Astrophysics: Cerro Paranal Astronomical Observatory

Located in Chile's arid Atacama Desert, at 2,635 meters above sea level, the Cerro Paranal Astronomical Observatory – a project of the European Southern Observatory (ESO) – is home to the famous Very Large Telescope (VLT), the world's most advanced optical instrument.

Hexapods for auxiliary telescopes

2004–present | Several of CSEM's devices have been installed at this exceptional site. The VLT consists of four main telescopes, each with a primary mirror of more than eight meters in diameter, as well as four removable rail-mounted auxiliary telescopes, each with a primary mirror over two meters in diameter. Taken together, these sophisticated instruments create a massive interferometer, the hypothetical equivalent of a telescope 200 meters across!

Auxiliary telescopes redirect light to enhance the main telescope's resolution, which means that mirror stability is critical. This is particularly true since the telescopes continue to rotate slowly while measurements are being carried out, and the weight of certain elements causes the structure to flex, resulting in inaccuracies. CSEM's engineers have developed precision mechanisms that are mechatronic masterpieces: extremely stiff hexapods that guide and control each telescope's secondary mirror with a precision and stability of around one micrometer. These devices compensate for the inaccuracies generated during the rotation of the telescopes. CSEM delivered five, six degrees of freedom hexapods, three of which have now been installed on the secondary mirrors of the VLT's auxiliary telescopes.

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Compensating for atmospheric disturbances with NAOS

2001–present | When viewed from Earth, stars appear to twinkle, yet the light they generate is constant. This misleading effect is due to turbulence in the Earth's atmosphere (variations in temperature, pressure, etc.), which disrupts incoming light from stars.

Yepun, one of the four main VLT telescopes at Cerro Paranal, uses optical techniques to actively compensate for these disturbances, via the NAOS (Nasmyth Adaptive Optics System) facility. When the light reaches the telescope, perturbations caused by atmospheric turbulence are analyzed, a correction signal is generated and then subsequently sent to a deformable mirror. This mirror is fitted with several hundred actuators, which adapt the wavefront in real time, allowing the light emitted by a star to be reconstructed as it was before it entered the atmosphere. This feature enables the eight-meter Yepun telescope to observe objects with a resolution close to the theoretical limit.

It was CSEM that developed the key mechanisms known as field selectors, which are used to precisely select the light of the brightest star. Image capture takes up to 20 minutes while the telescope is in motion. To ensure that the mirrors can follow the light undisturbed, CSEM developed two tip/tilt mechanisms, which have three degrees of freedom and stability close to one nanometer, and are capable of repositioning themselves very quickly.

These field selector units have been in operation since 2002. CSEM provides ongoing support, maintenance and training for the ESO’s Paranal teams.

(ESO project carried out in partnership with LAOG Grenoble and the Meudon Observatory in Paris)

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Actuators for a large-scale hexapod

2009–present | In addition to the VLT’s eight telescopes, the Cerro Paranal Astronomical Observatory is also home to the 4-meter Vista telescope and the 2.5-meter VLT Survey Telescope.

CSEM was involved in the design of actuators for the massive hexapod fitted to Vista's 4.5-meter diameter mirror. Other partners in the project included NTE (Spain) and ADS (Italy). The actuators were delivered in 2005 and went into service in 2009.