter concept (roughly 100 years from when the orbiter would be available). <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>
 
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willpittenger

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It was a pain to setup with Google Sketchup, but here is a concept of what my colony (which I labeled "Spaceland") would look like. The round hole is how spacecraft would get in and out. The other hole is my cutaway. The round hole might have windows looking at the ships and almost certainly a traffic control center. Outer layers (color coded as an orangish color compare to the peach I used inside and out) would be devoted to crops and recreations of Earth nature environments. The later would include the Serengeti, Everglades, and the Grand Canyon. Actually there would two Grand Canyons.<br /><br />Each environment would have a wilderness-type version maintained as close to what the real one would be like without man-made influences. The extra Grand Canyon would be the tourist special. It would offer easy access to the entire area. This would let the real Grand Canyon revert to the wild state (no dams or convenient trails). The point is that Spaceland would not have any shortage of space -- at least for a few centuries.<br /><br />Please note that I omitted the core. It was quite a bit of work just getting spheres. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>
 
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CalliArcale

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<blockquote><font class="small">In reply to:</font><hr /><p>I was under the impression that SOHO views the Sun from the side. That would require an L4 or L5 point. If you looked at the Sun from L1, you could not see any particles (like a Coronal Mass Ejection) headed towards Earth (behind you). This is because your glare shield would be in the way. <p><hr /></p></p></blockquote><br /><br />No. SOHO is definitely at L1. I'm just not sure I remember correctly how long it takes to orbit L1. It does not have an opaque glare shield. (And if it did, that would have to be pointed sunward anyway, so it wouldn't matter where SOHO sat. It still wouldn't see anything.)<br /><br />If SOHO was at L4, it actually would not be as useful for detecting CMEs about to hit Earth. Particles from the Sun hit SOHO on average about an hour before they hit Earth. (Time varies with the speed of the particles, obviously.) If it was at L4, it would receive the particles at about the same time as Earth -- assuming it even got hit by the same CME as the Earth. L4 is quite a long ways away. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>
 
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agnau

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Was never considering a "perfect point". would require boosters periodically to recorrect a massive sattellite (might not ever need it in the life of the sat if the virtual well of L4/5 is large enough). Although I wonder if there is even a virtual well at all..
 
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CalliArcale

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Earth's L4 and L5 should be roomy enough for a space station to be stable indefinitely. While the points themselves are infinitesimally small, you should be able to get even a pretty hefty asteroid there. There have been spirited searches for Trojan companions to the Earth; as it happens, there aren't any. But interestingly, Mars (which is smaller than Earth) does have a couple of Trojan companions. This should demonstrate the concept pretty well. <br /><br />EDIT: Such companions would wander quite a bit from the theoretical L4 and L5 points, but they would stay in the general vicinity. There's a lovely diagram at the MAP website. (MAP orbits L2.) Click here. Scroll down to the second image to get an idea of how the gravity gradients work out, and how large an area a Trojan satellite might get to wander. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>
 
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willpittenger

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<blockquote><font class="small">In reply to:</font><hr /><p>It does not have an opaque glare shield. (And if it did, that would have to be pointed sunward anyway, so it wouldn't matter where SOHO sat. It still wouldn't see anything.)<br /><br />If SOHO was at L4, it actually would not be as useful for detecting CMEs about to hit Earth. Particles from the Sun hit SOHO on average about an hour before they hit Earth. (Time varies with the speed of the particles, obviously.) If it was at L4, it would receive the particles at about the same time as Earth -- assuming it even got hit by the same CME as the Earth. L4 is quite a long ways away.<p><hr /></p></p></blockquote><br />I had assumed SOHO was at the L4/L5 points because CMEs would travel much slower than the light from them. The images I see have the Sun itself blotted out by a glare shield in visual wavelengths. However, I did check on SOHO on Wikipedia. They have SOHO at L1 as you stated -- except for being off to the side to allow us to "see" its transmissions. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>
 
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CalliArcale

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The images you're talking about are the coronograph images. SOHO's coronograph instrument has a shield to blot out the Sun, creating an artificial eclipse. It has other instruments that have an unobstructed view of the Sun.<br /><br />CMEs do travel much slower than light. When it's time to get worried about a CME is when you see a big "poof" on the coronograph in all directions (indicating that the expanding cloud is coming straight towards the camera) and then, an hour or so later, what looks like snow all over the image (caused by a sudden increase in protons striking the CCD imager). That means it's gonna hit Earth in another hour or possibly a bit less.<br /><br />SOHO is not off to the side in order to permit its signals to reach Earth. It's signals could reach Earth just fine from the actual L1 point -- there's nothing in the way. But it isn't possible to stay on L1 indefinitely. It's much simpler to orbit L1, which is what SOHO does. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>
 
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willpittenger

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<blockquote><font class="small">In reply to:</font><hr /><p>SOHO is not off to the side in order to permit its signals to reach Earth. It's signals could reach Earth just fine from the actual L1 point -- there's nothing in the way.<p><hr /></p></p></blockquote><br />Then you might want to update the Wikipedia article. I doubted there would be much in the way. The problem would be that really bright object behind (from our point of view) SOHO. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>
 
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vogon13

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The L4 and L5 spots (actually 'orbits' around them) are quite stable. The Jupiter (and other gas giants) Trojan populations are robust. We don't see them carreening off course.<br /><br />The subsatellites of Tethys, Dione, etc. seem to be similarly ensconsed per Saturn.<br /><br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>
 
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