EnVisS (Entire Visible Sky) is an all-sky camera specifically designed to fly on the space mission Comet Interceptor. This mission has been selected in June 2019 as the first European Space Agency (ESA) Fast mission, a modest size mission with fast implementation. Comet Interceptor aims to study a dynamically new comet, or interstellar object, and its launch is scheduled in 2029 as a companion to the ARIEL mission. The mission study phase, called Phase 0, has been completed in December 2019, and then the Phase A study had started. Phase A will last for about two years until mission adoption expected in June 2022. The Comet Interceptor mission is conceived to be composed of three spacecraft: spacecraft A devoted to remote sensing science, and the other two, spacecraft B1 and B2, dedicated to a fly-by with the comet. EnVisS will be mounted on spacecraft B2, which is foreseen to be spin-stabilized. The camera is developed with the scientific task to image, in push-frame mode, the full comet coma in different colors. A set of ad-hoc selected broadband filters and polarizers in the visible range will be used to study the full scale distribution of the coma gas and dust species. The camera configuration is a fish-eye lens system with a FoV of about 180°x45°. This paper will describe the preliminary EnVisS optical head design and analysis carried out during the Phase 0 study of the mission.
The Turin Astronomical Observatory recently completed construction in Altec, Turin, of, Italy, a new Optical Payload System (OPSys) facility for tests of contamination sensitive optical space flight instruments. The facility is specially tailored for tests on solar instruments like coronagraphs. The test facility includes a clean room for instrument assembly and a relatively large (4.e+3 liters) optical test and calibration vacuum chamber. After vacuum conditioning, the chamber will hace an ultimate pressure of 1.e‐7 torr. The Space Optics Calibration Chamber (SPOCC) consists of a test section with a vacuum‐ compatible motorized optical bench, and of a pipeline section with a solar simulator at the opposite end of the optical bench hosting the instrumentation under tests. The solar simulator is an off‐axis parabolic mirror collimating the light from the source with the solar angular divergence. This presentation will describe the SPOCC's vacuum system and optical design, and the post‐flight stray‐light tests to be carried out on the Sounding‐rocket Experiment (SCORE). This sub‐orbital coronagraph is the prototype of the METIS coronagraph for the ESA Solar Orbital mission. Solar Orbiter closest perihelion is one‐third the Sun‐Earth distances. The plans will be illustrated for testing METIS simulating in SPOCC the coronagraph observing conditions from the Solar Orbiter perihelion.
METIS, the Multi Element Telescope for Imaging and Spectroscopy, is the solar coronagraph foreseen for the ESA Solar Orbiter mission. METIS is conceived to image the solar corona from a near-Sun orbit in three different spectral bands: in the HeII EUV narrow band at 30.4 nm, in the HI UV narrow band at 121.6 nm, and in the polarized visible light band (590 – 650 nm). It also incorporates the capability of multi-slit spectroscopy of the corona in the UV/EUV range at different heliocentric heights.
METIS is an externally occulted coronagraph which adopts an “inverted occulted” configuration. The Inverted external occulter (IEO) is a small circular aperture at the METIS entrance; the Sun-disk light is rejected by a spherical mirror M0 through the same aperture, while the coronal light is collected by two annular mirrors M1-M2 realizing a Gregorian telescope. To allocate the spectroscopic part, one portion of the M2 is covered by a grating (i.e. approximately 1/8 of the solar corona will not be imaged).
This paper presents the error budget analysis for this new concept coronagraph configuration, which incorporates 3 different sub-channels: UV and EUV imaging sub-channel, in which the UV and EUV light paths have in common the detector and all of the optical elements but a filter, the polarimetric visible light sub-channel which, after the telescope optics, has a dedicated relay optics and a polarizing unit, and the spectroscopic sub-channel, which shares the filters and the detector with the UV-EUV imaging one, but includes a grating instead of the secondary mirror.
The tolerance analysis of such an instrument is quite complex: in fact not only the optical performance for the 3 sub-channels has to be maintained simultaneously, but also the positions of M0 and of the occulters (IEO, internal occulter and Lyot stop), which guarantee the optimal disk light suppression, have to be taken into account as tolerancing parameters.
In the aim of assuring the scientific requirements are optimally fulfilled for all the sub-channels, the preliminary results of manufacturing, alignment and stability tolerance analysis for the whole instrument will be described and discussed.
This presentation outlines a general optical design for coronagraphs working in both the visible-light (VL) and UV/EUV
wavelength ranges by combining the use of reflective, multilayer-coated or interference-coated optics with Lyot stops.
This design has been successfully applied to a sub-orbital coronagraph. Another version of this novel design for visiblelight/
EUV coronagraphs uses an inverted-occultation design in order to minimize the solar flux entering the instrument.
This design has been used for the coronagraph – METIS - on board the ESA Solar Orbital mission.
The current optical configuration of METIS adopted for the Solar Orbiter mission includes Visible-light and UV
imaging. However, the innovative inverted-occultation concept is flexible enough that it can also accommodate a EUV
spectrograph maintaining the same basic optical layout. The paper also describes the potential capabilities of the
inverted-occulter coronagraph as a VL/UV imager and EUV spectrograph for future solar missions.
METIS is the UV/VIS coronagraph of the ESA mission Solar Orbiter. One of the main technical drivers of the
instrument is the detailed stray-light control, as close to the disk edge the VIS coronal emission is six to about seven
order of magnitudes lower than the disk one. The instrument testing procedure must then include a measurement of its
stray-light rejection capability, which is a fundamental step in the whole instrument calibration / acceptance process. A
preliminary optical design of the optical light source for stray-light test is presented. The main requirements are
discussed and two possible solutions are outlined.
VUV polarimetry has been recognized as one of the most powerful diagnostic tools for remote sensing of the solar
corona, with the potential of providing accurate space resolved information on magnetic activity through observation of
resonance lines of the most abundant species. In an on-going collaboration between our groups from Spain and Italy, a
program to design, build and characterize optical components for the VUV region has been activated. In particular, using
the beamline BEAR at the synchrotron facility Elettra in Trieste (Italy) we have characterized some thin film reflecting
linear polarizers, designed and optimized for the study of polarimetric properties of the HI Ly-alpha at 121.6 nm. The
characterizations are performed from 100 to 150 nm at different angles of incidence (40 – 80 deg). Some polarizers have
shown excellent performances with an average reflectivity R ≈ 34% and a modulation factor exceeding 95%. The
calibration of several samples is reported and aging effects on some old samples is discussed. One of the calibrated
sample will be used for the evaluation of the performances of a new fast calibration set-up facility for VUV.
METIS, the Multi Element Telescope for Imaging and Spectroscopy, is the solar coronagraph foreseen for the ESA Solar
Orbiter mission. METIS is conceived to image the solar corona from a near-Sun orbit in two different spectral bands: in
the HI UV narrow band at 121.6 nm, and in the polarized visible light band (580 – 640 nm).
METIS is an externally occulted coronagraph which adopts an “inverted occulted” configuration. The inverted external
occulter (IEO) is a small circular aperture after which a small spherical mirror M0 rejects back the disk-light through the
IEO, then an annular mirror collects the signal coming from the corona and redirects it toward the telescope secondary
mirror.
This paper presents the error budget analysis for this new-concept coronagraph configuration, which incorporates two
different sub-channels: the UV imaging and the polarimetric visible one. The two sub-channels are sharing the telescope
optics, then an interference filter transmits the UV light towards the UV detector, while the visible-light is reflected
towards the polarimetric unit.
The tolerance analysis is rather complex, in fact not only the optical performance for the two sub-channels has to be
maintained simultaneously, but also the positions of the M0 and the occulters (IEO, internal occulter and Lyot stop),
which assure the optimal disk light suppression, have to be taken into account as tolerancing parameters.
To guarantee the scientific requirements are optimally fulfilled for the two sub-channels, the preliminary results of
manufacturing, alignment and stability tolerance analysis for the whole instrument will be described and discussed.
Polarimetry in the far ultraviolet (FUV) is a powerful tool for the interpretation of the role of the coronal plasma in the energy transfer processes from the inner parts of the Sun to the outer space. FUV polarimetry from space provides more accurate observations on the kinetics of the features and on local magnetic fields through the Doppler and Hanle resonant electron scattering effects. Particularly interesting lines for FUV polarimetry are H Lyman α (121.6 nm) and β (102.6 nm), along with OVI lines at 103.2 and 103.8 nm. One key element to perform polarimetry measurements at these wavelengths is the need of efficient polarizers. A limitation of the available polarizers, such as crystal plates of MgF2 and LiF working at Brewster angle, is their moderate reflectance at the non-extinguished component of the electric field, which results in a modest polarizer efficiency.
METIS (Multi Element Telescope for Imaging and Spectroscopy) METIS, the “Multi Element Telescope for Imaging
and Spectroscopy”, is a coronagraph selected by the European Space Agency to be part of the payload of the Solar
Orbiter mission to be launched in 2017. The mission profile will bring the Solar Orbiter spacecraft as close to the Sun as 0.3 A.U., and up to 35° out-of-ecliptic providing a unique platform for helio-synchronous observations of the Sun and its polar regions. METIS coronagraph is designed for multi-wavelength imaging and spectroscopy of the solar corona. This presentation gives an overview of the innovative design elements of the METIS coronagraph. These elements include: i) multi-wavelength, reflecting Gregorian-telescope; ii) multilayer coating optimized for the extreme UV (30.4 nm, HeII Lyman-α) with a reflecting cap-layer for the UV (121.6 nm, HI Lyman-α) and visible-light (590-650); iii) inverse external-occulter scheme for reduced thermal load at spacecraft peri-helion; iv) EUV/UV spectrograph using the telescope primary mirror to feed a 1st and 4th-order spherical varied line-spaced (SVLS) grating placed on a section of the secondary mirror; v) liquid crystals electro-optic polarimeter for observations of the visible-light K-corona. The expected performances are also presented.
Instrument software simulators are becoming essential both for supporting the instrument design and for planning the
future operations. In this paper we present the Software Simulator developed for the METIS coronagraph, an instrument
of the Solar Orbiter ESA mission. We describe its architecture and the modules it is composed of, and how they
interchange data to simulate the whole acquisition chain from the photons entering the front window to the stream of
telemetry? data received and analysed on ground.
Each software module simulates an instrument subsystem by combining theoretical models and measured subsystem
properties. A web-based application handles the remote user interfaces of the Institutions of the METIS Consortium,
allowing users from various sites to overview and interact with the data flow, making possible for instance input and
output at intermediate nodes.
Description of the modes of use of the simulator, both present and future, are given with examples of results. These
include not only design-aid tasks, as the evaluation and the tuning of the image compression algorithms, but also those
tasks aimed to plan the in-flight observing sequences, based on the capability of the simulator of performing end to end
simulations of science cases.
METIS, the “Multi Element Telescope for Imaging and Spectroscopy”, is a coronagraph selected by the European Space Agency to be part of the payload of the Solar Orbiter mission to be launched in 2017. The unique profile of this mission will allow 1) a close approach to the Sun (up to 0.28 A.U.) thus leading to a significant improvement in spatial resolution; 2) quasi co-rotation with the Sun, resulting in observations that nearly freeze for several days the large-scale outer corona in the plane of the sky and 3) unprecedented out-of-ecliptic view of the solar corona.
This paper describes the experiment concept and the observational tools required to achieve the science drivers of METIS. METIS will be capable of obtaining for the first time:
• simultaneous imaging of the full corona in polarized visible-light (590-650 nm) and narrow-band ultraviolet HI Lyman α (121.6 nm);
• monochromatic imaging of the full corona in the extreme ultraviolet He II Lyman α (30.4 nm);
• spectrographic observations of the HI and He II Ly α in corona.
These measurements will allow a complete characterization of the three most important plasma components of the corona and the solar wind, that is, electrons, hydrogen, and helium. This presentation gives an overview of the METIS imaging and spectroscopic observational capabilities to carry out such measurements.
METIS, the "Multi Element Telescope for Imaging and Spectroscopy", is a coronagraph of the Solar Orbiter mission to be launched in 2017. The METIS coronagraph includes three optical paths for i) broad-band imaging of the full corona in polarized visible-light (590-650 nm); ii) narrow-band coronal imaging in the UV HI Ly α (121.6 nm) and extreme-UV He II Ly α (30.4 nm), and iii) spectroscopic observations of the HI and He II Ly α. This presentation describes the optical design of the METIS visible-light path for imaging polarimetry of the K-corona. The achromatic polarimeter's requirements on polarization sensitivity, achromatic response and instrumental polarization control are described. The expected performances of the visible-light path are also presented.
Polarimeters based on electro-optically tunable liquid crystals (LC) represent a new technology in the field of
observational astrophysics. LC-based polarimeters are good candidates for replacing mechanically rotating polarimeters
in most ground-based and space-based applications. During the 2006 total solar eclipse, we measured the visible-light
polarized brightness (pB) of the solar K-corona with a LC-based polarimeter and imager (E-KPol). In this presentation,
we describe the results obtained with the E-KPol, and we evaluate its performances in view of using a similar device for
the pB imaging of the K-corona from space-based coronagraphs. Specifically, a broad-band LC polarimeter is planned
for the METIS (Multi Element Telescope for Imaging and Spectroscopy) coronagraph for the Solar Orbiter mission to
be launched in 2017. The METIS science driver of deriving the coronal electron density from pB images requires an
accuracy of better than 1% in the measurement of linear polarization. We present the implications of this requirement on
the METIS design to minimize the instrumental polarization of the broad-band visible-light (590-650 nm) polarimeter
and of the other optics in the METIS visible-light path. Finally, we report preliminary ellipsometric measurements of the
optical components of the METIS visible-light path.
The Turin Astronomical Observatory, Italy, has implemented in ALTEC, Turin, a new Optical Payload Systems
(OPSys) facility for testing of contamination sensitive optical space flight instrumentation. The facility is specially
tailored for tests on solar instruments like coronagraphs. OPSys comprises an ISO 7 clean room for instrument assembly
and a relatively large (4.4 m3) optical test and calibration vacuum chamber: the Space Optics Calibration Chamber
(SPOCC). SPOCC consists of a test section with a vacuum-compatible motorized optical bench, and of a pipeline section
with a sun simulator at the opposite end of the optical bench hosting the instrumentation under tests. The solar simulator
is an off-axis parabolic mirror collimating the light from the source with the solar angular divergence. After vacuum
conditioning, the chamber will operate at an ultimate pressure of 10-6 mbar.
This work describes the SPOCC's vacuum system and optical design, and the post-flight stray-light tests to be carried
out on the Sounding-rocket Experiment (SCORE). This sub-orbital solar coronagraph is the prototype of the METIS
coronagraph for the ESA Solar Orbital mission whose closest perihelion is one-third of the Sun-Earth distance. The plans
are outlined for testing METIS in the SPOCC simulating the observing conditions from the Solar Orbiter perihelion.
This article describes the calibration and alignment procedures of a demonstrator for the ASPIICS coronagraph proposed
for the ESA technology mission PROBA-3 aimed at demonstrating the feasibility of a Formation Flying coronagraph.
ASPIICS is distributed on two spacecrafts separated by 150 m, one hosting the external occulting disk and the other the
optical part of the coronagraph. The purpose of the demonstrator is to reproduce on ground the metrology systems that
will equip the coronagraph in order to realize the alignment of the two spacecrafts and the absolute pointing to the center
of the Sun. The demonstrator is composed of a device that reproduces the solar umbra/penumbra created by the solar
occulter[1] and of a Three Mirror Anastigmatic (TMA) telescope mounted on a hexapod, a new-generation platform that
allows 6 degrees of freedom. A large plane folding mirror is used on ground to obtain a distance between the occulter
and the TMA up to 30 m. Photo sensors located around the entrance pupil of the TMA determine the absolute positioning
of the instrument by sensing the penumbra behind the occulting disk. Light sources (LEDs) located on the rear-side of
the occulting disk allow verifying the alignment of the formation. The paper describes the whole demonstrator, its
integration, its calibration, and the performance of the metrology systems of the coronagraph. This study has been
conducted in the framework of an ESA "STARTIGER" Initiative, a novel approach aimed at demonstrating the
feasibility of a new and promising technology on a very short time scale (six months).
Formation Flying opens the possibility to conceive and deploy giant solar coronagraphs in space permanently
reproducing the optimum conditions of a total eclipse of the Sun ("artificial" eclipse) thus giving access to the inner
corona with unprecedented spatial resolution and contrast (low stray light). The first opportunity to implement such a
coronagraph "ASPIICS" will be offered by the European Space Agency (ESA) PROBA-3 technology mission devoted to
the in-orbit demonstration of formation flying technologies. Two spacecrafts separated by about 150 m form a giant
externally-occulted coronagraph: the optical part hosted by one spacecraft remains entirely protected from direct sunlight
by remaining in the shadow of an external occulter hosted by the other spacecraft. We developed and tested a scale-model
'breadboard' (i.e., 30m) of the PROBA-3/ASPIICS Formation Flying coronagraph. The investigations focused on
two metrology systems capable of measuring both the absolute pointing of the coronagraph (by sensing the projected
shadow and penumbra produced by the external occulting disk) and the alignment of the formation (by re-imaging light
sources located on the rear-side of the occulting disk with the optical part of the coronagraph). In this contribution, we
will describe the demonstrator and report on our results on the crucial question of the alignment and pointing in space of
long instruments (> 100 m) with an accuracy of a few arcsec. This study has been conducted in the framework of an ESA
"STARTIGER" Initiative, a novel approach aimed at demonstrating the feasibility of a new and promising technology on
a very short time scale (six months).
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