Is there any history of damage to space telescopes from meteoroids etc? If there is, would the James Webb be going up with any kit for detecting small bodies in near proximity (inside the L2 point) that might strike it?

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    $\begingroup$ For part 1 of your question, see ntrs.nasa.gov/api/citations/20100025563/downloads/… $\endgroup$ Commented Oct 7, 2021 at 19:38
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    $\begingroup$ Insight on first question: On Space Shuttle mission STS-109, one of our objectives was to conduct a photographic survey of every square inch of the Hubble Space Telescope's exterior surface. This was done from inside the spacecraft using the largest camera lens we had on board. The peeps on the ground wanted a record of all the debris hits the telescope had endured (our EVA guys told us that the surface panels were riddled with tiny pits). That task was extensive, time-consuming, and tedious... $\endgroup$
    – Digger
    Commented Oct 8, 2021 at 16:23

1 Answer 1


From Wikipedia:

The telescope will circle about the L2 point in a halo orbit, which will be inclined with respect to the ecliptic, have a radius of approximately 800,000 km (500,000 mi), and take about half a year to complete.

A sphere with a radius of 800,000 km has a surface of about 2 trillion square km. If we assume a million small bodies of detectable size placed at equal distances on that sphere, each one will occupy an area of 2 million square km. A circle with an an area of 2 million square km has a radius of 400 km.

So the mean distance between two of these one million small bodies will be about 800 km.

The risk of a small body in near proximity that might strike the telescope is very, very small.

“Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.” ― Douglas Adams, The Hitchhiker's Guide to the Galaxy

  • $\begingroup$ The probability of a strike is proportional to density times mean velocity (i.e. flux) times area, which will have units of inverse time (e.g. per second). LEO has a very low density of objects, but that high average relative velocity is enough to make newsworthy collisions and near-misses a regular thing. $\endgroup$
    – uhoh
    Commented Oct 7, 2021 at 23:29
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    $\begingroup$ So, numerically, what are the odds? And where can one legally place a wager? ;) $\endgroup$ Commented Oct 8, 2021 at 6:28
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    $\begingroup$ You can find an assessment on the meteoroid environment at L2 in this report: dept.aoe.vt.edu/~cdhall/courses/aoe4065/OtherPubs/SPECS/… (chapter 7, page 54 onwards) $\endgroup$
    – Dronir
    Commented Oct 8, 2021 at 6:37
  • $\begingroup$ Sorry, I asked before seeing this: link Glad I did ask though. Thanks all. $\endgroup$
    – calamus
    Commented Oct 8, 2021 at 19:50

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