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The ESA Euclid and Webb telescopes both occupy L2. How close are they, in terms of physical distance? Do they have to coordinate orbits so they don't collide?

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JWST is not at the L2 point exactly, it orbits around that point in a giant ellipse. The distance of JWST from the L2 point varies between 250,000 to 832,000 km. The period of the orbit is about 6 months.

Side view of JWST orbit

Euclid also orbits the L2 point, at a distance of "about 1 million km".

So they're very far away from each other.

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    $\begingroup$ I think of the L2 "point" as a bit like, say, the South magnetic pole - there's probably a small place that instruments could tell you is more South-pole-like than anywhere else at some particular time. But there's a vast region where the notable effects are indistinguishable for practical purposes - plus the point itself moves around. I've heard it called the L2 region - which I think is informally defined as "the volume of space where L2 effects dominate" and is about 1m km across - is there anything more formal than that? $\endgroup$ Commented Mar 24 at 11:56
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    $\begingroup$ @SusanW I have some relevant graphs & diagrams at space.stackexchange.com/a/58354/38535 & space.stackexchange.com/a/57679/38535 $\endgroup$ Commented Mar 24 at 12:08
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    $\begingroup$ @PM2Ring Thank you, nice. So, when I suggest that the L2 region is "vast", it's actually a pokey little cupboard compared to L3/4/5 :-) $\endgroup$ Commented Mar 24 at 12:18
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    $\begingroup$ L2 is a point, and it's unstable. Left to their own devices, spacecraft tend to drift away from L2. JWST and Euclid orbit L2 by regularly firing their thrusters to create that circle or ellipse around L2. $\endgroup$ Commented Mar 24 at 12:47
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    $\begingroup$ Yes. Those course corrections are small. A tiny thruster firing every few weeks is enough, thanks to the huge radius of those orbits. $\endgroup$ Commented Mar 24 at 16:23
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Euclid and Webb weave around the Sun-EMB L2 point in nice Lissajous trajectories. In 2D, it looks something like this: Eucid & Webb, 2D plot

That's for 2024-Jan-1 to 2025-Jan-1, with a 7 day timestep, so we can see that both of these spacecraft have a period of a little under 12 months. Euclid is the purple track, Webb is the blueish track. The colours of the dots indicate the time. The dot hues cycle around the rainbow, and equal dot colour means equal time. The orange dot in the middle is L2, the grey plane is parallel to the ecliptic, and the grey line is parallel to the X axis, which is the equinox direction. The plot was created (of course) using data from JPL Horizons.

It's much easier to see what's going on in the interactive 3D view. Click the "out.html" link to open the diagram in a new tab or window. (You can also save the HTML to your local drive, but you need to be online to view it with three.js). Here are the 3D interface controls.

  • Orbit - right mouse, or left mouse + ctrl/meta/shiftKey
    • touch: one-finger rotate
  • Zoom - middle mouse, or mousewheel
    • touch: two-finger spread or squish
  • Pan - left mouse, or arrow keys
    • touch: two-finger move

There's more info about the 3D plotting script here.

In my old JWST answer there's a 3D plotter that can show either of these trajectories in a corotating frame (as used in the "halo" plot of Hobbes's answer). But it can only show one spacecraft at a time.

There's no danger of a collision. Here's a distance plot covering the same time span, but with a two day timestep.

JWST-Euclid distance plot

The vertical axis is in millions of km, so the closest they get to each other is around 200,000 km.

Here are their distances from L2. We see that their mean distances from L2 are very similar. JWST & Euclid distances from L2

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    $\begingroup$ @uhoh As I said, you can use the scripts linked in my old JWST answer to see either spacecraft in a corotating frame. $\endgroup$ Commented Mar 24 at 6:04
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    $\begingroup$ @uhoh It's interesting to include Gaia as well. Its Lissajous track is very similar to JWST's, only smaller. $\endgroup$ Commented Mar 24 at 6:55
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    $\begingroup$ @uhoh - Now wondering when they were actually closest - It looks like at launch of Webb from French Guiana Euclid was assembled and in an Airbus France facility, so that may be the closest approach point, as Webb appears to have done a direct injection towards L2. $\endgroup$ Commented Mar 24 at 8:55
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    $\begingroup$ @PM2Ring if reading your very nice plot correctly, closest they have been post launch is more than 0.1 million km so probably means closest approach was while both Webb and Euclid were in their respective assembly facilities, which looks to be a couple of thousand km France<>Texas. $\endgroup$ Commented Mar 24 at 12:37
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    $\begingroup$ "Euclid is the purple track, Webb is the blueish track." I don't know about spatially, but the chromatic distance is tiny. $\endgroup$ Commented Mar 25 at 1:48

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