Instruments
 
 

    The proposed ASO-S mission has three payloads onboard, i.e., the Full-disk Vector Magnetograph, the Lyman-alpha Solar Telescope and the Hard X-ray Imager.


Full-Disc Vector Magnetograph (FMG)
    The Full-disk vector MagneoGraph (FMG) measures the magnetic fields of the photosphere over the entire solar disk. FMG consists of an imaging optical system, a polarization optical system, and a CCD image acquisition and processing system. The telescope is a telecentric optical design with 140 mm aperture, and the detector is a CMOS camera with 4k by 4k array and 16 fps. The polarization optical system consists of a traditional Lyot-type birefringent and LCVR-type polarimeter. The birefringent filter works in the Fraunhofer line FeI 532.4 nm with FWHM 0.01 nm.

    In order to get higher accuracy, FMG uses multi-frame add mode (deep-integration mode). In normal mode of observation, 512 frames (half for left and half for right) will be collected for one magnetogram. That means within 32s (for obtaining 512 frames) the pointing should be stabilized at least within half pixel, say 0.25". Thus, FMG has itself tip/tilt system. In normal mode, the sensitivities are 5G and 150G for longitudinal and transverse component, respectively.

    Compared with the magnetograph onboard Hinode (SP), FMG has a much larger field of view and higher time cadence. Comparing to the magnetographs onboard SDO (HMI) and SOHO (MDI), FMG has a simpler observation mode and a higher measurement precision.


Lyman-alpha Solar Telescope (LST)
     The Lyman-alpha Solar Telescope (LST) is composed of a solar disk imager (SDI) with an aperture of 60mm, a solar corona imager (SCI) also with an aperture of 60mm, a white-light solar telescope (WST) with an aperture of 80mm, and a guiding telescope (GT) with an aperture of 30mm.

     The SDI is to image the Sun from the disk center to 1.2 solar radii in the Lyman–alpha waveband (121.6±7.5nm) with a cadence of 4 - 60s. The SDI uses a 4k by 4k camera as the detector so that the pixel resolution is 0.56". The structure of SDI is similar to the LADI/LYOT for SMESE but with a larger aperture. Meanwhile, a piezoelectric image stabilization system is adopted for both the SDI and the SCI to achieve the high spatial resolution.

     The SCI uses a 2k by 2k camera to image the inner solar corona from 1.1 to 2.5 solar radii with a cadence of 3 - 120s in both the Lyman-alpha waveband (121.6±10nm) and white-light (700±40nm). A beam-splitter divided the coming coronal light into two beams: the reflected beam feeds the Lyman-alpha channel while the transmitted beam feeds the white-light channel. The Lyman-alpha channel consists of a Lyman-alpha filter and a detector; the white-light channel consists of a broadband filter centered at 700nm, linear polarizers and a detector. Three polarization angles (0, ±60°) are used to conduct the polarization brightness measurement in the white-light waveband.

     The WST is design to image the Sun in violet narrow-band continuum (360±2.0nm) from the disk center to 1.2 solar radii with a general cadence of 3 - 60s (it can be as high as 0.2s in the fast event mode). A 4k by 4k CMOS sensor is selected to be the detector, which can be easily windowed for output to get higher cadence in fast event mode.

     The guiding telescope works in 675.8 ±5 nm waveband. To guide, quadrant photodiode detectors are used to monitor the solar limb, calculate the displacement and produce the guiding signal, which is converted to triggering signals to the PZT actuators installed behind the main mirrors of both SCI and SDI. The GT together with the PZT actuators and relevant electronics forms the image stabilizing system.


Hard X-ray Imager(HXI)
    The Hard X-ray Imager (HXI) aims to image the full solar disk in the high-energy range of 30 to 200 keV with good energy resolution (27% @ 30 keV / 5.6% @ 1467 keV), high time cadence (0.5 s) and large effective area (200 cm ²). It is designed for flare observations with a field of view (FOV) of 1 degree and an angular resolution of 6" at 30 keV. The HXI adopts the same principle as the Hard X-ray Telescope (HXI) onboard the Japanese YOHKOH satellite and the Spectrometer Telescope for Imaging X-rays (STIX) for the Solar Orbiter mission, i.e., using indirect imaging technique via spatial modulation. This is different from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) that images the Sun with the indirect imaging technique via rotational modulation.

    A guiding telescope is implemented with the HXI to monitor the Sun in white-light, which provides positioning information of the HXI and locates eruptions on the Sun.