Presently TNO/Demcon are manufacturing nine Laser Projection Systems (LPS). TNO is responsible for the design and manufacturing of the Optical Tube Assembly (OTA), the baseplate and the LPS cover. Demcon designed and manufactured the Beam Conditioning and Diagnostic System (BCDS). TNO is also responsible for the system performance and its verification tests.
Six units will be used on the ELT. The other three are destined for the VLT. That will allow the operation of the adaptive mirrors enabling unprecedented image quality of the telescopes. The design of this system is based on the four laser guide stars units as used on the VLT.
The system has been upgraded considerably compared to the units used for the VLT. Its FOV has increased to 7 arcmin (half cone). The laser power goes up to 50W and the BCDS has been completely redesigned. The BCDS is located between the laser source and the OTA that produces the Ø300 mm output beam. Maintainability and accessibility of the system have also been much improved.
Prime qualities are its insensitivity to temperature changes (static and dynamic), its accuracy and its FOV. Assembly of the first unit is finished and in January the acceptance testing of the system started. The first unit is expected to be delivered to ESO in autumn 2024.
High throughput optical satellite communication (SATCOM) systems need to rely on effective and robust technology to enable wavelength-division multiplexing (WDM) in a commercially viable way. The main challenge to implement WDM in optical feeder links deals with the multiplexing of high power channels. Currently the levels of power required for communication, tens of watts per channel, make unfeasible to multiplex several channels in a waveguiding device. A free space architecture is devised to mitigate this issue. The paper describes the architectural choices made, the optical and mechanical design for a multiplexer to be employed in a Optical Feeder Link terminal combining 13 channels, each carrying 50W of optical power. Within the TOmCAT (Terabit Optical communiCation Adaptive Terminal) project a demonstrator of the full system has been realized. The demonstrator multiplexer supports 5 channels, each carrying up to 2W of optical power, with an optical bandwidth of 25 GHz, centered on the 200 GHz ITU grid. The design and the experimental results obtained during the integration of the multiplexer demonstrator are here presented and discussed.
TMT will be a telescope with 492 segments making up the primary mirror. Each of these segments is supported with a highly sophisticated Segment Support Assembly (SSA) and each of them is to be tested for acceptance using a tool called SMATT. This tool will be mounted on top of each SSA and provides the load distribution applied to its 27 support points. These loads will vary slightly due to mechanical tolerances which is perfectly acceptable and can be predicted using FE-analysis. However manufacturing errors and parasitic stiffness contributions may cause unacceptable deviations. This should be avoided. The article will describe the functioning of SMATT. The tool is designed such that the segment support loads can be measured in any position. In the SSA, 21 Warping Harnesses (WH) are implemented to actively compensate for Surface Form Errors (SFE). These WH can also be verified for proper functioning when using SMATT.
TNO, in close cooperation with Demcon, has designed the Laser Projection Subsystem (LPS) for ESO’s Extremely Large Telescope (ELT). The ELT LPS will consist of up to 8 laser projection subunits. The design is based on the Four Laser Guide Star Facility (4LGSF), built for the ESO Very Large Telescope (VLT) (5). The VLT AO system has been operational on the VLT UT4 in Paranal since early 2016. The system has demonstrated excellent performance and high reliability. The ELT LPS consist of a Baseplate with Beam Conditioning and Diagnostics System (BCDS), Optical Tube Assembly (OTA) and Cover Assembly. Control and driver electronics are mounted in a separate cabinet. TNO is responsible for the system design & verification and OTA. Demcon has designed the BCDS and Control Electronics. West End is building the Baseplate and Cover Assembly.
We report on progress at the University of Hawaii on the integration and testing setups for the adaptive secondary mirror (ASM) for the University of Hawaii 2.2-meter telescope on Maunakea, Hawaii. We report on the development of the handling fixtures and alignment tools we will use along with progress on the optical metrology tools we will use for the lab and on-sky testing of the system.
We report on the development of a Beam Conditioning and Diagnostics System (BCDS) that will be employed in the Laser Projection System (LPS) of the Extremely Large Telescope (ELT) of ESO. This conference article provides an overview about the detailed design of the BCDS and it summarizes the work of the development phase of this project. To this end, design challenges, concepts and analysis results of the optical layout and the opto-mechanical concept are discussed.
An adaptive secondary mirror (ASM) is currently being developed for the UH2.2 telescope, consisting of a slumped 620mm convex aspherical facesheet, manipulated by 210 variable-reluctance actuators and supported on a silicon aluminium alloy support structure. The total power dissipation of the actuators is expected to be under 3 Watts. The ASM will weigh around 55kg, which is about 15kg lighter than the original passive secondary mirror (M2). We present the design, breadboarding activities and manufacturing status of this adaptive mirror. The project is on track for delivery of the ASM in Hawaii in the middle of 2021.
The preparations for the design and construction of the Extremely Large Telescope (ELT) are in full swing. One of the most critical components of this enormous telescope is its segmented primary mirror (M1), for which Netherlands Organisation for Applied Scientific Research (TNO), in collaboration with VDL, has designed the mechanical segment support (M1SS) in the period 2015-2016.1 This new M1SS design is based on the previous M1SS prototypes developed in 2009-2010,2 but includes several enhancements to further improve its performance. Specific design drivers were, among others, the serviceability of the M1SS, the introduced surface form error at the segment, and the increased target values for the structural eigenfrequencies. The latter defines the dynamic performance of the structure (including the ~178 kg segment), which needed to be validated experimentally.
From the latest M1SS design one engineering model (EM) and six qualification models (QMs) have been manufactured recently, which have tested intensively to verify their performance. This work will present the test procedure employed to validate the dynamic behavior, describe these dynamic tests and present their results in detail. During these tests a QM, including a dummy segment, has been placed on a heavy rigid structure and three accelerometers have been mounted across the assembly. The structure has then been excited on several strategic locations using a roving hammer technique,3 resulting in a large collection of frequency responses. From these, the eigenfrequencies and accompanying mode shapes have been estimated, resulting in accurate determination of the clocking, lateral, piston and tip/tilt modes of the structure. This allows for correct assessment of the dynamic performance and comparison to the design objectives and finite element model (FEM) predictions.
This procedure has been applied to two different QMs, but since each M1SS consists of a fixed frame (FF) and a removable segment assembly (SA), four different configurations have been tested. The results demonstrate compliance with the challenging design objectives for all QMs, and they show only small variations among the configurations, demonstrating that the dynamic performance of the M1SS design is very reproducible.
Described is the M1 segment support, as designed by TNO in the period 2015-2016. The design has significantly changed and improved compared to the earlier designs. During the period 2009-2010 prototypes for the primary mirror support of the E-ELT have been developed. These have been extensively tested by ESO. Design improvement were found to be necessary, especially in the field of manufacturability and maintainability. Furthermore, the technical performance had to improve in specific areas as well. This has evolved into a new specifications which have resulted in a new design for the segment support structure. The design rules that have led to the prototype design have been maintained but the implementation has been much improved. Also considerable improvement has been obtained with respect to the dynamic behavior. Accessibility and visibility on all parts and subsystems has changed such that everything is now clearly visible. Despite the increased performance no mass increase has been recorded meaning that more efficient use has been made of the material.
The active means to influence the segment shape by use of the warping harness has been completely redesigned. A very important quality that has been achieved is simplicity. Hence a minimum amount of components is used. Reliability and safety are other aspects that have been greatly improved compared to the prototypes. The design for the M1 segment support provides a solution that not only performs to specification but one that can be operated in a telescope environment, all 798 of them.
The mirror segments for the E-ELT and TLT are nearly equal in size and shape (hexagonal, 1.2 m over flat sides). They
are very thin (about 50 mm) compared to their size. Supporting these mirrors and obtaining high optical performance is a
challenge from design and manufacturing point of view. TNO has designed and build (together with VDL-ETG) three
identical prototypes for supporting the mirror segments of the E-ELT. These mirror segments vary in size. Hence the
gravity induced deformation of the mirror segments will vary from mirror to mirror segment when no measures are
taken. The paper will concentrate on the design and analysis of the design features within the support structure to
minimize the mirror deformation due to gravity. These features concern passive and active means to influence the mirror
segment shape and to compensate for deformation differences.
KEYWORDS: Photoacoustic tomography, Actuators, Mirrors, Prototyping, Control systems, Sensors, Virtual colonoscopy, Large telescopes, Linear filtering, Systems modeling
Segmented primary mirror telescopes require dedicated piston-tip-tilt actuators for optimal optical performance. Netherlands Organisation for Applied Scientific Research (TNO) has developed various prototypes of such actuators, in particular for the E-ELT. This paper presents the dynamics analysis and feedback control results for a specific two-stage prototype. First, the dynamics of the actuator in interconnection with the to-be-positioned mass has been analyzed, both using frequency response measurements and first principles modeling, resulting in a detailed understanding of the dynamic behavior of the system. Next, feedback controllers for both the fine and the coarse stage have been designed and implemented. Finally, the feedback-controlled actuator has been subjected to a realistic tracking experiment; the achieved results have demonstrated that the TNO actuator is able to suppress wind force disturbances and ground vibrations with more than a factor 103, down to 1.4 nm root mean square, which is compliant with the requirements.
Segmented primary mirror telescopes require dedicated piston-tip-tilt actuators for optimal optical performance. TNO has developed various prototypes of such actuators, in particular for the E-ELT. In this paper the control results of a specific two-stage prototype will be presented. First, the dynamics of the actuator in interconnection with the to-be-positioned mass has been analyzed, both using frequency response measurements and first principles modeling, resulting in a detailed understanding of the dynamic behavior of the system. Next, feedback controllers for both the fine and the coarse stage have been designed and implemented. Finally, the feedback controlled actuator has been subjected to a realistic tracking experiment; the results have demonstrated that the TNO actuator is able to suppress wind force disturbances and ground vibrations with more than a factor 103, down to 1.4 nm RMS, which is compliant with the requirements.
Adhesives are widely used in optomechanical structures for bonding optical components to their mounts. The main
advantage of using adhesives is the excellent strength to weight ratio. Adhesive bonding is seen as a desirable joining
technique as it allows for greater flexibility in design. A disadvantage of adhesives however is the limited dimensional
stability and loadability. To design stable optical mounts, accurate prediction of stresses and deformation is therefore
needed.
Adhesives show strong temperature and loading history dependent behavior. Viscoelastic material models are needed for
accurate prediction of stresses and strains in bonded joints. However, representative material data for adhesives is
difficult to find.
In this research, an experimental framework is build up to determine relevant mechanical properties of adhesives for
improving stress and deformation prediction. This paper shows the results of the characterization experiments and
modeling techniques. Also the implementation of material models in finite element code is briefly discussed. The
obtained models are used in the mount design in the EUCLID and TROPOMI programs as described in “Ultra stable isostatic
bonded optical mount design for harsh environments, J.A.C.M Pijnenburg et al” (this conference).
The mirror segments for the E-ELT and TLT are nearly equal in size and shape (hexagonal, 1.2 m over flat sides). They
are very thin (about 50 mm) compared to their size. Supporting these mirrors and obtaining high optical performance is a
challenge from design and manufacturing point of view. TNO has designed and build (together with VDL-ETG) three
identical prototypes for supporting the mirror segments of the E-ELT. These mirror segments vary in size. Hence the
gravity induced deformation of the mirror segments will vary from mirror to mirror segment when no measures are
taken. The paper will concentrate on the design and analysis of the design features within the support structure to
minimize the mirror deformation due to gravity. These features concern passive and active means to influence the mirror
segment shape and to compensate for deformation differences.
ESO is preparing to build the E-ELT which will be the largest optical telescope in the world. Its primary mirror will be
(see manuscript)39.3 m and will consist of nearly 1000 hexagonal segments of 1.2 meter width. Each segment is to be supported by the
same structure although the segments vary in size and shape, hence this will cause variable surface deflection. Its support
structure must guarantee a maximum surface form error of 30 nm rms independent of the segment orientation and
environmental temperature. Measures, such as mass balancing and active surface form compensation are needed to
compensate for these effects.
To meet the main optical and mechanical performance requirements, numerous FEM analysis runs have been made.
Dedicated software was used to calculate mirror deformations under mechanical loads and to express these in Zernike
modes. Especially this tool proved to be very powerful in proving that the optical surface form requirements could be
met for all different sized mirror segments.
The largest optical telescope in the world will be the E-ELT. Its primary mirror will be 42m in diameter. This mirror will
consist of 984 hexagonal segments that are all individually supported. Each mirror will be controlled in six DOF while
local shaping of the segments is provided by so called warping harnesses. These will correct for focus, astigmatism and
trefoil. Hence a mirror with an extreme diameter to thickness ratio of almost 30 is obtained. Its support structure must
guarantee a maximum surface form error of 30 nm rms independent of the segment attitude. Furthermore its stiffness to
mass ratio must allow natural frequencies of 50Hz or higher to obtain sufficient bandwidth for the actuators that control
the piston and tip/tilt of the segment.
Designing such structure is a challenge that has been successfully completed. Three prototypes have been built and are
about to be delivered to ESO. This paper discusses the main performance requirements and how they could be
transferred into an elegant structure design. Furthermore an overview will be given on the main performance parameters
in order to see whether the present design can be further optimized.
TNO, together with its partners Micromega and SRON, have designed a cryogenic scanning mechanism for use in the
SAFARI Fourier Transform Spectrometer (FTS) on board of the SPICA mission.
The optics of the FTS scanning mechanism (FTSM) consists of two back-to-back cat's-eyes. The optics are mounted on a
central "back-bone" tube which houses all the important mechatronic parts: the magnetic bearing linear guiding system, a
magnetic linear motor serving as the OPD actuator, internal metrology with nanometer resolution, and a launch lock.
A magnetic bearing is employed to enable a large scanning stroke in a small volume. It supports the optics in a free-floating
way with no friction, or other non-linearities, enabling sub-nanometer accuracy within a single stage with a
stroke of -4 mm to +31.5 mm.
Because the FTSM will be used at cryogenic temperatures of 4 Kelvin, the main structure and optics are all constructed
from 6061 Aluminum. The overall outside dimensions of the FTSM are: 393 x 130 x 125 mm, and the mass is 2.2 kg.
To measure the relative motions of GAIA's telescopes, the angle between the telescopes is monitored by an all Silicon
Carbide Basic Angle Monitoring subsystem (BAM OMA). TNO is developing this metrology system. The stability
requirements for this metrology system go into the pico meter and pico radian range. Such accuracies require extreme
measures and extreme stability.
Specific topics addressed are mountings of opto-mechanical components, gravity deformation, materials and tests that
were necessary to prove that the requirements are feasible. Especially mounting glass components on Silicon Carbide
and mastering the Silicon Carbide material proved to be a challenge.
ESO is building the Phase Referenced Imaging and Microarcsecond Astronomy (PRIMA) facility for the Very Large
Telescope Interferometer (VLTI) in Chile. PRIMA will enable interferometric imaging of very faint objects and high
precision astrometry with both Unit (UT) and Auxiliary (AT) telescopes. The PRIMA facility consists of four major
sub systems: Star Separators, Differential Delay Lines, Metrology and Fringe Sensor Units. TNO has developed the
PRIMA Star Separator (STS) subsystems for both the UT and AT telescopes. The STS separates the light of two
astronomical objects and feeds it into the long stroke delay line. The STS compensates for field rotation, stabilizes the
beam tip tilt and adjust the lateral and axial alignment of the pupil. Chopping and/or counter-chopping on the science
object or the guide star has also been implemented.
The European Southern Observatory (ESO) has started technology development for their next generation optical
telescope. Due to its ultra large collecting area, The European Extremely Large Telescope (E-ELT) will require a
paradigm shift in telescope design to keep the overall program cost at an acceptable level. The E-ELT will feature a 42
meter segmented primary mirror and will make extensive use of active and adaptive optics. Each primary mirror segment
will be supported by three actuators that control piston and tilt. TNO has developed a low cost nanopositioning actuator
(PACT) for the primary mirror segments. The actuators will be tested by IAC and ESO, with support from TNO, under
operational conditions in a Wind Evaluation Breadboard (WEB) at the Roque de Los Muchachos observatory in La
Palma.
To measure the relative motions of GAIA's telescopes, the angle between the telescopes is monitored by an all Silicon
Carbide Basic Angle Monitoring subsystem (BAM OMA). TNO is developing this metrology system. The stability
requirements for this metrology system go into the pico meter and pico radian range. Such accuracies require extreme
measures and extreme stability.
Specific topics addressed are mountings of opto-mechanical components, gravity deformation, materials and tests that
were necessary to prove that the requirements are feasible. Especially mounting glass components on Silicon Carbide
and mastering the Silicon Carbide material proved to be a challenge.
Inside the Star Separator system for the Unit Telescopes for the ESO-VLTi two mechanisms are implemented to compensate for the earth rotation that complicates the simultaneous and continuous observations of two stars. The function of the mechanisms is comparable to a de-rotator without the drawback of having to add three folding mirrors. One of the mechanisms is a scan mechanism with two independent orthogonal rotations. It makes use of flexures to eliminate play and to guarantee long term maintenance free operation. It also uses piezo stages for extreme accurate pointing (< 1μrad) for rotations of around 0.1 rad without hysteresis. The second mechanism realizes the optical star splitting being the primary function of the Star Separator.
By using guide stars astronomers are able to detect very faint celestial objects that would otherwise be invisible. This however necessitates the simultaneous observations of two stars at the same time. A system called Star Separator will add this functionality to the ESO-VLTi. In case of the Unit Telescopes of the VLT this system has to be implemented in the existing infra structure while simultaneously fulfilling many functional requirements. The major one being that each set of stars have different relative positions while the star images rotate due to the earth rotation.
About two years ago TNO Science and Industry started to design and build the Star Separators for the Auxiliary Telescopes for the ESO VLTi. Now the Unit Telescopes will also be equipped with Star Separators. Obviously the design is based on that for the Auxiliary Telescopes. However additional functionality had to be implemented to compensate for the effect of earth rotation because no de-rotator, as for the Auxiliary Telescopes, can be implemented.
The presentation will explain the functionalities of the Star Separator and how the opto-mechanical design is done.
In the framework of the Phase-Referenced Imaging and Micro-arcsecond Astrometry facility (PRIMA) developed for the Very Large Telescope Interferometer (VLTI), a sophisticated opto-mechanical system has been developed by TNO-TPD. It will be placed at the Coudé focus of the telescopes and will allow picking up two stars anywhere in a 2 arcmin field-of-view and collimating their light into two beams that will propagate through the rest of the interferometer toward the instrument. These Star Separator systems have a very high optical quality, fast and accurate pointing and chopping, independent high speed remote control of the beam tip-tilt and of the pupil position. They are very rigid, accurate mechanical systems non-sensitive to temperature variations The Star Separator systems are described in this paper.
The European Southern Observatory (ESO) is presently developing the PRIMA facility (Phase Referenced Imaging and Microarcsecond Astronomy). PRIMA will enable the observation of very faint celestial objects. A key element in this facility is the Star Separator that has been designed and is being built by TNO TPD in the Netherlands. This Star Separator makes it possible in principle to simultaneously observe two objects, the guide star and the faint object, with one telescope.
The separation of the faint object and the guide star is case dependent i.e. the separation between the two objects depends on the observation direction. This necessitates the use of a very accurate and stable pointing mechanism. The required repeatability of such mechanism is < 0.5 arcsec while its resolution should be < 0.1 arcsec. By using a statically determined fully elastic guiding and actuation mechanism in combination with closed loop driven piezos the realization of such mechanism was successful. A unique feature of the mechanism is that only the guiding/actuating mechanism needed to be designed. The rest is readily available from piezo suppliers. This makes this pointing mechanism a true low budget solution with excellent performance.
Measuring the wind speed from a satellite is not new. However measuring with great precision is by far not trivial. Various methods are available for that. A common method is to use the Doppler effect. A UV-laser on board of the satellite is used to "fire" to the earth atmosphere. Some photons will be reflected back to the satellite. Because of the speed of the particles in the air the photons will experience a small Doppler shift. Wind speeds of 1 m/s are hereby
equivalent to a wave length shift of 1 femtometer.
The paper presents the patented method of how to measure these small wavelength shifts without running into trouble concerning the mechanical design. It will understood that such instrument will be very sensitive to thermal variations (a challenging requirement was that a temperature change of 0.2° in 7 seconds was specified at the interface surfaces). The optical system makes use of a modified Michelson interferometer while the mechanical system automatically
compensates for thermal expansion effects. Originally the idea was to make a complete Zerodur structure to eliminate the thermal effects. However it appeared to be possible to use a titanium structure with certain elements made from invar and aluminium. No need to say that this reduced risk and cost of the instrument drastically.
The two most important characteristics of mechanical structures used in space or astronomy are accuracy and stability. Much time, money and energy is invested in achieving this. However because the resources are limited it is important to realize that the cost of an instrument is mainly fixed during the design process. Three factors can influence the design to a great extend which are: creativity, design rules and analysis. The most important tool for analysis nowadays is the computer. This one has become so powerful that even large structures are no problem to model in detail in FEM. It is even tempting to spend much time and effort in optimizing structures with the computer. However the basis for the best result is creativity during the design phase and the application of design rules. Although design rules are used extensively it is surprising to see that one of the most important ones is so little used.
This lecture is therefore especially about the rule to make structures static determined. The importance can be invaluable because in applying this rule there is no need for computers. Furthermore the application often results in non-conventional structures and it helps to clearly define the basics of the structure. It also provides simple qualitative results that help to make decisions concerning alternatives. Results of computer models can be verified on their validity.
Some interesting results of the application of this design rule will be shown. Examples are the linear guiding system for the VLTI delay line and the mount of mirrors. Also existing structures like e.g. the secondary mirror mount of the VLT will be analysed and it will be shown how they could have looked like when they would have been static determined.
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