In this paper, a constellation of four low earth orbit nanosatellites for disaster monitoring is presented; their small size, low cost, and short time development give them the opportunity to be widely selected. The space segment is based on existing subsystems that are assembled on the bottom part of a developed structure and present acceptable performance for the mission. The payload is a multispectral camera which fulfills the mission's requirements (remote sensing). The ground segment is based on an existing modular ground station, used for the ALSAT-1 DMC, which will be adapted to fit with the specifications of the mission.
Radiometric performances of Earth Observation Satellite sensors vary between ground pre-launch calibration campaign, after launch and over satellite lifetime due to launching vibration, eventual optical element misalignments, degazin effect and most generally space harsh environment. Due to the inaccessibility of the satellite on orbit, the vicarious calibration method based on a ground site using simultaneous ground reference data is often considered as an essential step to ensure best accuracy tradeoffs. This method has the advantage of reproducing the real conditions of image data acquisition. Its accuracy depends closely on the radiometric stability of the calibration site, site reflectance measurements, and knowledge of the atmospheric parameters during image acquisition.
Abstracr-A space camera is essentially constituted of P sensor H hich transforms the optical signals inio electric ones and a control and command system where, amongst otber, the operstioni of clocks generation, amplification end digitalisation of tbe video signal are done, Finally the images obtained are stored in memories. The design of such systems tries to achieve a high Level integration of the maximum functions on a single chip In order to reduce the number of components, thus minimizing power consumption and saving space and weight onboard. This i s made possible by the creation of entirely VLSl reconfigurablc and progrummable components such as the PrugmmmubIe Fifld Gate Array (FPCA) and the Application SpeciJc Integraied Circuils (Asics) which are now commonly used an-board spacecraft because of their abilities io resist to the harsh radiation in space environment. Tbr actual levels of performances and qualilies arc more than satisfacIory (more than 20 FPGA circuits were used on the Mars Pathfinder robot). The aim of this work is the design, In a hardware-in-loop approach, of Sintuhk modules able to generate control commands and clocks signals for a three bands multispectral camera using CCD sensors.Once the Shrulink based controller is designed, it drives the s&rI & end ncquisition settings and the relative exposure times of the three CCD channels (Red, Green and Blue). This study was done using a Kodak KLI-10203 sensor. I-INTRODUCTIONThe growing number of emerging country seeking access io space techniques show an increasing interest for low cosr mission and therefore for microsatellite solutions [3). Besides. the actual technology permits to achieve scientific or 0-7803-8977-8/05/%20.00 a2005 IEEE. 248 operational missions including propulsion capability. Small satellite sector is strongly pushed by earth observation demand for operational law cost mission. Even if most of these missions use a COTS solution; a real space low cost access will be effective only when at least in-house design solutions are considered. The realization of a real-time embedded imaging system needs the use of complex logics where design and check requires often expensive software. Due to no financial encouragement it bccomes necessary to find an altemative to the use o f such expensive tools an optimum ratio performancdcost need to be found. In the case of an experimental satellite the solution comes with the reinforcement of the model development concept well known in the automotive area [I].It is based on a number of ideas amongst them the use of graphical representations of systems that should allow designers to work OR higher levels of abstraction. At the same time the underlying models should be formal to ailow model execution, analysis and synthesis tools to minimize the effort and steps in the transition [ I ,2]. Self-design capacities become possible by combining the already.existing design tools. Thus, a cost effectiveness and sophisticated imaging system can be envisaged.
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