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Grenoble, France

Kasper M.,ESO | Verinaud C.,IPAG | Mawet D.,ESO Vitacura
3rd AO4ELT Conference - Adaptive Optics for Extremely Large Telescopes | Year: 2013

Presently, dedicated instruments at large telescopes (SPHERE for the VLT, GPI for Gemini) are about to discover and explore self-luminous giant planets by direct imaging and spectroscopy. The next generation of 30m-40m ground-based telescopes, the Extremely Large Telescopes, have the potential to dramatically enlarge the discovery space towards older giant planets seen in reflected light and ultimately even a small number of rocky planets. The E-ELT Planetary Camera and Spectrograph (PCS) serves this purpose. Building on the heritage of the EPICS phase-A study, this paper presents revised requirements, a possible concept, and the R&D necessary to realize the instrument. Source

Shao M.,Jet Propulsion Laboratory | Nemati B.,Jet Propulsion Laboratory | Zhai C.,Jet Propulsion Laboratory | Goullioud R.,Jet Propulsion Laboratory | And 2 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2011

NEAT, Nearby Exo-Earth Astrometric Telescope is a medium-small telescope ∼ 1m in diameter that is designed to make ultra precise < 1 uas (microarcsec) astrometric measurements of nearby stars in a ∼ 1hr observation. Four major error sources prevent normal space telescopes from obtaining accuracies close to 1 uas. Even with a small 1m telescope, photon noise is usually not a problem for the bright nearby target stars. But in general, the reference stars are much fainter. Typically a field of view of ∼0.5 deg dia is needed to obtain enough bright reference stars. The NEAT concept uses a very simple but unusual design to avoid optically induced astrometric errors. The third source of error is the accuracy and stability of the focal plane. A 1uas error over a ∼2000 arcsec field of view implies the focal plane is accurate or at least stable to 5 parts in 1010 over the lifetime of the mission (∼5yrs). The 4th class of error has to do with our knowledge of the PSF and how that PSF is sampled by an imperfect detector. A Nyquist sampled focal plane would have > 2 pixels per λ/D, and centroiding to 1uas means centroiding to 10-5 pixels. This paper describes the mission concept, and an overview of the technology needed to perform 1uas astrometry with a small telescope, and how we overcome problems 1 and 2. A companion paper will describe the technical progress we've made in solving problems 3 and 4. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE). Source

Delpech M.,French National Center for Space Studies | Malbet F.,IPAG | Karlsson T.,OHB Sweden | Larsson R.,OHB Sweden | And 2 more authors.
Acta Astronautica | Year: 2014

PRISMA is a demonstration mission for formation-flying and on-orbit-servicing critical technologies that involves two spacecraft launched in low Earth orbit in June 2010 and still in operation. Funded by the Swedish National Space Board, PRISMA mission has been developed by OHB-Sweden (formerly Swedish Space Corporation) with important contributions from the German Aerospace Centre (DLR/GSOC), the French Space Agency (CNES), and the Technical University of Denmark (DTU). The paper focuses on the last CNES experiment achieved in September 2012 that was devoted to the preparation of future astrometry missions illustrated by the NEAT and μ-NEAT mission concepts. The experiment consisted of performing the type of formation maneuvers required to point the two-satellite axis to a celestial target and maintain it fixed during the observation period. Achieving inertial pointing for a LEO formation represented a new challenge given the numerous constraints from propellant usage to star tracker blinding. The paper presents the experiment objectives in relation with the NEAT/μ-NEAT mission concept, describes its main design features along with the guidance and control algorithms evolutions and discusses the results in terms of performances achieved during the two rehearsals. © 2014 IAA. Source

Costille A.,IPAG | Fusco T.,ONERA
AO for ELT 2011 - 2nd International Conference on Adaptive Optics for Extremely Large Telescopes | Year: 2011

In the frame of the design of instruments for Extremely Large Telescopes, new techniques of Adaptive Optics have been developed. These techniques, generically called Wide Field Adaptive Optics (WFAO), are based on a tomographic reconstruction of the turbulent volume followed by a projection onto Deformable mirrors (DM) in order to ensure a good correction in a specified field of view (FoV). All these systems require a representation of the turbulent volume through the knowledge of the Cn2 profile. It matters both for an accurate simulation of the input perturbations in the case of performance analysis and system design, but also for an efficient model description in the tomographic reconstruction process. We discuss and analyze the impact of the structure and the complexity of the real Cn2 profile onto the WFAO performance. We demonstrate that a classical integrated parameter is not sufficient and that a more complex criterion is mandatory. Then, we focus on the impact of Cn2 model error in the tomographic reconstruction process with respect to the input profile. We demonstrate that number and position of layers are two critical parameters. In conclusion, we show that it is critical to have access to high resolution Cn2 profile to ensure a good performance evaluation of a WFAO system. Source

Vojetta G.,CEA Grenoble | Guellec F.,CEA Grenoble | Mathieu L.,CEA Grenoble | Foubert K.,CEA Grenoble | And 2 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

Proportional photon detection has been demonstrated using linear mode HgCdTe avalanche photodiodes (APDs) hybridized on a specially designed read-out integrated circuit (ROIC). The ROIC was designed to detect photons at a moderate bandwidth (10 MHz) with a low noise of 10 electrons per characteristics time of the ROIC and to be compatible with large area-small pixel focal plane array (FPA) applications. Proportional photon counting was demonstrated by reproducing the Poisson statics for average photon number states ranging between m=0.8 to 8 photons, at low to moderate avalanche gains M=40-200, using both mid-wave infrared (MWIR) and (short-wave infrared) SWIR HgCdTe APDs. The probability distribution function of the gain was estimated from the analysis of the amplitude of detected residual thermal photons in the MWIR APDs. The corresponding probability distribution functions was characterized by a low excess noise factor F and high asymmetry which favours a high photon detection efficiency (PDE), even at high threshold values. An internal PDE of 90 % was estimated at a threshold level of 40 % of the average signal for a single photon. The dark count rate (DCR) was limited by residual thermal photons in the MWIR APD to about 1 MHz. A geometrical and spectral filtering of this contribution is important to achieve the ultimate performance with MWIR detectors. In this case, the DCR was estimated by interpolation to about 8 kHz. The SWIR HgCdTe APD device had a lower residual photon flux (60 kHz), but was found to be limited by tunnelling dark current noise at high gains at a rate of 100 kHz. © 2012 SPIE. Source

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