Grégory Lousberg

The design of an adaptive optics telescope: the case of DAG

In this paper, we describe in detail the optical design of DAG, a new 4 m telescope for Turkey. DAG is an adaptive optics friendly telescope, in a sense that each design decision is taken considering the potential impact on the AO performance (vibrations, static aberrations etc.) The objective is to make this telescope fully ready for AO at first light. It is designed as a Ritchey-Chrétien combination, 56 m focal length, with Nasmyth foci only, and active optics. Its total RMS error is expected to be 45 nm up to Zernike mode 78, and 26 nm for the higher, non AO corrected modes. A final design optimization has been done by the telescope manufacturers, demonstrating that our AO-based requirements can be satisfied, without much difficulty.

OAJ 2.6m survey telescope: optical alignment and on-sky evaluation of IQ performances

AMOS has recently completed the alignment campaign of the 2.6m telescope for the Observatorio Astrofisico de Javalambre (OAJ). AMOS developed an innovative alignment technique for wide field-of-view telescopes that has been successfully implemented on the OAJ 2.6m telescope with the active support of the team of CEFCA (Centro de Estudios de Física del Cosmos de Aragón). The alignment relies on two fundamental techniques: (1) the wavefront-curvature sensing (WCS) for the evaluation of the telescope aberrations at arbitrary locations in the focal plane, and (2) the comafree point method for the adjustment of the position of the secondary mirror (M2) and of the focal plane (FP). The alignment campaign unfolds in three steps: (a) analysis of the repeatability of the WCS measurements, (b) assessment of the sensitivity of telescope wavefront error to M2 and FP position adjustments, and (c) optical alignment of the telescope. At the end of the campaign, seeing-limited performances are demonstrated in the complete focal plane. With the help of CEFCA team, the image quality of the telescope are investigated with a lucky-imaging method. Image sizes of less than 0.3 arcsec FWHM are obtained, and this excellent image quality is observed over the complete focal plane.

Design and analysis of an active optics system for a 4-m telescope mirror combining hydraulic and pneumatic supports

AMOS has developed a hybrid active optics system that combines hydraulic and pneumatic properties of actuators to support a 4-m primary mirror. The mirror is intended to be used in the Daniel K. Inouye Solar Telescope (DKIST, formerly the Advanced Technology Solar Telescope) that will be installed by the National Solar Observatory (NSO) atop the Haleakala volcano in Hawaii. The mirror support design is driven by the needs of (1) minimizing the support-induced mirror distortions under telescope operating conditions, (2) shaping the mirror surface to the desired profile, and (3) providing a high stiffness against wind loads. In order to fulfill these requirements, AMOS proposes an innovative support design that consist of 118 axial actuators and 24 lateral actuators. The axial support is based on coupled hydraulic and pneumatic actuators. The hydraulic part is a passive system whose main function is to support the mirror weight with a high stiffness. The pneumatic part is actively controlled so as to compensate for low-order wavefront aberrations that are generated by the mirror support itself or by any other elements in the telescope optical chain. The performances of the support and its adequacy with the requirements are assessed with the help of a comprehensive analysis loop involving finite-element, thermal and optical modellings.

EUCLID: design, analysis, fabrication, and test of a 1.3 m collimator for the on-ground characterization of the EUCLID payload module

EUCLID is an optical/near-infrared survey mission to be launched towards the L2 Lagrange point. It will aim at studying the dark universe and providing a better understanding of the origin of the accelerating expansion of the universe. Through the use of cosmological sounding, it will investigate the nature of dark energy, dark matter and gravity by tracking their observational signatures on the geometry of the universe and on the cosmic history of large structures formation. The EUCLID PayLoad Module (PLM) consists of a 1.2 m-class telescope and will accommodate two instruments. As a subcontractor of AIRBUS Defence and Space, AMOS is responsible for the manufacturing of all the silicon carbide mirrors of EUCLID PLM except for the primary mirror. In addition, AMOS also produces the 1.3 m test collimator that is used for the on-ground validation of the optical performances of the payload module under operational thermal vacuum conditions. The 1.3m collimator is designed, manufactured, assembled and tested by AMOS. It is based on a Ritchey-Chretien optical configuration, with a f/2 primary mirror and a hyperbolic secondary mirror. The mirrors are made of ZERODUR and polished by AMOS. The high performance of EUCLID PLM calls for not less demanding requirements for the test collimator, in terms of image quality, thermal stability, line of sight stability under micro-vibration, etc. Here after are presented at first the design and the strategies elaborated to cope with the stringent requirements. Then, the manufacturing and metrology of the mirrors are reported. Finally, the Assembly, Integration and Verification by test (AIV) are discussed.

EUCLID: design, analysis, fabrication, and test of a 1.3m collimator for the on-ground characterization of the EUCLID Payload Module

EUCLID is an optical/near-infrared survey mission to be launched towards the L2 Lagrange point. It will aim at studying the dark universe and providing a better understanding of the origin of the accelerating expansion of the universe. Through the use of cosmological sounding, it will investigate the nature of dark energy, dark matter and gravity by tracking their observational signatures on the geometry of the universe and on the cosmic history of large structures formation. The EUCLID PayLoad Module (PLM) consists of a 1.2 m-class telescope and will accommodate two instruments. As a subcontractor of AIRBUS Defence and Space, AMOS is responsible for the manufacturing of all the silicon carbide mirrors of EUCLID PLM except for the primary mirror. In addition, AMOS also produces the 1.3 m test collimator that is used for the on-ground validation of the optical performances of the payload module under operational thermal vacuum conditions. The 1.3m collimator is designed, manufactured, assembled and tested by AMOS. It is based on a Ritchey-Chretien optical configuration, with a f/2 primary mirror and a hyperbolic secondary mirror. The mirrors are made of ZERODUR® and polished by AMOS. The high performance of EUCLID PLM calls for not less demanding requirements for the test collimator, in terms of image quality, thermal stability, line of sight stability under micro-vibration, etc. Here after are presented at first the design and the strategies elaborated to cope with the stringent requirements. Then, the manufacturing and metrology of the mirrors are reported. Finally, the Assembly, Integration and Verification by test (AIV) are discussed.

Commissioning and first scientific operations of the wide-field 2.6m Javalambre Survey Telescope

The Javalambre Survey Telescope (JST/T250) is a wide-field 2.6 m telescope ideal for carrying out large sky photometric surveys from the Javalambre Astrophysical Observatory in Teruel, Spain. The most immediate goal of JST is to perform J-PAS, a survey of several thousands square degrees of the Northern sky in 59 optical bands, 54 of them narrow (∼ 145 Å FWHM) and contiguous. J-PAS will provide a low resolution photo-spectrum for every pixel of the sky, hence promising crucial breakthroughs in Cosmology and Astrophysics. J-PAS will be conducted with JPCam, a camera with a mosaic of 14 CCDs of 9.2k × 9.2k pix, more than 1200 Mpix and an effective FoV of 4.3 deg2 . Before JPCam is on telescope, the project will work in 2018 with an interim camera, JPAS-Pathfinder, with a reduced FoV of ∼ 0.6 × 0.6 deg2 to perform commissioning and the first JST science. This paper presents the current status and performance of the JST telescope, describing the commissioning and first science of the JPAS-Pathfinder at JST.

DAG 4m telescope: assembly, integration and testing

AMOS with EIE as a main subcontractor, was awarded a contract in November 2014 for the design, manufacturing and installation of a 4m-class telescope for the Turkish Eastern Anatolia Observatory (DAG) situated at 3170 m above the sea level in Palandöken mountains. The telescope is based on a Ritchey-Chretien configuration with two folded Nasmyth focal planes and a focal length of 56m. Diffraction-limited performances will be reached thanks to the combination of the active optics system and the adaptive optics system that will be implemented on one of the Nasmyth ports. The active optics system aims at controlling the shape of the primary mirror by means of 66 axial force actuators and positioning actively the secondary and tertiary mirrors by means of hexapods. More than 30 years of experience in testing instruments and telescopes, including optical testing, alignment, metrology, mechanical static and dynamic measurements, system identification, etc. allow to implement an adequate verification strategy combining component level verifications with factory and site test in the most efficient and reliable manner. As a main contractor, AMOS is in charge of the overall project management, the system engineering, the optical design and the active optics development. As a main sub-contractor and partner of AMOS, EIE is in charge of the development of the mount. The factory test therefore takes place in EIE premises. In this paper is shortly presented the overall design of the telescope with a review of the specification, the optical design and a description of the major sub-systems, including the optics. The assembly, integration et test plan is outlined. The assembly sequence and the tests of the active optics and the mount are discussed. Finally, the site integration and tests are explained. The process to assess the image quality of the telescope and the verification instrument developed for this purpose by AMOS are presented.

Mt ABU 2.5m Telescope: design and fabrication

AMOS S.A. is in charge of the development and installation of a 2.5 m telescope for Physical Research Laboratory (PRL) of India. It is a 20 m focal length Ritchey Chretien Cassegrain configuration equipped with active optics. AMOS has acquired in more than 30 years a large experience in design, analysis, fabrication and commissioning of 2 to 4 m-class telescopes. Strong of this experience, the multidisciplinary integrated team of the project was able to design the Mt ABU 2.5-m telescope in one year with a great mastering of the technologies and sub-systems development which are used. This is the key point for the risk management of the project. In this paper is presented the overall design of the telescope. This includes the optical design, the opto-mechanical design of the mirror supports and, in particular the active primary mirror support, the mount design and the control system for which AMOS has developed a main axes servo control based on industrial programmable logic controller (PLC). The closed loops sensing devices (wavefront sensor and guider) and their associated control systems are also presented. The Assembly, Integration and Verification (AIV) activities are finally discussed.

Active optics system for the 4m telescope of the Eastern Anatolia Observatory (DAG)

An active optics system is being developed by AMOS for the new 4m-class telescope for the Turkish Eastern Anatolia Observatory (DAG). It consists in (a) an adjustable support for the primary mirror and (b) two hexapods supporting M2 and M3. The M1 axial support consists of 66 pneumatic actuators (for mirror shape corrections) associated with 9 hydraulic actuators that are arranged in three independent circuits so as to fix the axial position of the mirror. Both M1 support and the hexapods are actively controlled during regular telescope operations, either with look-up tables (openloop control) or using optical feedback from a wavefront sensor (closed-loop control).

New isostatic mounting concept for a space born Three Mirror Anastigmat (TMA) on the Meteosat Third Generation Infrared Sounder Instrument (MTG-IRS)

A novel isostatic mounting concept for a space born TMA of the Meteosat Third Generation Infrared Sounder is presented. The telescope is based on a light-weight all-aluminium design. The mounting concept accommodates the telescope onto a Carbon-Fiber-Reinforced Polymer (CRFP) structure. This design copes with the high CTE mismatch without introducing high stresses into the telescope structure. Furthermore a Line of Sight stability of a few microrads under geostationary orbit conditions is provided. The design operates with full performance at a temperature 20K below the temperature of the CFRP structure and 20K below the integration temperature. The mounting will sustain launch loads of 47g. This paper will provide the design of the Back Telescope Assembly (BTA) isostatic mounting and will summarise the consolidated technical baseline reached following a successful Preliminary Design Review (PDR).