SIMBIO-SYS

PI: E.Flamini (ASI)

CoPIs: F.Capaccioni (IAPS-INAF), G.Cremonese (OAPD-INAF), P.Palumbo (Universita’ Parthenope, Napoli), A.Dpressoundiram (LESIA, Observatoire de Meudon), Y.Langevin (IAS-Orsay, Paris).

The Spectrometer and Imagers for MPO BepiColombo Integrated Observatory System (SIMBIOSYS) instrument suite is an integrated package for the imaging and spectroscopic investigation of the surface of Mercury.

Scientific objectives

The science goals of SIMBIO-SYS are:

• surface geology (stratigraphy, geomorphology),

• volcanism (lava plain emplacement, volcanoes identification),

• global tectonics (structural geology, mechanical properties of lithosphere),

• surface age (crater population and morphometry, degradation processes),

• surface composition (maturity and crustal differentiation, weathering, rock-forming minerals abundance determination)

• geophysics (libration measurements, internal planet dynamics) .

SIMBIOSYS incorporates capabilities to perform 50-200 m spatial resolution global mapping in both stereo mode and color imaging, high spatial resolution imaging (5 m/px scale factor at periherm) in panchromatic and three broad-band filters, and imaging spectroscopy in the spectral range 400-2200 nm.

Stereo Camera (STC) for the BepiColombo mission

The STC is a double-wide-angle camera designed to image each portion of Mercury’s surface from two different perspectives, providing panchromatic stereo image pairs required for reconstructing the digital terrain model (DTM) of the planet’s surface. In addition, it has the capability of imaging some portion of the planet in four different spectral bands. It is composed by two channels with the orientation of +20° and −20° from the nadir direction and adopts a catadioptric optical design with common detector in order to save mass and power.

The figure shows the possible stereo imaging configurations:

(a) generic stereo imaging configuration: two independent cameras oriented along two slanted viewing directions;

(b) a single camera with large FoV simultaneously covering both stereo angles and also the nadir-looking direction, if needed;

(c) the stereo configuration proposed for STC, in which most of the optical elements and the detector are common to both subchannels.

They are not drawn to scale; the expected image aspect and size are reported as a square area placed near each configuration.

The adopted STC configuration is an intermediate solution between the “two cameras” and the “single camera” one. The proposed design can be consider as composed of two “sub-channels” looking at the desired stereo angles and that, thanks to the novel optical design, share the majority of the optical elements and the detector. With respect to classical two- or single-camera designs, this solution allows to reach good stereo performance with general compactness, saving of mass, volume and power resources.

STC scientific requirements.

STC overall optical design layout. The inset shows a different projection of the focal plane region.

At periherm, each panchromatic strip corresponds to an area of about 40  19 km² on the Mercury surface, and each colored strip to an area of about 40  3 km².

Considering that the two sub-channels are projecting their images side by side on the same plane, the useful area on the system focal plane has a rectangular shape, which would obviously be optimally coupled with a rectangular sensor array. However, due to programmatic reasons, a squared 2048  2048 pixel array had to be adopted, with the result that large part of the detector will not be used. See the following figure for useful filter strip image position and distribution on the 2kx2k detector. The selected detector is a hybrid Si_PIN device; that kind of detector is particularly useful both in term of radiation hardness, given the hostile Mercury environment, both for the capability of snapshot image acquisition, which is less demanding in terms of S/C pointing and stability.

Position and size of useful filter strips image on the full 2kx2k detector area (in black).

STC optical characteristics.

References

1. M.Sgavetti, L.Pompilio, C.Carli, C.De Sanctis, F.Capaccioni, G.Cremonese, E.Flamini, Mineral and rock composition of the Mercury and Moon surfaces: expected knowledge advances from BepiColombo SIMBIO-SYS data, 2007, Plan.Space Sci., 55, 1596-1613.

2. Massironi M., Giacomini L., Cremonese G., Capria M. T .,Da Deppo V. , Forlani G., Naletto G., Pasquaré G., Flamini E., Simulations using terrestrial geological analogues of the Hermean surface to examine 3D rendering potentialities of the STereoscopic imaging Channel of the SIMBIO-SYS package (Bepi-Colombo mission), 2008, Plan.Space Scie., 56, 1079.

3. G.Cremonese, D.Fantinel, E.Giro, M.T.Capria, V.Da Deppo, G.Naletto, G.Forlani, M.Massironi, L.Giacomini, M.Sgavetti, E.Simioni, C.Bettanini, S.Debei,. M.Zaccariotto, P.Borin, L.Marinangeli, E.Flamini, The stereo camera on the BepiColombo ESA/JAXA mission: a novel approach, 2009, Advances in Geosciences, 15, 305.

4. Flamini, E., Capaccioni, F., Colangeli. L., Cremonese, G., Doressoundiram, A., Josset, J.L., Langevin, Y., Debei, S., Capria, M.T., DeSanctis, M.C., Marinangeli, L., Massironi, M., Mazzotta Epifani, E., Naletto, G., Palumbo, P., Eng, P., Roig, J.F., Caporali, A., DaDeppo, V., Erard, S., Federico, C., Forni, O., Sgavetti, M., Filacchione, G., Giacomini, L., Marra, G.,Martellato, E., Zusi, M., Cosi, M., Bettanini, C., Calamai, L., Zaccariotto, M., Tommasi, L., Dami, M., Ficai Veltroni, I., Poulet, F., Hello, Y., and the SIMBIO-SYS Team, SIMBIO-SYS: the Spectrometers and Imagers Integrated Observatory SYStem for BepiColombo Orbiter, 2010, Plan.Space Sci., 58, 125.

5. V.Da Deppo, G.Naletto, G.Cremonese, L.Calamai, Optical design of the single-detector planetary stereo-camera for the BepiColombo ESA mission to Mercury, 2010, Applied Optics, 49, 2910.

6. E.,Segato, V.,Da Deppo, S.,Debei, G.,Cremonese, G.Cherubini, Effects of thermal deformation on the sensitivity of optical systems for space application, 2010, SPIE proc.7738.

7. V.Da Deppo, G.Cremonese, G.Naletto, Ghost images determination for the Stereoscopic Imaging Channel of SIMBIOSYS for the BepiColombo ESAmission, 2011, SPIE, 8167, 81671U.

9. E.Simioni, G.Naletto, G.Forlani, G.Cremonese, V. Da Deppo, M.Massironi, E.Segato, A new stereo algorithm based on snakes, 2011, Photogrammetry Engineering & Remote Sensing, 77, 495-507.

10. G.Naletto, M.Cesaro, A.Albasini, G.Cremonese, V.Da Deppo, G.Forlani, C.Re, R.Roncella, G.Salemi, E.Simioni, Innovative optical setup for testing a stereo camera for space application, 2012, SPIE Space Telescope and instrumentation. Vol.8442.

11. E.Simioni, V.Da Deppo, G.Naletto, D.Borrelli, M.Dami, I.Ficai Veltroni, G.Cremonese, Preliminary LSF and MTF determination for the Stereo Camera of the BepiColombo mission, SPIE, Space Telescopes and Instrumentation, 2014.

12. V.Da Deppo, E.Martellato, G.Rossi, G.Naletto, V.Della Corte, F.Capaccioni, M.Baroni, L.Tommasi, M.Dami, G.Cremonese, Characterization of the integrating sphere for the on-ground calibration of the SIMBIOSYS instrument for the BepiColombo ESA mission, SPIE, Space Telescopes and Instrumentation, 2014.