Since 2007 Sodern has successfully developed visible and near infrared multispectral filter assemblies for Earth remote sensing imagers. Filter assembly is manufactured by assembling several sliced filter elements (so-called strips), each corresponding to one spectral band. These strips are cut from wafers using a two dimensional accuracy precision process.
In the frame of a 2011 R&T preparatory initiative undertaken by the French agency CNES, the filter assembly concept was adapted by Sodern to the long wave infrared spectral band taken into account the germanium substrate, the multilayer bandpass filters and the F-number of the optics.
Indeed the current trend in space instrumentation toward more compact uncooled infrared radiometer leads to replace the filter wheel with a multispectral filter assembly mounted directly above the micro bolometer window. The filter assembly was customized to fit the bolometer size. For this development activity we consider a ULIS VGA LWIR micro bolometer with 640 by 480 pixels and 25 microns pixel pitch. The feasibility of the concept and the ability to withstand space environment were investigated and demonstrated by bread boarding activities.
The presentation will contain a detailed description of the bolometer and filter assembly design, the stray light modeling analysis assessing the crosstalk between adjacent spectral bands and the results of the manufacturing and environmental tests (damp heat and thermal vacuum cycling).
As a manufacturer of optical systems for space applications, Sodern is faced with the necessity to design optical systems which image quality remains stable while the environment temperature changes. Two functions can be implemented: either a wavefront control or the athermalization of the optical system. In both cases, the mechanical deformations and thermal gradients are calculated by finite-element modeling with the IDEAS NX7 software. The data is then used in CODE V models for wavefront and image quality evaluation purposes. Two cases are presented: one is a UV beam expander in which a wavefront control is implemented and the other is an athermalized IR camera. The beam expander has a wavefront–tuning capability by thermal control. In order to perform the thermo-optical analysis in parallel with the opto-mechanical development, the thermo-optical modeling is done step by step in order to start before the mechanical design is completed. Each step then includes a new modeling stage leading to progressive improvements in accuracy. The IR camera athermalization is achieved through interaction between the mechanical CAD software and the optical design software to simulate the axial thermal gradients, radial gradients and all other thermal variations. The purpose of this paper is to present the steps that have led to the final STOP (Structural, Thermal Optical) analysis. Using incremental accuracy in modeling the thermo-optical effects enables to take them into account very early in the development process to devise all adjustment and test procedures to apply when assembling and testing the optical system.
In many spatial systems, image is a core technology to fulfil the mission requirements. Depending on the application, the
needs and the constraints are different and imaging systems can offer a large variety of configurations in terms of
wavelength, resolution, field-of-view, focal length or sensitivity. Adequate image processing algorithms allow the
extraction of the needed information and the interpretation of images.
As a prime contractor for many major civil or military projects, Astrium ST is very involved in the proposition,
development and realization of new image-based techniques and systems for space-related purposes. Among the
different applications, space surveillance is a major stake for the future of space transportation. Indeed, studies show that
the number of debris in orbit is exponentially growing and the already existing population of small and medium debris is
a concrete threat to operational satellites. This paper presents Astrium ST activities regarding space surveillance for
space situational awareness (SSA) and space traffic management (STM). Among other possible SSA architectures, the
relevance of a ground-based optical station network is investigated. The objective is to detect and track space debris and
maintain an exhaustive and accurate catalogue up-to-date in order to assess collision risk for satellites and space vehicles.
The system is composed of different type of optical stations dedicated to specific functions (survey, passive tracking,
active tracking), distributed around the globe. To support these investigations, two in-house operational breadboards
were implemented and are operated for survey and tracking purposes.
This paper focuses on Astrium ST end-to-end optical-based survey concept. For the detection of new debris, a network of
wide field of view survey stations is considered: those stations are able to detect small objects and associated image
processing (detection and tracking) allow a preliminary restitution of their orbit.
Multispectral channels are required on many pushbroom optical sensors. A possible technology well suited for focal
plane miniaturization is to assemble several sliced filter elements (so-called stripes), each corresponding to one spectral
channel, and located close to the detectors.
The assembled filter is thus customized to fit detector size. These stripes are cut from a wafer using a two dimensional
accurate process. For the baseline concept, elementary stripes are then cemented edge-to-edge to form a single substrate.
The opaque epoxy used for the stripes assembly creates a light barrier between adjacent elements and thus provides an
interesting solution for cross channel image suppression inside the filter.
This paper recalls the current SODERN's multi-spectral filter assembly status. Since 2007 R&T activity, the feasibility
and the performances have been demonstrated by breadboards and qualification models. The selection of SODERN for
two current VNIR space programs consolidates its role as a leading supplier in this field. A complementary 2011 R&T
study will demonstrate the performances of this technology for the TIR range and the integration on a bolometer.
Since April 2008, the International Space Station (ISS) is supplied by the Automated Transfer Vehicle (ATV) developed
by EADS-Astrium for ESA. This ATV is the first entirely automated space docking system based on optical devices. Its
guidance was possible thanks to a device of the ATV developed by EADS-SODERN and named Videometer (VDM).
The VDM delivers range, line of sight (LOS) and attitude (among which roll) to the guidance and navigation system of
the ATV from 300 meters to docking.
During the development steps, tests and studies showed that the measurement of the ATV roll by VDM includes a bias
due to the diffraction of the emitted light by corner-cube retroreflectors located on the ISS. The sign and the magnitude
of this bias are linked with the distance ISS/ATV.
Since the accuracy of the VDM measurements determine the quality of the docking, it was important to evaluate with
precision this bias and and check that this bias is compatible with the required docking accuracy.