Key Parameters Optimization of Spacecraft Orbital Constellations in Low Circular Orbits for Priority Service of the Russian Federation Territory Ivanova Marina Pavlovna Engineer of 1 category Golovkov Vladimir Vladimirovich Engineer of 1 category Badertdinov Albert Mansourovich Head of sector Esipenko Anton Andreevich Engineer of 2 category Kuzovnikov Aleksander Vitalievich Head of department 1 ORCID: 0000-0002- 5219-8130, 2 ORCID: 0000-0003- 2360-7916 3 ORCID: 0000-0002- 5549-0233, 4 ORCID: 0000-0001- 7391-5111 5 ORCID: 0000-0002- 5085-646X Abstract The paper provides the results of a computer simulation for a mobile communications satellite system operation with the communications spacecraft orbital constellation in low circular orbits, as well as suggestions for optimization of its mains parameters based on the simulation results. This system is the development of the geostationary personal communications systems with the purpose to provide higher data transmission rate as well as the global coverage. The primary objective of the system is to provide high speed internet access to a wide range of users over the whole world through small-sized user terminals. Several options have been analyzed for the constellation deployment, depending on orbit height, number of orbital planes, and number of spacecraft in each orbital plane and in the constellation. The primary criterion of spacecraft deployment efficiency was the mean time of the whole Earth territory coverage (with a priority for the Russian Federation), estimated as a percentage of 24-hour period. Based on the simulation, suggestions have been made for the optimization of the constellation main parameters so that maximum possible coverage of the Earth would be achieved while maintaining a minimal number of spacecraft in orbit. Keywords: Satellite communication, spacecraft (SC), low circular orbit, in-orbit frequency resource, orbital plane, serviced area. 3394
INTRODUCTION During the simulation of the communications spacecraft orbital constellation in low circular orbits the following activity has been done with the purpose to develop a future satellite system: analysis of design variants of the personal communications system, performed in the framework of Agreement 14.585.21.0003, the project identifier RFMEFI58514X0003. serviced area design and optimization of the future satellite system with spacecraft in low circular orbits; design and simulation of the satellite system orbital constellation with spacecraft in low circular orbits; optimization of random time-response characteristics of the satellite system orbital constellation with spacecraft in low circular orbits. MAIN BASELINE DATA FOR THE PROJECT DESIGN Serviced area global Applied frequency range: for user links P-, L-, S-, Ka- (one of the frequency bands); for feed links Ka-band (in accordance with Radio Regulations); for intersatellite links Ka-band (if this data transmission link is used in the system) (Valov M. V. Future satellite communications system with small spacecraft in the geostationary orbit, 2016). Orbit height of the spacecraft in low circular orbits from 500 to 1500 km Main services: voice transmission; data transmission (Design concept of foreign personal mobile satellite communications systems. SPb: VKA named after A.F. Mozhaiskiy, 2008). ORBITAL CONSTELLATION DESIGN In the recent article there have been reviewed 2 variants of the orbital constellation with the following parameters (Golovkov V. V. The choice of optimum orbital constellation for the multifunctional satellite communications system, 2014): Variant 1: orbit height not less than 1500 km; orbit plane inclination 82,5о; number of spacecraft (Nsat_syst) 48; number of planes (n) 6; number of spacecraft in-plane (m) 8. Variant 2: orbit height not less than 1000 км; orbit plane inclination 82,5о; number of spacecraft (Nsat_syst) 128; number of planes (n) 8; number of spacecraft in-plane (m) 16. For each variant of the orbital constellation two subvariants have been reviewed (for variant 1 variants 1.1, 1.2, for variant 2 2.1, 2.2) taking into account the proposals for inorbit frequency resource allocation in the system, the difference of each variant is the parameters of longitude of ascending node and middle anomaly (A. Stepanov Design and operation features of communications satellite system orbital constellation, 2016). SERVICED AREAS In the course of the work on Agreement 14.585.21.0003 the orbital SC positions in the geostationary orbit was simulated. With the objective to provide higher rate of data transmission and the global coverage, as well as to perform some technical solutions, obtained during the fulfillment of the above mentioned activity, the orbital constellation serviced areas were simulated based on 48 spacecraft ( orbit height 1500 km), variants 1.1 and 1.2 considering the proposals for in-orbit frequency resource allocation are given in pictures 1 and 2. According to the computer simulation results there were modeled the orbital constellation serviced areas based on 128 spacecraft (variants 2.1 and 2.2 considering the proposals for in-orbit frequency resource allocation) are given in pictures 3 and 4. 3395
Picture 1. Orbital constellation serviced areas on variant 1.1 (the elevation is not less than 15 о ) according to the computer simulation results Picture 2. Orbital constellation serviced areas on variant 1.2 (the elevation is not less than 20 о ) according to the computer simulation results 3396
Picture 3. Orbital constellation serviced areas on variant 2.1 (the elevation is not less than 20 о ) according to the computer simulation results Picture 4. Orbital constellation serviced areas on variant 2.2 (the elevation is not less than 33 о ) according to the computer simulation results 3397
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 12 (2017) pp. 3394-3302 (in percentage) of the serviced area (as regard to 24 hours) concerning the orbital constellation based on 128 spacecraft for variants 2.1 and 2.2 (considering the proposals for in-orbit frequency resource allocation) (Knyazev V. V. Mathematical support of optimization for increasing of the low-orbiting satellite communications system constellation, 2015). COVERAGE TIME PERIOD OF SERVICED AREA In pictures 5 8 there are shown the serviced areas with the coverage time period in percentage as regard to 24 hours, when the area is covered by as minimum one spacecraft with specified elevation. In pictures 5 and 6 there are shown the coverage time periods (in percentage) of the serviced area (as regard to 24 hours) concerning the orbital constellation based on 48 spacecraft for variants 1.1 and 1.2 (considering the proposals for in-orbit frequency resource allocation). In pictures 7 and 8 there are shown the coverage time periods Picture 5. Serviced areas of the orbital constellation based on 48 SC, variant 1.1, according to the computer simulation results Picture 6. Serviced areas of the orbital constellation based on 48 SC, variant 1.2, according to the computer simulation results 3398
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 12 (2017) pp. 3394-3302 Picture 7. Serviced areas of the orbital constellation based on 128 SC, variant 2.1, according to the computer simulation results Picture 8. Serviced areas of the orbital constellation based on 128 SC, variant 2.2, according to the computer simulation results 3399
Calculation results of the coverage time period for 24 hours are given in table 1. Table 1 Calculation results of the coverage time period for 24 hours for the orbital constellation on variants 1.1, 1.2, 2.1 and 2.2. parameters Meaning Variant 1 Variant 2 Variant 1.1 Variant 1.2 Variant 2.1 Variant 2.2 orbit height, km 1500 1500 1000 1000 orbit plane inclination, dg. 82,5 82,5 82,5 82,5 number of spacecraft in the system 48 48 128 128 number of planes 6 6 8 8 number of spacecraft in-plane 8 8 16 16 serviced area intersection between two adjacent SC in-plane + - + - minimum elevation for users service, dg. 15 20 25 33 coverage time period for 24 hours in global area, % 99,45 75 98,25 67,5 coverage time period for 24 hours in global area, in hours 23,868 18 23,58 16,2 coverage time period for 24 hours higher 45 о of north latitude, % 99,7 90,0 98,75 87,5 coverage time period for 24 hours higher 45 о of north latitude (lower 45 о of south latitude), in hours 23,928 21,6 23,7 21 In table 1it is seen, that: the orbital constellation based on 48 spacecraft during the system operation under elevation not less than 15 о (condition of serviced areas intersection between two adjacent SC variant 1.1) provides the best value regarding the coverage time period for one day (24 hours) (99,45 %) with respect to system operation under minimum elevation, not less than 20 о (75 %, variant 1.2); the orbital constellation based on 128 spacecraft during the system operation under elevation not less than 33 о (condition of serviced areas intersection between two adjacent SC variant 2.1) provides the best value regarding the coverage time period for one day (24 hours) (98,25 %) with respect to system operation under minimum elevation not less than 25 о (67,5 %, variant 2.2); if the operation is within the area from 45 о of north latitude and higher (from 45 о of south latitude and lower), the coverage time period value of the specified area covered by spacecraft increases for 1 day: variant 1.1 not less than 99,7 % (23,928 hours) variant 1.2 not less than 90,0 % (21,6 hours); variant 2.1 not less than 98,75 % (23,7 hours); variant 2.2 not less than 87,5 % (21hours); CONCLUSION The main results of the work are based on theoretical estimates summary for design variants of the personal communications system, performed in the framework of Agreement 14.585.21.0003, the project identifier RFMEFI58514X0003. In the course of the simulation 4 design variants of the orbital constellation with spacecraft in low circular orbits have been 3400
reviewed (height 1000 and 1500 km). According to the analysis results it was defined that the most effective variants from viewpoint of the coverage time period of the Earth are variants 1.1 (with 48 SC) and 2.1 (with 128 SC). In order to provide more precise estimation of the communications satellite system design with application of these orbital constellations some additional calculations and technical-and-economical indexes are required, which includes: current and predicted requirements for satellite service based on low-orbiting satellite systems (Jaeyoung Choi A Survey on Content-Oriented Networking for Efficient Content Delivery, 2011); required serviced area of the satellite system with loworbiting spacecraft; minimum required quantity of spacecraft in the system to meet the requirements for satellite service; payload complexity and cost (number of channels per beam, availability to process the signal on the board, availability of intersatellite links, cost of frequency resource, frequency channels etc.) and a spacecraft (mini-class, micro-nano-class etc.) in general for different design versions of the constellation and system (John J. Knab Transponder Power Minimization Utilizing Optimum Channelizer Gains, 2012); launch cost (single /group) for the orbital constellation deployment in different operational orbits (from 500 to500 km) (Kuzovnikov A. V. Design proposals for multiplesatellite communications system in low orbits considering the available vehicles of group launch into the low earth orbit, 2016 ; Zimin I. I. Advanced unified platforms of small class, 2016 ; Tarletskiy I. S. Design concept of small communications spacecraft «Gonets-М1» based on the advanced platform «EXPRESS-500», 2016); cost of design and ground infrastructure arrangement in the territory of the Russian Federation and on a global basis (in the absence of intersatellite communications links and signals processing mode on board). REFERENCES [1] Valov, M. V. Future satellite communications system with small spacecraft in the geostationary orbit [Text] / M. V. Valov, I. S. Tarletskiy, I. I. Zimin, V. V. Golovkov, S. N. Leonov // Communications and range navigation systems: collection of abstracts / science editor V. F. Shabanov; responsible to sign-off A. Yu. Strukova. Krasnoyarsk: JSC «NPP «Radiosvaz», 2016. p. 254-256. [2] Design concept of foreign personal mobile satellite communications systems: study guide [Text] / A. M. Andreev, L. P. Boginskiy, M. V. Grishin etc. SPb.: VКА VKA named after A.F. Mozhaiskiy, 2008. 345 p. [3] Golovkov, V. V. The choice of optimum orbital constellation for the multifunctional satellite communications system [Text] // Youth. Society. Modern science, engineering and innovation: proceeding of the XIII International science conference of Bachelors, Master s students and Ph.D students / Siberian State Aerospace University Krasnoyarsk, 2014. 240 p. [4] Stepanov, А. Design and operation features of communications satellite system orbital constellation [Text] / Stepanov Aleksandr, Akimov Aleksandr, Gritsenko Andrey, Chazov Vadim //Satellite communication and broadcasting ; [special issue 2016. p. 72 87. ISSN 1562-7144. [5] Knyazev, V. V. Mathematical support of optimization for increasing of the low-orbiting satellite communications system constellation [Text] / V. V. Knayzev, V. V. Letunov: the 3 rd international conference / edited by A.V. Toloka. 2015. 26-28 October. p. 227 230. [6] Jaeyoung Choi A Survey on Content-Oriented Networking for Efficient Content Delivery [Text] / Jaeyoung Choi, Jinyoung Han, Eunsang Cho, Ted Kwon, Yanghee Choi ; [Seoul National University] // IEEE Communications Magazine. 2011. March. p. 121-127. [7] John J. Knab Transponder Power Minimization Utilizing Optimum Channelizer Gains [Text] / John J. Knab // IEEE Transactions On Aerospace And Electronic Systems. 2012. Vol. 48,. 1. p. 729-736. [8] Kuzovnikov, A. V. Design proposals for multisatellite communications system in low orbits considering the available vehicles of group launch into the low earth orbit [Text] / A. V. Kuzovnikov, V. E. Kosenko, S. N. Leonov, I. I. Zimin, V. V. Golovkov// High technologies. M.: Close JSC «Radiotekhnika», 2016. 8. p. 25 29. [9] Zimim I. I. Advanced unified platforms of small class [Text] / I. I. Zimin, M. V. Valov, A. V. Yakovlev // Bulletin of Siberian State Aerospace University named after academician M. F. Reshetnev 2016. Vol. 17. 1. p. 118-124 [10] Tarletskiy, I. S. Design concept of small 3401
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