Design Article
Curved monolithic focal plane array for wide-survey telescopes
Manuel Fendler, CEA-Leti, MINATEC
3/5/2012 8:19 AM EST
Co-authors: Delphine Dumas, CEA-Leti, MINATEC Campus (Grenoble, France), Jérôme Primot and Guillaume Druart, ONERA, DOTA/CIO (Palaiseau, France), Etienne Le Coerer, IPAG, UJF (Grenoble, France)
Systems requirements
The sky survey consists in detecting orphaned objects orbiting Earth or entering its atmosphere. They could be natural objects, like meteorites, or from human space activity, like satellites and debris from satellites or launch vehicles. Space surveillance is dedicated to various applications, ranging from scientific research to security, and involves national and international projects. Survey telescopes require wide field of view (WFOV) because this is the primary way to observe large areas of the sky simultaneously. For instance, the Large Synoptic Survey Telescope (LSST) covers the sky twice each week (1).
Space observation has several goals, but mainly it contributes to the inventory of near-Earth objects in order to improve the known population distribution or to scan the sky rapidly for fast-moving satellites. This kind of projects would be able to detect weak light appearance in the large observed space; this requires a WFOV telescope, as well as a higher resolution, to determine the light’s origin (meteorites, debris, supernovae, exoplanets, gamma-ray bursts etc.). Moreover, increasing the instrument’s sensibility would allow scientists to realize a 3D map of the universe with numerous details; these maps open new possibilities for detecting and localizing dark matter and perhaps characterizing dark energy.
Unknown space objects are a risk for future launches. Space and security surveillance by military and government agencies is designed to track space objects, especially satellites or asteroids, and to build a full catalogue with their characterizations and exact orbit locations. This register also would help warn of potential collisions between asteroids and the Earth, or terrorist attacks. But to catalogue exactly where space objects are, the register must be updated constantly, and this represents an important task, especially with the increasing amount of space debris, the growing number of satellites and the miniaturization of launched microsatellites. To meet these challenges, this survey would require a WFOV instrument with good resolution in order to cover a large part of the sky.
Architecture considerations
Telescopes with large field of view and high resolution require a large aperture diameter and a very fast camera. However, these cameras present a challenge of correcting aberrations of curvature. Correction of aberrations has been investigated through two solutions. The traditional approach adds optical correction elements. However, telescopes working around the aberrations’ limitation need very complex compensators and these solutions are difficult and expensive, and are limited for the large telescope size. Moreover, this solution complicates the design and increases the system size. So the traditional way to correct these aberrations seems to be insufficient, leading to systems limited by the poor sensitivity and field of view achieved.
Interestingly, nature has solved this problem. Indeed, most animals’ eyes have large field of view and high resolution vision systems; small insects have a small volume dedicated to the vision system but they do have good resolution and large field of view. In all eye architecture, the focal plane is curved (Figure 1), which enlarges the field of view and decreases some aberrations, especially aberration of curvature.
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Systems requirements
The sky survey consists in detecting orphaned objects orbiting Earth or entering its atmosphere. They could be natural objects, like meteorites, or from human space activity, like satellites and debris from satellites or launch vehicles. Space surveillance is dedicated to various applications, ranging from scientific research to security, and involves national and international projects. Survey telescopes require wide field of view (WFOV) because this is the primary way to observe large areas of the sky simultaneously. For instance, the Large Synoptic Survey Telescope (LSST) covers the sky twice each week (1).
Space observation has several goals, but mainly it contributes to the inventory of near-Earth objects in order to improve the known population distribution or to scan the sky rapidly for fast-moving satellites. This kind of projects would be able to detect weak light appearance in the large observed space; this requires a WFOV telescope, as well as a higher resolution, to determine the light’s origin (meteorites, debris, supernovae, exoplanets, gamma-ray bursts etc.). Moreover, increasing the instrument’s sensibility would allow scientists to realize a 3D map of the universe with numerous details; these maps open new possibilities for detecting and localizing dark matter and perhaps characterizing dark energy.
Unknown space objects are a risk for future launches. Space and security surveillance by military and government agencies is designed to track space objects, especially satellites or asteroids, and to build a full catalogue with their characterizations and exact orbit locations. This register also would help warn of potential collisions between asteroids and the Earth, or terrorist attacks. But to catalogue exactly where space objects are, the register must be updated constantly, and this represents an important task, especially with the increasing amount of space debris, the growing number of satellites and the miniaturization of launched microsatellites. To meet these challenges, this survey would require a WFOV instrument with good resolution in order to cover a large part of the sky.
Architecture considerations
Telescopes with large field of view and high resolution require a large aperture diameter and a very fast camera. However, these cameras present a challenge of correcting aberrations of curvature. Correction of aberrations has been investigated through two solutions. The traditional approach adds optical correction elements. However, telescopes working around the aberrations’ limitation need very complex compensators and these solutions are difficult and expensive, and are limited for the large telescope size. Moreover, this solution complicates the design and increases the system size. So the traditional way to correct these aberrations seems to be insufficient, leading to systems limited by the poor sensitivity and field of view achieved.
Interestingly, nature has solved this problem. Indeed, most animals’ eyes have large field of view and high resolution vision systems; small insects have a small volume dedicated to the vision system but they do have good resolution and large field of view. In all eye architecture, the focal plane is curved (Figure 1), which enlarges the field of view and decreases some aberrations, especially aberration of curvature.
Figure1: Concave human retina and convex curved multichannel architectures of insect vision systems
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