The EnVisS (Entire Visible Sky) instrument is one of the payloads of the European Space Agency Comet Interceptor mission. The aim of the mission is the study of a dynamically new comet, i.e. a comet that never travelled through the solar system, or an interstellar object, entering the inner solar system. As the mission three-spacecraft system passes through the comet coma, the EnVisS instrument maps the sky, as viewed from the interior of the comet tail, providing information on the dust properties and distribution. EnVisS is mounted on a spinning spacecraft and the full sky (i.e. 360°x180°) is entirely mapped thanks to a very wide field of view (180°x45°) optical design selected for the EnVisS camera. The paper presents the design of the EnVisS optical head. A fisheye optical layout has been selected because of the required wide field of view (180°x45°). This kind of layout has recently found several applications in Earth remote sensing (3MI instrument on MetOp SG) and in space exploration (SMEI instrument on Coriolis, MARCI on Mars reconnaissance orbiter). The EnVisS optical head provides a high resolved image to be coupled with a COTS detector featuring 2kx2k pixels with pitch 5.5µm. Chromatic aberration is corrected in the waveband 550-800nm, while the distortion has been controlled over the whole field of view to remain below 8% with respect to an Fθ mapping law. Since the camera will be switched on 24 hours before the comet closest encounter, the operative temperature will change during the approaching phase and crossing of the comet’s coma. In the paper, we discuss the solution adopted for reaching these challenging performances for a space-grade design, while at the same time respecting the demanding small allocated volume and mass for the optical and mechanical design. The view expressed herein can in no way be taken to reflect the official opinion of the European Space Agency.
EnVisS (Entire Visible Sky) is a space camera aboard the Comet Interceptor ESA mission. This is the first F-class space mission, a new generation of fast ESA missions, and it is scheduled for launch in 2029. Comet Interceptor aims to study, by means of in situ observations, a dynamically new comet, or interstellar object, that enters the Solar System for the first time. Approaching the comet, three modules will detach: spacecraft A will provide remote sensing and communications, while spacecraft B1 and B2 will cross the coma and fly-by the nucleus. EnVisS is a fish-eye camera with a field of view (FOV) of 180° × 45°. It is mounted on B2, which is spin stabilized; the spin provides the scanning motion for the camera allowing imaging the whole sky (180° × 360°) including the comet. The EnVisS optical head is composed of ten lenses; the collected visible light passes through a three-strip filter assembly before reaching the detector. The central filter strip is a broadband filter, while the sides filter strips are linear polarizers, with the aim of studying the polarization state of the light reflected by both the comet coma and its core. The optical performance of EnVisS has been evaluated through ray tracing analyses. In this paper, the ghost study will be described and ghost images will be shown. This analysis, performed in the ZEMAX OpticStudio®, highlights which optical element causes the most intense ghost images and shows their distribution over the detector.
JANUS (Jupiter Amorum ac Natorum Undique Scrutator) is a high-resolution camera to be flown on board JUICE Spacecraft, devoted to investigate the atmosphere of Jupiter and the surfaces of his icy moons (Europa, Ganymede and Callisto), in the frame of ESA “Cosmic Vision” program. The scientific objectives that JANUS will reach constrained the design of JANUS Optical Head Unit (OHU), and in particular the specific measurement of Ganymede Libration, imposes highly stringent requirement on the Line of Sight (LoS) knowledge of the instrument. The differential thermal environment conditions of the mission orbits, as well as the instrument heat dissipation timelines, induce optical elements translation and rotations that correspond to a Line of Sight variation. During the mission, the LoS can be characterized with a stellar field or single star observation but none direct measurement of its variation can be retrieved during the scientific imaging sessions. To recover the LoS knowledge, a Structural Thermal Optical and Performance Analysis (STOP) is implemented. The optics and the instrument structure are Finit Element Modeled and processed (NASTRAN) imposing the temperature distributions obtained by the OHU Thermal Model (ESATAN-TMS). The obtained thermo-elastic deformations are then considered in the OHU Optical Model (ZEMAX). The resulting LoS and the dominant OHU temperature gradients are finally entangled with a proportionality relation, as well as its direction uncertainty. The indirect estimation of the LoS variation, and its uncertainty, can be establish, thanks to STOP analysis, in real time during operations as function of installed temperature sensor measurements.
The BepiColombo mission represents the cornerstone n.5 of the European Space Agency (ESA) and it is composed of two satellites: the Mercury Planetary Orbiter (MPO) realized by ESA and the Mercury Magnetospheric Orbiter (MMO) provided by the Japan Aerospace Exploration Agency (JAXA). The payload of the MPO is composed by 11 instruments. About half of the entire MPO data volume will be provided by the Spectrometer and Imagers for MPO BepiColombo Integrated Observatory System" (SIMBIO-SYS) instrument suite. The SIMBIO-SYS suite includes three imaging systems, two with stereo and high spatial resolution capabilities, which are the Stereoscopic Imaging Channel (STC) and High Resolution Imaging Channel (HRIC), and a hyper-spectral imager in the Vis-NIR range, named Visible and near Infrared Hyper-spectral Imager (VIHI). In order to test and predict the instrument performances, a radiometric model is needed. It consists in a tool that permits to know what fraction of the incoming light is measured by the detector. The obtained signal depends on the detector properties (such as quantum efficiency and dark current) and the instrument transmission characteristics (transmission of lenses and filter strips, mirrors reflectivity). The radiometric model allows to correlate the radiance of the source and the signal measured by each instrument. We used the Hapke model to obtain the Mercury reflectance, and we included it in the radiometric model applied to the STC, HRIC and VIHI channels. The radiometric model here presented is a useful tool to predict the instruments performance: it permits to calculate the expected optical response of the instrument (the position in latitude and longitude of the filter footprints, the on-ground px dimensions, the on-ground speed, the smearing and the illumination angles of the observed points), and the detector behavior (the expected signal and the integration time to reach a specific SNR). In this work we derive the input flux and the integration times for the three channels of SIMBIO-SYS, using the radiometric model to obtain the source radiance for each Mercury surface area observed.
JANUS is the camera of the ESA mission JUICE, dedicated to high-resolution imaging in the extended-visible wavelength region (340 – 1080nm). The camera will observe Jupiter and its satellites providing detailed maps of their surfaces and atmospheres. During the mission, the camera will face a huge variety of observing scenarios ranging from the imaging of the surfaces of the satellites under varying illumination conditions to limb observation of the atmospheres. The stray-light performance of JANUS has been studied through non-sequential ray-tracing simulations with the aim to characterize and optimize the design. The simulations include scattering effects produced by micro-roughness and particulate contamination of the optical surfaces, the diffusion from mechanical surfaces and ghost reflections from refractive elements. The results have been used to derive the expected stray-light performance of the instrument and to validate the instrument design.
KEYWORDS: Space operations, Optical components, Ions, Particles, Electrons, Particles, Coating, Gold, Platinum, Monte Carlo methods, Information technology
Space exploration is linked to the development of increasingly innovative instrumentation, able to withstand the operation environment, rich in ion particles and characterized by high temperatures. Future space missions such as JUICE and SOLAR ORBITER will operate in a very harsh and extreme environment-. Electrons and ions are considered among the causes of potential damage of the optical instrumentation and components. Development of hard coatings capable to preserve their optical properties is pivotal. Different coating materials have been exposed to ion irradiation in particle accelerators. Change in optical performances has been observed in the extreme ultraviolet and visible spectral region and structural properties have been analyzed by different techniques. The knowledge of the damage mechanisms and thresholds allows the selection of more promising candidate materials to realize the optical components for the new frontiers space missions.
JANUS (Jovis Amorum Ac Natorum Undique Scrutator) is a high-resolution visible camera designed for the ESA space
mission JUICE (Jupiter Icy moons Explorer). The main scientific goal of JANUS is to observe the surface of the Jupiter
satellites Ganymede and Europa in order to characterize their physical and geological properties. During the design phases,
we have proposed two possible optical configurations: a Three Mirror Anastigmat (TMA) and a Ritchey-Chrétien (RC)
both matching the performance requirements. Here we describe the two optical solutions and compare their performance
both in terms of achieved optical quality, sensitivity to misalignment and stray light performances.
SIMBIOSYS is a highly integrated instrument suite that will be mounted on-board BepiColombo, which is the fifth cornerstone mission of the European Space Agency dedicated to the exploration of the planet Mercury and it is expected to be launched in 2016. The SIMBIOSYS instrument consists of three channels: the STereo imaging Channel (STC), with broad spectral bands in the 400–950 nm range and medium spatial resolution (up to 50 m/px); the High Resolution Imaging Channel (HRIC), with broad spectral bands in the 400–900 nm range and high spatial resolution (up to 5 m/px), and the Visible and near- Infrared Hyperspectral Imaging channel (VIHI), with high spectral resolution (up to 6 nm) in the 400–2000 nm range and spatial resolution up to 100 m/px. The on-ground calibration system has to cover the full spectral range of the instrument, i.e. from 400 to 2000 nm, and the emitted radiance has to vary over a range of four decades to account for both simulations of Mercury surface acquisition and star field observations. The methods and the results of the measurements done to calibrate the integrating sphere needed for the on-ground radiometric testing of the SIMBIOSYS instrument will be given and discussed. Temporal stability, both on short and long periods, spatial and spectral uniformity, and the emitted radiance for different lamp configurations and different shutter apertures have been measured. The results of the data analysis confirm that the performance of the integrating sphere is well suited for the radiometric calibration of all the three different channels of the SIMBIOSYS instrument.
The JANUS (Jovis, Amorum ac Natorum Undique Scrutator) will be the on board camera of the ESA JUICE satellite dedicated to the study of Jupiter and its moons, in particular Ganymede and Europa. This optical channel will provide surface maps with plate scale of 15 microrad/pixel with both narrow and broad band filters in the spectral range between 0.35 and 1.05 micrometers over a Field of View 1.72 × 1.29 degrees2. The current optical design is based on TMA design, with on-axis pupil and off-axis field of view. The optical stop is located at the secondary mirror providing an effective collecting area of 7854 mm2 (100 mm entrance pupil diameter) and allowing a simple internal baffling for first order straylight rejection. The nominal optical performances are almost limited by the diffraction and assure a nominal MTF better than 63% all over the whole Field of View. We describe here the optical design of the camera adopted as baseline together with the trade-off that has led us to this solution.
JANUS (Jovis, Amorum ac Natorum Undique Scrutator) is the visible camera selected for the ESA JUICE mission to the Jupiter system. Resources constraints, S/C characteristics, mission design, environment and the great variability of observing conditions for several targets put stringent constraints on instrument architecture. In addition to the usual requirements for a planetary mission, the problem of mass and power consumption is particularly stringent due to the long-lasting cruising and operations at large distance from the Sun. JANUS design shall cope with a wide range of targets, from Jupiter atmosphere, to solid satellite surfaces, exosphere, rings, and lightning, all to be observed in several color and narrow-band filters. All targets shall be tracked during the mission and in some specific cases the DTM will be derived from stereo imaging. Mission design allows a quite long time range for observations in Jupiter system, with orbits around Jupiter and multiple fly-bys of satellites for 2.5 years, followed by about 6 months in orbit around Ganymede, at surface distances variable from 104 to few hundreds km. Our concept was based on a single optical channel, which was fine-tuned to cover all scientific objectives based on low to high-resolution imaging. A catoptric telescope with excellent optical quality is coupled with a rectangular detector, avoiding any scanning mechanism. In this paper the present JANUS design and its foreseen scientific capabilities are discussed.
One of the key issues concerning the measurement of size and density of dust grains based on light scattering system is
the compensation of the stray light due to the optical components misalignment and to the possible contamination of
these components by the dust particles during the measurement runs. This paper focuses on the case study of MEDUSA
(Martian Environmental DUst Systematic Analyzer), one of the experiments initially selected for the ExoMars mission,
planned by the European Space Agency (ESA), with the scientific objective to study water and dust in Mars atmosphere.
The MEDUSA experiment foresees an Optical System (OS) aimed at measuring atmospheric dust content and size
distribution. One pump assures that the proper gas and dust flow circulates inside the instrument. This paper reports the
description and trade off analysis of several techniques for the stray-light compensation implemented on the MEDUSA
OS Proximity Electronics (PE) Test Board (2006), designed and manufactured by INAF-Osservatorio Astronomico di
Capodimonte, in the frame of the MEDUSA Bread Board (B/B) activities. The PE Test Board can implement more than
one compensation mode, such as: AC coupling, DC coupling with offset compensation via external loop and DC
coupling with offset compensation via on board HW loop. The choice among the mentioned compensation modes shall
be done also according to the configuration of the overall acquisition system, implemented by the Main Electronics
(ME), as explained in the reported trade-off analysis. For the architecture configuration of the industrial breadboard
(2008) the preferred solution was the one based on the DC coupling with on board HW loop, for which some test results
are reported.
MEDUSA (Martian Environmental DUst Systematic Analyzer) is one of the experiments selected for the ExoMars
mission, planned by the European Space Agency (ESA), with the scientific objective to study water and dust on Mars, in
relation to the search of signs of life forms. To achieve this goal, the MEDUSA experiment is based on an optical system
and two micro-balances, integrated together with a dust deposition and electrification sensor. This paper focuses on the
Proximity Electronics (PE) envisaged for the Optical System and reports the results obtained during the development
activities carried out in the breadboard implementation of the instrument. A photodiode amplifier with very high gain
(107) and large output dynamics was developed. The compensation of the offset due to stray light and electronic bias has
been implemented via an adaptive control. The environmental constraints imposed by the space mission to Mars have
been taken into account during the design, not only for the qualified components selection, but also for the minimization
of the overall mass and power consumption.
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