After a brief introduction of the SDSS-V optical instrumentation installed at the Apache Point 2.5m telescope, the presentation will be mainly focused onto the optical production and testing of the 3 large lenses (diameter 700-800mm) constituting the wide field optical corrector (WFC). Special emphasis will be made onto the measurement issues and solutions of the deep aspherical surfaces as well as the review of the specific anti-reflection (AR) coating with development of a dual band anti-reflective coating, carried out by Thales SESO-France. Before concluding, a dedicated paragraph will address on-sky imaging performances results with this new WFC. The presentation will conclude by a brief overview of the corresponding existing “state of the art” at Thales SESO for future manufacturing of similar or large optics for next generation of very wide field corrector.
Molecular adhesion is a well-known process used on terrestrial optics and other fields. This process consists in joining two surfaces without the use of any adhesive or additional material. Molecular adhesion is a high-precision production process, and assemblies obtained present a dimensional stability due to the absence of mechanical part or glue. In addition, since no adhesive materials are used in this process, the risks of contamination associated with degassing are avoided. Based on this benefits, this process is of particular interest for optical system manufacturing for spatial applications. For over the past 20 years, Thales SESO develop its own process of molecular adhesion. For example among others, it has been applied on the manufacturing of Fabry-Perot interferometers. Such as fused silica Fabry-Perot for ALADIN program in the frame of AEOLUS mission (launched in August 2018) or fused silica/Zerodur® Fabry-Perot for ATLID program. Both interferometer have under vacuum cavity. On the ATLID Fabry-Perot the sealing is also made using molecular adhesion. Back then, the molecular adhesion mechanical strength admissible was around 1 MPa. Then, Thales SESO improve its molecular adhesion process - through lots of collaborations with CNES and other partners – in order to be able to bond more complex designs and increase the mechanical resistance. Today the molecular adhesion mechanical strength admissible has been multiplied by a factor five. Those improvement have been applied in the frame of the Third Generation Meteorological satellite (MTG-IRS) for the manufacturing of corner cubes in accordance with the mechanical and thermal environments of a geostationary orbit coupled with very strict optical performances. Today, several corner cubes have been manufactured, and the strength of adhered bond have been demonstrated in terms of thermal, shock and random solicitations through mechanical qualifications. The major advantage of molecular adhesion for the corner cube application is the stability of the WFE under vacuum – which have been also demonstrated. Here, an overview of the Thales SESO realizations starting from Fabry-Perot first results to the latest results on corner cubes performances as well as the future of molecular adhesion for space applications imagined by Thales SESO.
The field of earth observation requires increasingly complex optical instruments to meet the final requirements . The anticipation of instrument integration and alignment activities on the subsystem side is essential. Thales SESO manufactures opto-mechanical subsystems assembled in such different space instruments. The evolution of instruments, as TMA type, concerning the reduction of the space allocated requires Thales SESO to offer opto-mechanical components and associated measurements that are increasingly precise and reliable. The challenge here for Thales SESO is to manufacture, integrate and measure off-axis mirrors while ensuring accurate apex positioning. We will share here the results on the instrument of the MTG program for Telescope Optics subsystems of the two instruments FCI and IRS. Through a specific metrology scheme, including accurate scanning of the optical surface Thales SESO delivers to the customer a reliable and accurate location of the optical reference frame of each sub - assembly toward its mechanical reference frame. From these relative location, the customer is able, in its assembly process, to “plug” the sub-assembly directly in its nominal position to start the alignment process with interferometric system. The data transmitted by Thales SESO made it possible to anticipate each adjustment of the optical subsystems and to make a very accurate prediction of the alignment requirement. With the data measures by Thales SESO, our customers realize a very quick final alignment procedure, with minimum displacements, to meet the final goal. In this process, the alignment budget is also minimized, leading to a final WFE largely under the predictions made by the customer before receiving the assemblies.
For space Astronomy as well as Earth Observation from space, more and more focal plane instruments are operating in the near or mid infrared and require optics operating at cryogenic temperature. The challenge here is to design an optical system reaching all optics, mechanics and thermal requirements. Thales SESO is presently under manufacturing of different opto-mechanical sub-assemblies for Meteosat Third Generation program. The imager missions MTG-I will produce images of the Earth simultaneously in different spectral channels, ranging from the visible spectrum to thermal infra-red, in order to fulfill the scientific, governmental & population needs. The sounder mission MTG-S addresses some interferometric measurements in the MWIR and LWIR ranges on the same instrument. The four CO-I objectives and the four one of CO-S work in different infrared ranges, thus, materials and coating have been chosen and designed especially for each spectral group. Each objectives is a stack of lenses bonded into barrels, themselves bonded inside a main barrel. Each objective is optimized based on the opto-mechanical values measured on each component. The objectives need to resist to mechanical and thermal environments in terms of opto-mechanical stability and work under vacuum, thus, with cleanliness specifications. All these requirements need to be taken into account on the design of different part of the cold optics. Through this on-going realization, the main technical issues and corresponding solutions in terms of design, manufacturing and testing of lens assemblies, mirrors and relevant optical coatings will be pointed out.
Silver protected is one of the most required coating for space observation telescopes covering the wavelength range from 430 nm to infra-red. Many challenges have to be addressed in such coatings including high efficiency over the wide spectrum, high durability with behavior in AIT conditions and during flight. Thales SESO has already produced more than 166 total space mirrors from which 87 are flying successfully since many years. Most of them are coated with protected silver coatings. For over the past 20 years, Thales SESO has enhanced the characteristics of our coating related to its durability in acceptance test conditions, its mechanical stability when going to vacuum and its behavior toward space aggressions such as ATOX or radiations. A lot of the corresponding developments were substantially sustained by CNES, together with Thales Alenia Space through different French programs. Previous realizations include Pléiades, French national program, MTG mirrors both for sounders (IRS instrument) and imagers (FCI instrument), Sentinel 3 with Na and Ob mirrors and different other export programs. The last improvements were made in the frame of TANGO program for Thales Alenia Space/CNES, with improved adhesion during acceptance tests, with ability to apply the full coating process on sub-assemblies including glued parts, and with reduction in the stress induced on the substrate. The performance and uniformity were demonstrated on 1700 mm diameter in Thales SESO STEP large coating chamber. Through these different developments Thales SESO has gained maturity in the contribution of the coating on stress induced in the mirror as well as its stability when going to vacuum. We now perfectly anticipate this effect in the polishing process. Here after, you find an overview of the Thales SESO realizations starting from Pléiades first results to the status achieved with the last improvements on TANGO program and future prospective developments.
Future scientific space missions require ever more demanding large optics that work at cryogenic temperatures. In the frame of a Darwin assessment study conducted under ESA contract by TAS, the need of future very lightweight cryogenic mirrors with superior optical quality has been identified. Such mirrors need to be of size up to 3.5 m in diameter, with a mass of less than 250 kg (i.e. 25 kg/m2) and possess excellent optical quality at cryogenic temperature down to 40 K.
For space born Astronomy as well as Earth Observation from space, more and more focal plane instruments are operating in the near or mid infrared and require therefore optics operating at cryogenic temperature (down to liquid nitrogen temperature or less).
Through several examples of typical past or on-going realizations for different projects requiring such cryogenics optics (e.g. MTG=Meteosat Third Generation program for ESA), the presentation will point out the main technical issues and corresponding solutions for design, manufacturing and testing of necessary lens assemblies, mirrors and relevant optical coatings.
A brief review of the corresponding existing “state of the art” for these technologies in Thales Seso will conclude the presentation.
During the past two years, ECM, Germany, together with Mitsubishi Electric Corporation (MELCO), Japan, developed a
new carbon-fiber-reinforced SiC material, called HB-Cesic®, which possesses superior mechanical and thermal
cryogenic properties compared to traditional Cesic®. This combination makes HB-Cesic® an excellent choice for large
cryogenic mirrors, which will be required for future scientific space missions, such as SPICA and DARWIN.
ESA contracted Thales Alenia Space (TAS), France, to design a super-lightweighted HB-Cesic® mirror with a diameter
of 600 mm, isostatic fixations, and a special astigmatism compensation device (ACD) for mirror shape control. The
mirror was manufactured by ECM, polished and coated by Société Européenne de Systèmes Optiques (SESO), France,
and tested to cryogenic temperatures by TAS. The measured wave-front error at ambient and cryogenic temperatures
demonstrated the excellent homogeneity of HB-Cesic® and TAS' expertise in mirror mounting. Furthermore, when
thermally actuated, the ACD exhibited perfect control of the mirror shape.
This success confirmed HB-Cesic®'s superior material properties and its applicability to future cryogenic space mirrors.
In this paper we describe the design and fabrication process of this cryogenic mirror and give test results at ambient and
cryogenic temperatures.
Optical Components improvements generally call specific improvements of optical coatings. SESO introduce here, some examples of new coatings, developed for applications in its activity fields such as, space, defense, synchrotrons and high power laser programs, astronomy.
To answer to a need of coating, in a very wide wavelength range, from X rays to FAR IR:
- Metallic reflective coating for X Rays.
- Specific Aluminium coating for EUV up to 190 nm
- Dielectric coatings for wavelength broadband, double or triple bands (VIS + IR)
To answer to a need of High Level Laser damage:
- Hf/Metal coating (R and AR) to face energies up to 40J/cm2
To answer to a need of long lifetime for coatings submitted to stringent environmental conditions:
- enhanced silver coating for astronomical mirrors
- Hard Gold for Space applications
- Protected aluminium for solar simulators
To answer to a need of coating a large variety of substrates:
- R and AR coatings on Silicium, ZnS, ZnSe, Ge, Saphyr...
At least to answer to a need of high uniformity coatings and to realise coating on very large optical components, SESO recently installed a large coating machine able to work with optical components up to Φ 1100mm.
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.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.