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:
- NASA’s Wilkinson Microwave Anisotropy Probe,
- NASA’s WIND spacecraft, measuring solar wind,
- European Space Agency’s (ESA’s) Herschel Space Observatory, an infrared telescope,
- ESA’s Planck spacecraft, mapping anisotropies of the cosmic microwave background, and
- China National Space Administration’s (CNSA’s) Chang’e 2 spacecraft.
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.