The optics of ATHENA (Advanced Telescope for High-ENergy Astrophysics) – the next high-energy astrophysical mission of the European Space Agency – consists of 678 Silicon Pore Optics mirror modules integrated and co-aligned onto a common supporting structure. The integration process, already proved, exploits an optical bench to capture the focal plane image of each mirror module when illuminated by an ultra-violet plane wave at 218 nm. Each mirror module focuses the collimated beam onto a CCD camera placed at the 12 m focal position of the ATHENA telescope and the acquired point spread function is processed in real time to calculate the centroid position and intensity parameters. This information is used to guide the robot-assisted alignment sequence of the mirror modules. To implement the above process for the entire ATHENA optics, a dedicated vertical optical bench is being designed. The facility consists of a paraboloid mirror that collects the light from an ultraviolet point source and generates a single reference plane wave large enough to illuminate the 2.6 m aperture of the X-ray telescope; at 12 m from the ATHENA optics (focal plane position) a tower will support the CCD camera, where the light from each mirror module is focused. The facility must also allow an alignment accuracy of 1 arcsec for the integration of two mirror modules per day in any arbitrary integration sequence, including the option of removing, re-aligning, or replacing any mirror module. The detailed design of the optical bench and the status of the construction activities are presented.
Mission studies and technology preparation for the ATHENA (Advanced Telescope for High ENergy Astrophysics) [1- 5] mission are continuing to progress. The X-ray optics of this future space observatory are based on the Silicon Pore Optics (SPO) technology [6-58], and is being evolved in a joint effort by industry, research institutions and ESA. The SPO technology benefits from substantial investments made by the semiconductor industry, and spins-in materials, processes and equipment into the development of novel X-ray optics. A comprehensive Technology Development Plan (TDP) is being implemented, funded by ESA and involving a large number of experts in key areas ranging from micro machining of Silicon, over sophisticated automation and robotic systems, to hybrid manufacturing. The performance, environmental compatibility and serial automated production and testing are being addressed in parallel, aiming at the demonstration of the required technology readiness for the ATHENA Mission Adoption Review (MAR) expected by the end of 2021. A formal Technology Readiness Assessment is in place and is being currently exercised in preparation of the ATHENA Mission Formulation review (MFR). The programmatics for the flight model implementation is being defined in detail, and preparations are starting for the design and implementation of the necessary facilities. An overview of the ATHENA optics technology preparation, the technology readiness assessment and the related activities is provided.
Polishing and testing methods used in the manufacture of the 3.4 m primary mirror of the Iranian National Observatory (INO) telescope are described and the test results of the finished mirror are presented. Mirror lapping and polishing was performed using several rectangular non-rotating tools arranged in a linear array across the mirror radius. Each tool is equipped with two computer controlled force actuators for regulating the surface pressure and removal efficiency during the lapping and polishing operations. The same tool system was used from the lapping phase to the end of the final polishing. The principal optical test method was the interferometric Hartmann test with the aid of a two component null lens in the mirror center of curvature. Mirror measurements were made also with pentaprism test to verify its correct conic constant. The mirror was finished to extremely good surface accuracy and smoothness.
Herschel space observatory of ESA has a parabolic M1mirror of silicon carbide (SiC) with large diameter of 3.5 m, fast focal ratio of f/0.5 and extreme light-weighting to 25 kg/m2, which make the polishing of the mirror a very challenging task. Use of very high surface pressure is necessary to polish efficiently this hard material, which increases the risk of quilting effects to the shape of the only 2.5 mm thick front face of the mirror. In this paper we present descriptions of the testing and polishing methods used during Herschel M1 lapping and polishing to the specified surface shape accuracy < 1.5 μm rms and micro roughness <30 nm rms.
The Aladin instrument on the ADM-Aeolus satellite of ESA has a parabolic M1 mirror of silicon carbide (SiC) with diameter of 1.5 m, fast focal ratio of f/0.9 and light-weighting to 25 kg/m2. The lidar instrument is operated at the near ultraviolet wavelength of 355 nm, which requires high optical quality and good smoothness of the polishing finish. In this paper we present descriptions of the testing and polishing methods used during ALADIN M1 lapping and polishing to the specified wave front shape accuracy <150 nm rms and surface micro roughness < 5 nm rms.
For extremely large telescopes, there is strong need for thin deformable mirrors in the 3-4 m class. So far, feasibility of such mirrors has not been demonstrated. Extrapolation from existing techniques suggests that the mirrors could be highly expensive. We give a progress report on a study of an approach for construction of large deformable mirrors with a moderate cost. We have developed low-cost actuators and deflection sensors that can absorb mounting tolerances in the millimeter range, and we have tested prototypes in the laboratory. Studies of control laws for mirrors with thousands of sensors and actuators are in good progress and simulations have been carried out. Manufacturing of thin, glass mirror blanks is being studied and first prototypes have been produced by a slumping technique. Development of polishing procedures for thin mirrors is in progress.
We describe the 1-meter Swedish solar telescope which replaces the former 50-cm solar telescope (SVST) in La Palma. The un-obscured optics consists of a singlet lens used as vacuum window and two secondary optical systems. The first of these enables narrow-band imaging and polarimetry with a minimum of optical surfaces. The second optical system uses a field mirror to re-image the pupil on a 25 cm corrector which provides a perfectly achromatic image, corrected also for atmospheric dispersion. The adaptive optics system is integrated with the design of the telescope but is sufficiently flexible to allow future upgrades. It consists of a low-order bimorph modal mirror with 37 electrodes, allowing near-diffraction-limited imaging a reasonable fraction of the observing time on La Palma.
The new telescope became operational at the end of May 2002 and has already proven to be the most highly resolving solar telescope ever built. In this paper, we describe its mechanical and optical design, the polishing and testing of the optics and the instrumentation in use or planned for this telescope.
A novel computer-controlled method has been developed for grinding and polishing thin and a flexible mirrors and other optical components. The method makes use of the surface pressure induced by a partial vacuum between the tool and the workpiece. Based on the measured errors of the shape of the workpiece, the surface pressure is regulated dynamically by varying the partial vacuum under computer control while the tool is moving on the workpiece. To increase the figuring efficiency, several non-rotating tools are used simultaneously in a linear array across the optics. The method has been developed and tested using a 0.5 m thin blank and a small computer-controlled polishing machine. A description is presented of the developed equipment and of the experience gained in the use of the method.
Computer-controlled methods have been applied for figuring two telescope mirrors of 1.25 m in diameter to a very high optical quality. Figuring and testing are performed in a closed loop scheme. The polishing tool comprises several non-rotating subtools in a linear array. The subtools are equipped with force actuators to regulate dynamically the polishing forces on the basis of the mirror metrology results. Fast and continuous convergence of the mirror surface accuracy has been achieved. A discussion is presented of the applicability of the developed methods for manufacturing very large mirrors.
A feasibility study of a 25 m class telescope for optical wavelengths is presented. A short summary of the scientific background is given. A possible optical design is presented and discussed. Technical and engineering aspects are detailed. Tentative solutions are proposed for manufacture of mirrors and mirror segments. The suitability of metal mirrors is discussed. Comments are given on procedures for optical testing. Details on the mechanical design of the telescope are given. A first tentative proposal for the enclosure is presented. The control system is briefly discussed. Brief comments are given on the maintenance of the telescope. Finally, a tentative implementation plan is presented, including budget and time schedule.
The use of the Hartmann interferometric optical testing method is described. The method is applied for laboratory testing during mirror manufacturing. Possibilities and advantages of the method in testing mirrors of the 8 m class are discussed. A telescope wavefront sensor based on the method is described and test results of the 2.5 m Nordic Optical Telescope are presented.
Technology developed for computer-controlled mirror manufacturing is described. The polishing tool is equipped with
electromagnetic force actuators to regulate the local polishing forces according to the measured mirror errors. Optical
testing with the interferometric modification of the Hartmann test and a CCD-camera as a detector allow accurate and fast
measurement with high sampling frequency. Air turbulence and vibration effects are minimized in the workshop which is
blasted into the bedrock and equipped with good thermal insulation.