[Lewis Thomson (OP)]

Daniel wrote into The Naked Scientists to find an answer to this question.

"How do they stop the mirror on the Hubble telescope from getting dirty?"

Can you shed some light on some answers to this question? Leave your thoughts in the comments below...

[evan_au]

This was answered on the show:
https://www.thenakedscientists.com/articles/questions/qotw-how-hubbles-telescope-mirror-stays-clean

[evan_au]

Part of the answer was that the enclosed barrel of the telescope keeps off micrometeorite impacts.

This poses a bigger problem for the James Webb Space Telescope, which has a large, open mirror, with no protection.
- At least the JWST is far beyond the Moon, where man-made space debris is very rare.
- And L2 is an unstable equilibrium point, so any dust that ends up there will tend to drift away (unlike L4 & L5, where dust tends to accumulate).