309 research outputs found
Distortion definition and correction in off-Axis systems
No full textOff-axis optical configurations are becoming more and more used in a variety of applications, in particular they are the
most preferred solution for cameras devoted to Solar System planets and small bodies (i.e. asteroids and comets) study.
Off-axis designs, being devoid of central obstruction, are able to guarantee better PSF and MTF performance, and thus
higher contrast imaging capabilities with respect to classical on-axis designs. In particular they are suitable for observing
extended targets with intrinsic low contrast features, or scenes where a high dynamical signal range is present.
Classical distortion theory is able to well describe the performance of the on-axis systems, but it has to be adapted for the
off-axis case.
A proper way to deal with off-axis distortion definition is thus needed together with dedicated techniques to accurately
measure and hence remove the distortion effects present in the acquired images.
In this paper, a review of the distortion definition for off-axis systems will be given. In particular the method adopted by
the authors to deal with the distortion related issues (definition, measure, removal) in some off-axis instruments will be
described in detail
EFFECTS OF THERMAL DEFORMATION ON OPTICAL INSTRUMENTS FORSPACE APPLICATION
No full textOptical instruments for space missions work in hostile environment, it’s thus necessary to accurately study the
effects of ambient parameters variations on the equipment.
In particular optical instruments are very sensitive to ambient conditions, especially temperature. This variable
can cause dilatations and misalignments of the optical elements, and can also lead to rise of dangerous stresses
in the optics. Their displacements and the deformations degrade the quality of the sampled images.
In this work a method for studying the effects of the temperature variations on the performance of imaging
instrument is presented. The optics and their mountings are modeled and processed by a thermo-mechanical
Finite Element Model (FEM) analysis, then the output data, which describe the deformations of the optical
element surfaces, are elaborated using an ad hoc MATLAB routine: a non-linear least square optimization
algorithm is adopted to determine the surface equations (plane, spherical, nth polynomial) which best fit the data.
The obtained mathematical surface representations are then directly imported into ZEMAX for sequential
raytracing analysis. The results are the variations of the Spot Diagrams, of the MTF curves and of the
Diffraction Ensquared Energy due to simulated thermal loads.
This method has been successfully applied to the Stereo Camera for the BepiColombo mission reproducing
expected operative conditions.
The results help to design and compare different optical housing systems for a feasible solution and show that
it is preferable to use kinematic constraints on prisms and lenses to minimize the variation of the optical
performance of the Stereo Camera
A freeform optical design of a 12U CubeSat for Earth observation
No full textLarge-scale, multi-redundant satellite platforms are well known for their high cost and the extensive time required for their construction and deployment. In recent decades, small satellites like CubeSats have gained significant popularity and transformed the field of space exploration.
This article presents a preliminary optical design for a CubeSat dedicated to Earth observation in the 400-900 nm spectral range. The CubeSat is based on a 12U platform, with the optical part occupying 8U and featuring a two-mirror off-axis Schwarzschild configuration. The satellite will perform hyperspectral imaging of the Earth using the pushbroom acquisition technique, all within a compact and efficient system. To achieve this, a linear variable filter will be placed in front of the detector.
Due to their small size, CubeSats present some limitations compared to larger, traditional satellites, which degrade the optical performance of the imaging systems. To overcome these limitations, an optical design based on freeform optics has been developed. A preliminary analysis of a two-mirror system, both with and without freeform optics, will be presented to demonstrate how the integration of freeform surfaces can substantially improve the system optical performance
Preliminary error budget analysis of the coronagraphic instrument METIS for the solar orbiter ESA mission
No full textMETIS, the Multi Element Telescope for Imaging
and Spectroscopy, is the solar coronagraph foreseen for the ESA
Solar Orbiter mission. METIS is conceived to image the solar
corona from a near-Sun orbit in three different spectral bands: in
the HeII EUV narrow band at 30.4 nm, in the HI UV narrow
band at 121.6 nm, and in the polarized visible light band (590 –
650 nm). It also incorporates the capability of multi-slit
spectroscopy of the corona in the UV/EUV range at different
heliocentric heights.
METIS is an externally occulted coronagraph which adopts an
“inverted occulted” configuration. The Inverted external occulter
(IEO) is a small circular aperture at the METIS entrance; the
Sun-disk light is rejected by a spherical mirror M0 through the
same aperture, while the coronal light is collected by two annular
mirrors M1-M2 realizing a Gregorian telescope. To allocate the
spectroscopic part, one portion of the M2 is covered by a grating
(i.e. approximately 1/8 of the solar corona will not be imaged).
This paper presents the error budget analysis for this newconcept
coronagraph configuration, which incorporates 3
different sub-channels: UV and EUV imaging sub-channel, in
which the UV and EUV light paths have in common the detector
and all of the optical elements but a filter, the polarimetric visible
light sub-channel which, after the telescope optics, has a
dedicated relay optics and a polarizing unit, and the
spectroscopic sub-channel, which shares the filters and the
detector with the UV-EUV imaging one, but includes a grating
instead of the secondary mirror.
The tolerance analysis of such an instrument is quite complex:
in fact not only the optical performance for the 3 sub-channels
has to be maintained simultaneously, but also the positions of M0
and of the occulters (IEO, internal occulter and Lyot stop), which
guarantee the optimal disk light suppression, have to be taken
into account as tolerancing parameters.
In the aim of assuring the scientific requirements are optimally
fulfilled for all the sub-channels, the preliminary results of
manufacturing, alignment and stability tolerance analysis for the
whole instrument will be described and discussed
A novel optical design for the stereo channel of the imaging system SIMBIOSYS for the BepiColombo ESA mission
No full textIn this paper the design of a novel catadioptric optical
solution for the Stereo Channel (STC) of the imaging
system SIMBIOSYS for the BepiColombo ESA
mission to Mercury is presented.
The main scientific objective is the 3D global mapping
of the entire surface of Mercury with a scale factor of
50 m per pixel at periherm in five different spectral
bands.
The system consists of two sub-channels looking at
±20° from nadir. They share the detector and all the
optical components with the exception of the first
element, a rhomboid prism. The field of view of each
channel is 5.3° ́ 4.5° and the scale factor is 23
arcsec/pixel. The system guarantees an aberration
balancing over all the field of view and wavelength
range with optimal optical performance.
For stray-light suppression, an efficient baffling system
able to well decouple the optical paths of the two subchannels
has been designed
Preliminary optical design of the stereo channel of the imaging system simbiosys for the BepiColombo ESA mission
No full textThe paper describes the optical design and
performance budget of a novel catadioptric instrument
chosen as baseline for the Stereo Channel (STC) of the
imaging system SIMBIOSYS for the BepiColombo
ESA mission to Mercury.
The main scientific objective is the 3D global mapping
of the entire surface of Mercury with a scale factor of
50 m per pixel at periherm in four different spectral
bands.
The system consists of two twin cameras looking at
±20° from nadir and sharing some components, such as
the relay element in front of the detector and the
detector itself. The field of view of each channel is 4° x
4° with a scale factor of 23’’/pixel. The system
guarantees good optical performance with Ensquared
Energy of the order of 80% in one pixel.
For the straylight suppression, an intermediate field
stop is foreseen, which gives the possibility to design
an efficient baffling system
Radiometric model for the stereo camera STC onboard the BepiColombo ESA mission
No full textThe STereoscopic imaging Channel (STC) is one of the instruments on-board the BepiColombo mission, which is an
ESA/JAXA Cornerstone mission dedicated to the investigation of the Mercury planet. STC is part of the Spectrometers
and Imagers for MPO BepiColombo Integrated Observatory SYStem (SIMBIO-SYS) suite. STC main scientific
objective is the 3D global mapping of the entire surface of Mercury with a mean scale factor of 55 m per pixel at
periherm.
To determine the design requirements and to model the on-ground and in-flight performance of STC, a radiometric
model has been developed. In particular, STC optical characteristics have been used to define the instrument response
function. As input for the model, different sources can be taken into account depending on the applications, i.e. to
simulate the in-flight or on-ground performances. Mercury expected radiance, the measured Optical Ground Support
Equipment (OGSE) integrating sphere radiance, or calibrated stellar fluxes can be considered.
Primary outputs of the model are the expected signal per pixel expressed in function of the integration time and its
signal-to-noise ratio (SNR). These outputs allow then to calculate the most appropriate integration times to be used
during the different phases of the mission; in particular for the images taken during the calibration campaign on-ground
and for the in-flight ones, i.e. surface imaging along the orbit around Mercury and stellar calibration acquisitions.
This paper describes the radiometric model structure philosophy, the input and output parameters and presents the
radiometric model derived for STC. The predictions of the model will be compared with some measurements obtained
during the Flight Model (FM) ground calibration campaign. The results show that the model is valid, in fact the foreseen
simulated values are in good agreement with the real measured ones
Ghost images determination for the Stereoscopic Imaging Channel of SIMBIOSYS for the BepiColombo ESA mission
No full textThe Narrow Angle Camera of the MPCS suite for the MarcoPolo ESA mission: requirements and optical design solutions
No full textPossible optical designs of a Narrow Angle Camera (NAC) suitable for being the high resolution channel of the
MarcoPolo Camera System for the MarcoPolo ESA mission are presented. The MarcoPolo mission objective is the
rendezvous with a Near Earth Asteroid in order to fully characterize the body, to land on the surface and to return to
Earth a sample of the asteroid soil. Science goals for the NAC are global mapping of the object, detailed investigations of
the surface at high spatial resolution (order of millimeters), and deep examination of possible landing sites from a close
distance.
The instrument has a 3”/pixel scale factor, corresponding to 80 mm/px at 5 km from the surface, on a 1.75° × 1.75° FoV;
imaging in 5 to 8 different spectral bands (panchromatic and broadband), in the range between 400 and 900 nm, is
foreseen. Since the target is an extended low contrast object, to avoid image contrast degradation, only off-axis
unobstructed optical layouts have been considered. Solutions with two mirrors plus a refractive corrector, or allreflective
three mirrors ones, have been studied, both allowing to reach good aberration balancing over all the field of
view: the diffraction Ensquared Energy inside one pixel of the detector is of the order of 70%. To cope with the
hazardous radiation environment in which the spacecraft will be immersed in during the mission, all the glasses selected
for the design are rad-hard typ
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