CHEOPS (CHaracterizing ExOPlanets Satellite) is an ESA Small Mission, planned to be launched in early 2019 and whose main goal is the photometric precise characterization of the radii of exoplanets orbiting bright stars (V<12) already known to host planets. The telescope is composed by two optical systems: a compact on-axis F/5 Ritchey-Chrétien, with an aperture of 320 mm and a Back-End Optics, reshaping a defocused PSF on the detector. In this paper we describe how alignment and integration, as well as ground support equipment, realized on a demonstrator model at INAF Padova, evolved and were successfully applied during the AIV phase of the flight model telescope subsystem at LEONARDO, the Italian industrial prime contractor premises.
PLATO (Planetary Transits and Oscillations of stars) is a new space telescope selected by ESA to detect terrestrial exoplanets in nearby solar-type stars. The telescope is composed by 26 small telescopes to achieve a large instantaneous field of view. INAF-OAPD is directly involved in the optical design and in the definition and testing of the alignment strategy. A prototype of the Telescope Optical Unis (TOU) was assembled and integrated in warm condition (room temperature) and then the performance is tested in warm and cold temperature (-80C). The mechanical structure of the TOU is representative in terms of thermal expansion coefficient and Young's modulus with respect to the actual one. A dedicated GSE (Ground Support Equipment) is used to manipulate the lenses. By co-align an interferometer and a laser with respect to the center of the third CaF2 lens, a several observables references are used to define the position and tilt of the chief ray. The total procedure tolerances for every lens is 30'' in tilt, between 15-40 μm for focus and 22 μm for decentering and the total error budget of the optical setup bench is below this requirement. In this paper, we describe the AIV procedure and test performed on the prototype of the TOU in the INAF laboratory.
PLATO (PLAnetary Transits and Oscillation of stars) is the ESA Medium size dedicated to exo-planets discovery, adopted in the framework of the Cosmic Vision program. The PLATO launch is planned in 2026 and the mission will last at least 4 years in the Lagrangian point L2. The primary scientific goal of PLATO is to discover and characterize a large amount of exo-planets hosted by bright nearby stars, constraining with unprecedented precision their radii by mean of transits technique and the age of the stars through by asteroseismology. By coupling the radius information with the mass knowledge, provided by a dedicated ground-based spectroscopy radial velocity measurements campaign, it would be possible to determine the planet density. Ultimately, PLATO will deliver the largest samples ever of well characterized exo-planets, discriminating among their ‘zoology’. The large amount of required bright stars can be achieved by a relatively small aperture telescope (about 1 meter class) with a wide Field of View (about 1000 square degrees). The PLATO strategy is to split the collecting area into 24 identical 120 mm aperture diameter fully refractive cameras with partially overlapped Field of View delivering an overall instantaneous sky covered area of about 2232 square degrees. The opto-mechanical sub-system of each camera, namely Telescope Optical Unit, is basically composed by a 6 lenses fully refractive optical system, presenting one aspheric surface on the front lens, and by a mechanical structure made in AlBeMet.
CHEOPS (CHaracterizing ExOPlanets Satellite) is an ESA Small Mission, planned to be launched in mid-2018 and
whose main goal is the photometric precise characterization of radii of exoplanets orbiting bright stars (V<12) already
known to host planets.
Given the fast-track nature of this mission, we developed a non-flying Demonstration Model, whose optics are flight
representative and whose mechanics provides the same interfaces of the flight model, but is not thermally representative.
In this paper, we describe CHEOPS Demonstration Model handling, integration, tests, alignment and characterization,
emphasizing the verification of the uncertainties in the optical quality measurements introduced by the starlight simulator
and the way the alignment and optical surfaces are measured.
The optical quality of the LLT unit of SUBARU NAOJ telescope was improved by new athermalized supports of the
optics, in order to operate at the best performance at temperatures below 0°C. The ultimate wavefront correction of
the whole LLT, that expands a laser beam from 40 mm to 500 mm, was made by Ion Beam Figuring on the small 40
mm LLT entrance window, in accordance to the WFE measured in operating conditions. The correction of small
optics including high spatial frequencies, resulting by the LLT expanding ratio, was possible by a special technique
of IBF process developed at the Astronomical Observatory of Brera (INAF-OAB), using a concentrator of the ion
beam size, able to force the broader beam emitted from an ion source into a smaller spot having large removal rate.
This paper reports some details about the optical technologies used for manufacturing the mirrors of the Refocusing
Mechanism Assembly (RMA). The RMA is a novel cryogenic mechanism designed by Galileo Avionica for the Near
Infrared Spectrograph (NIRSpec), one of the instruments of the James Webb Space Telescope (JWST). The RMA
contains two flat mirrors in Zerodur coated with Protected Silver. Severe constraints for accommodation in the
Nirspec imposed very lightweighted substrates to the RMA mirrors and required state of art technologies in order to
achieve the specified quality and its maintenance at cryogenic temperatures.
A new technology has been developed to grow layers of amorphous hydrogenated Silicon Carbide in vacuum, at
temperatures below 100-120°C by Physical Enhanced Chemical Vapour Deposition (PE-CVD) technology. The layers
have been used either to improve the surface quality of SiC mirror substrates (produced by methods different of the
CVD approach, like e.g. sintered SiC) as a super-polishable cladding coatings, or to form self-sustaining thin mirrors in
SiC. It should be noted that the PE-CVD claddings can be applied also to substrates different than SiC, as e.g. metals
like Al or Kanigen, in order to create a high durability polishable external layer. It this paper we present the results of a
wide characterization of the new material, considering the mechanical, structural and optical properties that are the most
indicative parameters for its application in optics, with particular reference to the production of mirrors for ground and
space astronomical applications.
The Ion Beam Figuring is a well known technique able to correct shape errors on optical surfaces with high accuracy.
The size of the ion beam dictates strongly the higher spatial frequencies that can be corrected on the optical surface. The
correction of small optics of some cm in diameter or containing high spatial frequencies can be very time consuming or
impossible. A system that permits the Ion Beam Figuring of small optical components has been developed in the
Astronomical Observatory of Brera (INAF-OAB). It has a small ion beam size and large removal rate. The system
employs a concentrator able to force the broader beam emitted from an ion source into a smaller spot having large
removal rate. The concentrator is placed between the ion source and the optical surface to be figured and doesn't
influence the long term stability of the source. It consists of a conical cavity in which is injected the beam extracted from
the grids of the source. The grazing incidence angle of impact of the ions with the walls of the cone ensure a very low
level of sputtering of the cone material and meanwhile permits the creation of a very small spot removal function having
large removal rate. To demonstrate its functionality a number of test optics has been figured using this system with very
The Launch Telescope Assembly (LTA) consists of a 50 cm class beam expander (angular magnification 12.5x) and it is an essential subsystem of Laser Guide Star Facility (LGSF), which provides an artificial reference star for adaptive compensation of atmospheric turbulence for one of the VLT (Very Large Telescope) 8-meters telescopes of ESO (European Southern Observatory). LTA is an afocal system, with parabolic primary and secondary mirrors, a flat 45° tertiary mirror and an exit window. It is fed with collimated Sodium laser beam, expanding and directing it along the line of sight of the 8-m telescope. Resonance backscatter from atmospheric Sodium layer at about 90 km altitude produces a point like artificial source at this altitude. The high optical quality requested for very fast optics, the severe constraints of the layout accommodation and the mass reduction made LTA a technological challenge that Galileo Avionica has been able to design, realise, align and test as requested. LTA will be positioned atop the secondary mirror unit of one of the four VLTs.
Mirror prototypes in cold-pressed sintered SiC-54 and in Carbon-SiC (Cesic) have been designed, manufactured and optically tested. The scope of the work was the development of materials, technologies and manufacturing processes to get high quality optics very stable at cryotemperatures. The activity has been performed under ESA funding in the frame of the technology development for the JWST/NIRSpec program. A description of the polishing performance and final testing results are discussed.
In view of the NIRSpec-JWST program, a trade-off study is currently in progress under an ESA-ESTEC contract, to select design, blank materials, coatings and relevant technologies for high quality mirrors operating at cryogenic temperatures. The behavior of two prototype lightweight mirrors, made in cold- pressed-sintered SiC and in Carbon-SiC (Cesic) are compared by interferometric measurements at 20 K. The prototypes are spherical mirrors, but realized using optical manufacturing technologies suitable for highly demanding aspherics (i.e. computer controlled polishing, ion beam figuring), in the perspective of the foreseen NIRSpec-TMA(s) optics.
By combining the excellent intrinsic thermo-mechanical properties of the silicon carbide (SiC) with a structural design based on a sandwich structure composed of two SiC face sheets deposited on a foam core of the same material, it is possible to manufacture very light and stiff mirrors for space applications. This paper presents some results of a technological development study, including the realization of a lightweight athermalized SiC telescope with a 310 mm diameter foamed-SiC primary mirror. An ion beam figuring equipment has been developed to improve the optical quality of the mirror.
Aspherics up to 500 nm diameter in optical glass or in ceramic substrates have been fabricated using area- compensated polishing tools and conventional optical shop machines. The tool forms are derived starting from the actual shape of the part under figuring. The figure error is measured using an interferometer mounted on-line with the polishing machine. Measurements are taken after each polishing step to compute the new tool form. The process speeds up the fabrication of aspheres and it improves repeatability in the manufacturing of axisymmetrical optics using moderate cost equipment's up to astronomical requirements. In the paper we present some examples of polishing results using the above mentioned approach on different aspherics for space applications.
The in-flight radiometric calibration of satellite multispectral sensor for earth and atmospheric observations can be conveniently based on solar diffusers. Theoretically, a knowledge of the spectral bi-directional scatter distribution function (BSDF) of the diffuser panel, and the solar incidence angle is all that is needed to allow the retrieval of the earth albedo in the observed direction. At the request of the ESA, the Centre Spatial de Liege, with the support of Officine Galileo as subcontractor, is currently designing a high-versatility high-accuracy BSDF measurement set-up with application to the calibration of space solar diffusers. This instrument will allow a BSDF measurements uncertainty within 1 percent for any angle in the wavelength range from 200 nm to 2400 nm. Vacuum measurements, polarization analysis capabilities and thermalization of the test sample between 200K and 300K are other unique features of this set-up.
The Optical Monitor is an ancillary instrument of the JET-X experiment on board of the satellite SPECTRUM-X-GAMMA. It consists of a Ritchey-Chretien telescope with an aperture of 230 mm, and two CCD detectors. The scientific objectives are the observations in the optical and UV band simultaneously with X-ray observations, the real time identification of X- ray sources with Mv <EQ 22 and detection of their variability, the improvement of the post-facto spacecraft attitude reconstruction (as a backup of the Attitude Monitor), and the serendipitous mode search for microvariability of the bright stars falling in the field of view.
The XMM Optical Monitor (XMM/OM) is a co-aligned telescope devoted to make observations of the X-ray sources both in the UV, visible and near-IR spectral bands, simultaneously with the X-ray instrument on the X-ray Multi-Mirror (XMM) satellite. The OM telescope is a Ritchey-Chretien with 300 mm clear aperture, for real time identification of sources up to magnitude mv equals 24. In the design of the telescope, particular care was paid in the selection of the optomechanical architecture and in the thermal and structural analysis, since the adopted optical scheme requires high stability of the structure. The paper highlights the major critical aspects and the criteria followed in the trade-off and design phases.
HRTIR for High Resolution Thermal Infrared Radiometer is an earth observation instrument candidate to the European Space Agency polar platform beyond Envisat 1. A preliminary design of the instrument has been performed in order to identify the most critical points and breadboard them. The instrument is a push broom concept providing an on ground spatial resolution of 50 m for a swath width of 50 km and a temperature sensitivity of 0.1 K in 3 spectral bands in the 8 to 12.5 micrometers range. A compact dioptric system has been selected for the optics and the focal plane consists of three linear arrays of 1000 HgCeTe photovoltaic elements hybridized on a CCD multiplexer and cooled down to 50 K inside a cryostat by mechanical cryocoolers. The HgCdTe IRCCD with a cut-off wavelength longer than 12.5 micrometers has been identified as the most critical technology and breadboarded. A complete detection chain with a long wavelength linear array of 222 pixels obtained by butting of three sub-arrays, a CCD multiplexer, a driving and processing electronics up to digital signal has been manufactured. The linear array is housed in a cryostat similar to the foreseen flight model but coupled to a laboratory cryogenic system. The IRCCD has been tested at unit level and the complete detection chain have been characterized in laboratory in conditions close to the flight. The test results have demonstrated the feasibility of the IRCCD at long wavelength with excellent performances. The instrument radiometric performances have been validated from the breadboard test results.
HRIS is proposed as a spaceborne, high-resolution imaging spectrometer designed to image a variable (+/- 30 degree(s)) 30 km swath with 40 m SSP pixel size in the spectral range from 450 to 2340 nm with an average 10 nm spectral bandwidth. HRIS is conceived as a push-broom imager with two-dimensional detector arrays for spectral and spatial coverage. The challenging requirements for this instrument will be discussed as well as the concept derived against these requirements. Emphasis is on the optical definition, particularly the spectrometer optics, the focal plane assembly--here mostly the hybrid SWIR CMT detector array--and the calibration concept which includes two external references, ratioing radiometers and an internal reference. The other subunits will be described briefly only. The presentation will conclude with a preliminary development plan.