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 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.
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.
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 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.
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.
Sunrise is a balloon-borne solar observatory dedicated to the investigation of key processes of the magnetic field and the plasma flows in the lower solar atmosphere. The observatory operates in the stratosphere at an altitude of around 37 km in order to avoid image degradation due to turbulence in the Earth’s atmosphere and to access the UV range. The third science flight of Sunrise will carry new instrumentation which samples the solar spectrum over a broad wavelength domain from the UV to the near IR and covers an extended height range in the solar atmosphere. A key feature of the Sunrise UV Spectropolarimeter and Imager (SUSI) operating between 309 nm and 417 nm, is its capability to simultaneously record a large number of spectral lines. By combining the spectral and polarization information of many individual lines with different formation heights and sensitivities, the accuracy and the height resolution of the inferred atmospheric parameters can be significantly increased. The spectral bands of SUSI are selected one at a time by rotating a diffraction grating with respect to a fixed polarimetry unit. The spatial and spectral field of view on the 2k x 2k cameras is 59” and 2.0 - 2.3 nm, respectively. A further innovation is the numerical restoration of the spectrograph scans by means of synchronized 2D context imaging, a technique that has recently produced impressive results at ground-based solar observatories.
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.
KEYWORDS: Space operations, Ultraviolet radiation, Space telescopes, Telescopes, Space telescopes, Solar processes, Sensors, X-ray imaging, Plasma, Ions, Magnetosphere
The Solar Ultraviolet Imaging Telescope (SUIT) is an instrument onboard the Aditya-L1 spacecraft, the first dedicated solar mission of the Indian Space Research Organization (ISRO), which will be put in a halo orbit at the Sun-Earth Langrage point (L1). SUIT has an off-axis Ritchey–Chrétien configuration with a combination of 11 narrow and broad bandpass filters which will be used for full-disk solar imaging in the Ultravoilet (UV) wavelength range 200-400 nm. It will provide near simultaneous observations of lower and middle layers of the solar atmosphere, namely the Photosphere and Chromosphere. These observations will help to improve our understanding of coupling and dynamics of various layers of the solar atmosphere, mechanisms responsible for stability, dynamics and eruption of solar prominences and Coronal Mass ejections, and possible causes of solar irradiance variability in the Near and Middle UV regions, which is of central interest for assessing the Sun’s influence on climate.
This paper describes the flight control software of the wave-front correction system that flew on the 2009 science
flight of the Sunrise balloon telescope. The software discussed here allowed fully automated operations of the
wave-front sensor, communications with the adaptive optics sub-system, the pointing system, the instrument
control unit and the main telescope controller. The software was developed using modern object oriented
analysis and design techniques, and consists of roughly 13.000 lines of C++ code not counting code written for
the on-board communication layer. The software operated error free during the 5.5 day flight.
The Exo-Planets Imaging Camera and Spectrograph (EPICS), is the Planet Finder Instrument concept for the European
Extremely Large Telescope (ELT). The study made in the frame of the OWL 100-m telescope concept is being up-dated
in direct relation with the re-baselining activities of the European Extremely Large Telescope.
SUNRISE is an international project for the development, construction, and operation of a balloon-borne solar telescope with an aperture of 1 m, working in the UV/VIS spectral domain. The main scientific goal of SUNRISE is to understand the structure and dynamics of the magnetic field in the atmosphere of the Sun. SUNRISE will provide near diffraction-limited images of the photosphere and chromosphere with an unpredecented resolution down to 35 km on the solar surface at wavelengths around 220 nm. The focal-plane instrumentation consists of a polarization sensitive spectrograph, a Fabry-Perot filter magnetograph, and a phase-diverse filter imager working in the near UV. The first stratospheric long-duration balloon flight of SUNRISE is planned in Summer 2009 from the swedish ESRANGE station. SUNRISE is a joint project of the german Max-Planck-Institut fur Sonnensystemforschung (MPS), Katlenburg-Lindau, with the Kiepenheuer-Institut fur Sonnenphysik (KIS), Freiburg, Germany, the High-Altitude Observatory (HAO), Boulder, USA, the Lockheed-Martin Solar and Astrophysics Lab. (LMSAL), Palo Alto, USA, and the spanish IMaX consortium. In this paper we will present an actual update on the mission and give a brief description of its scientific and technological aspects.
SUNRISE is a balloon-borne solar telescope with an aperture of 1m, working in the UV/VIS optical domain. The main scientific goal of SUNRISE is to understand the structure and dynamics of the magnetic field in the atmosphere of the Sun. SUNRISE will provide diffraction-limited images of the photosphere and chromosphere with an unpredecented resolution down to 35km at wavelengths around 220nm. Focal-plane instruments are a spectrograph/polarimeter, a Fabry-Perot filter magnetograph, and a filter imager. The first stratospheric long-duration balloon flight of SUNRISE over Antarctica is planned in winter 2006/2007. SUNRISE is a joint project of the Max-Planck-Institut fur Sonnensystemforschung (MPS), Katlenburg-Lindau, with the
Kiepenheuer-Institut für Sonnenphysik (KIS), Freiburg, the High-Altitude Observatory (HAO), Boulder, the Lockheed-Martin Solar
and Astrophysics Lab. (LMSAL), Palo Alto, and the Instituto de Astrofisica de Canarias, La Laguna, Tenerife.
In this paper we will present an overview on the mission and give a
description of the instrumentation, now, at the beginning of the
hardware construction phase.
Four different designs for a polarising beamsplitter (BS) are compared under the aspect of their suitability for high resolution solar spectropolarimetry. The four designs are: A solution based on a Savart-plate, two air-spaced Wollaston prisms, and a glass beamsplitter cube with polarisation sensitive dielectric coating, and a single Wollaston prism inside a focal reducer. Using ray-tracing algorithms these beamsplitters are characterised with the help of spot diagrams for the two light paths of orthogonal polarisation.
It is shown that with the current spectrographs employed in solar research, the differential optical aberrations introduced by the beamsplitter are negligible, thanks to the slow F/#-ratio of existing solar telescopes and the limited field of view of currently used array detectors. It will, however, be demonstrated that with the new generation of large solar telescopes care must be exercised on the design of the beamsplitter. This will be shown using an example spectrograph, as could be used in a new 1.5 m class solar telescope.
New highly sensitive polarimetric instruments and observational techniques allow to observe weak polarization signals in the visible and near ultraviolet part of the solar spectrum. Many of these signals are caused by scattering processes in the upper photosphere and lower chromosphere and thus reflect the thermodynamics of these layers. Also magnetic fields lead to polarization via the Zeeman effect or alter scattering polarization via the Hanle effect. The observation of both effects requires highest polarimetric sensitivity in combination with very high spectral resolution. In the following the instrumental and observational concepts are described. Special emphasis will be given to the Zurich Imaging Polarimeter II, which is now sensitive to the near ultraviolet part of the solar spectrum down to the atmospheric cut-off around 300 nm thanks to the use of a special CCD sensor, which for the first time combines so-called 'open electrod structure' with fast on-chip demodulation in the kHz regime.
The design of an achromatic polarisation modulator is presented. The modulator is based on a combination of three electrically switchable non-achromatic ferroelectric liquid crystal retarders. The design follows the idea by Pancharatnam who first introduced suitable achromatic combinations of crystal retarders. We combined three ferroelectric liquid crystal retarders to create an electrically switchable achromatic halfwave plate which can be used in the
spectral range from 400 nm to 750 nm. Different designs are theoretically modeled and compared under the aspects of their individual response to temperature fluctuations and useful wavelength range. First results of laboratory tests are presented to experimentally evaluate the feasibility of the concept.
Sunrise is a light-weight solar telescope with a 1 m aperture for spectro-polarimetric observations of the solar atmosphere. The telescope is planned to be operated during a series of long-duration balloon flights in order to obtain time series of spectra and images at the diffraction-limit and to study the UV spectral region down to ~200 nm, which is not accessible from the ground.
The central aim of Sunrise is to understand the structure and dynamics of the magnetic field in the solar atmosphere. Through its interaction with the convective flow field, the magnetic field in the solar photosphere develops intense field concentrations on scales below 100 km, which are crucial for the dynamics and energetics of the whole solar atmosphere. In addition, Sunrise aims to provide information on the structure and dynamics of the solar chromosphere and on the physics of solar irradiance changes.
Sunrise is a joint project of the Max-Planck-Institut fuer Aeronomie (MPAe), Katlenburg-Lindau, with the Kiepenheuer-Institut fuer Sonnenphysik (KIS), Freiburg, the High-Altitude Observatory (HAO), Boulder, the Lockheed-Martin Solar and Astrophysics Lab. (LMSAL), Palo Alto, and the Instituto de Astrofi sica de Canarias, La Laguna, Tenerife. In addition, there are close contacts with associated scientists from a variety of institutes.
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