The CARLINA project is the first experimental trial aiming to demonstrate the feasibility of hypertelescopes, such as that proposed by A. Labeyrie. It is being carried out by the Observatoire de Haute Provence.

Several spherical mirrors, 250 mm in diameter and with a radius of curvature of 70 m are located on a sphere. The bundles of rays are combined at the focus

Fig. 8.18 Schematic diagram of the CARLINA instrument. The gondola beneath the captive balloon carries the recombiner. The position of the whole assembly is controlled by cables

of the sphere where suitable instrumentation is held in place by a captive balloon (Fig. 8.18).

This arrangement means that the overall focal length is 35 m.

The first trials took place in May 2004, and were able to obtain fringes of Vega, using 2 mirrors, stopped down to 50-mm pupils, spaced 400 mm apart at the ground. The balloon was held in position at an altitude of 120 m.

The next stage, in February 2006, consisted of installing the spherical aberration corrector (the Mertz corrector) in the suspended gondola. The first images of Tania Australis were obtained with three mirrors on the ground on a sphere 10.5 m in diameter, together with the corrector, in a non-interferometer mode (superimposing the images at the focal plane, but without attempting to adjust the segments to correct for phase differences).

The next stage will consist of using an optical-adjustment method to superimpose the images, and equally, to ensure the segments are in phase (precise control of the position of the mirrors to ensure that they are precisely on the sphere of the virtual mirror that they are synthesizing). This stage is currently under way.

Carlina is a very long-term experiment, which anticipates the very large arrays of space telescopes, such as that proposed in the Exo Earth Imager concept (Labeyrie et al., 2003). Space Observatories

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