Luciola hypertelescope space observatory: versatile, upgradable high-resolution imaging, from stars to deep-field cosmology

Abstract

Luciola is a large (1 km) "multi-aperture densified-pupil imaging interferometer", or "hypertelescope" employing many small apertures, rather than a few large ones, for obtaining direct snapshot images with a high information content. A diluted collector mirror, deployed in space as a flotilla of small mirrors, focuses a sky image which is exploited by several beam- combiner spaceships. Each contains a "pupil densifier" micro-lens array to avoid the diffractive spread and image attenuation caused by the small subapertures. The elucidation of hypertelescope imaging properties during the last decade has shown that many small apertures tend to be far more efficient, regarding the science yield, than a few large ones providing a comparable collecting area. For similar underlying physical reasons, radio-astronomy has also evolved in the direction of many-antenna systems such as the proposed Low Frequency Array having "hundreds of thousands of individual receivers". With its high limiting magnitude, reaching the m v = 30 limit of HST when 100 collectors of 25 cm will match its collecting area, high-resolution direct imaging in multiple channels, broad spectral coverage from the 1,200 Å ultra-violet to the 20 μm infra-red, apodization, coronagraphic and spectroscopic capabilities, the proposed hypertelescope observatory addresses very broad and innovative science covering different areas of ESA's Cosmic Vision program. In the initial phase, a focal spacecraft covering the UV to near IR spectral range of EMCCD photon-counting cameras (currently 200 to 1,000 nm), will image details on the surface of many stars, as well as their environment, including multiple stars and clusters. Spectra will be obtained for each resel. It will also image neutron star, black-hole and micro-quasar candidates, as well as active galactic nuclei, quasars, gravitational lenses, and other Cosmic Vision targets observable with the initial modest crowding limit. With subsequent upgrade missions, the spectral coverage can be extended from 120 nm to 20 μm, using four detectors carried by two to four focal spacecraft. The number of collector mirrors in the flotilla can also be increased from 12 to 100 and possibly 1,000. The imaging and spectroscopy of habitable exoplanets in the mid infra-red then becomes feasible once the collecting area reaches 6 m 2 , using a specialized mid infra-red focal spacecraft. Calculations (Boccaletti et al., Icarus 145:628-636, 2000) have shown that hypertelescope coronagraphy has unequalled sensitivity for detecting, at mid infra-red wavelengths, faint exoplanets within the exo-zodiacal glare. Later upgrades will enable the more difficult imaging and spectroscopy of these faint objects at visible wavelengths, using refined techniques of adaptive coronagraphy . Together, the infra-red and visible spectral data carry rich information on the possible presence of life. The close environment of the central blackhole in the Milky Way will be imageable with unprecedented detail in the near infra-red. Cosmological ...

The Earth as an extrasolar planet: the vegetation spectral signature today and during the last Quaternary climatic extrema

“…More ambitious instruments that might fly later this century will allow us to make a step furthermore in the characterization of these planets and the observation of 'exovegetation'. Hypertelescopes in space -interferometric sparse arrays of small telescopeswill indeed allow us to see Earth-like planets as small resolved disks several resels across [Labeyrie 1999, Labeyrie et al 2008] and this clearly will help us to detect photosynthetic life on these planets! For example, a 150-km hypertelescope would provide 40 resolution elements (resels) across an Earth at 3 pc in yellow light [Labeyrie 1999].…”

Intensity interferometry: optical imaging with kilometer baselines

“…However, the stability requirements on amplitude (phase-) interferometers, together with the atmosphere above, to within a small fraction of an optical wavelength, constrain their operation for long baselines, especially at shorter visual wavelengths. The great scientific potential of stellar surface imaging has been realized by several, and concepts for longbaseline interferometers have been worked out for construction at ground-based observatories [10][11] , in Antarctica 12 , as free-flying telescopes in space [13][14] , or even placed on the Moon [15][16] . Further concepts include the use of giant diffraction screens in space 17 .…”

Multi-Pixel Imaging of Exoplanets with a Hypertelescope in Space

“…With a dilute optical interferometric array, instead, these scale respectively as D m , the baseline or meta-aperture size, and N d 2 if it contains N mirrors, the size d of which can be small compared to their average spacing s D D m N 1/2 . A much higher resolution is then obtainable, without affecting the light collecting area, by spreading apart the small mirrors for a metaaperture much larger than D. As discussed in Labeyrie et al (2009), the DIF size and the image's dynamic range of a hypertelescope both improve, as well as the science yield if it has many small mirrors, rather than fewer large ones, at given collecting area. Their size should, however, exceed a few centimeters to avoid a broad diffraction which would require large collecting optics in the focal spaceship.…”