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.

19 thoughts on “Ground-based Hypertelescope Has First Operational Components”

  1. “The reference light is coupled in through a grating coupler and split into 64 paths. Each path goes through a PIN diode phase shifter and feeds a directional coupler. A receive beam is formed by adjusting the phase shifts of each path so that the amplitude of the signal arriving from a certain direction add constructively”
    Very interesting! Seems like iterferometry measures the phase difference over a separation, this tweaks the phase(s) to get constructive *direction* to look at. My guess!
    At some point, being able to extend the optical bench to very large separations will be harder than sending the photon info some other method like this camera uses, which would be more robust and perhaps storable.
    “It would allow skipping the suspended optical nacelle”
    I think the nacelle has to see at least two of the mirrors to work, tho the test only saw one. It moves around to capture the reflection of the target object. If some of the cameras here directionally focused then reflected to a bench or stationary nacelle, seems it would work(?)

  2. Well, that is optical interferometry, first shown in Coast, England in the 80’s, I believe. You get the same precision in the direction, but nowhere near the signal strength as the *equivalent* dia full detector would get.
    But that is done real time on an optical bench, as is the Hypertelescope.
    (I think!) To just collect the incoming light with dispersed CCDs would require also saving the phase of the photons, pretty sure we are not there yet. Then, the sigs would be processed later. That IS what we do with radio scopes, as we can save the phase at those much lower frequencies.

  3. We can sort of do that now for light, but I don’t think it works when you’re trying to accumulate lots of light, the source needs to be bright.

  4. It won’t be rigidly mounted to the wires, but instead actively stabilized. Which would be needed for a mast, too, so no extra expense there.

  5. I believe the reason for the wires instead of mast is that they need to be able to move the nacelle in order to image different parts of the sky.

  6. Part of this telescope is just brilliant: mass produce smaller (cheaper) mirrors and combine the image as if it were an enormous mirror (albeit with only part of the light collecting ability of a mirror that covers the entire valley floor) and parts are not so great.

    Why, for instance, have the detector suspended on wires? Why not just build a cheap mast? Surely, having the detector suspended on wire must mean that it is moving a lot more than if it were on a rigid support? Gusts of wind must be able to deflect it micrometers – and that is surely the required positional stability – and hence ruin the image.

    Also, how do you reach the necessary pointing accuracy for the separate mirrors? If the image from one mirror hits the detector, but is displaced 1 um – of the order of size of the pixels – then it will blur the image from the other mirrors. So, we need to point with arctan(1 um / 1000 m) ~6.3*10^-9 degrees. Is that possible? What if a gust of wind moves one of the tripod mirrors just 1 um, then the image from this mirror would be “off” in position, right?

  7. Only a fraction of the valey floor is covered with mirrors. 800 mirrors of 15 cm diameter equals a single mirror of sqrt(800)*15cm diameter, or 424 cm in diameter.

  8. I doubt it will work because there is too much you have to compensate for.

    You could layout a field of CCD sensors. Gather their data then correlated the data for time and space.

  9. There was a presentation at Space Access Conference
    of sparse source beam forming technology.
    That seemed to be based on microwaves, but the theoretical
    results were similar;
    extremely large apertures that allow reconvergence of
    beamed power at large distances, maybe dozens or 100s
    of kms.

  10. Am I missing something here. This telescope has twice the collecting power
    of the Hubble? But the Hubble has only a 2.4m mirror.

  11. Makes much better sense to spend money on hypertelescopes to image exoplanets now than attempt interstellar probes that will take decades to develop or more decades to travel to just the nearest star at one or two magnitudes more cost.

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