The Herschel space telescope has completed what could be called the "blue phase" of its pre-launch preparations for Arianespace's next Ariane 5 mission, with the spacecraft's mirror inspected for cleanliness using ultraviolet light.

This activity, which is part of verifications to ensure the 3.5-meter-diameter mirror is free of particles after it was cleaned earlier this month, occurred in the S1B facility at Europe's Spaceport, where Herschel is being readied for an April 16 liftoff from French Guiana. As the largest space telescope of its kind ever built, Herschel will investigate how stars and galaxies are formed, as well as provide information on how they continue to evolve. Its large mirror was built by joining 12 pieces into one single element, which was ground, lapped and polished to the correct shape — and then coated with a reflective aluminum layer.

Herschel is part of the European Space Agency's space science program, and it will be launched by the next Ariane 5 with another of the agency's spacecraft — Planck, which will observe the Cosmic Microwave Background to provide new data on how the universe began. The Herschel spacecraft arrived at the Spaceport in early February, and is to be joined by Planck, which is en-route for a landing this evening (February 18) at the country's Rochambeau International Airport near the capital city of Cayenne. Ariane 5's April 16 flight will deploy Herschel and Planck into very elliptical orbits, enabling both spacecraft to follow transfer trajectories for their voyage to the second Lagrange point (L2) of the Sun-Earth system.

(Photo: Herschel’s 3.5-meter-diameter mirror is checked using ultraviolet light in the S1B clean room at Europe’s Spaceport. This spacecraft will be launched along with the Planck payload on Arianespace’s second Ariane 5 mission of 2009. Courtesy of Arianespace)