Athena is ESA’s X-ray observatory mission designed to address the Hot and Energetic Universe theme. The instrument consists of a single x-ray telescope, supported by a large area mirror based on Silicon Pore Optics technology, focusing the photon flux alternatively onto two different instruments: the Wide Field Imager (WFI) and the X-ray Integral Field Unit (X-IFU). The process of switching the focus between the two instruments is produced by a hexapod structure changing the pointing of the main X-ray mirror. To verify that the mirror optical axis is aligned with each of the instruments, an optical On-board Metrology System (OBM) will be used to estimate the telescope pointing with accuracy better than 0.5 arcsec. The OBM system currently in development at the Institute of Astrophysics and Space Sciences is based on the concept of a projective metrology where a pattern of active fiducials is imaged by an array detector. The position and orientation of the imaged pattern provides the necessary information to reconstruct the fiducial displacements with respect to the calibrated reference points, allowing obtaining an estimate of the pointing absolute knowledge error.
The design of the metrology system is presently at Engineering Model level, although it will be tested for performance in normal laboratory conditions.
In this work we will present the experimental setup and processing architecture designed for calibration and testing the OBM demonstrator close to operational conditions, namely in what respects to the distance from the OBM Optical Head to the fiducial plane (12 meter). This experimental setup is calibrated to reproduce verifiable fiducial displacements over the OBM telescope field of view at 7.5 micrometre level (1 sigma). This setup allows evaluating the performance of OBM and verify its compliance with requirements of the on-board metrology system for the Athena X-ray Observatory mission.
The advanced telescope for high energy astrophysics (Athena) is an ESA X-ray observatory mission to address the hot and energetic universe theme. The instrument consists of a single x-ray telescope, supported by a large area mirror/ lens based on silicon pore optics technology, which will focus the photon flux alternatively onto two different instruments, 12m away: the wide field imager (WFI) and the x-ray integral field unit (X-IFU). The process of switching the focus between the two instruments is produced by a large hexapod structure that is able to change the pointing of the main mirror and the focus plane position, according to strict operational requirements. In order to verify that the mirror optical axis is perfectly aligned with each of the instruments, the telescope shall be supported by an optical on-board metrology system (OBM) that is able to estimate the telescope pointing with accuracy better than 0.5 arcsec.
The Athena OBM system currently under development is based on the concept of a projective metrology where a pattern of active fiducials point sources is imaged onto an array detector. The position and orientation of the imaged pattern provides the necessary information to reconstruct the fiducial displacements with respect to the calibrated reference points, thus allowing obtaining an estimate of the pointing absolute knowledge error. In the present implementation, the fiducials shall be located close to the instrument’s detectors and will be imaged by a specially designed camera system located at the center of the Athena mirror. In this paper we will present the overall architecture and requirements of the metrology system under development for the Athena x-ray observatory mission.
Human activities have been identified as critical contributors to climate changes. Modern industrial development and increasing urbanisation have been affecting the environment at an unprecedented scale since the 19th century. In the two last decades the process has become even faster, also due to the impressive development of largely populated countries like India and China. Historical data records testify a direct correlation between increase in atmospheric CO2 levels and Earth's temperatures but processes underlying climate regulation and changes are only partially known. The improvement of knowledge of atmosphere and climate processes needs the availability of complete and reliable data about atmospheric composition and properties and space-based observations play a primary role. Implementation of a demonstration mission based on an occultation technique at optical wavelengths is proposed. Observations in the infrared spectral range vest a particular importance because this band exhibits many absorptive spectral lines due to greenhouse gases, identified as the main responsible of global warming, thus H2O, CO2, CH4, N2O, O3, and others can be observed with high accuracy. It is expected that the mission will demonstrate technical feasibility of an optical payload for limb sounding observations and provide useful inputs to climatic benchmarking (greenhouse gases and wind profile, as well as atmospheric thermodynamic properties). The identification and the preliminary definition of the instrument architecture and the identification of the critical technologies have been among the main tasks. Possible design options for the laser transmitter and the receiver are discussed, considering available technological solutions and technical constraints. Potential technological criticalities are illustrated too. The creation of performance models, analytical and numerical, facilitates and addresses the payload design activity, both at instrument level and at general system level.
Metis is a solar coronagraph mounted on-board the Solar Orbiter ESA spacecraft. Solar Orbiter is scheduled for launch in February 2020 and it is dedicated to study the solar and heliospheric physics from a privileged close and inclined orbit around the Sun. Perihelion passages with a minimum distance of 0.28 AU are foreseen.
Metis features two channels to image the solar corona in two different spectral bands: in the HI Lyman ∝ at 121.6 nm, and in the polarized visible light band (580 – 640 nm). Metis is a solar coronagraph adopting an “inverted occulted” configuration. The inverted external occulter (IEO) is a circular aperture followed by a spherical mirror which back rejects the disk light. The reflected disk light exits the instrument through the IEO aperture itself, while the passing coronal light is collected by the Metis telescope. Common to both channels, the Gregorian on-axis telescope is centrally occulted and both the primary and the secondary mirror have annular shape.
Classic alignment methods adopted for on-axis telescope cannot be used, since the on-axis field is not available. A novel and ad hoc alignment set-up has been developed for the telescope alignment.
An auxiliary visible optical ground support equipment source has been conceived for the telescope alignment. It is made up by four collimated beams inclined and dimensioned to illuminate different sections of the annular primary mirror without being vignetted by other optical or mechanical elements of the instrument.
Measurement of the static and temporal variation of Earth’s gravity field yields important information on water storage, seasonal and sub-seasonal water cycles, their impact on water levels and delivers key data to Earth’s climate models. The satellite mission GOCE (ESA) and GRACE (US-GER) resulted in in a significant improvement on our understanding of the system Earth. On GRACE and GRACE Follow-On two satellites are following each other on the same orbit with approx. 200 km distance to each other. A microwave inter-satellite ranging system measures the variation of the intersatellite distance from which the gravity field is derived. In addition, on GRACE Follow-On, which has been launched May 22nd 2018, a laser interferometer is added as an experiment to demonstrate the capability of this system to improve the ranging accuracy by at least one order of magnitude. To significantly improve the gravity field measurement accuracy, ESA is investigating the concept of a ‘Next generation gravity mission’ (NGGM), consisting of two pairs of satellites and a laser interferometer as the sole inter-satellite ranging system. Based on the heritage of the development of the laser ranging interferometer for GRACE Follow-On and the former and ongoing studies for NGGM, several concepts for the laser metrology instrument (LMI) for NGGM, namely the on- and off-axis variants of the transponder and the retroreflector concept have been investigated in detail with respect to their application for an inter-satellite distance of approx. 100 km. This paper presents the results of the detailed tradeoff between different concepts, including laser link acquisition, ranging noise contributors, instrument performance analyses, technology readiness levels of the individual instrument units and an instrument reliability assessment.
Within the ESA technology research project "Laser Interferometer High Precision tracking for LEO", Thales Alenia Space Italia is developing a laser metrology system for a Next Generation Gravimetric Mission (NGGM) based on satellite-to-satellite tracking. This technique is based on the precise measurement of the displacement between two satellites flying in formation at low altitude for monitoring the variations of Earth’s gravity field at high resolution over a long time period.
The laser metrology system that has been defined for this mission consists of the following elements:
• an heterodyne Michelson interferometer for measuring the distance variation between retroreflectors positioned on the two satellites;
• an angle metrology for measuring the orientation of the laser beam in the reference frames of the two satellites;
• a lateral displacement metrology for measuring the deviations of the laser beam axis from the target retro-reflector.
The laser interferometer makes use of a chopped measurement beam to avoid spurious signals and nonlinearity caused by the unbalance between the strong local beam and the weak return beam.
The main results of the design, development and test activities performed on the breadboard of the metrology system are summarized in this paper.
The Laser Metrology and Optic Active Control (LM&OAC) program has been carried out under ESA contract with the purpose to design and validate a laser metrology system and an actuation mechanism to monitor and control at microarcsec level the stability of the Basic Angle (angle between the lines of sight of the two telescopes) of GAIA satellite. As part of the program, a breadboard (including some EQM elements) of the laser metrology and control system has been built and submitted to functional, performance and environmental tests. In the followings we describe the mission requirements, the system architecture, the breadboard design, and finally the performed validation tests. Conclusion and appraisals from this experience are also reported.
A typical issue of modern space missions is the measurement of the relative attitude (orientation and position in space) of one part of the satellite with respect to the reference frame (main body) of the satellite or the relative attitude of two parts of the same satellite or even two or more satellites flying in formation.
We will describe the LAUE project, supported by the Italian Space Agency, whose aim is to demonstrate the capability to build a focusing optics in the hard X-/soft gamma-ray domain (80{600 keV). To show the lens feasibility, the assembling of a Laue lens petal prototype with 20 m focal length is ongoing. Indeed, a feasibility study, within the LAUE project, has demonstrated that a Laue lens made of petals is feasible. Our goal is a lens in the 80-600 keV energy band. In addition to a detailed description of the new LARIX facility, in which the lens is being assembled, we will report the results of the project obtained so far.
This paper summarizes the development of a successful project, LAUE, supported by the Italian Space Agency
(ASI) and devoted to the development of long foca length (up to 100—m) Laue lenses for hard X–/soft gamma–
ray astronomy (80-600 keV). The apparatus is ready and the assembling of a prototype lens petal is ongoing.
The great achievement of this project is the use of bent crystals. From measurements obtained on single crystals
and from simulations, we have estimated the expected Point Spread Function and thus the sensitivity of a lens
made of petals. The expected sensitivity is a few ×10−8 photons cm−2 s−1 keV−1). We discuss a number of open astrophysical questions that can settled with such an instrument aboard a free-flying satellite.
We present the status of LAUE, a project supported by the Italian Space Agency (ASI), and devoted to develop
Laue lenses with long focal length (from 10–15 meters up to 100 meters), for hard X–/soft gamma–ray astronomy
(80-600 keV). Thanks to their focusing capability, the design goal is to improve the sensitivity of the current
instrumention in the above energy band by 2 orders of magnitude, down to a few times 10−8 photons/(cm2 s keV).
We present the LAUE project devoted to develop an advanced technology for building a high focal length Laue
lens for soft gamma-ray astronomy (80-600 keV). The final goal is to develop a focusing optics that can improve
the current sensitivity in the above energy band by 2 orders of magnitude.
The capability to perform Phased-Reference Imaging and Narrow-Angle Astrometry with the VLTI will be given by the PRIMA instrument, which is based on the simultaneous observation of two celestial objects separated by 2 to 60 arcsec. PRIMA facility will allow VLTI instruments like MIDI and AMBER to observe objects with magnitude fainter than in single field mode. PRIMA astrometric camera will allow to measure relative angular positions of stars with 10 uas accuracy. This paper reviews the concept and the implementation of the Fringe Sensor Unit, the PRIMA fringe sensor/astrometric instrument, which is currently under integration/test at Alenia Spazio.
We describe a software tool developed to simulate the behaviour of the angle between two lines of sight in a dual view telescope assembly (usually referred to as basic angle) due to optical misalignments induced by thermo-mechanical fluctuations. The tool applies to a variety of reflective optical designs. In principle, not only the basic angle behaviour can be simulated, but also other optical parameters. As a practical example, we present and discuss results obtained from application of our software to the case of the Gaia baseline optical design. We show that the final error can be severely degraded by fluctuations of the basic angle due to thermo-mechanical effects.
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