نشریه فناوری در مهندسی هوافضا
سال چهارم شماره 3 (پیاپی 14، پاییز 1399)

The main purpose of this paper is to design a navigation CubeSat constellation for local positioning system (LPS) that provides the postiong of Iran, based on COTS approach. To this end, the initial processing of subsystems' information was carried out using statistical processing of CubeSats with the same mission. According to the resultant data, common specifications of different subsystems (structure, electric power, attitude determination and control, thermal control, and communication), including required mass, power, volume and price were determined. Furthemore, the payload design was performed based on the specific mission, design matrix requirements, etc. by utilizing similar subsystem class catalogues (called COTS). Also, local positioning and coverage of the satellite constellation for the Iran was analyzed and simulated from the availabile datd in the Satellite Tool Kit (STK). Finally, the CubeSats constellation with specified subsystem (based on COTS approach) has been suggested for the acceptable coverage percentage to determine the local positioning in Iran. ‌‌

Navigation errors in synthetic aperture radar (SAR) applications lead to phase errors in SAR echo signal and image quality degradation. Among different phase errors, zero and first order errors have no effect on image quality, while second and higher order terms are very important. The majority of second and higher order phase errors are due to initial alignment errors, and bias and random errors of inertial sensors. Integrated INS/GPS navigation systems are used for solving this problem. However, discontinuities in integrated navigation data lead to severe SAR image quality degradation. In this paper, the effect of different navigation approaches on SAR azimuth impulse response was studied and the importance of specially-designed algorithms to integrate INS and GPS was illustrated. Then, the proposed algorithm for navigation in SAR application was presented according to navigation errors behavior, and its benefit in azimuth impulse response, and imaging quality was illustrated. ‌‌

Manned space missions account for a large proportion of future space travel missions.Van Allen radiation belts are major challenges of space missions with an astrobiology approach. In general, every living-being in space is affected by cosmic rays and solar charged particles. The amount of this radiation in two areas around the Earth, named Van Allen belts is significant. For example, planets exposed to radiation stress, due to DNA damage, has destructive effect on its growth, leading to reduced growth and genetic alteration. In this paper, effects of a Van Allen radiation belt on living organisms during space travel are investigated.

This article presents a novel and comprehensive approach to conceptual design of expander cycle liquid engines. One advantage of the computational code developed is the possibility of considering the working regime without cavitation of pumps by maximizing specific impulse of the engine system. Based on the proposed algorithm, the steady state regime of the mathematical modeling engine becomes static. This is important to increase reliability and to reduce costs during conceptual design phase, as well as optimization. One of the factors affecting the reliability of a system is its simplicity, which eliminates complexity. Here, the generator has been eliminated. In addition to the dimensional and functional estimations of the engine system, the proposed algorithm examines the performance of the propulsion system (engine specific impulse, turbine efficiency, and pumps) at various work stations. The computational algorithm of the static mathematical model was developed in Microsoft Visual Studio language.

Hyperspectral images provide worthful spectral information for target detection. Since these images are not available in Iran, we use multi-spectral images with approximately 10 bands. Due to differences of hyperspectral and multi-spectral images, a target detection system (using multi-spectral images) is designed in this work. An algorithem for selection and adaptation of an appropriate target detector was proposed to this end. The algorithmic approach assess the target detectors performances on hyperspectral images and designs a systematic target detector system. This system assess which of target detectors of hyperspectral images can be useful for multi-spectral images. Two images from Abadan and Ahvaz acquired by Landsat 8 and Sentinel 2 were selected for our experiments. According to our results, the Kernel based spectral angle mapper shows superior results for targets detection using multi-spectral images. ‌‌

Hyperspectral images provide worthful spectral information for target detection. Since these images are not available in Iran, we use multi-spectral images with approximately 10 bands. Due to differences of hyperspectral and multi-spectral images, a target detection system (using multi-spectral images) is designed in this work. An algorithem for selection and adaptation of an appropriate target detector was proposed to this end. The algorithmic approach assess the target detectors performances on hyperspectral images and designs a systematic target detector system. This system assess which of target detectors of hyperspectral images can be useful for multi-spectral images. Two images from Abadan and Ahvaz acquired by Landsat 8 and Sentinel 2 were selected for our experiments. According to our results, the Kernel based spectral angle mapper shows superior results for targets detection using multi-spectral images. ‌‌