The polarimetric and helioseismic imager instrument for the Solar Orbiter mission from the European Space Agency requires a high stability while capturing images, specially for the polarimetric ones. For this reason, an image stabilization system has been included in the instrument. It uses global motion estimation techniques to estimate the jitter in real time with subpixel resolution. Due to instrument requirements, the algorithm has to be implemented in a Xilinx Virtex-4QV field programmable gate array. The algorithm includes a 2-D paraboloid interpolation algorithm based on 2-D bisection. We describe the algorithm implementation and the tests that have been made to verify its performance. The jitter estimation has a mean error of 125 pixel of the correlation tracking camera. The paraboloid interpolation algorithm provides also better results in terms of resources and time required for the calculation (at least a 20% improvement in both cases) than those based on direct calculation.
Solar Orbiter is a joint mission of ESA and NASA scheduled for launch in 2020. Solar Orbiter is a complete and unique heliophysics mission, combining remote sensing and in-situ analysis; its special elliptical orbit allows viewing the Sun from a distance of only 0.28 AU, and - leaving the ecliptic plane - to observe the solar poles from a hitherto unexplored vantage point. One of the key instruments for Solar Orbiter’s science is the "Polarimetric and Helioseismic Imager" (PHI), which will provide maps of the solar surface magnetic fields and the gas flows on the visible solar surface. Two telescopes, a full disc imager, and a high resolution channel feed a common Fabry-Perot based tunable filter and thus allow sampling a single Fraunhofer line at 617.3 nm with high spectral resolution; a polarization modulation system makes the system sensitive to the full state of polarization. From the analysis of the Doppler shift and the magnetically induced Zeeman polarization in this line, the magnetic field and the line-of-sight gas motions can be detected for each point in the image. In this paper we describe the opto-mechanical system design of the high resolution telescope. It is based on a decentred Ritchey-Chrétien two-mirror telescope. The telescope includes a Barlow type magnifier lens group, which is used as in-orbit focus compensator, and a beam splitter, which sends a small fraction of the collected light onto a fast camera, which provides the error signals for the actively controlled secondary mirror compensating for spacecraft jitter and other disturbances. The elliptical orbit of the spacecraft poses high demands on the thermo-mechanical
stability. The varying size of the solar disk image requires a special false-light suppression architecture, which is briefly described. In combination with a heat-rejecting entrance window, the optical energy impinging on the polarimetric and spectral analysis system is efficiently reduced. We show how the design can preserve the diffraction-limited imaging performance over the design temperature range of -20°C to +60°C. The decentred hyperbolical mirrors require special measures for the inter-alignment and their alignment with respect to the mechanical structure. A system of alignment flats and mechanical references is used for this purpose. We will describe the steps of the alignment procedure, and the dedicated optical ground support equipment, which are needed to reach the diffraction limited performance of the telescope. We will also report on the verification of the telescope performance, both - in ambient condition - and in vacuum at different temperatures.
The tip/tilt driver is part of the Polarimetric and Helioseismic Imager (PHI) instrument for the ESA Solar Orbiter (SO), which is scheduled to launch in 2017. PPHI captures polarimetric images from the Sun to better understand our nearest star, the Sun. The paper covers an analog amplifier design to drive capacitive solid state actuator such ass piezoelectric actuator. Due to their static and continuous operation, the actuator needs to be supplied by high-quality, low-frequency, high-voltage sinusoidal signals. The described circuit is an efficiency-improved Class-AB amplifier capable of recovering up to 60% of the charge stored in the actuator. The results obtained after the qualification model test demonstrate the feasibility of the circuit with the accomplishment of the requirements fixed by the scientific team.
The Polarimetric and Helioseismic Imager (PHI) instrument is part of the remote instruments for the ESA Solar Orbiter
(SO), which is scheduled to launch in 2017. PHI captures polarimetric images from the Sun to better understand our
nearest star, the Sun. A set of images is acquired with different polarizations, and afterwards is processed to extract the
Stokes parameters. As Stokes parameters require the subtraction of the image values, in order to get the desired quality it
is necessary to have good contrast in the image and very small displacements between them. As a result an Image
Stabilization System (ISS) is required. This paper is focused in the behavior and the main characteristics of this system.
This ISS is composed of a camera, a tip-tilt mirror and a control system. The camera is based on a STAR1000 sensor that
includes a 10 bits resolution high-speed Analog-to-Digital Converter (ADC). The control system includes a Correlation
Tracking (CT) algorithm that determines the necessary corrections. The tip-tilt mirror is moved based on this corrections
to minimize the effects of the spacecraft (S/C) drift and jitter with respect to the Sun. Due to its stringent requirements, a
system model has been developed in order to verify that the required parameters can be satisfied. The results show that
the ISS is feasible, although the margins are very small.
A very high precision Image Stabilization System has been designed for the Solar Orbiter mission. The different components that have been designed are the Correlation Tracking Camera (CTC), Tip-Tilt controller (TTC) and the system control in order to achieve the specified requirements. For the CTC, in order to achieve the required resolution of 12 bits and reduced power consumption, we used an external ADC. For the TTC, a special focus has been dedicated to a 55 V linear regulator in a QUASI-LDO configuration and a Tip-Tilt driver in a transconductance amplifier architecture. Results show that the full system reaches an attenuation of 1/10th of a pixel at 10Hz. The TTC provides a high voltage span, enough slew-rate and the needed stability levels.
The GREGOR Fabry-Pérot Interferometer (GFPI) is one of three first-light instruments of the German 1.5-m GREGOR solar telescope at the Observatorio del Teide, Tenerife, Spain. The GFPI allows fast narrow-band imaging and postfactum image restoration. The retrieved physical parameters will be a fundamental building block for understanding the dynamic sun and its magnetic field at spatial scales down to ∼50 km on the solar surface. The GFPI is a tunable dual-etalon system in a collimated mounting. It is designed for spectrometric and spectropolarimetric observations between 530–860 nm and 580–660 nm, respectively, and possesses a theoretical spectral resolution of R≈250,000. Large-format, high-cadence charged coupled device detectors with sophisticated computer hard- and software enable the scanning of spectral lines in time-spans equivalent to the evolution time of solar features. The field-of-view (FOV) of 50″×38″ covers a significant fraction of the typical area of active regions in the spectroscopic mode. In case of Stokes-vector spectropolarimetry, the FOV reduces to 25″×38″. The main characteristics of the GFPI including advanced and automated calibration and observing procedures are presented. Improvements in the optical design of the instrument are discussed and first observational results are shown. Finally, the first concrete ideas for the integration of a second FPI, the blue imaging solar spectrometer, are laid out, which will explore the blue spectral region below 530 nm.
The GREGOR Fabry-P´erot Interferometer (GFPI) is one of three first-light instruments of the German 1.5-meter GREGOR
solar telescope at the Observatorio del Teide, Tenerife, Spain. The GFPI allows fast narrow-band imaging and post-factum
image restoration. The retrieved physical parameters will be a fundamental building block for understanding the dynamic
Sun and its magnetic field at spatial scales down to 50 km on the solar surface. The GFPI is a tunable dual-etalon system
in a collimated mounting. It is designed for spectropolarimetric observations over the wavelength range from 530–860 nm
with a theoretical spectral resolution of R ≈ 250,000. The GFPI is equipped with a full-Stokes polarimeter. Large-format, high-cadence CCD detectors with powerful computer hard- and software enable the scanning of spectral lines in time spans equivalent to the evolution time of solar features. The field-of-view of 50′′×38′′ covers a significant fraction of the typical area of active regions. We present the main characteristics of the GFPI including advanced and automated calibration and observing procedures. We discuss improvements in the optical design of the instrument and show first observational results. Finally, we lay out first concrete ideas for the integration of a second FPI, the Blue Imaging Solar Spectrometer, which will explore the blue spectral region below 530 nm.
The Photospheric and Helioseismic imager (PHI) on board of the ESA mission Solar Orbiter, to be launched in 2017,
will provide measurements with high polarimetric accuracy of the photospheric solar magnetic field at high solar
latitudes. The needed pointing precision requires an image stabilisation (ISS) to compensate for spacecraft jitter. The
image stabilisation system works as a correlation tracker with a high-speed camera and a fast steerable mirror. The optomechanical
and electronic design of the system will be presented.
A study is presented for the realization of the heat stop for the 4-m European Solar Telescope EST, whose
feasibility study will be completed in 2011. EST is an on-axis Gregorian telescope, equipped with a four-meter
diameter primary mirror and primary focal length of about six meters. The heat stop, positioned at the primary
focus, must be able to remove a heat load of 13 kW, while maintaining its surfaces very close to room temperature,
to avoid the onset of seeing. In order to remove the heat, three configurations have been taken into consideration:
1) a flat 45° inclined heat rejecter, 2) a 45° conical heat rejecter and 3) a heat trap (made of a conical heat
rejecter and a cylindrical heat absorber). All devices include an air removal system to avoid the formation of
The European Solar Telescope is a project for a 4-meter class telescope to be located in the Canary Islands. EST is
promoted by the European Association for Solar Telescopes (EAST). This is a consortium formed by a number of
research organizations from fifteen European countries (Austria, Croatia, Czech Republic, France, Germany, Hungary,
Italy, the Netherlands, Norway, Poland, Slovak Republic, Spain, Sweden, Switzerland, and United Kingdom). EST will
specialize in high spatial and temporal resolution using diverse instruments that can efficiently produce two-dimensional
spectropolarimetric information of the thermal, dynamic and magnetic properties of the plasma over many scale heights
in the solar atmosphere. In this contribution, the status of the development of the Design Study of EST is presented,
emphasizing the most important aspects of the optical design, mechanical structure, AO and MCAO systems for
wavefront correction, instruments and polarization analysis.
With the integration of a 1-meter Cesic primary mirror the GREGOR telescope pre-commissioning started. This is the
first time, that the entire light path has seen sunlight.
The pre-commissioning period includes testing of the main optics, adaptive optics, cooling system, and pointing system.
This time was also used to install a near-infrared grating spectro-polarimeter and a 2D-spectropolarimeter for the visible
range as first-light science instruments. As soon as the final 1.5 meter primary mirror is installed, commissioning will be
completed, and an extended phase of science verification will follow. In the near future, GREGOR will be equipped with
a multi-conjugate adaptive optics system that is presently under development at KIS.
The solar telescope EST is currently in the conceptual design phase. It is planned to be build on the Canary Islands until
end of the decade. It is specialized on polarimetric observations and will provide high spatial and spectral observations of
the different solar atmospheric layers.
The diameter of the primary mirror blank is 4.2m. Different types of mirror shapes were investigated with respect to
thermal and mechanical characteristics.
To remove the absorbed heat an air cooling system from the back side will be applied. Additional an air flushing system
will remove remaining warm air from the front side.
A major problem of a large open telescope will be the wind load. Results of the investigations will be shown. To achieve
optimal optical performance an active support system is planned. The primary mirror cell needs to be stiff enough to
support the primary mirror without deformation at strong wind in case of the open telescope option, but sufficient room
for the active support system and cooling system below the backside of the mirror is also required. Preliminary designs
and analysis results will be presented.
After suffering from serious problems in the course of the SiC 1.5m M1 manufacturing, the existing design of the M1,
it's cell and the associated mirror cooling system was investigated in terms of modification efforts to be compatible for a
different M1 substrate (Zerodur). The analysis included the system requirements, the M1 design, the M1 support system,
the M1 cooling system as well as the M1 cell.
The investigations resulting in a modified design of the above mentioned system. Driven by the choice of material,
different requirements became design driving factors. The consequences on the detail design of the M1 Mirror as well as
on the support system and the cooling system are presented.
The GREGOR Fabry-P´erot Interferometer (GFPI) is one of the first-light instruments of the 1.5-meter GREGOR solar
telescope currently being commissioned at Observatorio del Teide (OT), Tenerife, Spain. A spectral resolution of
R ≈ 250, 000 over the wavelength range from 530-860 nm can be achieved using a tunable dual etalon system. A high
spectral resolving power is needed to extract physical parameters (e.g., temperature, plasma velocity and the magnetic
field vector) from inversions of photospheric and chromospheric spectral lines. The GFPI is outfitted with a polarimeter,
which accurately measures the full Stokes vector. Precision polarimetry is facilitated by a calibration unit in the immediate
vicinity of GREGOR's secondary focus. The GFPI operates close to the diffraction limit of GREGOR, thus providing
access to fine structures as small as 60 km on the solar surface. The field-of-view (FOV) of 52" × 40" is sufficiently
large to cover significant portions of active regions. Large-format, high-cadence CCD detectors are an integral part of the
instrument to ensure that scans of spectral lines can be obtained in time spans corresponding to the evolution time scale of
solar phenomena such as granulation, evolving magnetic fields or dynamic chromospheric features. Besides describing the
technical features of the GFPI and providing a status report on commissioning the instrument, we will use two-dimensional
spectropolarimetric data obtained with the Vacuum Tower Telescope (VTT) at OT to illustrate GFPI's science capabilities.
The solar telescope GREGOR is under construction on the canary island Tenerife. A large effort was made to thermally
characterize the telescope during the design phase. The image quality is very sensitive to differences between ambient
and structure or main mirror temperatures. Tests with the GREGOR telescope structure and an integrated dummy mirror
were made to investigate the distribution and temporal behavior of the temperature of the telescope and main mirror.
The GREGOR telescope of the Teide Observatory will be upon start of operations the first ground-based telescope with
main optics made entirely of a silicon carbide composite material, namely, "carbon-fiber reinforced silicon carbide" or
"Cesic(r)," a product of ECM, Germany.
This paper describes the configuration and manufacturing of the GREGOR telescope's main optics: the primary (1.5 m),
secondary (0.42 m), and tertiary (0.35 m) mirrors.
The integration of the three main silicon carbide mirrors into the new 1.5 m solar telescope GREGOR at Izana on Tenerife, Spain is planned during 2006. We expect first light at the end of 2006. A progress report about integration of the optics and mechanics and planning of the commissioning phase of the telescope and post focus instruments will be presented at the meeting. The GREGOR telescope is build by a consortium of the Kiepenheuer Institut fur Sonnenphysik in Freiburg, the Astrophysikalische Institut Potsdam, the Institut fur Astronomie Gottingen and additional national and international Partners.
The new German solar 1.5 m telescope (GREGOR) will be equipped with an adaptive optic system. GREGOR has a relatively complicated optical scheme with small tolerances. We therefore have to expect certain aberrations due to misalignments and mechanical/optical imperfections. This is why the AO will play an important role as an auxiliary tool for telescope alignment from the very beginning of the commissioning phase. The paper will cover the alignment strategies taking advantage of the AO system.
The telescope structure including control system and the complete retractable dome of the new 1.5 m solar telescope GREGOR were assembled during 2004 at Izana on Tenerife, Spain. The GREGOR telescope is build by a consortium of the Kiepenheuer Institut fuer Sonnenphysik, the Astrophysikalische Institut Potsdam, the Institut fuer Astrophysik Goettingen and additional national and international Partners. Pointing, tracking and thermal tests were made to verify the proposed performance. The results of these tests and a progress report of the project will be presented.
GREGOR is the new 1.5 m solar telescope assembled on Tenerife, Spain, by the German consortium of the Kiepenheuer Institut fur Sonnenphysik, the Astronomischen Institut Potsdam, the Universitats-Sternwarte Gottingen and other national and international Partners. The refurbishment of the building is almost finished. The manufacturing of the telescope structure and the optics is still in progress. After the integration of the new complete retractable dome in July 2004 the telescope structure, optic and post focus instruments will be assembled during the rest of the year. First light is planned during May 2005.
The optical and thermal design of the 1.5 m solar telescope GREGOR is presented. The three first main mirrors of GREGOR will be made from Cesic, a silicon carbide material. One major constraint of large solar telescopes is the thermal load of the structure and the mirrors. The mirrors are heated by the solar radiation and introduce potentially harmful mirror seeing. GREGOR will use an active mirror cooling system and an open telescope structure to reduce these negative effects. A thermal analysis shows that the equilibrium temperature of the Cesic Mirror without active cooling is 6° above ambient temperature. Additional cooling will reduce the temperature difference of the optical surface and ambient air to below 0.1° K. With tempered airflow (about 2.5 m3/s per square meter mirror surface) the temperature gradient on the surface of the face sheet is less than 0.1°K. The telescope will have an open structure and a complete retractable dome to support mirror and structure cooling by wind.
The new 1.5 m high resolution telescope will be build up on the reused solar tower of the German 45 cm Gregory Coude Telescope at the Teide Observatory, Izana, Tenerife. The new telescope is a Gregory type with open telescope structure, alt-azimuth mount, complete retractable dome, and a pool of well established and new developed post focus instruments. An adaptive optics system provides the capability for diffraction limited observations at visible wavelengths and the polarimetry device in the secondary focus reduces the perturbation due to instrumental polarization in an efficient way. We describe the main optical characteristics and the focal plane instrumentation with respect to the latest status of the project.