The optical design of the Moons And Jupiter Imaging Spectrometer (MAJIS), is discussed. MAJIS is a compact visible and near-infrared imaging spectrometer covering the spectral range from 0.5 to 5.54 μm (split into two channels), designed for the Jupiter Icy moons Explorer (JUICE) mission. The MAJIS optical layout is constituted by a TMA telescope shared between the two channels, as well as the slit and a collimator, a dichroic filter that splits the light between the channels (VIS-NIR and IR), each one endowed with its own grating, objective and detector. A flat mirror mounted in a Scan Unit before the telescope allows scanning the line of sight in a direction perpendicular to the slit. The collimator has a Schmidt off-axis configuration, with a specular correcting plate for each channel (the dichroic is inserted between the collimator primary mirror and the correcting plate). With the same conceptual layout in both channels, the collimated light is reflected by a flat ruled grating and crosses a completely dioptric objective. The objectives have the same focal length of the collimator, so both spectrometers have unitary magnification. A linear variable order rejection filter is placed in front of the detector so to reject the higher orders dispersed by the grating. A calibration unit allows radiometric and spectral calibration of both channels, with an incandescent lamp and a black body illuminating a common diffuser. Calibration is realized thanks to an extra-rotation of the Scan Unit. The developed design is optimized to work at cryogenic temperatures, with a good optical quality along the whole FOV and a good correction for transverse chromatic aberration and distortions.
In the present work we describe a dedicated and fast monochromatic radiative transfer code, developed for computing Martian radiance spectra as seen by the Thermal Emission Spectrometer (TES), and its Jacobians with respect to gas, dust aerosol and ice concentrations, atmospheric temperatures, and surface emissivity. The code accuracy has been tested comparing its results with a state-of-art line-by-line radiative transfer model, and it has been optimized for simulating nadir-viewing spectra. The model is well-suited to simulate spectra with di erent amounts of methane in the atmosphere, whose detection is currently one of the most fascinating issues concerning the Martian atmospheric chemistry and planetary dynamics.
The Mars Infrared MApper (MIMA) is a FT-IR miniaturised spectrometer which is being developed for ESA ExoMars
Pasteur mission. MIMA will be mounted on the rover mast and so it must be compact and light-weight. The scientific
goals and its thermo-mechanical design are presented in two companion papers [1] and [2]. In this work the optical
design will be reviewed and the results of the tests performed on some optical components will be presented. The design
has faced challenging constraints mainly linked to the requirement of keeping the performances good enough to fulfil the
scientific objectives of the mission, while, at the same time, it was imperative to keep the overall size and weigh within
the allocated resources. In addition the instrument must be able to operate in the very harsh environment of the Martian
surface and to withstand, without permanent damage, even harsher conditions as well as the severe dynamic loads
expected at landing on Mars. The chosen solution is a single channel double pendulum interferometer, covering the
spectral range between 2 and 25 micron, crucial for the scientific interpretation of the recorded spectra, with a resolution
variable between 10 and 5 cm-1. Since the spectral range is too wide to be covered by a single detector, it has been
decided to use two different detectors, mounted side by side, in a customised case. Such innovative solution has
obviously pros and cons and the optical design has been driven by the need to reduce the inconveniences, while
maintaining the advantages.
The Mars Infrared MApper (MIMA) is a FT-IR miniaturised spectrometer which is being developed for ESA ExoMars
Pasteur mission. The Martian Infrared MApper Fourier Spectrometer is designed to provide remote measurements of
mineralogy and atmosphere of the scene surrounding a Martian rover and guide it to key targets for detailed in situ
measurements by other rover experiments. Among the main scientific objectives of the MIMA instrument are to assist
the rover in rock/soils selection for further in-situ investigation and to identify rocks and soils on the Martian surface
which provide evidence of past/present biological activity. The instrument is also designed to measure the water vapour
abundance and vertical distribution and its diurnal and seasonal variation, dust opacity, optical properties, composition,
diurnal and seasonal variation. The instrument is a double pendulum interferometer providing spectra in the 2 - 25 μm
wavelength domain with a resolving power of 1000 at 2 μm and 80 at 25 μm. The radiometric performances are SNR >
40 in the near infrared and a NEDe = 0.002 in the thermal region. The instrument design is very compact, with a total
mass of 1kg and an average power consumption of 5 W.
The Mars Infrared MApper (MIMA) is a FT-IR miniaturized spectrometer which is being developed for ESA ExoMars
Pasteur mission. MIMA will be mounted on the rover mast and so it must be compact and light-weight. The scientific
goals and its optical design are presented in two companion papers [1] [2]; the focus of this work is on the thermomechanical
design and testing. The instrument design faces challenging constraints both from the expected environment
and the allocated resources. The temperatures during operation are expected to be from -120 °C to +30 °C with the
presence of a low density but thermally effective atmosphere. Severe dynamic loads are foreseen during launch and
moreover at landing on Mars. The overall size is limited to an envelope of 140 mm x 140 mm x 120 mm and the mass to
less than 1 kg. The expected performances of this instrument should be comparable with those of much heavier ones
built in the past. An instrument compliant with these constraints has been conceived, introducing many innovative
solution with respect to the past experiences and making use of intensive modeling and testing to prove the survival to
the harsh environment.
Among the most challenging problems the mounting of the brittle KBr optics and the matching of its thermal expansion
coefficient with that of the supporting aluminium structure, in a temperature interval of more than 200 °C. Most of the
components have undergone thermovacuum tests in the low temperature range because none of them was expected to be
used in the -100 °C range.
Francis Reininger, Angioletta Coradini, Fabrizio Capaccioni, M. Capria, Priscilla Cerroni, M. De Sanctis, G. Magni, Pierre Drossart, Maria Barucci, D. Bockelee-Morvan, Jean-Michel Combes, J. Crovisier, T. Encrenaz, Jean-Michel Reess, Alain Semery, Didier Tiphene, Gabriele Arnold, Uri Carsenty, Harald Michaelis, Stefano Mottola, Gerhard Neukum, G. Peters, Ulrich Schade, Fredric Taylor, Simon Calcutt, Tim Vellacott, P. Venters, R. Watkins, Giancarlo Bellucci, Vittorio Formisano, Francesco Angrilli, Gianandrea Bianchini, Bortolino Saggin, E. Bussoletti, L. Colangeli, Vito Mennella, S. Fonti, Jean-Pierre Bibring, Yves Langevin, B. Schmitt, M. Combi, U. Fink, Thomas McCord, Wing Ip, Robert Carlson, Donald Jennings
The visible infrared thermal imaging spectrometer (VIRTIS) is one of the principal payloads to be launched in 2003 on ESA's Rosetta spacecraft. Its primary scientific objective s are to map the surface of the comet Wirtanen, monitor its temperature, and identify the solids and gaseous species on the nucleus and in the coma. VIRTIS will also collet data on two asteroids, one of which has been identified as Mimistrobell. The data is collected remotely using a mapping spectrometer co-boresighted with a high spectral resolution spectrometer. The mapper consists of a Shafer telescope matched to an Offner grating spectrometer capable of gathering high spatial, medium spectral resolution image cubes in the 0.25 to 5 micrometers waveband. The high spectral resolution spectrometer uses an echelle grating and a cross dispersing prism to achieve resolving powers of 1200 to 300 in the 1.9 to 5 micrometers band. Both sub-systems are passively cooled to 130 K and use two Sterling cycle coolers to enable two HgCdTe detector arrays to operate at 70 K. The mapper also uses a silicon back-side illuminated detector array to cover the ultra-violet to near-infrared optical band.
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