Largest space mirror

The primary mirror built for ESA's Herschel Space Observatory measures 3.5 m (11 ft 6 in) across. It was constructed from a single piece of silicon carbide ceramic, making it much lighter than glass. The mirror will allow Herschel to study objects in the Solar System as well as deep space in the infrared spectrum. Scheduled for launch on 14 May 2009, Herschel is expected to last for three years with its instruments cooled by liquid helium down to just 2 K (-271.15°C; -456.07°F).