Now that caught my attention. OK, guys, don't start rubbing the surface of your mirrors with big lumps of dry ice!
"From 15 to 17 February the delicate process of the final cleaning of the 3.5-metre diameter primary telescope mirror and the smaller secondary mirror was performed to reach the good cleanliness level required for the telescope at launch. This was carried out using carbon dioxide snow (more commonly known as dry ice) which is produced by highly compressed liquid CO2 being expelled under high pressure. The snow particles, which are sprayed onto the mirror surface at an angle, vapourize and in the process carry off any contaminants which may have rested on the mirror surface. This technique is widely used also for ground-based astronomical telescopes and has the major advantage of not requiring any physical contact with the optical surface."
Neat and Cool! (really cool, actually!) Thanks, David
Here is the full story:-
http://sci.esa.int/science-e/www/obj...objectid=44312