PROBA3 is the first high precision formation flying (FF) mission under responsibility of the European Space Agency (ESA). It is a technology mission devoted to in-orbit demonstration of the FF techniques, with two satellites kept at an average inter-satellite distance of 144m. The guiding scientific rationale is to realize a diluted coronagraph with the telescope (ASPIICS) on one satellite and the external occulter on the other satellite to observe the inner Solar corona at high spatial and temporal resolution, down to 1.08R⊙. The two spacecraft will be orbiting in a high eccentricity geocentric trajectory with perigee at 600km and the apogee at 60000Km and with an orbital period of 19hrs. The FF acquisition and operations will last about 6 hrs around the apogee and different metrology systems will be used for realizing and controlling the FF. The alignment active most critical sub-system is the Shadow Positioning Sensors (SPS), a series of Si-PM (Silicon Photomultiplier) disposed around the ASPIICS telescope's entrance aperture and measuring the proper positioning of the penumbra generated by the occulter at the center of the coronagraph’s optical reference frame. The FF alignment measurement accuracies required to the SPS are: 500μm for lateral movements and 50mm for longitudinal movements. This paper gives an overview of the opto-mechanical and electronic design and of the software algorithm for the FF intersatellite positioning. The expected performance of the SPS metrology system are reported.
The SPECtro-heliograph for the Transition REgion (SPECTRE) experiment is one of the instruments of the Solar Heliospheric Activity Research and Prediction Program (SHARPP) suite initially foreseen aboard the NASA mission Solar Dynamics Observatory (SDO) of the International Living With a Star (ILWS) program. The scientific objective of the SPECTRE experiment was to characterize the rapid evolution of plasma in the transition region of the solar atmosphere, producing full-disk 1.2 arcsec-resolution images of the solar atmosphere at the very critical 63 nm OV spectral line, characterizing a solar plasma temperature of about 250,000 K. Unfortunately, NASA very recently and unexpectedly, during the instrument Phase A study, decided not to proceed with the realization of SHARPP. The authors of this paper think that all the work done so far in the definition of SPECTRE should not be lost. So, they have decided to summarize in this paper the main characteristics of this instrument and the results of the analysis so far performed: the hope is that in a next future this work can be used again for realizing an instrument having similar characteristics.
METIS, the Multi Element Telescope for Imaging and Spectroscopy, is an instrument proposed to the European Space Agency to be part of the payload of the Solar Orbiter mission. The instrument design has been conceived for performing extreme ultraviolet (EUV) spectroscopy both on the solar disk and off-limb, and near-Sun coronagraphy and spectroscopy. <p> </p>The proposed instrument suite consists of three different interconnected elements, COR, EUS and SOCS, sharing the same optical bench, electronics, and S/C heat shield aperture. COR is a visible-EUV multiband coronagraph based on a classical externally occulted design. EUS is the component of the METIS EUV disk spectrometer which includes the telescope and all the related mechanisms. Finally, SOCS is the METIS spectroscopic component including the dispersive system and the detectors. The capability of inserting a small telescope collecting coronal light has been added to perform also EUV coronal spectroscopy. <p> </p>METIS can simultaneously image the visible and ultraviolet emission of the solar corona and diagnose, with unprecedented temporal coverage and space resolution the structure and dynamics of the full corona in the range from 1.2 to 3.0 (1.6 to 4.1) solar radii (R⊙, measured from Sun centre) at minimum (maximum) perihelion during the nominal mission. It can also perform spectroscopic observations of the solar disk and out to 1.4 R⊙ within the 50-150 nm spectral region, and of the geo-effective coronal region 1.7-2.7 R⊙ within the 30-125 nm spectral band.
Present telescopes and future extremely large telescopes make use of fiber-fed spectrographs to observe at optical and
infrared wavelengths. The use of fibers largely simplifies the interfacing of the spectrograph to the telescope. At a high
spectral resolution (R>50,000) the fibers can be used to achieve very high spectral accuracy.
GIANO is an infrared (0.95-2.5μm) high resolution (R=50,000) spectrometer   that was recently commissioned
at the TNG telescope (La Palma). This instrument was designed and built for direct feeding from the telescope .
However, due to constraints imposed on the telescope interfacing during the pre-commissioning phase, it had to be
positioned on the rotating building, far from the telescope focus. Therefore, a new interface to the telescope, based on
IR-transmitting ZBLAN fibers with 85μm core, was developed.
In this article we report the first, preliminary results of the effects of these fibers on the quality of the recorded spectra
with GIANO and with a similar spectrograph that we set-up in the laboratory. The effects can be primarily associated to
modal-noise (MN) that, in GIANO, is much more evident than in optical spectrometers, because of the much longer
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 m<sup>3</sup>) 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<sup>-6</sup> 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.
The "Association de Satellites Pour l'Imagerie et l'Interférométrie de la Couronne Solaire", ASPIICS, is a solar
coronagraph to be flown on the PROBA 3 Technology mission of the European Space Agency. ASPIICS heralds the
next generation of coronagraphs for solar research, exploiting formation flying to gain access to the inner corona under
eclipse-like conditions in space. The science goal is high spatial resolution imaging and two-dimensional
spectrophotometry of the Fe XIV, 530.3 nm, emission line. This work describes a liquid crystal Lyot tunable-filter and
polarimeter (LCTP) that can implement this goal. The LCTP is a bandpass filter with a full width at half maximum of
0.15 nm at a wavelength of 530.3 nm. The center wavelength of the bandpass is tunable in 0.01 nm steps from 528.64
nm to 533.38 nm. It is a four stage Lyot filter with all four stages wide-fielded. The free spectral range between
neighboring transmission bands of the filter is 2.7 nm. The wavelength tuning is non-mechanical using nematic liquid
crystal variable retarders (LCVR's). A separate LCVR of the Senarmont design, in tandem with the filter, is used for the
polarimetric measurements. A prototype of the LCTP has been built and its measured performances are presented here.
The Dual Rotating Retarder Polarimeter technique has been used for the calibration of the EKPol polarimeter, which is a
K-corona imaging instrument based on a Liquid Crystal Variable Retarder (LCVR), and designed to measure the linear
polarized radiation coming from the solar corona during total solar eclipses. We put a major emphasis on the EKPol
properties at different wavelengths and temperature. In particular, the chromatic dependence of the LCVR rotation
prevents from using large band observations, owing to the loss of contrast in the measured modulation curves. This study
is also intended as a basis for the design of achromatic LCVRs.
We describe the design and first calibration tests of an imaging polarimeter based on Liquid Crystal Variable Retarders (LCVRs), for the study of the solar K-corona. This K-polarimeter (KPol) is part of the visible light path of the UltraViolet and Visible-light Coronal Imager (UVCI) of the Sounding-rocket Coronagraphic Experiment (SCORE). SCORE/UVCI is an externally occulted, off-axis Gregorian telescope, optimized for the narrow-band (i.e., λ/▵λ ~10) imaging of the HeII, λ 30.4 nm and HI λ 121.6 nm coronal emission. We present some preliminary results of the application of LCVR plates to measurements of linear polarized radiation. LCVR plates replace mechanically rotating retarders with electro-optical devices, without no moving parts. LCVR are variable waveplates, in which the change of the retardance is induced by a variable applied voltage. The retardance of a LCVR is a function of the wavelength. KPol observations of the visible coronal continuum of the Sun (K-corona) will be made over the 450-600 nm wavelength band. We have studied the LCVR's properties in this bandpass. We tested a LCVR plate assembled in a linear polarization rotator configuration to measure the polarization plane rotation of input radiation as a function of wavelength. We estimated the LCVR's chromatic response in the KPol wavelength bandpass. The preliminary results show reasonable achromatic behaviour at high regimes of the driving voltage, V<sub>d</sub> (i.e., V<sub>d</sub>>3 volt).
A new concept CCD camera is currently under development at the XUVLab of the Department of Astronomy and Space Science of the University of Florence. This CCD camera is the proposed detector for the space- and ground-based solar corona observations. This camera will be the detector for the polarimetric channels of the UVC coronagraph of the HERSCHEL rocket mission to observe the solar corona in an optical broadband. The ground-based application consists in a UVC prototype for coronagraphic measurements from Earth in the visible range. Within this project, a CCD camera with innovative features has been produced: the camera controller allows the fine tuning of all the parameters related to charge transfer and CCD readout, i.e., the use of virtually any CCD sensor, and it implements the new concept of high level of versatility, easy management, TCP/IP remote control and display.