Mechanical Group


 The Mechanical Group serves three areas within R&D:

  • Industrial: mechanical development for mass production of large sensor systems
  • Instrumental: mechanical development for one-off and small series instruments
  • Production and Prototyping: production of parts for optical and radio domain including assembly

The work ranges from development of instruments for the biggest optical telescope E-ELT to a revolutionary tile for SKA radio telescope made of polyester foil (as used for flower packaging) and EPS (Expanded Polystyrene, like used in any ordinary package).
Challenging factor in the design of large sensor systems are the low-cost/high volume requirements. A close and good interaction with a variety of industries is crucial.
Challenging factors in the design of infrared optical instruments are the cryogenic working temperature, the stability, the high precision of design and accuracy of mounting.
Very important here is the close cooperation of the mechanical designers with the antenna designers, the optical designers and the workshop engineers. Only this close cooperation results in state of the art astronomical instruments at the edge of the technical possibilities.

Some Highlights
The Mechanical Group does the mechanical design and production, production control of:
  • Radio telescopes based on sensor networks like LOFAR and SKA-pathfinders
  • Optical instruments for astronomical space projects like MIRI an infrared camera and spectrometer for the James Webb Space Telescope
  • Optical instruments for astronomical telescopes like X-shooter for the European Southern Observatory
  • Radio instruments for astronomy like the Multi Frequency Front End in the Westerbork telescope
  • Also advising small enterprises for example in design and manufacture of skates, horse shoes, wooden toys
Personnel and management

The staff of the Mechanical Group of ASTRON includes instrument engineers, instrument designers, industrial designers and CAD/CAM engineers with technical and management capabilities.

Section head:
Group members:                          

Johan Pragt
Raymond van den Brink
Marco Drost
Hiddo Hanenburg
Jan Idserda
Sjouke Kuindersma
Niels Tromp


The Mechanical Group in more detail  

Knowledge and techniques

The Mechanical Group is using state of the art design technologies enabling the design and construction of complex scientific instruments. ASTRONs capabilities are supported by modern design and engineering tools as Pro-Engineer 3D-CAD, Pro-Mechanica finite element package and thermal analysis simulation, FloEFD.Pro, Engineering Fluid Dynamics for analyzing heat and flow and MasterCAM for computer aided manufacturing. For prototyping and small production activities a state of the art machinery park is available.

Modern design philosophies are used, like:

  • Methodological design approach, build on guided "out of the box" thinking processes.
  • Design choices based on functional decision processes
  • Design and constructions are based on "Koster principles" where applicable
  • Design tools like Design for Assembly and Design for Manufacturing are applied

Current work are several developments for the Square Kilometer Array, the upgrade of the Westerbork Radio Telescope by the APERTIF focal plane array antenna and a variety of optical instruments for the ESO Very Large Telescope and the coming Extremely Large Telescope.

Our advanced lightweighting technology now is available for licensing.
It may serve as an example of applying cutting-edge technology.

Near future steps

The Mechanical Group is continuously conducting research for the Square Kilometer Array and will build a large demonstrator in the coming years. Important here is the need for a low cost station design and innovative signal distribution. The policy is to publish the progress achieved in mechanical developments. Several ELT projects are running and new projects are coming.


Characteristics of the Mechanical Group are:

  • Development, Design and Prototyping, Serving the astronomical community in wavelength ranging from 300 nanometer to 30 meters
  • Strong interaction with internal production and optical design group.
  • CAD, simple modeling up to complete complex instrument assemblies.
  • FEM, static and dynamic FEM analysis.EFD, thermal and flow analysis.
  • Cryogenic and vacuum design.
  • Troubleshooting in different fields outside ASTRON:
    • From CNC-introduction to 5-axis simultaneous design- and production optimization.
    • From horseshoe production advice to space qualified optical instrumentation.
  • Product design and Finite Element Modeling support (FEM)
  • Project management
  • Running project from study phase to turn-key delivery
  • Implementation support on:
    • 5-axis simultaneous design and production
    • CNC machine selection

CNC turning
Turn diameter:           

CNC milling
Table dim:

Table dim:

Schaublin 125 CCN D
Fanuc 20-T

Hermle C40
x800, y700, z600mm
18000 rpm, A+25°/-110°

Fehlmann Picomax 54
Heidenhain 310
x500, y260, z490mm
9000 rpm


General design philosophy

In general the design philosophy is about thinking in functions and parameters and with these being able to be creative in an analytical way. This is done by using creative processes like brainstorming and by continuously reviewing ideas with colleagues. Thinking in function modules makes is possible to design in a modular way. A flexible design can easily be changed if showstoppers arise in one of the modules. This leads to a relatively short and straightforward design process and shorter time-to-market.
In particular within the mechanical group design for production is an important aspect of the process. Together with the extraordinary environment, like vacuum and cryogenics, in which the instruments should function this is leading.
Mechanical stresses can cause positional displacements and can also deform the optical surfaces. This is very important for cryogenic instruments. During cool down the instruments shrinks several millimeters. Mounting stress free special lugs, will prevent any stress around the optical surface while the position will not be influenced. Weight reduction is desired for reducing the cool-down and warm-up time of the instrument and to optimize the structural stability. To increase mechanical stability, the parts whenever possible, are made out of one single piece of material.

Research activities

The mechanical group also performs a lot of research activities. The main research will be found in the field of technology and material development to serve the development of the Square Kilometer Array. For instance low cost potential printed circuit board materials were characterized. Dielectric properties like dielectric constant and dielectric losses are determined. Several types of plastics were evaluated on radio signal transparency for the development of the radômes for the SKA, LOFAR and various demonstration models. The group is constantly looking for alternative and innovative production methods to apply conductive materials on cheap carriers for signal distribution. Also cryogenic research is done to find low friction cryogenic suitable materials and mechanisms.

Completed projects
MFFE (Multi Frequency Front End)

The Westerbork Synthesis Radio Telescope is one of the leading radio astronomical instruments in the world. Since the operations started in 1970 numerous modifications have been made to improve and extend the instrument. With the MFFE (Multi Frequency Front End) another major upgrade has been made on the WSRT. This front end gained in frequency bands then previously used, and those are instantaneous available in a compact package mounted at the focal point of the parabolic disc. The user can choose between eight frequency bands ranging from 250 MHz to 8600 MHz. Some feed-arrangements and two independent local oscillator systems allows to observe in two frequency bands simultaneously.

LFFE (Low Frequency Front End)

An addition to the MFFE to receive even lower frequencies a set of four low frequency dipole antennas were added. Special attention in the mechanical design was given to a lightweight construction for moving the antennas between observing and stowed position. The stowed antennas should have no effect on the observations in other bands. The result of this work heavily relied on cooperation of the Antenna Design and Mechanical Design Groups, as well as cooperation with the Astronomy Group for telescope tests and evaluation. The resulting design is presented in the figures, showing the final antenna configuration of four dipoles for two polarizations and the mechanisms to move the individual antennas in and out of the observing position.

LOFAR LBA (Low Band Antenna)

For the astronomy application LOFAR is a radio interferometric array consisting of many low-cost antennae. There are two distinct antennae types: the Low Band Antennae (LBA) operating between 10 and 80 MHz and the High Band Antennae (HBA) operating between 120 and 240 MHz. The antennae are organized in aperture array stations. LBAs sample the frequency range between 10 and 80 MHz and consist of simple dual polarization (X and Y) droop dipoles above a conducting ground plane with the wires at an angle of 45 degrees with the ground. The field of view of an LBA extends to the horizon. The Mechanical Group made it possible to produce the LBA out of common low cost available part reducing the cost for this enormous large telescope.

LOFAR HBA (High Band Antenna)

LOFAR HBAs sample the frequency range between 120 to 240 MHz. They are assemblies (tiles) of 16 bowtie shaped dual dipole antennae arranged in a 4x4 grid with a spacing of 1.25 m between the dipoles. Each HBA tile is equipped with an analogue radio frequency (RF) beamformer, which limits the field of view of an individual tile to approximately 30 degrees full-width at half-maximum (FWHM) at a frequency of 150 MHz. Over the past years the mechanical group was involved in the development of the HBA. Several project delivered designs and prototypes for the instrument. After most important design issues were cleared a final design tender procedure was started. This resulted in a final design and production in cooperation with Autonational (IJLST, The Netherlands)


The European demonstrator is denoted as the Electronic MultiBeam Radio Astronomy Concept Evaluation (EMBRACE) which is planned as a 200 square meter aperture array with multiple independent Field of View (FoV) capabilities. The main objectives of EMBRACE are to demonstrate the technical and scientific potential of the aperture array concept using a low cost phased array station with the essential Square Kilometer Array (SKA) functionality in combination with the Westerbork Synthesis array.
The EMBRACE project is embedded in a bigger framework project known as SKADS (SKA Design Studies). The SKADS Consortium, consisting of 32 institutes from around the globe, has submitted a research proposal to the European Commission under the Sixth Framework Programme (FP6) to further develop and demonstrate the Aperture Array concept suitable for the SKA, to develop and select the enabling technologies and to arrive at a system design for the SKA.

A small team of mechanical engineers was responsible for the design of the EMBRACE front-end and the EMBRACE radôme. For the front-end a modular design was made which contains square meters of Vivaldi antennae. The instrument is divided into two parts. 144m2 is placed in the Netherlands at close to the WSRT, another 80m2 is placed in France close to the Radio Observatoire de Paris. The design of EMBRACE was a first step towards the mass fabrication for the Square Kilometer Array. During the design phase special attention was paid to low cost and large numbers.
The radômes are constructed out of EPS (Expanded Polystyrene) which is a common low cost packaging material. It is coated with a polyurethane film to gain in stiffness and to protect the EPS for sun load and rain.


FLOWPAD3 stands for Foilbased LOW cost PAcman Differential Dualpolarized Demonstrator. It is the first differential Vivaldi designed and built at ASTRON. The demonstrator consists of antennas, a low noise differential amplifier stage and a beamformer network.
The innovative concept is an outcome of PACMAN research. Some challenging features are implemented to get a feeling with possible low-cost SKA solutions. On a polyester foil the pattern is printed with silver ink. With electro-chemical plating a copper layer is grown onto the silver layer. The technology is called Flexible Antenna Plating and has been developed by MECO Equipment Engineers. For the housing of the demonstrator a low cost foam (EPS, normally used as packaging material) is used which, after research, turned out to be very suitable for radio astronomy purposes.
The FLOWPAD3 concept was also used for a larger focal plane array in the UK at the Jodrell Bank Observatory.


In the ASTRON R&D lab a photonic phased array receiver demonstrator tile is constructed and tested. This work is part of the photonic phased array technology R&D at ASTRON. In the demonstrator, which is being developed in a collaborative project with the University of Twente and Lionix BV, the received RF signals will be processed in the optical domain with an instantaneous bandwidth between 500 MHz - 1.5 GHz.
For the transfer of the RF signals within the tile, each radiator is equipped with an optical analog link. In the current phase of the project, the components of these links (DFB laser, intensity modulator and optical amplifier) are placed on the main tile PCB and tested.
An EMBRACE tile was redesigned and modified to make the photonic tests possible. A frame was designed for use in the antenna measuring chamber. The housing was almost completely made out of transparent material give the engineer the opportunity to see all hardware. A cooling systems was designed in order the get the optical fibers as stable as possible.


The VISIR instrument for ESO's Very Large Telescope VLT is a thermal-infrared imager/spectrometer under development by a Saclay/Dwingeloo consortium.
The spectrometer design comprises two arms, one with low-order gratings for the low and medium resolutions and one with a largedouble-sided echelle grating for high resolutions.
This is a complex optical instrument with tenths of optical units. An extra complicating factor is : the whole instrument operates at cryogenic temperatures (25K) in a vacuum and rotates with the movements of the telescope. Nevertheless no adjustments are applied; all parts are positioned by production accuracy to guarantee a stable, simple and reliable instrument.
The opto-mechanical design for the spectrometer is based upon the assumption of one material (baseline choice: aluminium alloy 6061-T651), both for all reflective optical elements and for mountings and structures. Since the optical design is purely reflective, this ensures strictly homologous behavior of the whole optical train as a function of temperature. The only cases where temperature-dependent optical scale variations have to be considered are the few refractive components (filters, grisms, FP-etalons) and the grating constants.

In 2009 the colleagues working on the optical instruments formed the NOVA Optical / IR Group which is still hosted by ASTRON in Dwingeloo. More information on the NOVA Optical / IR Group can be found here.

MIDI (MID-INFRARED INTERFEROMETRIC INSTRUMENT) is used on ESO’s Very large Telescope at Cerro Paranal, Chile. At mid-infrared wavelengths it combines the light of two VLT telescopes interferometrically to produce images of unprecedented resolution. This will make it possible to study very fine detail in compact astronomical sources, such as proto-planetary disks around stars.
This instrument is operated at 40K. A special cryogenic slider and positioning system was developed by the Mechanical Design Group.

In 2009 the colleagues working on the optical instruments formed the NOVA Optical / IR Group which is still hosted by ASTRON in Dwingeloo. More information on the NOVA Optical / IR Group can be found here.


SPIFFI - SPectrometer for Infrared Faint Field Imaging - was developed at the Max Planck Institute for Extraterrestrische Physik (MPE) in Garching (Germany), in a collaboration with the Nederlandse Onderzoekschool Voor Astronomie (NOVA) in Leiden and the Netherlands Foundation for Research in Astronomy (ASTRON), and ESO.
For IR observations SPIFFI is cooled extremely. (77K) A special lens mount was designed and manufactured by the Mechanical Design Group to compensate for the difference in shrinkage between the glass lens and the aluminum housing to prevent the lens from misalignment or even breaking during cool-down.
ASTRON designed and produced the 2K camera for the SINFONI project for the VLT.

In 2009 the colleagues working on the optical instruments formed the NOVA Optical / IR Group which is still hosted by ASTRON in Dwingeloo. More information on the NOVA Optical / IR Group can be found here.


Since 1999, various concept studies for the instrument have been carried out sponsored by ESA and NASA. The earlier studies had 4-6 modules in the instrument, with two modules each for the camera and spectroscopy channels to accommodate different plate scales and cope with the different background levels.
MIRI is an infrared camera and spectrometer for the James Webb Space Telescope (JWST). MIRI will have three advantages over other infrared instruments. Firstly, its location in space will remove the blocking and large background noise effects of the atmosphere which limit ground-based telescopes. Secondly, MIRI will be cooled to a very low temperature, thus reducing the emission from the telescope and greatly improving its sensitivity. Thirdly, the JWST will provide a far larger mirror than any other infrared space telescope, giving improved angular resolution and high sensitivity for weak objects.
For optimal performance and reduction of thermal background emission, the optics should be as cold as possible ( <24 K), with an enclosure temperature of ~18 K and the detectors themselves cooled to < 7.5 K. This will be accomplished by a solid-hydrogen cryostat, to be procured by ESA.

In 2009 the colleagues working on the optical instruments formed the NOVA Optical / IR Group which is still hosted by ASTRON in Dwingeloo. More information on the NOVA Optical / IR Group can be found here.


X-shooter is a new high-efficiency spectrograph observing the complete spectral range of 300-2500 nm in a single exposure, with a spectral resolving power R>5000. The instrument will be located at the Cassegrain focus of one of the VLT UTs and consists of three spectrographs: UV, VIS and Near-IR. The instrument was built in en European consortium in which ASTRON designed and produced the Near-IR arm.
Bare aluminium mirrors are produced and polished to optical quality to preserve high shape accuracy at cryogenic conditions. The cryogenic collimator and dispersion boxes, on which the optical components are mounted, feature integrated baffles for improved stiffness and integrated leaf springs to reduce tension on optical components, thereby challenging 5 axis simultaneous CNC milling capabilities. ASTRON Extreme Light Weighting is used for a key component to reduce the flexure of the cryogenic system; some.

In 2009 the colleagues working on the optical instruments formed the NOVA Optical / IR Group which is still hosted by ASTRON in Dwingeloo. More information on the NOVA Optical / IR Group can be found here.

ALMA Mirrors

High on the Chajnantor plateau in the Chilean Andes, the European Southern Observa­tory (ESO), together with its international partners, is building the Atacama Large Millimeter/submillimeter Array, ALMA - a state-of-the-art telescope to study light from some of the coldest objects in the Universe. This light has a typical wavelength of around a millimeter, lying between infrared light and radio waves in the electromagnetic spec­trum, and is therefore known as millimeter and submillimeter radiation. ASTRON wasn't involved in the design of the mechanical parts, but because of its extraordinary production capabilities the production of complicated mechanical parts was outsourced at ASTRON.

Current projects

APERTIF stands for APERture Tile In Focus and is the system which is going to upgrade the Westerbork Synthesis Radio Telescope (WSRT). APERTIF aims to increase the field of view of the WSRT with a factor 25. This remarkable performance gain is achieved by placing a receiver array in the focus of each parabolic dish of the WSRT, instead of the single receiver element that the current system employs. Such an array in the focus of a dish is called, for obvious reasons, a focal-plane array (FPA).
Several prototypes of APERTIF have been designed, produced and installed.
The first APERTIF-prototype (called DIGISTIF) is mounted in one of the WSRT dishes in 2007. In early 2008, this was used to make a spectroscopic observation of the nearby galaxy M31. Just before the end of 2008, the team managed to obtain the first interferometric results between the APERTIF prototype, DIGISTIF, and other WSRT dishes.
At this time already the third prototype is installed and is under evaluation. During the optimization of the different prototypes a huge progress was made on the stability, easy in assembly and accessibility of the system. Change in the mechanical design made it possible to increase the stability and accessibility.
At this time astronomical institutes from different countries show huge interest in the design of APERTIF.


With a collecting area of about one square kilometer, the SKA will be about ten times more sensitive than the largest single dish telescope (305 m diameter) at Arecibo (Puerto Rico), and fifty times more sensitive than the currently most powerful interferometer, the Expanded Very Large Array (EVLA, at Socorro/USA). The SKA will continuously cover most of the frequency range accessible from ground, from 70 MHz to 10 GHz (corresponding to wavelengths of 3 cm to 4 m) in the first and second phases, later to be extended to at least 25 GHz (1.2 cm). The third major improvement is the enormously wide field of view, ranging from 200 square degrees at 70 MHz to at least 1 square degree at 1.4 GHz. The speed to survey a large part of the sky, particularly at the lower frequencies, will hence be ten thousand to a million times faster than what is possible today.
Technical developments around the world are being coordinated by the SKA Science and Engineering Committee and its executive arm, the SKA Program Development Office. The technical work itself is funded from national and regional sources, and is being carried out via a series of verification programs. The global coordination is supported by funds from the European Commission under a program called PrepSKA, the Preparatory Phase for SKA, whose primary goals are to provide a costed system design and an implementation plan for the telescope by 2012.
Dense aperture arrays comprise up to millions of receiving elements in planar arrays on the ground which can be phased together to point in any direction on the sky. Due to the large reception pattern of the basic elements, the field of view can be up to 250 square degrees. Dense aperture arrays have been the subject of a European Commission-funded design study named SKA Design Study (SKADS) which has resulted in a prototype array of 140 square meters area (EMBRACE).

On the basis of results from the earlier SKADS R&D program and drawing on results from current low frequency arrays, in particular LOFAR, the consortium is now engaged in the next development step. The Aperture Array Verification Program (AAVP) involves 15 participants from nine EU nations, Australia and substantional input from South Africa and the US.
AAVP is developing and selecting the necessary technologies which will enable construction of the SKA radio telescope beginning around 2015 and which will result in the required performance at an affordable cost.
This is an important part of the EC-FP7 PrepSKA project led by the SKA Program Development Office (SPDO) and is under the umbrella of the European SKA Consortium (ESKAC)


Our Technology Transfer Program makes it easy for you to develop new products, processes and strategies with three different ways of commissioning research and consultancy.
Our AstroTec Holding BV can partner up with your business; undertake synergistic joint ventures or license unique and cutting edge technologies to your company, enabling you to introduce new innovations in your sector.
For information contact ASTRONs Bureau of Technology Transfer (BTT)


"Design of a Low-Loss(-Noise) Tapered Slot Phased Array Feed for Reflector Antennas"
"Aperture Array Frontend Design for Production"
"Piezo-driven adjustment of a cryogenic detector"
"Herontwerp en optimalisatie van het mechanische deel van High Band Antenna"
"Towards the Design of a Low-Cost Wideband Demonstrator Tile for SKA"
"A scalable pick-off technology for multi-object instruments"    
"Polarization and optical aperture synthesis: the problem and a solution"
"CHEOPS/ZIMPOL: a VLT instrument study for the polarimetric search of scattered light from extrasolar planets"
"Calibrating SPHERE, the exo-planet imager for the VLT"
"SPHERE: the VLT planet imager in the post FDR phase"
"Smart instrument technologies to meet extreme instrument stability requirements"
"Directly polished lightweight aluminum mirror"
"Piezo-driven adjustment of a cryogenic detector"
"Opto-mechanical design for transmission optics in cryogenic IR instrumentation"
"X-shooter near infra-red spectrograph cryogenic design"
"SPHERE ZIMPOL: overview and performance simulation"
"SPHERE: a planet finder instrument for the VLT"
"SPEX: an in-orbit spectropolarimeter for planetary exploration"
"SixPak: a wide-field IFU for the William Herschel Telescope"
"METIS: the mid-infrared E-ELT imager and spectrograph"
"MATISSE: perspective of imaging in the mid-infrared at the VLTI"
"Cryogenic wheel mechanisms for the Mid-Infrared Instrument (MIRI) of the James Webb Space Telescope (JWST) "
"ESPRIT: a study concept for a far-infrared interferometer in space"
"System design and analysis of the exo-planet imaging camera and spectrograph (EPICS) for the European ELT"
"EPICS: the exoplanet imager for the E-ELT"
"The SPHERE exoplanet imager: status report at PDR"
"Mid-infrared instrumentation for the European Extremely Large Telescope"
"JWST-MIRI spectrometer main optics qualification and verification"
"JWST-MIRI spectrometer main optics alignment and tolerancing philosophy"
"Observational capabilities and technical solutions of a thermal and MIR instrument at E-ELT"
"A scalable pick-off technology for multi-object instruments"
"X-shooter UV- to K-band intermediate-resolution high-efficiency spectrograph for the VLT: status report at the final design review"
"X-shooter near-IR spectrograph arm realisation"
"The optical design of the X-shooter for the VLT"
"X-shooter near-IR spectrograph arm: design and manufacturing methods"
"VISIR two years after its installation at the VLT"
"SPHERE: A planet finder instrument for the VLT"
"MIDIR/T-OWL: the thermal/mid-IR instrument for the E-ELT"
"Applied systems engineering in a small scale project"
"The MIRI medium resolution spectrometer for the James Webb Space Telescope"
"GLAS: engineering a common-user Rayleigh laser guide star for adaptive optics on the William Herschel "TelescopeESPRIT: a space interferometer concept for the far-infrared"
"The EPICS project for the European Extremely Large Telescope: outcome of the Planet Finder concept study for OWL"
"MIRI-JWST spectrometer main optics opto-mechanical design and prototyping"
"Astron extreme lightweighting"
"X-shooter: UV-to-IR intermediate-resolution high-efficiency spectrograph for the ESO VLT"
"PRIMA astrometry operations and software"
"Positioning of optical elements in the cryogenically cooled mid-infrared instrument MIRI for the James Webb Space Telescope"
"Exploratory Submm Space Radio-Interferometric Telescope (ESPRIT) "
"Final design of VISIR: the mid-infrared imager and spectrometer for the VLT"
"Calibration of VISIR, the VLT mid-infrared imager/spectrometer"
"Characterization in the laboratory of VISIR, the mid-infrared imager and spectrometer for the VLT"
"MIDI scientific and technical observing modes"
"Realization of the MIDI cold optics"
"Cryomechanisms for positioning the optical components of the mid-infrared instrument (MIRI) for NGST"
"Optical Design for the 5-28μm NGST MIRI spectroscopy channel (MIRI-S) "
"10-μm interferometry on the VLTI with the MIDI instrument: a preview"
"Cold optics of MIDI: the mid-infrared interferometric instrument for the VLTI"
"VISIR: the mid-infrared imager and spectrometer for the VLT"

Design: Kuenst.    Development: Dripl.    © 2014 ASTRON