Solar-C (EUVST) is the next Japanese solar physics mission to be developed with significant contributions from US and European countries. The mission carries an EUV imaging spectrometer with slit-jaw imaging system called EUVST (EUV High-Throughput Spectroscopic Telescope) as the mission payload, to take a fundamental step towards answering how the plasma universe is created and evolves and how the Sun influences the Earth and other planets in our solar system. In April 2020, ISAS (Institute of Space and Astronautical Science) of JAXA (Japan Aerospace Exploration Agency) has made the final down-selection for this mission as the 4th in the series of competitively chosen M-class mission to be launched with an Epsilon launch vehicle in mid 2020s. NASA (National Aeronautics and Space Administration) has selected this mission concept for Phase A concept study in September 2019 and is in the process leading to final selection. For European countries, the team has (or is in the process of confirming) confirmed endorsement for hardware contributions to the EUVST from the national agencies. A recent update to the mission instrumentation is to add a UV spectral irradiance monitor capability for EUVST calibration and scientific purpose. This presentation provides the latest status of the mission with an overall description of the mission concept emphasizing on key roles of the mission in heliophysics research from mid 2020s.
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.
Solar adaptive optics (AO) systems are developed at the 60cm domeless solar telescope in the Hida Observatory, Japan.
An AO system currently used has a deformable mirror with high-speed 97 electromagnetic actuators and a Shack-
Hartmann wavefront sensor with a 10x10-microlens array and 4000fps-CMOS camera. Its control frequency is about
1100-1400 Hz, and hence the -3dB cutoff frequency of the system is theoretically above 100 Hz. In parallel to
developing the system, a new full-scaled AO system is designed to be applicable to various observations, such as highdispersion
spectroscopy and simultaneous wide-range spectroscopy. The new system will work as classical AO at first.
The details of the current system, observational results using it, and the design of the new AO system are described.
A solar adaptive optics system for a high-dispersion spectrograph is developed at the 60 cm domeless solar telescope of
the Hida Observatory in Japan. Details of its optical setup are described for implementing a scanning slit spectroscopy
with wavefront correction. A wavefront sensor used in the system is specified and a technique of reducing computational
cost in wavefront sensing is also described. In solar observations, the improvement of contrast in images obtained with
the adaptive optics system was demonstrated when a sunspot was used as a target of wavefront sensing.
In order to perform precise and high time cadence magnetic field measurement across the solar surface, the Tandem
Fabry-Perot filter imaging spectro-polarimeter for the Solar Magnetic Activity Research Telescope (SMART) is revised.
By using the CCD with moderate frame rate of 30fps, full Stokes vectors on the field-of-view 320"x240" can be obtained
at 4 wavelengths around FeI6302 line within about 15s. The optical performance of the Tandem Fabry-Perof filters is
investigated by using the spectrograph at the Domeless Solar Telescope at Hida Observatory. The test results show the
full-width-half-maximum (FWHM) of the tandem filters is about 0.017nm over the 60mm clear aperture is achieved. The
system is developed to start the regular observations from 2010.
A solar adaptive optics system for the 60 cm domeless solar telescope of the Hida Observatory in Japan is developed. A
high-speed deformable mirror with 52 electromagnetic actuators is newly used in an experimental adaptive optics system.
The use of the mirror resulted in the improvement of Strehl ratios in laboratory experiments. In solar observations, the
system worked well when solar granulation was used as a target for wavefront sensing. An adaptive optics system being
developed for a vertical spectrograph of the domeless solar telescope is described.
A solar adaptive optics system is developed for the 60 cm domeless solar telescope of the Hida Observatory in Japan. It
is designed for compensating low order turbulence in G-band using a 52-electromagnetic-actuator deformable mirror, a
6x6 Shack-Hartmann wavefront sensor and standard personal computers. The details of the system, particularly features
of the deformable mirror are described. Laboratory experiments show that the use of adaptive optics raises the Strehl
ratio by a factor of five for turbulence of under 99Hz. In solar observations, the improvement of resolution in
long-exposure images with the adaptive optics system is demonstrated.
Extremely stable pointing of the telescope is required for images on the CCD cameras to accurately measure the nature of magnetic field on the sun. An image stabilization system is installed to the Solar Optical Telescope onboard SOLAR-B, which stabilizes images on the focal plane CCD detectors in the frequency range lower than about 20Hz. The system consists of a correlation tracker and a piezo-based tip-tilt mirror with servo control electronics. The correlation tracker is a high speed CCD camera with a correlation algorithm on the flight computer, producing a pointing error from series of solar granule images. Servo control electronics drives three piezo actuators in the tip-tilt mirror. A unique function in the servo control electronics can put sine wave form signals in the servo loop, allowing us to diagnose the transfer function of the servo loop even on orbit. The image stabilization system has been jointly developed by collaboration of National Astronomical Observatory of Japan/Mitsubishi Electronic Corp. and Lockheed Martin Advanced Technology Center Solar and Astrophysics Laboratory. Flight model was fabricated in summer 2003, and we measured the system performance of the flight model on a laboratory environment in September 2003, confirming that the servo stability within 0-20 Hz bandwidth is 0.001-0.002 arcsec rms level on the sun.
In recent years, it is beginning to be shown observationally and theoretically that the existence of the magnetic field is
indispensable for active phenomena on the solar surface. In particular, the rotation or helicity of the magnetic field and
their temporal variation are considered to be important factors which influence solar activity. In order to confirm this, it
is necessary to compute vector components of the magnetic field with a higher accuracy than before. Therefore, we developed two kinds of filter-type magnetographs for the Solar Magnetic Activity Research Telescope (SMART) at Hida observatory, which allow us to observe the polarization components in sunlight with high accuracy. We use a Lyot filter in one of two sets of magnetographs. On the other hand, a tandem-typed Fabry-Perot filter is used in one more set. For these two instruments, we made the following concrete advances. 1. The method of coating of the pre-filters. 2. Special fine-anneal on the main lenses. 3. Highly accurate rotating wave-plate. 4. Simultaneous observation of two kinds of filtergrams which have orthogonally polarized light mutually by using Fabry-Perot channel. 5. Observation in four wavelengths which can suppress various errors.
6. Low apparent Doppler shift in the FOV due to the oblique incidence of the rays to the filters. 7. Large format CCD (large-sized chip, large full-well). 8. High speed data transfer interface between the CCD and PC. In this paper, we report the details of these points, the expected effect of them, and the results of initial measurements.
KEYWORDS: Rockets, Mirrors, Telescopes, Extreme ultraviolet, Space telescopes, Sun, Actuators, Content addressable memory, Control systems, Control systems design
This paper describes the design and prelaunch performance of the tip-tilt mirror (TTM) system developed for the XUV Cassegrain telescope aboard the ISAS sounding rocket experiment. The spatial resolution of the telescope is about 5 arcsec, whereas the rocket pointing is only controlled to be within +/- 0.5 degree around the target without stability control. The TTM is utilized to stabilize the XUV image on the focal planes by tilting the secondary mirror with two-axes fixed-coil type actuators. The two position- sensitive detectors in the telescope optics and in the TTM mechanical structure from the normal and local closed-loop modes. The TTM has four grain modes with automatic transition among the modes. The low gain mode is used in the initial acquisition, and in case the TTM loses the tracking. The high gain mode is used in the normal tracking mode. This arrangement provides us with the wide initial acquisition angle with single TTM system as well as the high pointing accuracy once the tracking is established. The TTM has a launch-lock mechanism against the launch vibration of 16G. The closed-loop control with command and telemetry interface is done by the flight software against the launch vibration of 16G. The closed-loop control with command and telemetry interface is done by the flight software on the DSP processor. The use of the fast processor brings in the significant reduction in the weight and size of the control- electronics, more flexible control system, and shorter design and testing period.
We present an overview of a sounding-rocket experiment that is scheduled to be launched by the Institute of Space and Astronautical Science (ISAS) in January 1998, the rising phase of the 11-year activity cycle of the sun. The purpose of this experiment is (1) to obtain whole-sun images taken in an XUV emission line, Fe XIV 211 A, using the normal incidence multilayer optics with a high spectral resolution of about 40, and (2) to carry out the velocity-field measurement with a detection limit as high as 100 km/s.
We present the development status of the normal incidence XUV multilayer mirrors for XUV Doppler telescope, which observes coronal velocity fields of the whole sun. The telescope has two narrow band-pass multilayer mirrors tuned to slightly longer and shorter wavelengths around the Fe XIV line at 211.3 Angstrom. From the intensity difference of the images taken with these two bands, we can obtain Dopplergram of 1.8 MK plasma of the whole sun. It is required that the multilayer has high wavelength-resolution ((lambda) /(Delta) (lambda) approximately 30 per mirror), anti-reflection coating for intense He II 304 angstrom emission line and high d-spacing uniformity of approximately 1%.
We present an overview of an ongoing Japanese sounding rocket project with the Solar XUV Doppler telescope. The telescope employs a pair of normal incidence multilayer mirrors and a back-thinned CCD, and is designed to observe coronal velocity field of the whole sun by measuring line- of-sight Doppler shifts of the Fe XIV 211 angstroms line. The velocity detection limit is estimated to be better than 100 km/s. The telescope will be launched by the Institute of Space and Astronautical Science in 1998, when the solar activity is going to be increasing towards the cycle 23 activity maximum. Together with the overview of the telescope, the current status of the development of each telescope components including multilayer mirrors, telescope structure, image stabilization mechanism, and focal plane assembly, are reviewed. The observation sequence during the flight is also briefly described.
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