Laboratoire dEtudes Spatiales et dInstrumentation en Astrophysique

Le Touquet – Paris-Plage, France

Laboratoire dEtudes Spatiales et dInstrumentation en Astrophysique

Le Touquet – Paris-Plage, France
Time filter
Source Type

Bolton S.J.,Southwest Research Institute | Adriani A.,National institute for astrophysics | Adumitroaie V.,Jet Propulsion Laboratory | Allison M.,Goddard Institute for Space Studies | And 40 more authors.
Science | Year: 2017

On 27 August 2016, the Juno spacecraft acquired science observations of Jupiter, passing less than 5000 kilometers above the equatorial cloud tops. Images of Jupiter's poles show a chaotic scene, unlike Saturn's poles. Microwave sounding reveals weather features at pressures deeper than 100 bars, dominated by an ammonia-rich, narrow low-latitude plume resembling a deeper, wider version of Earth's Hadley cell. Near-infrared mapping reveals the relative humidity within prominent downwelling regions. Juno's measured gravity field differs substantially from the last available estimate and is one order of magnitude more precise. This has implications for the distribution of heavy elements in the interior, including the existence and mass of Jupiter's core. The observed magnetic field exhibits smaller spatial variations than expected, indicative of a rich harmonic content.

Crifo J.-F.,French National Center for Scientific Research | Zakharov V.V.,University Pierre and Marie Curie | Zakharov V.V.,Laboratoire dEtudes Spatiales et dInstrumentation en Astrophysique | Rodionov A.V.,RAS Institute for Nuclear Research | Lukyanov G.A.,Polytechnic University of Mozambique
AIP Conference Proceedings | Year: 2016

One of the objectives of the ESA "ROSETTA" mission to the comet 67P was to insert, in August 2014, an orbiter probe around the so-called nucleus of the comet, and to deposit the "PHILAE" lander at the surface of the nucleus in November 2014. The selection of the landing site and the definition of the release point and initial descent velocity vector were made in the period August to October 2014 on the basis of simulations of the descent trajectory. This requested an assessment of the gravitational and aerodynamic forces on PHILAE. We here describe the so-called RZC model developed to predict the gas environment of 67P in November 2014 and compute the aerodynamic force. We first outline the unusual difficulties resulting from (1) the complexity of the nucleus surface on all scales, (2) the absence of direct measurements of the gas flux at the surface itself, (3) the time-dependence of the gas production induced by the fast nucleus rotation, (4) the need to perform the whole program within less than three months. Then we outline the physical approach adopted to overcome these difficulties, and describe the RZC model which included three differing tools: (1) a set of gasdynamic/gaskinetic codes to compute the vacuum outflow of a rarefied gas mixture from a highly aspherical rotating solid source; (2) an heuristic approach to deal with the solid/gas initial boundary conditions, and (3) an iterative procedure to derive the gas production parameters on the nucleus surface from the observational data acquired from the orbiter probe. The satisfactory operation of the RZC code in the weeks preceding the November 2014 PHILAE descent is shown, and the forecasted aerodynamic force during the PHILAE descent is compared to the gravitational force.

Araujo-Hauck C.,University of Cologne | Fischer S.,University of Cologne | Gillessen S.,Max Planck Institute for Extraterrestrial Physics | Straubmeier C.,University of Cologne | And 11 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

A two stage blocking system is implemented in the GRAVITY science and the fringe tracking spectrometer optical design. The blocking system consists of a dichroic beam splitter and two long wave band-pass filters with the top level requirements of high transmission of the science light in the K-Band (1.95 - 2.45 μm) region and high blocking power optical density (OD) ≥ 8 for each filter at the metrology laser wavelength of 1.908 μm. The laser metrology blocking filters were identified as one critical optical component in the GRAVITY science and fringe tracker spectrometer design. During the Phase-C study of GRAVITY all the filters were procured and individually tested in terms of spectral response at K-band, transmission, blocking (OD) and reflection at the metrology laser wavelength. We present the measurements results of the full metrology blocking system in its final configuration as to be implemented in the GRAVITY spectrometers. © 2012 SPIE.

Pascale E.,University of Cardiff | Waldmann I.P.,University College London | MacTavish C.J.,University of Cambridge | Papageorgiou A.,University of Cardiff | And 11 more authors.
Experimental Astronomy | Year: 2015

EChOSim is the end-to-end time-domain simulator of the Exoplanet Characterisation Observatory (EChO) space mission. EChOSim has been developed to assess the capability of the EChO mission concept to detect and characterise the atmospheres of transiting exoplanets. Here we discuss the details of the EChOSim implementation and describe the models used to represent the instrument and to simulate the detection. Software simulators have assumed a central role in the design of new instrumentation and in assessing the level of systematics affecting the measurements of existing experiments. Thanks to its high modularity, EChOSim can simulate basic aspects of several existing and proposed spectrometers including instruments on the Hubble Space Telescope and Spitzer, ground-based and balloon-borne experiments. A discussion of different uses of EChOSim is given, including examples of simulations performed to assess the EChO mission. © 2015, The Author(s).

Boudjada M.Y.,Austrian Academy of Sciences | Galopeau P.H.M.,Laboratoire Atmospheres | Rucker H.O.,Austrian Academy of Sciences | Lecacheux A.,Laboratoire dEtudes Spatiales et dInstrumentation en Astrophysique | And 3 more authors.
Journal of Geophysical Research: Space Physics | Year: 2011

We study the frequency and time variations of Jovian hectometric emissions (HOM) recorded by the Radio and Plasma Wave Science (RPWS) experiment onboard the Cassini spacecraft during its Jupiter flyby. The capabilities of the RPWS experiment enable us to analyze the intensity extinction of HOM radiation, the so-called attenuation band. Using about 7 weeks of RPWS data obtained around the closest approach, a statistical analysis investigates the spectral variations of this phenomenon with respect to the spacecraft magnetic latitude and central meridian longitude. We show that the trace of the attenuation band is usually not a full sinusoid as reported in previous studies and only parts of the curve are observed. Also, the intensity extinction can occur when the spacecraft is not in the planetary magnetic equator plane. This specific feature appears or vanishes when the observer (e.g., Cassini or Galileo spacecraft) is far from or close to the planet, respectively. The regular and systematic observations of the attenuation band suggest that the plasma medium at the origin of these features is steady and stable. The Io torus may be considered to be the most probable plasma medium where HOM emission is refracted through its raypath propagation. Furthermore, intensity extinction at frequencies higher than 3 MHz and up to 5 MHz implies the presence of particular electronic density irregularities in the Io torus. Volcanic activity, particularly in the northern hemisphere of the Io satellite, may be the source of such Io torus plasma irregularities. Copyright 2011 by the American Geophysical Union.

Hofstadter M.,Jet Propulsion Laboratory | Lamy L.,Laboratoire dEtudes Spatiales et dInstrumentation en Astrophysique
Eos | Year: 2014

Ice giant planets such as Uranus have become a hot topic in the planetary and exoplanetary communities. This interest is driven by several factors, including the realization that these planets are fundamentally different from terrestrial and gas giant planets, the fact that they challenge current understanding of solar system formation and planetary evolution, and the new discovery that ice giants are abundant in our galaxy. © 2014 American Geophysical Union.

Segret B.,Laboratoire dEtudes Spatiales et dInstrumentation en Astrophysique | Semery A.,Laboratoire dEtudes Spatiales et dInstrumentation en Astrophysique | Vannitsen J.,National Cheng Kung University | Mosser B.,Laboratoire dEtudes Spatiales et dInstrumentation en Astrophysique | And 5 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

The AGILE principles in the software industry seems well adapted to the paradigm of CubeSat missions that involve students for the development of space missions. Some of well-known engineering and program processes are revisited on the example of an interplanetary CubeSat mission profile that has been developed by several teams of students in various countries and at various educational levels since 02/2013. The lessons learned at adapting traditional space mission methods are emphasized and they produce a metaphoric image of paving stones. © 2014 SPIE.

Clark B.E.,Ithaca College | Ziffer J.,University of Southern Maine | Nesvorny D.,Southwest Research Institute | Campins H.,University of Central Florida | And 11 more authors.
Journal of Geophysical Research E: Planets | Year: 2010

B-type asteroids have a negative slope from ∼0.5 to ∼1.1 m and beyond. What causes this? Visible to near-infrared reflectance spectra (0.4-2.5 m) are assembled for 22 B-type asteroids. The spectra fall naturally into three groups: (1) those with negative (blue) spectral shapes like 2 Pallas (7 objects), (2) those with concave curve shapes like 24 Themis (11 objects), and (3) everything else (4 objects). The asteroid spectra are compared to mineral and meteorite spectra from the Reflectance Experiment Laboratory library of 15,000 samples, in a least squares search for particulate analogs, constrained by spectral brightness. The Pallas group objects show a trend of analogs from the CV, CO, and CK meteorite groups. Only three of the seven Pallas-like objects are determined to be dynamically related (2, 1508, and 6411). The Themis group objects show a trend of analogs from the CI, CM, CR, CI-Unusual, and CM-Unusual meteorites (as expected from the work of Hiroi et al. (1996)). Seven of the 11 Themis-like objects are dynamically related (24, 62, 222, 316, 379, 383, and 431). Allowing for reasonable uncertainties in the spectral matches, we find no need to invoke mineralogies that do not exist in the meteorite collection to explain B-type spectra or their negative slopes. Our Themis group results are as expected and are consistent with previous work, but our Pallas group results are new and, in some cases, in conflict with previous work. © 2010 by the American Geophysical Union.

Emica B.,ONERA | Meimon S.,ONERA | Conan J.-M.,ONERA | Fusco T.,ONERA | Glanc M.,Laboratoire DEtudes Spatiales et dInstrumentation en Astrophysique
Progress in Biomedical Optics and Imaging - Proceedings of SPIE | Year: 2011

Neglecting pupil irradiance fluctuations using a Hartmann Shack wavefront sensor leads to phase reconstruction bias. This bias depends on the pupil irradiance profile, the Hartmann Shack geometry and the amplitude and structure of the aberrations. In order to quantify the impact on real eye aberrations measurement, pupil irradiance and ocular aberrations of three trained subjects have been acquired on the LESIA testbed at Hospital des Quinze-Vingts. The pure WFS error is quantified with these data sets, on various lenslet array geometries. The propagation of this pure WFS error on actual systems, namely a static aberro- meter and an AO imager, is addressed. We find that, for a large enough lenslet array and with a reasonably clean optical path, the induced error is negligible. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

Sivo G.,University of Paris 13 | Sivo G.,ONERA | Raynaud H.-F.,University of Paris 13 | Conan J.-M.,ONERA | And 4 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

Many concepts of Wide Field AO (WFAO) systems are under development, especially for Extremely Large Telescopes (ELTs) instruments. Multi-Object Adaptive Optics (MOAO) is one of these WFAO concepts, well suited to high redshifts galaxies observations in very wide Field of View (FoV). The E-ELT instrument EAGLE will use this approach. CANARY, the on-sky pathfinder for MOAO, has obtained the first compensated images on Natural Guide Stars (NGSs) at the William Herschel Telescope in September 2010. We present in this paper numerical and experimental validations of a Linear Quadratic Gaussian (LQG) control. This is an appealing strategy that provides an optimal control in the sense of minimum residual phase variance. It also provides a unified formalism that allows accounting for multi WaveFront Sensors (WFSs) channels, both on Laser Guide Stars (LGSs) and NGSs, and for various disturbance sources (turbulence, vibrations). We show how the specific MOAO CANARY configuration can be embedded in a state-space framework. We present experimental laboratory validations that demonstrate the gain brought by tomographic LQG control for CANARY, together with comparative simulations. Model identification necessary for a robust on-sky operation is discussed. © 2012 SPIE.

Loading Laboratoire dEtudes Spatiales et dInstrumentation en Astrophysique collaborators
Loading Laboratoire dEtudes Spatiales et dInstrumentation en Astrophysique collaborators