Infrastructure (labs, sensors, software,…)
Bahman Ghorbani Vaghei; Alireza Shahri Razlighi
Volume 14, Issue 2 , June 2021, , Pages 61-69
Abstract
Magnetometer is one of the most sensors due to its lightness and low power consumption in satellites. Therefore, the magnitude of the magnetic field at the location of the magnetometer should be less than the magnetic cleanliness characteristics defined for the satellite. One of the best solutions is ...
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Magnetometer is one of the most sensors due to its lightness and low power consumption in satellites. Therefore, the magnitude of the magnetic field at the location of the magnetometer should be less than the magnetic cleanliness characteristics defined for the satellite. One of the best solutions is to properly placement included position and angular position of the equipments in such a way the magnetic field is minimized at the magnetometer location. In this paper, a cost function is defined based on the norm of the magnetic field generated by the equipments at the magnetometer location, and the cost function is minimized by adjusting the angular position of the equipments using the particle swarm optimization (PSO) algorithm. Position adjustment compensates the generated magnetic field and helps to passively achieve the magnetic cleanliness characteristics of a satellite. Finally, by simulating the magnetics of a satellite equipments, the performance of the algorithm in achieving magnetic cleanliness is shown.
H. Bazrafshan; Sh. Baradaran Shokouhi; B. Ghorbani Vagheii
Volume 3, Issue 1 , July 2010, , Pages 45-54
Abstract
In this paper, the complete block diagram of the imaging payload of a spin satellite capable of real time imaging is designed. Because of the satellite spin, the system needs to recognize the suitable camera angle in order to start imaging. The angle is the starting point of the observation of the part ...
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In this paper, the complete block diagram of the imaging payload of a spin satellite capable of real time imaging is designed. Because of the satellite spin, the system needs to recognize the suitable camera angle in order to start imaging. The angle is the starting point of the observation of the part of the earth to be imaged. In this paper, at first the suitable imaging method and detector for this kind of satellite are elected and then the angle and the time of the spin camera imaging and the necessary number of lines and pixels are calculated. If the system is also capable of real time imaging, the captured images should be transmitted to the earth station before the next imaging starts. The completion of the above scenario needs a complete and parallel relationship between the satellite image payload subsystem and other subsystems such as power, communication and specially satellite on-board computer. For imaging and transmission, image payload status information such as temperature, voltage and current should be sampled and transmitted to the on-board computer for processing. Also this information should be attached to the image frames and transmitted to the earth station. All this processing is summarized into time pulses with exact timing between subsystems. Because of resource limitation in a space mission, satellite systems design must have the minimum mass, power and cost. But these shouldn’t cause the efficiency and specially system processing speed to decline. Imaging payload with real time capability needs a high processing speed requiring high resource utilization. In this paper, an imaging system is designed with the mentioned characteristics based on FPGA high parallel processing speed but having low mass, volume and power.
H. Bazrafshan; Sh. Baradaran Shokouhi; B. Ghorbani Vagheii
Volume 2, Issue 3 , December 2009, , Pages 19-26
Abstract
Satellite camera Charged Coupled Device (CCD) read out system needs a high Signal to Noise Ratio (SNR). This is because of the special and inevitable space imaging payload noises. These noises include CCD noises, satellite noises such as lack of complete stability, and environmental noises such as atmospheric ...
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Satellite camera Charged Coupled Device (CCD) read out system needs a high Signal to Noise Ratio (SNR). This is because of the special and inevitable space imaging payload noises. These noises include CCD noises, satellite noises such as lack of complete stability, and environmental noises such as atmospheric interferences, charged particles, relative earth and satellite movement and electromagnetic interferences. CCD noises because of their low output voltage compose the main part of the final read out system noise. Therefore if the CCD read out system is not designed properly, SNR declines significantly. These noises depend on CCD characteristics and design parameters such as temperature and frequency. On the other hand, in a satellite temperature and frequency range is partially controllable. The algorithm presented in this paper, with respect to the applied limitations and dependencies, designs the system parameters so that the optimized SNR is achieved.
H. Bolandi; F. Fani- Saberi; B. Ghorbani-Vaghei
Volume 1, Issue 2 , December 2008, , Pages 9-15
Abstract
In this paper, the main stereo-imaging methods by high resolution satellites, including Along-Track and Across-Track, have been evaluated and then we will combine the two main stereo-imaging configurations of along track and across track as a new idea to obtain the advantages of both methods. In the ...
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In this paper, the main stereo-imaging methods by high resolution satellites, including Along-Track and Across-Track, have been evaluated and then we will combine the two main stereo-imaging configurations of along track and across track as a new idea to obtain the advantages of both methods. In the proposed stereo-imaging scenario, fast and simultaneous large maneuvers of the satellite around pitch and roll axes is one of the versatile methods. So, highly nonlinear characteristics of the governing equations because of large angle slewing maneuvers are very effective on pointing accuracy and stability and should be considered to design control laws. The purpose of this paper is to design a nonlinear control method using four reaction wheels based on PD controller that can be used to perform a spacecraft large angle maneuver using quaternion attitude variables. The configuration of reaction wheels in the simulated spacecraft has been arranged as a skewed four-wheel reaction. Reaction wheels unloading is also accomplished through the use of three magnetic torquers to prevent the speeds of the reaction wheels exceeding their designed limits, largely as a result of the action of secular components of disturbing torque. Simulation study has verified the performance and effectiveness of the proposed algorithm to achieve the proposed stereo-imaging scenario.
H. Bolandi; B. Ghorbani-Vaghei; F. Fani- Saberi
Volume 1, Issue 2 , December 2008, , Pages 27-33
Abstract
Attitude control system of satellite with Gravity Gradient stabilization requires high moments of inertia ratio for providing stability and continuous orientation toward Earth. Although, this high ratio causes satellite has small body and reduce mission capability. In this paper, moments of inertia ratio ...
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Attitude control system of satellite with Gravity Gradient stabilization requires high moments of inertia ratio for providing stability and continuous orientation toward Earth. Although, this high ratio causes satellite has small body and reduce mission capability. In this paper, moments of inertia ratio is reduced using a closed form formula based on our previous work, in such a way that it could be provided more missions by augmented solar panels to satellite. Solar orientation could be yielded by rotating satellite about gravity gradient boom (yaw rotation). Interaction between yaw rotation and satellite rotation around Earth causes biased-attitude error in roll axis. To overcome this problem, it is necessary to reduce yaw rotation by adding a reaction wheel toward boom direction. To realization this method, stability criteria of gravity gradient is developed and control law for small and large angles rotation is designed in such a way that angular momentum and moment constraints of reaction wheel to be satisfied. Finally, fine performance of attitude control system will be illustrated with simulation based on specification of an on-orbit satellite and actual consideration
H. Bolandi; B. Ghorbani Vaghei
Volume 1, Issue 1 , September 2008, , Pages 11-19
Abstract
In this paper, attitude control system of an axisymmetric satellite will be designed in such a way that required stability is provided with slow spinning about yaw axis. In this regard, dynamic of motion and coupling between satellite’s axes is modeled. As a result, a closed form formula is yielded ...
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In this paper, attitude control system of an axisymmetric satellite will be designed in such a way that required stability is provided with slow spinning about yaw axis. In this regard, dynamic of motion and coupling between satellite’s axes is modeled. As a result, a closed form formula is yielded included moment of inertia ratio, angular velocity about yaw axis and pointing accuracy of control system. Then, magnetic control is designed for providing capture range of gravity gradient stabilization and requirements of pointing accuracy. Finally, fine performance of designed control system will be illustrated with simulation based on specification of a near axisymmetric satellite.
