L2 is crowded

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I imagine that most readers have been closely following the launch of the Webb telescope and the successful deployment of its solar panels.  As we all know, it is headed toward a particular place in space called the Earth-Sun Second Lagrange Point, shorthanded as L2.  I was intrigued to learn that L2 is actually a crowded place. 

You can see a list on Wikipedia of objects located at the L2 place where the Webb telescope is headed.  Quite a few spacecraft have been located at L2 in the past and are not there any more:

Two spacecraft are located at L2 now:

  • ESA’s Gaia probe, and
  • A Russian-German spacecraft called Spektr-RG, a high-energy astrophysics observatory.

There are plans for eight more space probes to be located at L2 in the future!

It turns out that nobody actually places a spacecraft exactly at L2.  If you were to do that, it would be constantly in Earth’s shadow and there would be insufficient light for solar panels.  So what everybody always does is place their spacecraft in a small orbit around L2.  

I have not seen any discussion in the popular press about how and why nobody is worried about the Webb telescope smashing into the Gaia probe or the Spektr-RG spacecraft, or indeed why the latter have not smashed into each other already.  I’d guess the answer is that they are in orbits around L2 that are of non-identical radius.

5 Replies to “L2 is crowded”

    1. I believe it’s a stable location that allows shielding the IR instruments from heat from the sun, Earth, and Moon, all back in the same direction.

  1. OK, dumb question: how do you place an object in a “small orbit around L2”? L2 itself is not an object with mass, it is merely a position in which there is a stable orbit around the sun that is stable relative to the Earth’s position. I’m not disagreeing, I just don’t understand orbital mechanics. Based on my limited understanding of physics, though, an orbit usually requires a large enough object in the center of the orbit to keep the smaller object from breaking away. So, for example, the moon orbits the earth and the sun, as do other man-made satellites in earth orbit.

    1. Yes, it’s a fascinating question and a fascinating concept. You can actually model any Lagrange point as a mass of modest size. And then if the object of interest is small enough, you can define an orbit around the (modeled) modest-sized mass that is imagined to be at the Lagrange point. It turns out that if the Lagrange point being modeled is L1, L2, or L3, the orbit will require at least a small amount of station maintenance. If the Lagrange point being modeled is L4 or L5, the orbit will not need station maintenance.

      1. Thanks! Fascinating that a point in space with no mass can actually act on other objects as though it does have mass (presumably because it’s actually the objects that create the Lagrange point exerting the gravitational pull). I am definitely going to have to do some further reading on the subject.

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