SUNRISE III is the third flight of the international stratospheric balloon project Sunrise. The SUNRISE III carries a 1-meter aperture Gregorian telescope and provides a unique platform to perform seeing-free observations at UV-Visible-IR wavelengths. It is designed in the framework of NASA's long-duration balloon program to be launched at ESRANGE, Sweden, and to fly to Canada at float altitudes of 35 – 37 km. For the third flight, the post-focal instrumentation was extensively upgraded to enhance spectro-polarimetric capability; SUSI for 309 – 417 nm, TuMag for 525 nm and 517 nm, and SCIP for 765 – 855 nm. The gondola was also renewed to achieve stable pointing to a target on the solar surface. The team led by NAOJ provided SCIP through international collaboration with the Spanish and German teams. SUNRISE III was launched in July 2022 but was terminated because of a hardware problem. The telescope and instruments were successfully recovered and will be flown again in June 2024.
The ESA mission Solar Orbiter was successfully launched in February 2020. The Photospheric and Helioseismic Imager (PHI) provides measurements of the photospheric solar magnetic field and line of sight velocities at high solar latitudes with high polarimetric accuracy. The required pointing precision is achieved by an image stabilisation system (ISS) that compensates for spacecraft jitter. The ISS consists of a high-speed correlation tracker camera (CTC) and a fast steerable tip-tilt mirror operated in closed loop. We will present the results of the calibration measurements and performance tests from ground measurements, during commissioning and science phase. In addition, the correlation tracker was used to directly measure the pointing stability of the satellite.
The Sunrise Chromospheric Infrared spectroPolarimeter (SCIP) has been developed for the third flight of the Sunrise balloon-borne stratospheric solar observatory. The aim of the SCIP is to reveal the evolution of three-dimensional magnetic fields in the solar photosphere and chromosphere using spectropolarimetric measurements with a polarimetric precision of 0.03% (1σ). Multiple lines in the 770 and 850 nm wavelength bands are simultaneously observed with two 2 k × 2 k CMOS cameras at a frame rate of 31.25 Hz. Stokes profiles are calculated onboard by accumulating the images modulated by a polarization modulation unit, and then compression processes are applied to the two-dimensional maps of the Stokes profiles. This onboard data processing effectively reduces the data rate. SCIP electronics can handle large data formats at high speed. Before the implementation into the flight SCIP electronics, a performance verification of the onboard data processing was performed with synthetic SCIP data that were produced with a numerical simulation modeling the solar atmospheres. Finally, we verified that the high-speed onboard data processing was realized on ground with the flight hardware using images illuminated by natural sunlight or an LED light.
The ESA/NASA Solar Orbiter space mission has been successfully launched in February 2020. Onboard is the Polarimetric and Helioseismic Imager (SO/PHI), which has two telescopes, a High Resolution Telescope (HRT) and the Full Disc Telescope (FDT). The instrument is designed to infer the photospheric magnetic field and line-of-sight velocity through differential imaging of the polarised light emitted by the Sun. It calculates the full Stokes vector at 6 wavelength positions at the Fe I 617.3nm absorption line. Due to telemetry constraints, the instrument nominally processes these Stokes profiles onboard, however when telemetry is available, the raw images are downlinked and reduced on ground. Here the architecture of the on-ground pipeline for HRT is presented, which also offers additional corrections not currently available on board the instrument. The pipeline can reduce raw images to the full Stokes vector with a polarimetric sensitivity of 10−3 · Ic or better.
SUNRISE III mission is a one-meter aperture telescope onboard a balloon within NASA Long Duration Balloon Program. Three post-focus instruments are used for studying the Sun’s dynamics and magnetism, among which the Tunable Magnetograph (TuMag) is a tunable imaging spectropolarimeter. TuMag is a diffraction-limited imager, a high sensitivity polarimeter (< 10-3 ), and a high-resolution spectrometer ( ~ 65 mÅ). It will be able to study solar magnetic fields at high spatial resolution (~100 km on the solar surface). It will make images of the solar surface magnetic field after measuring the state of polarization of light within three selected spectral lines: the Fe I lines at 525.02 nm and 525.06 nm, and the Mg I b2 line at 517.27 nm. It will be sensitive to the solar vector magnetic fields and line-of-sight velocities, in the photospheric and chromospheric layers. TuMag will be the first solar magnetograph onboard an aerospace platform with the capability of tuning the solar line to be observed. In this paper the TuMag end-to-end tests carried out during the verification phase are described. These tests are performed to characterize and calibrate the instrument. Specifically, they determine the polarimetric and spectroscopic performances of the instrument as well as the image quality. The availability of a singular facility, an ISO6 clean room with a coelostat on the building roof, allowed the use of solar light during the verification campaign. This was key to a complete instrument verification due to the unique spectroscopic and polarimetric characteristics of solar light.
The High Resolution Telescope (HRT) of the Polarimetric and Helioseismic Imager (SO/PHI) on-board the Solar Orbiter mission (SO) provides near diffraction limited observations of the solar surface. The HRT Refocus Mechanism (HRM) allows for acquiring calibration data in flight which are used in post processing on ground to estimate the image quality of SO/PHI-HRT data products and its dependence on the SO-Sun distance. Our aim is to characterise the wavefront aberrations in the optical path of SO/PHI-HRT and consequently the image quality in the focal plane of the telescope. We use calibration data taken during the Near Earth Commissionning Phase (NECP) and the second Remote Sensing Check-out Window (RSCW2) of Solar Orbiter’s Cruise Phase (CP). In particular, we apply a Phase Diversity (PD) analysis to estimate the low-order wavefront aberrations. The restoration with the retrieved Point Spread Function (PSF) from the PD analysis increases the RMS contrast of the solar granulation in the visible continuum from 4 % to 10−11%.
KEYWORDS: Data processing, Calibration, Image processing, Space operations, Polarimetry, Demodulation, Polarization, Sensors, Magnetism, Imaging systems
A frequent problem arising for deep space missions is the discrepancy between the amount of data desired to be transmitted to the ground and the available telemetry bandwidth. A part of these data consists of scientific observations, being complemented by calibration data to help remove instrumental effects. We present our solution for this discrepancy, implemented for the Polarimetric and Helioseismic Imager on-board the Solar Orbiter mission, the first solar spectropolarimeter in deep space. We implemented an on-board data reduction system that processes calibration data, applies them to the raw science observables, and derives science-ready physical parameters. This process reduces the raw data for a single measurement from 24 images to five, thus reducing the amount of downlinked data, and in addition, renders the transmission of the calibration data unnecessary. Both these on-board actions are completed autonomously.
Polarization measurements of the solar chromospheric lines at high precision are key to present and future solar telescopes for understanding magnetic field structures in the chromosphere. The Sunrise Chromospheric Infrared spectroPolarimeter (SCIP) for Sunrise III is a spectropolarimeter with a polarimetric precision of 0.03 % (1 σ). The key to high-precision polarization measurements using SCIP is a polarization modulation unit that rotates a waveplate continuously at a constant speed. The rotating mechanism is a DC brushless motor originally developed for a future space mission, and its control logic was originally developed for the sounding rocket experiment CLASP. Because of our requirement on a speed of rotation (0.512 s/rotation) that was 10 times faster than that of CLASP, we optimized the control logic for the required faster rotation. Fast polarization modulation is essential for investigating the fine-scale magnetic field structures related to the dynamical chromospheric phenomena. We have verified that the rotation performance can achieve the polarization precision of 0.03 % (1 σ) required by SCIP and such a significant rotation performance is maintained under thermal vacuum conditions by simulating the environment of the Sunrise III balloon flight. The waveplate was designed as a pair of two birefringent plates made of quartz and sapphire to achieve a constant retardation in a wide wavelength range. We have confirmed that the retardation is almost constant in the 770 nm and 850nm wavelength bands of SCIP under the operational temperature conditions.
The Sunrise balloon-borne solar observatory carries a 1 m aperture optical telescope and provides us a unique platform to conduct continuous seeing-free observations at UV-visible-IR wavelengths from an altitude of higher than 35 km. For the next flight planned for 2022, the post-focus instrumentation is upgraded with new spectro- polarimeters for the near UV (SUSI) and the near-IR (SCIP), whereas the imaging spectro-polarimeter Tunable Magnetograph (TuMag) is capable of observing multiple spectral lines within the visible wavelength. A new spectro-polarimeter called the Sunrise Chromospheric Infrared spectroPolarimeter (SCIP) is under development for observing near-IR wavelength ranges of around 770 nm and 850 nm. These wavelength ranges contain many spectral lines sensitive to solar magnetic fields and SCIP will be able to obtain magnetic and velocity structures in the solar atmosphere with a sufficient height resolution by combining spectro-polarimetric data of these lines. Polarimetric measurements are conducted using a rotating waveplate as a modulator and polarizing beam splitters in front of the cameras. The spatial and spectral resolutions are 0.2" and 2 105, respectively, and a polarimetric sensitivity of 0.03 % (1σ) is achieved within a 10 s integration time. To detect minute polarization signals with good precision, we carefully designed the opto-mechanical system, polarization optics and modulation, and onboard data processing.
The Sunrise Chromospheric Infrared spectroPolarimeter (SCIP) is a near-IR spectro-polarimeter instrument newly designed for Sunrise III, which is a balloon-borne solar observatory equipped with a 1 m optical telescope. To acquire high-quality 3D magnetic and velocity fields, SCIP selects the two wavelength bands centered at 850 nm and 770 nm, which contain many spectrum lines that are highly sensitive to magnetic fields permeating the photosphere and chromosphere. To achieve high spatial and spectral resolution (0.21 arcsec and 2 × 105), SCIP optics adopt a quasi-Littrow configuration based on an echelle grating and two high-order aspheric mirrors. Using different diffraction orders of the echelle grating, dichroic beam splitter, and polarizing beam-splitters, SCIP can obtain s- and p-polarization signals in the two wavelength bands simultaneously within a relatively small space. We established the wavefront error budget based on tolerance analysis, surface figure errors, alignment errors, and environmental changes. In addition, we performed stray light analysis, and designed light traps and baffles needed to suppress unwanted reflections and diffraction by the grating. In this paper, we present the details of this optical system and its performance.
The Sunrise Chromospheric Infrared spectroPolarimeter (SCIP) is a near-IR spectro-polarimeter instrument newly designed for Sunrise III, a balloon-borne solar observatory with a 1-m diameter telescope. In order to achieve the strict requirements the SCIP wavefront error, it is necessary to quantify the errors due to environmen- tal effects such as gravity and temperature variation under the observation conditions. We therefore conducted an integrated opto-mechanical analysis incorporating mechanical and thermal disturbances into a finite element model of the entire SCIP structure to acquire the nodal displacements of each optical element, then fed them back to the optical analysis software in the form of rigid body motion and surface deformation fitted by polynomials. This method allowed us to determine the error factors having a significant influence on optical performance. For example, no significant wavefront degradation was associated with the structural mountings because the optical element mounts were well designed based on quasi-kinematic constraints. In contrast, we found that the main factor affecting wavefront degradation was the rigid body motions of the optical elements, which must be mini- mized within the allowable level. Based on these results, we constructed the optical bench using a sandwich panel as the optical bench consisting of an aluminum-honeycomb core and carbon fiber reinforced plastic skins with a high stiffness and low coefficient of thermal expansion. We then confirmed that the new opto-mechanical model achieved the wavefront error requirement. In this paper, we report the details of this integrated opto-mechanical analysis, including the wavefront error budgeting and the design of the opto-mechanics.
The SUNRISE Chromospheric Infrared spectroPolarimeter (SCIP) is a balloon-borne long-slit spectrograph for SUNRISE III to precisely measure magnetic fields in the solar atmosphere. The scan mirror mechanism (SMM) is installed in the optical path to the entrance slit of the SCIP to move solar images focused on the slit for 2-dimensional mapping. The SMM is required to have (1) the tilt stability better than 0.035″ (3σ) on the sky angle for the diffraction-limited spatial resolution of 0.2″, (2) step response shorter than 32 msec for rapid scanning observations, and (3) good linearity (i.e. step uniformity) over the entire field-of-view (60″x60″). To achieve these performances, we have developed a flight-model mechanism and its electronics, in which the mirror tilt is controlled by electromagnetic actuators with a closed-loop feedback logic with tilt angles from gap-based capacitance sensors. Several optical measurements on the optical bench verified that the mechanism meets the requirements. In particular, the tilt stability achives better than 0.012″ (3σ). Thermal cycling and thermal vacuum tests have been completed to demonstrate the performance in the vacuum and the operational temperature range expected in the balloon flight. We found a small temperature dependence in the step uniformity and this dependence will be corrected to have 2-demensional maps with the sub-arcsec spatial accuracy in the data post-processing.
KEYWORDS: Data processing, Image processing, Calibration, Image sensors, Digital imaging, Space operations, Field programmable gate arrays, Polarimetry, Sensors
The extension of on-board data processing capabilities is an attractive option to reduce telemetry for scientific instruments on deep space missions. The challenges that this presents, however, require a comprehensive software system, which operates on the limited resources a data processing unit in space allows. We implemented such a system for the Polarimetric and Helioseismic Imager (PHI) on-board the Solar Orbiter (SO) spacecraft. It ensures autonomous operation to handle long command-response times, easy changing of the processes after new lessons have been learned and meticulous book-keeping of all operations to ensure scientific accuracy. This contribution presents the requirements and main aspects of the software implementation, followed by an example of a task implemented in the software frame, and results from running it on SO/PHI. The presented example shows that the different parts of the software framework work well together, and that the system processes data as we expect. The flexibility of the framework makes it possible to use it as a baseline for future applications with similar needs and limitations as SO/PHI.
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.
In this paper we present a novel FPGA implementation of the Consultative Committee for Space Data Systems Image Data Compression (CCSDS-IDC 122.0-B-1) for performing image compression aboard the Polarimetric Helioseismic Imager instrument of the ESA’s Solar Orbiter mission. This is a System-On-Chip solution based on a light multicore architecture combined with an efficient ad-hoc Bit Plane Encoder core. This hardware architecture performs an acceleration of ~30 times with respect to a software implementation running into space-qualified processors, like LEON3. The system stands out over other FPGA implementations because of the low resource usage, which does not use any external memory, and of its configurability.
In this contribution we present a multi-core system-on-chip, embedded on FPGA, for real-time data processing, to be used in the Daniel K. Inouye Solar Telescope (DKIST). Our system will provide “quick-look” magnetic field vector and line-of-sight velocity maps to help solar physicists to react to specific solar events or features during observations or to address specific phenomena while analyzing the data off line. The stand-alone device will be installed at the National Solar Observatory (NSO) Data Center. It will be integrated in the processing data pipeline through a software interface, and is competitive in computing speed to complex computer clusters.
In this work we propose a multiprocessor architecture to reach high performance in floating point operations by using radiation tolerant FPGA devices, and under narrow time and power constraints. This architecture is used in the PHI instrument that carries out the scientific analysis aboard the ESA’s Solar Orbiter mission. The proposed architecture, in a SIMD flavor, is aimed to be an accelerator within the Data Processing Unit (it is composed by a main Leon processor and two FPGAs) for carrying out the RTE inversion on board the spacecraft using a relatively slow FPGA device – Xilinx XQR4VSX55–. The proposed architecture squeezes the FPGA resources in order to reach the computational requirements and improves the ground-based system performance based on commercial CPUs regarding time and power consumption. In this work we demonstrate the feasibility of using this FPGA devices embedded in the SO/PHI instrument. With that goal in mind, we perform tests to evaluate the scientific results and to measure the processing time and power consumption for carrying out the RTE inversion.
Liquid-crystal variable retarders (LCVRs) are an emergent technology for space-based polarimeters, following its
success as polarization modulators in ground-based polarimeters and ellipsometers. Wide-field double nematic
LCVRs address the high angular sensitivity of nematic LCVRs at some voltage regimes. We present a work
in which wide-field LCVRs were designed and built, which are suitable for wide-field-of-view instruments such
as polarimetric coronagraphs. A detailed model of their angular acceptance was made, and we validated this
technology for space environmental conditions, including a campaign studying the effects of gamma, proton
irradiation, vibration and shock, thermo-vacuum and ultraviolet radiation.
The use of Liquid Crystal Variable Retarders (LCVRs) as polarization modulators are envisaged as a promising novel
technique for space instrumentation due to the inherent advantage of eliminating the need for conventional rotary
polarizing optics hence the need of mechanisms. LCVRs is a mature technology for ground applications; they are wellknow,
already used in polarimeters, and during the last ten years have undergone an important development, driven by
the fast expansion of commercial Liquid Crystal Displays.
In this work a brief review of the state of the art of imaging polarimeters based on LCVRs is presented. All of them are
ground instruments, except the solar magnetograph IMaX which flew in 2009 onboard of a stratospheric balloon as part
of the SUNRISE mission payload, since we have no knowledge about other spaceborne polarimeters using liquid crystal
up to now. Also the main results of the activity, which was recently completed, with the objective to validate the LCVRs
technology for the Solar Orbiter space mission are described. In the aforementioned mission, LCVRs will be utilized in
the polarisation modulation package of the instruments SO/PHI (Polarimetric and Helioseismic Imager for Solar Orbiter)
and METIS/COR (Multi Element Telescope for Imaging and Spectroscopy, Coronagraph).
In this work, it is described the Imaging Magnetograph eXperiment, IMaX, one of the three postfocal instruments of
the Sunrise mission. The Sunrise project consists on a stratospheric balloon with a 1 m aperture telescope, which will fly
from the Antarctica within the NASA Long Duration Balloon Program.
IMaX will provide vector magnetograms of the solar surface with a spatial resolution of 70 m. This data is relevant
for understanding how the magnetic fields emerge in the solar surface, how they couple the photospheric base with the
million degrees of temperature of the solar corona and which are the processes that are responsible of the generation of
such an immense temperatures.
To meet this goal IMaX should work as a high sensitivity polarimeter, high resolution spectrometer and a near
diffraction limited imager. Liquid Crystal Variable Retarders will be used as polarization modulators taking advantage of
the optical retardation induced by application of low electric fields and avoiding mechanical mechanisms. Therefore, the
interest of these devices for aerospace applications is envisaged. The spectral resolution required will be achieved by
using a LiNbO3 Fabry-Perot etalon in double pass configuration as spectral filter before the two CCDs detectors. As well
phase-diversity techniques will be implemented in order to improve the image quality.
Nowadays, IMaX project is in the detailed design phase before fabrication, integration, assembly and verification.
This paper briefly describes the current status of the instrument and the technical solutions developed to fulfil the
scientific requirements.
The SUNRISE balloon project is a high-resolution mission to study solar magnetic fields able to resolve the critical scale of 100 km in the solar photosphere, or about one photon mean free path. The Imaging Magnetograph eXperiment (IMaX) is one of the three instruments that will fly in the balloon and will receive light from the 1m aperture telescope of the mission. IMaX should take advantage of the 15 days of uninterrupted solar observations and the exceptional resolution to help clarifying our understanding of the
small-scale magnetic concentrations that pervade the solar surface. For this, IMaX should act as a diffraction limited imager able to carry out spectroscopic analysis with resolutions in the 50.000-100.000 range and capable to perform polarization measurements. The solutions adopted by the project to achieve all these three demanding goals are explained in this article. They include the use of Liquid Crystal Variable Retarders for the polarization modulation, one
LiNbO3 etalon in double pass and two modern CCD detectors that allow for the application of phase diversity techniques by slightly changing the focus of one of the CCDs.
The description of the Imaging Magnetograph eXperiment
(IMaX) is presented in this contribution. This is a magnetograph
which will fly by the end of 2006 on a stratospheric balloon,
together with other instruments (to be described elsewhere).
Especial emphasis is put on the scientific requirements to
obtain diffraction-limited visible magnetograms, on the optical
design and several constraining characteristics, such as the
wavelength tuning or the crosstalk between the Stokes
parameters.
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