By Dr David Whitehouse
BBC News Online science editor
Scientists have completed a significant part of what will become the largest mirror ever put into a space telescope.
Someday it will be big and shiny
It will be launched into orbit in the European Space Agency's Herschel Space Observatory in 2007 and will study the cosmos by gathering infrared radiation.
The mirror is made of silicon carbide, an advanced ceramic material, and will be 3.5 metres across. This will make it lighter than if it was made of metal.
Larger space mirrors are planned but they will be made of segments.
Precise parabolic surface
The next step is to machine the mirror to reduce its mass. Its internal stiffeners, used to provide stability during manufacture, will be taken out and the mirror's thickness taken down to 2.5 millimetres.
After that it will be taken to Finland where it will be polished to produce a parabolic surface with a roughness of less than 30 millionths of a mm.
Following that the mirror will be coated with a microscopically-thick layer of highly reflective nickel-chrome.
It will then be shipped to Toulouse, France, where the company EADS Astrium SAS are constructing the spacecraft.
Herschel will be launched on a nominal four-year mission to study the molecular chemistry of the Universe.
It will study the formation of stars and galaxies and their interaction with interstellar clouds of dust and gas.
Herschel will be launched in 2007
Herschel will be positioned at the L2 Lagrange point of gravitational balance between the Earth and the Sun.
Located 1.5 million kilometres further away from the Sun than the Earth, the L2 point will allow the spacecraft to maintain a stable position in space with minimal expenditure of energy.
L2 is also the favoured position for the US space agency's James Webb Space Telescope - Hubble's successor.