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.

This will be Arianespace's first mission with payloads destined for the L2 point, where both spacecraft will be placed into Lissajous orbits. Thales Alenia Space is the prime contractor to the European Space Agency for Herschel and Planck.

Arianespace is targeting six to eight missions in 2009, with the upcoming Herschel/Planck dual-payload launch being this year's second flight.

The initial mission was performed on February 12, placing the HOT BIRD 10 and NSS-9 telecommunications satellites into highly accurate geostationary transfer orbits. They were accompanied by a pair of Spirale piggyback passengers, which are demonstrators for a defense early warning system.