Construction of the European Space Agency's Herschel Space Observatory is well underway, and engineers recently completed a significant part of what will become the largest mirror on a space telescope. The 3.5 metre primary mirror was built from silicon carbide, which reduces its mass by a factor of 5 from using traditional materials. The mirror will next be machined to reduce its mass even more and then coated with a reflective surface. Herschel is due to launch in February 2007, and will cover the far infrared and sub-millimetre waveband.