Editing Beryllium (section)

===Mirrors===
Large-area beryllium [[mirror]]s, frequently with a [[honeycomb mirror|honeycomb support structure]], are used, for example, in [[meteorological satellite]]s where low weight and long-term dimensional stability are critical. Smaller beryllium mirrors are used in [[optical guidance]] systems and in [[fire-control system]]s, e.g. in the German-made [[Leopard 1]] and [[Leopard 2]] [[main battle tank]]s. In these systems, very rapid movement of the mirror is required, which again dictates low mass and high rigidity. Usually the beryllium mirror is coated with hard [[electroless nickel plating]] which can be more easily polished to a finer optical finish than beryllium. In some applications, the beryllium blank is polished without any coating. This is particularly applicable to [[cryogenic]] operation where thermal expansion mismatch can cause the coating to buckle.<ref name="Behrens-2003" />

The [[James Webb Space Telescope]] has 18 hexagonal beryllium sections for its mirrors, each plated with a thin layer of gold.<ref>{{Cite web|url=https://www.quantamagazine.org/why-nasas-james-webb-space-telescope-matters-so-much-20211203|title=The Webb Space Telescope Will Rewrite Cosmic History. If It Works.|date=3 December 2021|access-date=5 December 2021|publisher=Quanta Magazine|archive-date=5 December 2021|archive-url=https://web.archive.org/web/20211205004057/https://www.quantamagazine.org/why-nasas-james-webb-space-telescope-matters-so-much-20211203/|url-status=live}}</ref> Because JWST will face a temperature of 33 K, the mirror is made of gold-plated beryllium, which is capable of handling extreme cold better than glass. Beryllium contracts and deforms less than glass and remains more uniform in such temperatures.<ref>{{Cite journal|title=The James Webb Space Telescope|first=Jonathan P.|last=Gardner|date=2007|journal=Proceedings of Science|volume=52 |url=http://pos.sissa.it/archive/conferences/052/005/MRU_005.pdf|bibcode=2007mru..confE...5G|page=5|doi=10.22323/1.052.0005 |s2cid=261976160 |access-date=15 January 2009|archive-date=4 June 2016|archive-url=https://web.archive.org/web/20160604034944/http://pos.sissa.it/archive/conferences/052/005/MRU_005.pdf|url-status=live |doi-access=free }}</ref> For the same reason, the optics of the [[Spitzer Space Telescope]] are entirely built of beryllium metal.<ref>{{Cite journal|title=The Spitzer Space Telescope Mission|arxiv=astro-ph/0406223|journal=Astrophysical Journal Supplement|date=2004|doi=10.1086/422992|volume=154|issue=1|pages=1–9|last1=Werner|first1=M. W.|last2=Roellig|first2=T. L.|last3=Low|first3=F. J.|last4=Rieke|first4=G. H.|last5=Rieke|first5=M.|last6=Hoffmann|first6=W. F.|last7=Young|first7=E.|last8=Houck|first8=J. R.|last9=Brandl|first9=B.|bibcode=2004ApJS..154....1W|s2cid=119379934|display-authors=8}}</ref>