TNO and partners at University of Hawai’i (UH), the NASA InfraRed Telescope Facility (IRTF), and the Center for Adaptive Optics (CfAO) at UCSC have been working on the realization of a 244 mm Adaptive Secondary Mirror (ASM) for the NASA IRTF called the IRTF-ASM-1. After successful performance testing of several laboratory prototypes, this project provided the first on-sky demonstration of TNO’s ASM technology at M2 location with an optically powered mirror shell.
The ASM is designed to retrofit the current passive M2. The ASM consists of a 244mm-diameter slumped convex aspherical mirror shell, manipulated by 36 hybrid variable reluctance actuators mounted on a light-weighted backing structure. The mirror shell is manufactured to the required accuracy at reduced cost through slumping by UCSC. The mirror shell is finished to final figure with Magnetorheological Finishing (MRF) by TNO before it was coated.
The ASM was shipped to UH in Hilo in February 2024, where performance was tested in the lab. The IRTF ASM saw ‘first light’ on telescope on the 23rd of April, already achieving stable closed-loop performance that was diffraction limited at the H-band (1.62 microns) with a long-exposure Strehl ratio of 35%-40% in sub-arcsecond seeing during the first night.
This paper will report on the status and first results of the IRTF ASM, including the latest status of the deformable mirror technology at TNO and an outlook to a second generation IRTF ASM with improved dynamic performance and increased actuator count.
This paper describes the preliminary design of the Adaptive Secondary Mirror (ASM) for the European Solar Telescope (EST), as designed by TNO. This ASM will contain 1950 actuators over an optical aperture of Ø80cm. The mirror-shell of this ASM is concave with a radius of 2.156m and has a thickness of 2.5mm. To cope with the high optical heat-load, the mirror shell will be cooled actively by means of conduction through a small (0.3mm) airgap between the mirror shell and the cooled SiC supporting structure. One of the unique characteristics of this ASM are the highly efficient actuators by TNO, delivering 30N Peak-to-Valley of linear force range within a packaging of Ø15x40mm. These actuators are based on the proven electromagnetic actuation principle by TNO but have been significantly redesigned to improve manufacturability and integration. The actuators are interfaced to the mirror shell via a stiff carbon fiber strut assembly and are designed to be replaceable during off-telescope maintenance. For overall alignment of the ASM a hexapod is used, while a faster tip-tilt stage is used to compensate for tip-tilt disturbances up to 20Hz bandwidth. The optical performance of the ASM under various environmental conditions has been extensively studied with Finite-Element-Analysis. To verify the performances of the actuator and the cooling systems, an actuator and thermal- breadboard are being constructed.
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 describe the current plans for developing an adaptive secondary mirror-based (ASM) adaptive optics (AO) system for WMKO. An ASM allows for the integration of AO into the telescope itself, broadening use of AO to include wide-field enhanced seeing, high contrast observations, and enabling future multi-conjugate upgrades. Such a system has the potential for enhancing a range of science objectives, improving the performance of both existing and future instrumentation at Keck. We describe a system level ASM-AO concept based on hybrid variable reluctance actuators, developed by TNO that simplifies the implementation of ASM’s.
Advancements in making high-efficiency actuators are an enabling technology for building the next generation of large-format deformable mirrors. The Netherlands Organization for Applied Scientific Research (TNO) has developed a new style of variable-reluctance actuator that requires approximately eighty times less power to operate as compared to the traditional style of voice-coil actuators. We present the performance results from laboratory testing of TNO's 57-actuator large-format deformable mirror from measuring the influence functions, linearity, hysteresis, natural shape flattening, actuator cross-coupling, creep, repeatability, and actuator lifetime. We measure a linearity of 99.4 ± 0.33% and hysteresis of 2.10 ± 0.23% over a stroke of 10 microns, indicating that this technology has strong potential for use in on-sky adaptive secondary mirrors (ASMs). We summarize plans for future lab prototypes and ASMs that will further demonstrate this technology.
TNO and industrial partners are developing a new type of adaptive secondary mirrors (ASM) for the University of Hawaii 2.2-meter telescope, consisting of 210 actuators, in an overall volume of ø63cm by 15cm height, and having an aspherical convex mirror-shell of 3,5mm thickness. The novel actuator technology enables a compact system without active cooling that can be retro-fitted within the same mass and volume of an existing passive secondary mirror. This development enables affordable and reliable ASM systems for the world’s larger telescopes as well as the many telescopes in the 2-4 meter class. This paper presents the overall design of this ASM and focusses on the performance analysis regarding its figure quality, its dynamical behavior and the related closed loop performances.
An Adaptive secondary mirror (ASM) allows for the integration of adaptive optics (AO) into the telescope itself. Adaptive secondary mirrors, based on hybrid variable reluctance (HVR) actuator technology, developed by TNO, provide a promising path to telescope-integrated AO. HVR actuators have the advantage of allowing mirrors that are sti↵er, more power ecient, and potentially less complex than similar, voice-coil based ASM’s. We are exploring the application of this technology via a laboratory testbed that will validate the technical approach. In parallel, we are developing conceptual designs for ASMs at several telescopes including the Automated Planet Finder Telescope (APF) and for Keck Observatory. An ASM for APF has the potential to double the light through the slit for radial velocity measurements, and dramatically improved the image stability. An ASM for WMKO enables ground layer AO correction and lower background infrared AO observations, and provides for more flexible deployment of instruments via the ability to adjust the location of the Cassegrain focus.
We are developing a new adaptive secondary mirror (ASM) for the University of Hawaii 2.2-meter telescope based on a novel and very efficient hybrid variable reluctance actuator developed by TNO. The actuator technology has broad implications on the ASM design and results in an ASM with a thicker facesheet, lower power dissipation, and simple controls. We report here preparations and plans for lab testing as well as on-sky demonstration of the ASM. The lab calibrations of the ASM influence functions will use a phase measuring deflectometry setup. The on-sky tests will include the evaluation of the use of the ASM for narrow field AO observations at visible through near infrared wavelengths, for very wide fields of view ground-layer adaptive optics, and for seeing limited non-adaptive optics observations.
TNO is developing Deformable Mirror (DM) technology, targeted for aberration correction in high-end Adaptive Optics (AO) applications in the field of lithography, astronomy, space and laser communication. The heart of this deformable mirror technology is a unique actuator technology based on the variable reluctance principle. The main advantages of this technology are the inherent high reliability, linearity (>99%), and high efficiency in terms of force per volume and unit power. Based on this actuator technology TNO built and tested a prototype DM, with 57 actuators, and a mirror diameter of Ø160mm. The test results show a highly linear actuator response, with less than 1% hysteresis over a stroke of 40μm. Atmospheric aberration correction has been shown with these DM’s in a free space laser-communication bread board. The same actuator technology is also used in the application of a highly compact Fine Steering Mirror (FSM), with an overall volume of Ø27x30mm, with a Ø20mm mirror. This FSM is targeted for satellite-based laser-communication terminals. Furthermore, a design study has been carried out to show the scalability of this technology towards large (~Ø1m to ~Ø3m) adaptive (secondary) mirrors with several hundreds, up to thousands of actuators. In this paper these different DM and FSM’s are discussed, and the latest test results obtained with the DM prototypes are presented.
In this paper we present a newly developed Fiber Optic measurement system, consisting of Fiber Bragg Grating (FBG) sensors and an FBG interrogator. The development of the measuring system is part of the PiezoElectric Assisted Smart Satellite Structure (PEASSS) project, which was initiated at the beginning of 2013 and is financed by the Seventh Framework Program (FP7) of the European Commission. Within the PEASSS project, a Nano-Satellite is being designed and manufactured to be equipped with new technology that will help keep Europe on the cutting edge of space research, potentially reducing the cost and development time for more accurate future sensor platforms including synthetic aperture optics, moving target detection and identification, and compact radars. After on ground testing the satellite is planned to be launched at the end of 2015.
Within the satellite, different technologies will be demonstrated on orbit to show their capabilities for different in-space applications. For our application the FBG interrogator monitors the structural and thermal behaviour of a so called “smart panel”. These panels will enable fine angle control and thermal and vibration compensation in order to improve all types of future Earth observations, such as environmental and planetary mapping, border and regional imaging. The Fiber Optic (FO) system in PEASSS includes four FBG strain sensors and two FBG temperature sensors.
The 3 channel interrogator has to have a small footprint (110x50x40mm), is low cost, low in mass and has a low power consumption. In order to meet all these requirements, an interrogator has been designed based on a tunable Vertical-Cavity Surface-Emitting Laser (VCSEL) enabling a wavelength sweep of around 7 nm. To guarantee the absolute and relative performance, two reference methods are included internally in the interrogator. First, stabilized reference FBG sensors are used to obtain absolute wavelength calibrations. This method is used for the temperature sensors in the system, which will be measured with an accuracy of ±1°C. Second, the strain sensors will be used to monitor deformation of piezo actuators (bimorph plates) in a way that temperature compensation is not required. Using FBGs on top and on the bottom of the plates, relative wavelength differences are measured. In order to have a high accuracy, inside the interrogator a fiber interferometer is used to track the wavelength change. Using this reference technology we are able to measure the (relative) wavelength difference between two FBGs well below 0.1pm.
An active tilt mirror mechanism, meant for correction of the constellation breathing of the evolved Laser Interferometer Space Antenna, has been designed and realized. Its open-loop performance has been characterized in both time and frequency domain. Based on this, a feedback controller has been designed and the resulting closed-loop performance has been assessed. Up to what is measurable in a normal lab environment, these experiments demonstrate compliance with the extreme pointing jitter requirement, even when using the internal encoder as feedback sensor.
Stefan Kuiper, Niek Doelman, Evert Nieuwkoop, Ton Overtoom, Tjeerd Russchenberg, Martijn van Riel, Justin Wildschut, Max Baeten, Jet Human, Helma Spruit, Sanneke Brinkers, Matthew Maniscalco
Over the last decade TNO has developed a deformable mirror concept using electromagnetic actuators with the main advantages of having very low non-linearity and hysteresis, low power consumption, and high inherent reliability of the actuators. TNO recently started a program to redesign the electromagnetic actuator to improve the actuator efficiency, allowing higher actuator force per volume and per wattage. The increased actuator efficiency gives improvement of the DM performance in terms of dynamical performance, actuation range, and power dissipation. With this technology various applications in the fields of ground-based astronomy and space missions are targeted.
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