On-board the Solar Orbiter ESA/NASA mission there is Metis, a coronagraph designed to study the solar corona by providing an artificial solar eclipse. Metis features two channels working at the ultraviolet Lyman-α (121.6 nm) and in the visible light (580-640 nm). On-ground, the Metis radiometric performance has been tested using a flat-field panel (uniform illumination); the stability of the performance can be verified in-flight through the analysis of the stars passing in the Metis Field of View. Care must be taken to ensure the quality of the calibration, both before launch and for the long period associated with the space mission lifetime. For this reason, we are carrying out long period research of stars that cross the Field of View of Metis. In this paper, we describe the vignetting function acquired: on-ground, simulated via a raytracing code and in-flight derived from on-ground measurements (performing some adjustments to account for the real Metis flight configuration). These vignetting functions are then compared with the vignetting data derived from the passage of the star Theta Ophiuchi in March and December 2021. Additional presentation content can be accessed on the supplemental content page.
Metis is a multi-wavelength coronagraph onboard the European Space Agency (ESA) Solar Orbiter mission. Thanks to the selected Solar Orbiter mission profile, for the first time the poles of the Sun and the circumsolar region will be seen and studied from a privileged point of view near the Sun (minimum distance 0.28 AU). Metis features an innovative instrument design conceived for simultaneously imaging the visible (580-640 nm) and ultraviolet (Lyman α at 121.6 nm) emission of the solar corona. METIS is an externally occulted coronagraph which adopts an “inverted occulted” configuration. The inverted external occulter (IEO) is a circular aperture after which a spherical mirror M0 rejects back the solar disk light, which exits the instrument through the IEO aperture itself. The passing coronal light is then collected by the METIS telescope. Common to both channels, the Gregorian on-axis telescope is centrally occulted and both the primary and the secondary mirrors have annular shape. The optical and radiometric performance of the telescope is strongly dependent on the huge degree of vignetting presented by the optical design. The internal fields are highly vignetted by M0 and further vignetted by the internal elements, such as the internal occulter and the Lyot stop, furthermore the presence of some spiders, needed to mount the internal elements, are vignetting even more, in some parts of the FoV, the light beams. During the instrument commissioning, in the visible light channel some out-of-focus sources have been imaged while moving in the Metis FoV. At a first glance, the out-of-focus images exhibit a very strange pattern. The pattern can be explained by taking into account the peculiar design of the Metis coronagraph instrument; in fact, the not fully illuminated pupil gives rise to “half moon” shape out-of-focus images with the spiders casting their shadow in different positions. In this work, the ray-tracing simulation results for the out-of-focus images are compared with some of the images taken in flight; some considerations relating the shape and dimension of the acquired images with the distance from Metis of the sources are also given.
After the 10th February 2020 launch (04:03 UTC), Solar Orbiter has recently begun its Nominal Mission Phase and is collecting imaging data as never seen before due to its peculiar orbit. The Metis coronagraph produces maps of the linearly polarized visible light corona in the wavelength band 580-640 nm and UV maps in the Lyman alpha H i 121.6 nm line. Metis is a coronagraph characterized by an innovative external occultation system that has a twofold function: reduce the thermal load and remove the diffraction due to the external occulter support. The positions of the entrance pupil (which is called Inverted External Occulter, IEO) and of the actual occulter are switched so that the pupil is the surface facing the solar disk and the occultation is performed by a spherical mirror, M0. M0 is positioned 800 mm behind IEO and reflects the disk light back through the IEO aperture. An Internal Occulter (IO) is conjugated to the IEO with respect to the primary mirror. IO is mounted on a motorized 2-axis stage that allows to perform in-flight fine adjustments to its position. During the on-ground calibration campaign the contribution of the stray light due to the diffraction from the IEO and scattering off the optics was measured. The measurement was carried out by using the OPSys facility in Torino (Italy), which is equipped with a clean environment and a source that simulates the solar disk divergence. A stray light measurement in flight is not trivial due to the presence of the solar corona. Nevertheless, an IO position optimization campaign has been conducted in order to reduce the stray light. A procedure was developed in order to minimize the stray light level on the instrument focal plane. This contribution reports on the procedure and on the results.
Metis is the coronagraph on board the Solar Orbiter ESA/NASA mission, it is designed to study the solar corona by providing an artificial solar eclipse. Metis features two channels: the ultraviolet H I (121.6 nm) and the visible light (580-640 nm). This work is focalised on the latter. Radiometric performances have been tested on-ground using a flatfield panel (uniform illumination), and the in-flight stability can be verified through the light reflected from the instrument door. When the Sun light impacts on the spacecraft shield, a fraction is reflected in the direction of the door, which then partly reflects it inside Metis. The analysis of the door images confirms its integrity and that of its subsequent optical components, since the reflected intensity follows as expected a 1/r2 law, r being the Sun-spacecraft distance. Further analysis is being performed on such images to verify the operating status of various elements of Metis. Complementary ray-tracing simulation studies on the door retro-reflectivity properties are also in progress.
Metis coronagraph is one of the remote-sensing instruments of the Solar Orbiter mission launched at the begin of 2020. The mission profile will allow for the first time the remote-sensing observation of the Sun from a very close distance and increasing the latitude with respect to the ecliptic plane. In particular, Metis is aimed at the overall characterization and study of the solar corona and solar wind. Metis instrument acquires images of the solar corona in two different wavelengths simultaneously; ultraviolet (UV) and visible-light (VL). The VL channel includes a polarimeter with an electro-optically modulating Liquid Crystal Variable Retarder (LCVR) to measure the linearly polarized brighness pB) of the K-corona. This paper presents part of the in-flight calibration results for both wavelength channels together with a comparison with on-ground calibrations. The orientation of the K-corona linear polarization was used for the in-flight calibration of the Metis polarimeter. This paper describes the correction of the on-ground VL vignetting function after the in-flight adjustment of the internal occulter. The same vignetting function was adaptated to the UV channel.
Metis is a multi-wavelength coronagraph onboard the European Space Agency (ESA) Solar Orbiter mission. The instrument features an innovative instrument design conceived for simultaneously imaging the Sun's corona in the visible and ultraviolet range. The Metis visible channel employs broad-band, polarized imaging of the visible K-corona, while the UV one uses narrow-band imaging at the HI Ly , i.e. 121.6 nm. During the commissioning different acquisitions and activities, performed with both the Metis channels, have been carried out with the aim to check the functioning and the performance of the instrument. In particular, specific observations of stars have been devised to assess the optical alignment of the telescope and to derive the instrument optical parameters such as focal length, PSF and possibly check the optical distortion and the vignetting function. In this paper, the preliminary results obtained for the PSF of both channels and the determination of the scale for the visible channel will be described and discussed. The in-flight obtained data will be compared to those obtained on-ground during the calibration campaign.
Metis coronagraph is one of the remote-sensing instruments of the Solar Orbiter mission launched in February 2020. The mission profile will allow for the first time the remote-sensing observation of the Sun from as close as 0.28 AU and from ecliptic latitudes as high as 30?. Metis, in particular, is aimed at the study and the overall characterization of the solar corona and solar wind. This instrument is an innovative inverted-occultation coronagraph that will image the solar corona for the first time simultaneously in two different wavelength band-passes: in the linearly-polarized visible-light (VL), between 580 and 640 nm, and in the ultraviolet (UV) Lyman-a line of hydrogen, HI at 121.6 nm by combining in the same telescope UV interference mirror coatings (Al/MgF2) and spectral bandpass filters. The visible channel includes a broad-band polarimeter to observe the linearly polarized component of the K corona. These measurements will allow a complete characterization of the physical parameters, such as density and outflow speed, of the two major plasma components of the corona and the solar wind: electrons (protons) and hydrogen. After a period of commissioning, by the summer of 2020, Metis will have performed the First-light Science Observations during the “Remote-Sensing Check-out Window” (RSCW) that is a telemetry contact period, specifically allocated before entering the operational phase at the end of 2021. This presentation will report the first-light science observations of Metis represented by the UV and polarized VL images of the corona. The calibration results from the commissioning will be used for the correction of the instrumental effects. The resulting first-light maps of the coronal electron and hydrogen distributions will be presented.
Metis is the visible light and UV light imaging coronagraph on board the ESA-NASA mission Solar Orbiter that has been launched February 10th, 2020, from Cape Canaveral. Scope of the mission is to study the Sun up close, taking high-resolution images of the Sun’s poles for the first time, and understanding the Sun-Earth connection. Metis coronagraph will image the solar corona in the linearly polarized broadband visible radiation and in the UV HI Ly-α line from 1.6 to 3 solar radii when at Solar Orbiter perihelion, providing a diagnostics, with unprecedented temporal coverage and spatial resolution, of the structures and dynamics of the full corona. Solar Orbiter commissioning phase big challenge was Covid-19 social distancing phase that affected the way commissioning of a spacecraft and its payload is typically done. Metis coronagraph on-board Solar Orbiter had its additional challenges: to wake up and check the performance of the optical, electrical and thermal subsystems, most of them unchecked since Metis delivery to spacecraft prime, Airbus, in May 2017. The roadmap to the fully commissioned coronagraph is here described throughout the steps from the software functional test, the switch on of the detectors of the two channels, UV and visible, to the optimization of the occulting system and the characterization of the instrumental stray light, one of the most challenging features in a coronagraph.
Solar Orbiter, launched on February 9th 2020, is an ESA/NASA mission conceived to study the Sun. This work presents the embedded Metis coronagraph and its on-ground calibration in the 580-640 nm wavelength range using a flat field panel. It provides a uniform illumination to evaluate the response of each pixel of the detector; and to characterize the Field of View (FoV) of the coronagraph. Different images with different exposure times were acquired during the on-ground calibration campaign. They were analyzed to verify the linearity response of the instrument and the requirements for the FoV: the maximum area of the sky that Metis can acquire.
Solar Orbiter is a solar mission that will approach the Sun down to a minimum perihelion of 0.28 AU and will increase its orbit inclination with respect to the ecliptic up to a maximum angle of 34 deg. For imagers aboard Solar Orbiter there will be three 10-days remote sensing windows per orbit. Observations shall be carefully planned at least 6 months in advance. The Multi Instrument Sequence Organizer (MISO) is a web based platform developed by the SPICE group and made available to support Solar Orbiter instruments teams in planning observations by assembling Mission Database sequences. Metis is the UV and visible light coronagraph aboard Solar Orbiter. Metis is a complex instrument characterized by a rich variety of observing modes, which required a careful commissioning activity and will need support for potential maintenance operations throughout the mission. In order to support commissioning and maintenance activities, the Metis team developed a PDOR (Payload Direct Operation Request) and MDOR (Memory Direct Operation Request) module integrated in MISO and made available to all Solar Orbiter instruments. An effort was made in order to interpret the coding philosophy of the main project and to make the additional module as homogeneous as possible both to the web interface and to the algorithm logic, while integrating characteristics which are peculiar to PDORs and MDORs. An user friendly web based interface allows the operator to build the operation request and to successively modify or integrate it with further or alternative information. In the present work we describe the PDOR/MDOR module for MISO by addressing its logic and main characteristics.
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