Ground-based Hypertelescope Has First Operational Components

Ground-based hypertelecope project has first images from a suspended camera and light from mirrors.

They acquired the star Vega in the camera of the nacelle, for about twenty minutes, from one of the two mirrors on the ground. The image shows Vega in the center of the field of 1mn of arc, and part of its light forming the image of the North mirror in the upper left, used to check the orientation of the nacelle. They motorized the micrometric screws supporting the mirror (made by the Loma laboratory) and the training work on their flathead mounting in Calern last winter and spring that made this success possible.

A first prototype of a ground-based Hypertelescope type “Carlina” is currently under study in France in the Ubaye Valley in the Alps of Haute Provence. When it is completed, it will be 200 meters in diameter. With 800 mirrors 15 centimeter, it will accumulate two times more of collecting area than the Hubble Space Telescope and have visual acuity almost one hundred times greater. It will be five times as powerful in resolution that the future european E-ELT which will have a 39-meter in diameter whose construction is scheduled for 2024 by ESO to the Chile.

It is planned to install and operate several optical nacelles on the same hypertelescope. This will make it possible to make simultaneous observations of different stars in strictly identical technical conditions. Each new nacelle installed will therefore add a new telescope to the telescope already in service, and at an incredibly low cost – that of an optical nacelle. Such a hypertelescope will therefore also be a multi-telescope.

The hypertelescope lends itself to a scalable modular installation. From the first group of installed mirrors, it will be able to produce scientific results. Well before the complete completion of the installation.

The current prototype model will consist of a set of floor mirrors totaling already a diameter of 57 meters. The concept being scalable, it will in principle make it possible to enlarge the diameter of the diluted mirror to 200 meters, which would give it a resolution of 0.5 milliseconds of arc, which is 80 times better than the Hubble Space Telescope when the effect of atmospheric turbulence will be corrected by an adaptive optics system.

In a second phase, it is envisaged to proceed to an installation whose overall diameter would reach one kilometer and whose number of mirrors could be gradually increased to contain a thousand. It would allow a considerable gain in sensitivity and limiting magnitude as well as a greatly improved resolution.

Above the valley, located 100 meters high on a cable, a nacelle with a novel optical device developed at the College de France collects the light from the stars reflected by the mirrors on the ground. This gondola is positioned very precisely with the help of six “dynamic” stays, maneuvered by winches in the manner of a giant yarn puppet. The cables are controlled from three locations located about 300 m from each other and connected by a local WiFi network powered by solar energy. Their winding / unwinding, controlled by a computer, makes it possible to compensate for the rotational movement of the Earth and thus to point the pod in the direction of the star throughout the observation period. The collected light is received by a camera that can be installed on the nacelle, or on the ground,

The image produced by a hypertelescope, if it is equipped with an adaptive corrector compensating the atmospheric turbulence, is an instantaneous direct image and not an image reconstructed after computations from successive images. With conventional interferometers equipped with a small number of mirrors, it is necessary to reconstitute an image to make multiple observations spread over time, in order to benefit from the geometric variation that the rotation of the Earth engenders. Because of the greater number of mirrors available to a hypertelescope, thus improving the sampling of the light wave and the formation of a more intense peak of interference, the observations made are immediately exploitable.

The scientific team has estimated that they could build a ground-based Hypertelescope with a diameter of the order of 1 kilometer and install it in the depression of a former impact crater, in the crater of a dormant volcano or some high valleys of the Andes or of the Himalayas.

The feasibility of a space hypertelescope consisting of a flotilla of mirrors placed on a virtual surface of 100 km in diameter has already been explored. The numerical simulations carried out demonstrated that it would be possible to obtain direct images of an exo-Earth gravitating around a celestial body ten light-years from Earth. The level of detail would be such that we would see the seas and the continents, the vegetation areas.

A future space-based Hypertelescope diameter may be extended at least eight to ten times more than the diameter of the Earth. It would have a 100,000-kilometer diameter. It will produce with sharpness some images of the surface of an extrasolar planet at approximately 10 light-years away.

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