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This project, realized as part of a CNES/CSO Mesure contract, concerns the study and the industrial realization of a sensor aimed at the relative position control of space telescope mirrors.

PILOT is a balloon borne experiment, which will measure the polarized emission of dust grains, in the interstellar medium, in the sub millimeter range (with two photometric channels centered at 240 and 550 μm). The primary and secondary mirror must be positioned with accuracies better than 0.6 mm and 0.06°. These tolerances include environmental conditions (mainly gravity and thermo-elastic effects), uncertainties on alignments, and uncertainties on the dilatation coefficient. In order to respect these tolerances, we need precise characterization of each optical component. The characterization of the primary mirror and the integrated instrument is performed using a dedicated submillimeter test bench. A brief description of the scientific objectives and instrumental concept is given in the first part. We present, in the second and in the third part, the status of these ground tests, first results and planned tests.

PILOT is a balloon borne experiment which aims at measuring precisely the polarized emission of the interstellar dust emission, in the submm range (240 and 550 μm). These measurements will be used to reach a better understanding of the galactic magnetic field role in the structure of the Galaxy and the star formation process. They will be useful too for CMB experiments by providing a precise knowledge of galactic foreground emission. Simulations including realistic instrument performances show that after three flights (around 24 hours each), it will be possible to cover the full galactic plane map (±30° in latitude). In addition, several deep surveys will be performed at high galactic latitude. As the level of polarized emission of interstellar dust is less than 5%, an accurate knowledge of the instrumental polarization is mandatory for the data processing and analysis.

PILOT is a balloon-borne experiment designed to perform large-scale surveys of the polarized interstellar emission in the submillimeter. It is based on the use of an off-axis Gregorian type telescope, with a 1 m diameter primary mirror, and a large focal plane equipped with detectors arrays providing a \(\sim 1\circ\times 1\circ\) field of view. All optical elements except the primary mirror are located inside a large liquid He cryostat, cooled down to 3 K. Strong constraints are then imposed on the alignment between the primary mirror and the cold optics. The characterization and optimization of the optical system performances are critical to the success of the mission. In this paper, we present the modelling and measurements performed on the primary mirror for this purpose. The optical and mechanical parameters of the as-built primary mirror have been determined using a method based on 3D measurements of the mirror surface. The deformations expected under flight conditions due to temperature variations and flexion under gravity have been estimated. We have also performed measurements using a submillimeter test bench in order to control the image quality and derive the main optical parameters. The parameters derived from the modeling using 3D measurements are in agreement with the requirements except for the conic constant. The best positioning of the mirror has been optimized consequently. The modeling has also allowed us to determine the pre-flight alignment parameters of the mirror as a function of the expected structure temperature at ceiling altitude. We have shown that this adjustment will enable to keep the tight requirements on the focus position (\(\pm \)600 μm) within a range of \(\pm 40\:\circ\)C around the ceiling temperature value. The submillimeter measurements have validated the results derived from the 3D measurement based modeling. The image quality was investigated by performing a spatial exploration in azimuth and elevation around the nominal focus position, and along the optical axis. The deviation between the predicted and measured positions of the best focus are 80 μm and 11″ in translation along the optical axis and in rotation respectively. The best image pattern is also close to the nominal one, with a sphericity deviation lower than 2 μm RMS. These results will be used for the end-to-end tests of the integrated instrument, and for the optimization of the alignment before flight.

PILOT is a balloon borne experiment, which will measure the polarized emission of interstellar dust grains, in the submillimeter range. We present the instrumental concept and the associated ground tests in progress and planned.

I.A.S.I (Infrared Atmospheric Sunding Interferometer), developed by the CNES (French Spatial Agency), will be the major intrument of the european meteorological METOP satellites. The optical part of this instrument is mainly composed of a Fourier spectrometer, followed by a three channel infrared detection device (cold box), as shown in figure 1. The spectral range of this instrument extends from 3.62 µm up to 15.5 µm. Two dichoïc filters, placed in the cold box, permit to divide this spectrum in three channels, B1, B2 and B3. A 1.54 µm laser beam serves as wavelength reference in the interferometer.

The aim of this paper is to shortly present the main applications of space optics. The author will describe successively: earth-observation in visible and near infra-red; meteorological satellite; robotic-laser-data-link between two satellites; attitude sensors; scientific applications. It will be concluded by the future developments in the field of electro-optical technology.

Dans le cadre d’un projet developpe en collaboration avec le Centre national d’etudes spatiales (cnes), les auteurs ont realise la maquette d’un separateur spectral pour les telecommunications entre satellites. On decrit rapidement le principe du systeme. Les mesures de diaphonie sur les differentes voies du demultiplexeur ne concordent pas bien avec les performances theoriques que l’on pourrait en attendre. Au degre de precision qui est necessaire, on ne peut pas negliger la lumiere parasite qui provient de la diffusion par les irregularites des surfaces et interfaces des differents filtres mis en jeu dans chacune des voies du demultiplexeur. Compte tenu des conditions d’eclairement de chacun des elements de l’eclateur spectral, on peut theoriquement mettre en evidence les points les plus critiques du systeme du point de vue de la diffusion et chercher a la diminuer autant que possible pour reduire la diaphonie.