Over more than 50th years Thales SESO represent a world leading designer and manufacturer of high-end, optical components such as telescopes and satellite-based space observation optics operating over the entire spectral range from infrared to x-ray wavelengths. Since early 90th we are actively working in the EUV, Soft-X-ray and hard X-ray spectral range, by developing new equipment and introducing metrology innovations and brand new patented products such as bender and bimorphs mirrors (1st and 2nd generation). In particular a set of customized solution and integrated system for imaging and spectroscopy have been developed basing on the original Wolter and Kirckpatrick-Baez design. Few example of reflective optics behaving both, as collimator, focusing and imaging device are discussed in this paper. A set of solutions to realize fixed curvature optics and dynamically bended device will be detailed to illustrate the flexibility and performances of these products..
Regarding the progress of optical design in favor of freeform surfaces, it becomes necessary to scale their feasibility with appropriate criteria in order to get a standard between an optical designer and an optical manufacturer. Two criteria are necessary, one linked to polishing process and one appropriate for measurement limitation. First criterion can be the extension to freeform surfaces (defined here by first Zernike terms) of a previous criterion which was calculated using conical equation. This criterion is representative of surface’s curvatures fluctuations which limit polishing efficiency and can generate high frequency defects. The second criterion should take into account the difficulty to measure the surface as feasibility needs also good knowledge of the correction polishing cycle to be performed. Different solutions exist for an accurate measurement in the range of nm. As demonstrated in the article, slopes versus reference surface is the limiting factor for a majority of measurement solutions. Therefore the criterion will be linked to a slope parameter. The governing principle of these criteria is to remain close to some relevant physical dimensions. In this idea, the polishing feasibility criterion defined in this paper will be comparable to tool diameter of Computer Controlled Polishing which refers to equipment resolution of optical manufacturers. In the same idea, we project to define a dimensioned criterion for measuring feasibility which can be compared to engraving resolution for a given Computer Generated Hologram.
The interferometer of the third generation meteorological satellite is composed by two corner cubes. The specifications, in terms of optical performances - wave front error (WFE) - and mechanical and thermal environments are very stringent compared to the actual knowledge. To answer to the mass, optical and mechanical specifications, a lightweighted hollow corner cube have been designed. An integration process based on enhanced molecular adhesion have been developed and tested in collaboration with CNES and LMA. This process required a fine polishing of the three mirrors of the corner cube before adhesion in order to obtain a very low flatness, roughness and angle precision. The mechanical resistance of the enhanced molecular adhesion process have been validated on three mockups submitted to shock and vibrations. The optical performances have been demonstrate on flight model corner cubes.
Thales Alenia Space has been involved in the design and the development of space observation instruments for over 40 years. This paper will explain why active optics is needed for next generation of instruments for Earth observation. We will also describe what kind of solution is preferred and why. We will give an overview of the development status on the associated technologies. Indeed, the future missions will have to deal with better performance, better optical quality while from manufacturing point of view, the total mass, the development schedule and the final cost have to be reduced. These constraints induce a new generation of solutions based on large entrance optics associated to high lightweight ratio which naturally provide solutions sensitive to gravity deformation. In these conditions, the enhancement of the final performance can only be guaranteed by using active optics in flight. A deformable mirror is therefore foreseen to be implemented in future large telescopes in order to correct manufacturing residues, ground/flight evolution including gravity. Moreover, low mass and low cost require more compact designs which entail solutions more sensitive to misalignment. An active positioning mechanism is then also needed in order to correct the telescope alignment during operation conditions. Thales Alenia Space has been selected by CNES to develop and qualify active optics building blocks and then to test and demonstrate the improvement that new active technologies can bring in a full size instrument representative of the next generation of observation instruments. An overview of the current development status and the achievable performances is given.
Earth observation space instruments require very tight optical performances in the most stringent configuration (observation in the optical wavelengths range). The optical quality of mirrors, mainly in term of both shape and roughness polishing quality, has to reach very tight specifications down to a few nanometers. In this paper, we present a new manufacturing process, based on Stress-Mirror Polishing (SMP) technique, dedicated to lightweight mirrors aspherisation. We consider specific features or constraints due to the structure of the honeycomb, while reducing footprint effects and inhomogeneous surface effects. We also identify the most efficient way to correct and/or anticipate these issues taking into account industrial constraints on real-scale mirrors. In this new process, both SMP technique and lightweight design have to be optimized.
For the Pleiades space program, SESO has been awarded the contract (fully completed), for the manufacturing of the whole set of telescope mirrors (4 mirrors, 2 flight models). These works did also include the mechanical design, manufacturing and mounting of the attachment flexures between the mirrors and the telescope main structure. This presentation is focused on the different steps of lightweighting, polishing, integration and control of these mirrors as well as a presentation of the existing SESO facilities and capabilities to produce such kind of aspherical components/sub-assemblies.
CNES (French spatial agency) will provide the AltiKa high resolution altimeter, Doris instrument and the LRA (Laser Retroreflector Array) for SARAL (Satellite with Argos and AltiKa) in cooperation with ISRO (Indian space agency).
The LRA is a passive equipment reflecting the laser beams coming from the Earth ground stations. Computing the send-return time travel of the laser beams allows the determination of the satellite altitude within an accuracy of a few millimeters. The reflective function is done by a set of 9 corner cube reflectors, with a conical arrangement providing a 150 degrees wide field of view over the full 360 degrees azimuth angle.
According to CNES optomechanical specifications, the LRA has been developed by SESO (French optical firm). SESO has succeeded in providing the corner cube reflectors with a very stringent dihedral angle error of 1.6 arcsec and an accuracy within ±0.5 arcsec. During this development, SESO has performed mechanical, thermal and thermo-optical analyses. The optical gradient of each corner cube, as well as angular deviations and PSF (Point Spread Function) in each laser range finding direction, have been computed. Mechanical and thermal tests have been successfully performed. A thermo-optical test has successfully confirmed the optical effect of the predicted in-flight thermal gradients.
Each reflector is characterized in order to find its best location in the LRA housing and give the maximum optimization to the space telemetering mission.
Space telescopes pupil diameter increases continuously to reach higher resolutions and associated optical scheme become more sensitive. As a consequence the size of these telescopes but also their stability requirements increase. Therefore, mass of space telescopes becomes a strong design driver to be still compatible with price competitive launcher capabilities. Moreover satellite agility requirements are more and more severe and instruments shall be compatible with quick evolution of thermal environment.
CNES (French spatial agency) will provide the AltiKa high-resolution altimeter, Doris instrument and the LRA (Laser Retro-reflector Array) for SARAL (Satellite with ARgos and Altika) in cooperation with ISRO. The paper presents the LRA, its design and its key performances. The nine corner cube reflectors have been manufactured with very stringent dihedral angle offset precision. The tests done will be described. Specific modelisation and analysis (thermal gradient), specific test (thermo-optical test) and optimizations will be described.
The increase of optical resolution and size of astronomical telescopes needs to: (1) Improve surface quality of optical components. (2) Use more and more complex aspherical shape for lenses and mirrors. Due to these 2 constraints, the optical manufacturers had to improve theirs equipments such as the Computer Controlled Polishing and to appreciate the feasibility of very complex aspherical shape. Concerning this second point, we propose a new criterion based on surface definition, on quality specification for the polishing and on limitations of equipments. Manufacturing examples show that this criterion is well representative, and particularly for direct off-axis polishing.
In view of the NIRSpec-JWST program, a trade-off study is currently in progress under an ESA-ESTEC contract, to select design, blank materials, coatings and relevant technologies for high quality mirrors operating at cryogenic temperatures. The behavior of two prototype lightweight mirrors, made in cold- pressed-sintered SiC and in Carbon-SiC (Cesic) are compared by interferometric measurements at 20 K. The prototypes are spherical mirrors, but realized using optical manufacturing technologies suitable for highly demanding aspherics (i.e. computer controlled polishing, ion beam figuring), in the perspective of the foreseen NIRSpec-TMA(s) optics.
The Rayleigh lidar concept is based on the measurement of Rayleigh scattering when a laser beam is sent in the atmosphere. The principle of such a detection by Rayleigh scattering was developed thanks to the CNRS team of Service d'Aeronomie (M. L. Chanin and A. Hauchecorne). The Rayleigh lidar provides the spacial and temporal atmosphere density and temperature information which have a direct impact on the space device trajectory. This measurement can be obtained thanks to balloon probes or radar up to 30 km in height. The Rayleigh lidar enables these measurements to be made continuously, up to 90 km in height. It can be used for several applications such as: space device assistance, constitution of the statistical data bank of the atmosphere, and the study of physical phenomena in the atmosphere. The new SESO Rayleigh lidar system `LIRA' is transportable and commercially available. Description, characteristics, and results are presented.