Assertion: beryllium mirror | /r/ObjectUse | used without first surface coating
Facets:
value: in cases
type: TEMPORAL
value: in order to obviate buckling
type: PURPOSE
Source sentences:
text: In cases where the mirror is subjected to extreme cold (as low as 33 K as in the James Webb Space Telescope), a polished pure beryllium mirror is used without a first surface coating in order to obviate buckling caused by differing coefficients of thermal expansion.