Original Article
Telecommunication
elham sharifi; Arash Ahmadi; Mohammad Fazaelifar
Abstract
The antenna of a high throughput satellite payload should generate multiple spot beams simultaneously to provide frequency reuse by creating cellular coverage for the satellite. The phased array antenna is a proper option for this application. In geostationary orbit, the satellite field of view is limited, ...
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The antenna of a high throughput satellite payload should generate multiple spot beams simultaneously to provide frequency reuse by creating cellular coverage for the satellite. The phased array antenna is a proper option for this application. In geostationary orbit, the satellite field of view is limited, and dividing it to several tight beams poses many challenges to the antenna design. The large dimensions of the radiating aperture, high number of radiant elements, the need for dividing the array to several sub-arrays, which lead to appearance of grating lobes, and the orthogonality of the beams with tiny angular distance are the challenges of the antenna design. In this article, a multiple beam phased array antenna in Ka-band with microwave beam forming network is synthesized and designed to meet aforementioned challenges. The sub-beam technique has been used for decreasing the array dimensions. For eliminating the grating lobes, the array has been divided into interleaved sub-arrays in two dimensions. A new beam forming network which can generate 20×20 simultaneous orthogonal beams in an area with coverage widths of 10˚ and 8.8˚ in longitude and latitude directions has been devised in this paper.
reviewed article
Ehsan Mousivand; Sajjad Ghazanfarinia; Yaser Saffar; Masoud Khoshsima
Abstract
Satellite Constellations are the new approach to achieve the applications that were presumably expected from large and complex satellites. This paper reviews activities and related satellite constellation of about 130 companies and research institutes, showing that Communication Missions (Internet of ...
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Satellite Constellations are the new approach to achieve the applications that were presumably expected from large and complex satellites. This paper reviews activities and related satellite constellation of about 130 companies and research institutes, showing that Communication Missions (Internet of Things and Machine to Machine Services) are the most desirable for Constellations with 27% of all. Earth Observation constellations are in the next rank with 19%. The most favorite configuration in Constellations is based on Microsatellites with 42%, out of which Cubesats are of more interest. The research is going to present the role of Cubesats with some statistical analysis to show how these Space Systems may affect the future of Space Industry and Economy with Solutions based on Constellations. Results discuss the Future of Constellations and Cubesats and their common effect on New Space both in Space Industry Level and Space Economy. This review may help researchers to work on similar studies with business approaches, too.
Original Article
mohamad ali amirifar; alireza rajabi; nooredin ghadiri masoom; Zahra Amirsardari
Abstract
In this study, the pulse mode performance of a monopropellant hydrazine thruster has been studied. For this purpose, a laboratory sample of a monopropellant hydrazine thruster under atmospheric pressure was fabricated and tested. The thruster catalyst is natively synthesized. The pulse mode performance ...
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In this study, the pulse mode performance of a monopropellant hydrazine thruster has been studied. For this purpose, a laboratory sample of a monopropellant hydrazine thruster under atmospheric pressure was fabricated and tested. The thruster catalyst is natively synthesized. The pulse mode performance of this monopropellant hydrazine thruster has been experimentally evaluated and the results are presented. The results of this study show that the monopropellant hydrazine thruster made with a synthesized catalyst produces reproducible impulses for pulses less than 10 milliseconds wide. The minimum impulse of this monopropellant hydrazine thruster is measured at 32 mNS. Also, the standard deviation of the impulse is less than 6% for 100 pulses. The thruster response time is also very reproducible. The results of this study showed that the centroid of the thruster changes linearly with the pulse width. However, the transient behavior of the chamber pressure is relatively slow, leading to a large centroid.
Original Article
Farhad Bagheroskouei
Abstract
Reliability assessment of power converters is extremely important due to the degradation of the converter performance under the thermal and electrical stresses. The space environment is one of the stressful environments for electronic components and equipment due to the range and high speed of temperature ...
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Reliability assessment of power converters is extremely important due to the degradation of the converter performance under the thermal and electrical stresses. The space environment is one of the stressful environments for electronic components and equipment due to the range and high speed of temperature changes.The normal or abnormal operation of a converter depends on the quality of the manufacturing process and the environmental and operating conditions. The failure indices usually are obtained based on the previous failures data which are calculated using the history of the main parameter of the converter. These indices are strongly influenced by the aging process. In this article, a new real-time indicator is introduced using the monitoring of the main parameters of the converter. The indicators are calculated using Replicator Neural Network (RNN). In fact, these indicators are obtained based on a comparison between a reference model of the converter in normal conditions and the estimation of abnormal operation of the converter in the future. In the proposed method, a normal distribution function is used to find the limits of error signals. The proposed method has several advantages such as considering all the uncertainties during the process of manufacturing the device, no need for the aging test data, and including all the failure types. In the Electrical power subsystem of a spacecraft, the reliability of power converters can be assessed based on the obtained data from the qualification models, benefiting the proposed method.
