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Optical bench of ESPRESSO has arrived

After the arrival of the vacuum vessel that was installed last October 2014 in a temporary clean room, it is now the turn of the optical bench of ESPRESSO to be delivered to the University of Geneva Biotech Campus basement. An optical bench arrived by ship and truck from the Canary Islands in a box weighing about 5 tons. “It is on this bench that all optical elements of ESPRESSO wil be installed” explains Francesco Pepe, a member of Planets and PI instrument.

ESPRESSO is the new high-resolution spectrograph built under the direction of the astronomy department of the University of Geneva. It can measure the radial velocities with an accuracy of 10cm/s, “this is the necessary precision to calculate the mass of extrasolar planets similar to the Earth,” says Francesco Pepe with a hint of pride in his voice. The optical bench is the fundamental mechanical part of ESPRESSO, it weighs about 4 tons and its rigidity must be foolproof, any dilatation or deformation may cause measurement errors. The steel-made piece was built in Spain and sent to Germany for a nickel bath supposed to protect it from rust. It was then shipped back to the Canaries for final verification before being transported by boat in Geneva.

It took a day to get the bench out of its wooden straitjacket and install it in the truck specially built by the Geneva Observatory. A second day was then necessary to introduce the piece within the tank and position it on its special trolley. These operations are essential for the integration to take place in the future Geneva Observatory cleanroom, before the last complete disassembly for travel in Chile scheduled for late 2017.

ESPRESSO and CHEOPS will be the two spearheads of the Swiss Planetology, two instruments developed by the Universities of Geneva and Bern in order to characterize planets earth. “CHEOPS gives us the size of the planet,” says Willy Benz, leader of PlanetS, while “ESPRESSO givse us its mass,” ensures Francesco Pepe, project leader of PlanetS project 3. Two quantities required for determining the composition of the planets. (pb)