Telecom satellite panel optimization via payload performance merits. and equipment specifications

Transcription

1 Telecom satellite panel optimization via payload performance merits and equipment specifications Erdem DEMİRCİOĞLU * TURKSAT International Satellite and Cable TV AS R&D and Satellite Design Department, Golbasi, Ankara, 00, Turkey * Correspondence: [email protected] Abstract: Telecommunication satellites are operational over 0 years in various geosynchronous (GEO) orbital slots and frequency spectrums all around the globe. Lack of available orbital slots and frequency spectrum allocations lead the satellite design engineers to optimize payload systems on space. Traditional telecom satellite design activities tend to be conservative and heritage based. Nowadays, GEO telecom satellites are designed to be lighter and smaller with adequate payload performance realization. In this study, a telecom payload analysis tool, TPAT, is proposed to optimize satellite panel accommodations in terms of equipment specifications, thermal and power concerns. The obligatory payload performance metrics are utilized to compute payload link, mass, power consumption and dissipation budgets. Platform and equipment specifications are considered to adjust panel layout under thermal dissipation characteristics. TPAT aims to demonstrate the optimum panel accommodation rapidly and makes the necessary tradeoffs to calculate payload mass and power budgets. The manufacturing and launch cost of a telecom satellite is directly related with these budgets and also the satellite platform with possible launcher options can be examined shorn of undesirable high proposal preparation costs. Key words: Panel optimization, payload budgets, telecommunications satellite, thermal equipment layout 1

2 1. Introduction Satellite systems employ mobile and wireless communication opportunity independent of location with wide coverage areas comprising countries, continents and oceans where end users access wide bandwidth data independent of terrestrial infrastructure. Satellite business is composed of service providers, satellite operators, ground terminal manufacturers, satellite manufacturers and launch providers. Although satellite manufacturing and launch campaign have indispensable role on developing state-of-the art technologies, service providers cover 0% of the market share. Satellite manufacturing occupies only $.Billion of the overall market value of $Billion. On board communication satellite systems are complicated and inter-disciplinary compared to ground networks which are comparatively easy to deploy and operate. Along with easy and rapid installation, cost of raising additional users on ground networks side is quite modest [1]. Telecommunication satellites play a critical role in modern communication systems by serving large areas on earth and connecting remote places to each other. Satellite communication systems allow us to transfer large amount of data, broadcast TV, radio signals and carry telephone traffic where other communication systems are unfeasible []. Satellite architectural design process takes into consideration a massive amount of constraints. As the beginning of preliminary design, the general architecture determines the satellite practice besides the basic principles determining the design of its structural subsystem including payload and platform panels. Design engineers` decisions are guided by the specific development requirements such as selected platform and qualified/tested technologies with reliable heritage. Design and manufacturing cost is the leading constraint for satellite manufacturers. As the platform size increases, overall

3 manufacturing cost also elevates with lower slope. This causes manufacturers to prefer larger platforms. Electric propulsion and solar cells are also two significant size associated cost items. However launch cost is high as well and primarily size related []. A medium sized communication satellite (roughly 0 transponders) costs around $00Million which the launch campaign covering half of the overall cost. Satellite design work mainly includes forming necessary budgets such as mass, link and power which gives an inclusive idea for cost and manufacturing process. Then system and subsystem level trade-offs are applied to keep satellite performances between user requirements window. Satellite manufacturers get into a threatening proposal process with time and cost spending studies to satisfy user requirements such as Equivalent Isotropic Radiated Power (EIRP) and Gain/Noise Temperature (G/T) values over desired coverage areas. Typically proposal routines comprise recurring computations to demonstrate satellite system performances. Commercial payload optimization tools [], genetic particle swarm optimization methods [] and multi-objective evolutionary approaches [] are given in literature to optimize payload performance values. In this study, TPAT is proposed considering payload performance requirements, equipment specifications and satellite platform characteristics. 1. Architectural design process 0 1 Conceptual design phase of a telecom satellite initiates with the subsystem level tradeoffs done by the design engineer. Architectural design notion includes; Configuration plans for all satellite phases such as integration, launch, cruise, operational, Equipment and subsystem layout with sizing and attachment principles,

4 Description of structural principles and thermal control, Analyses of mass/centering/inertia, Integration principles []. The architectural design methodology of a telecom satellite begins with laying out the onboard payload which includes the main instruments. The rest of the spacecraft architecture is adapted to support its constraints and survival over operational life time. Boresight axes orientation of the payload sensors with respect to orbital and launcher coordinate systems are frozen in this step. Payload side on launch configuration is also determined. Next step prepares the operational configuration as taking into account the payload, platform, outer sensors, solar array and engines. Satellite configurations are examined considering mission. Then the possible launchers are investigated for determining allotted volumes for payload, platform and stowed appendages. Steps two and three are related with the external design of the satellite associated with mainly launcher specifications. The internal satellite design steps begin with defining structural principles and thermal control aspects. This step covers determining platform shape and primary structure concept such as central cylinder, truss, and shear panels. Thermal control concept and reduced-scale drawing of the structure and handing points identification is stated in this stage. Layout of stowed appendages (solar panels, payload antennas) and main equipment (propulsion, batteries and etc.) is formed in the next step. Internal modularity and integration principles with radiation zone definitions, stowing mechanisms and anchoring points are also inspected in this step. Finally all remaining internal and external equipment are regulated. Element layout and secondary structures (brackets, panels or equipment shelves) are identified. Heating power, structure and cabling mass budget are also

5 estimated in this final stage []. Figure 1 depicts the architectural design methodology of the commercial telecom satellite counting internal and external parts. 1. Payload description GEO telecom satellites payload functions as radio relay links between remote stations. Two main telecom payload architectures, regenerative and bendpipe (transparent), are currently operational. Regenerative payloads demodulate and decode uplink signal in order to recover the originally transmitted data []. The original transmitted data is recovered and routing can be performed based on packet level and flexible channelization schemes can be adopted []. Bendpipe payload simply receives the uplink signal, converts the uplink carrier frequency to downlink carrier frequency, amplifies the downlink signal without demodulating the received waveform and retransmits the signal to the ground station [] In this study, TPAT is applied to a conceptual satellite with practical coverage areas [] also illustrated in Figure. Telecom satellite is planned to serve three fixed coverages of West, East and Turkey as shown in Ku-band and Turkey coverage in C-band. Satellite electrical power subsystem parameters [1] and reliability analyses [1-1] are evaluated to compare necessary budgets. Figure presents the service areas covering Turkey, Europe and Mid-Asia. 0 1 Satellite repeater receives the uplink signal from the receive antenna, then the received signal is filtered by bandpass input filters to eliminate unwanted out-of-band signals. Filtered signals pass through the low noise amplification, frequency down conversion and medium power amplification stages respectively. Channelization is applied to the amplified signal to divide and filter into various channels. Linearization, gain adjustment

6 and high power amplification are performed to channelized signals in which signal power levels are elevated to accomplish downlink performance values. Final function of the repeater is combining the channels into beams by output multiplexers (OMUX) which are passive and reliable assemblies []. Repeater redundancy is provided by using multiport switches which are connecting equipment in communication satellite payload. In case of a failure, signal path is re-routed by changing suitable switch positions without loss of mission. Robust switch configuration yields the designed system to compensate more TWTA failures [1]. Key design specifications for communication satellite payload are EIRP and G/T. Least possible EIRP and G/T requirements for secure broadcasting link establishment in Ku/Cband beams and corresponding receive/transmit antenna gain specs are given in Table Proposed payload analysis tool, TPAT A typical satellite manufacturing process can be split into three main phases (design, integration and test) independent of its mission. The design procedures include PDR (Preliminary Design Review) and CDR (Critical Design Review) stages where the satellite architecture is almost finalized. However the design duties of the manufacturer are initiated with the proposal and negotiations phases. A typical communication satellite proposal costs the manufacturer around a $1Million depends on the work load. The satellite design phases focus on various types of budgets (power, mass, thermal, and electrical etc.) with associated margins. In this work, the proposed tool, TPAT, can be utilized to calculate these budgets and margins in a rough but rapid manner to lessen the design costs and duration.

7 Microsoft Office Excel offers a convenient development environment for such a computational based design work. The satellite design requirements can be transformed into numerical forms as the analysis tool input. Then the cots satellite equipment specifications are also inserted into the tool to generate necessary equipment databases. Finally the individual budgets are calculated and margins are found. Detailed tool specifications are illustrated in Figure as a flowchart. 1 1 Since Excel enables adding macros, a GUI can be generated to improve visualization and automation. As additional analyses are required to insert in TPAT such as payload and TCR reliability analyses to confirm the subsystem reliability performance over the satellite lifetime, new spread sheets or screens can added to the tool. In this proposed work, spread sheets are preferred rather than macros owing to the easiness of adding new equipment specifications and analyses. Figure depicts a snapshot of the design environment. 1. Payload trade-offs and panel layout Satellite EIRP performance strictly depends on the TWTA s (Travelling Wave Tube Amplifier) end of life RF (Radio Frequency) power output and cumulative summation of the worst case output losses from TWTA to antenna feed. The satellite design architect applies trade-offs in order to minimize output losses and number of equipment ensuring reliable broadcast links. Figure illustrates the single signal flow chain after high power amplification through TWTAs. This chain carries a single channel where multiple broadcast channels are carried up with parallel TWTA blocks. Post TWTA signal chain includes high power isolator (HPI), R and C type waveguide switches, output multiplexer (OMUX), and output test coupler. Every single equipment

8 has its internal loss value and waveguides connecting these equipment introduce additional loss, mass and complexity to the overall system architecture. Since this chain carries high power, equipment connections are done with WR flexible rectangular waveguides. Waveguide insertion loss is assumed to be 0.1 db/m and estimated output loss budget from TWT to antenna feed given in Figure is calculated in Table. 1 Repeater RF power output values for service areas can be computed using system specifications and output losses. The cumulative worst case output losses are calculated and deducted from generated satellite EIRP. Both beginning of life (BOL) and end of life (EOL) payload output RF power values are computed. Since the EOL obtains worst case scenario, EOL performance merits are took into account for the rest of design step in order to set precise margin values. The repeater power output for coverage areas are computed and given Table according to Equation (1). 1 (1) One of the peculiar characteristics of commercial telecom satellites is represented by great number of amplifiers that they embark. The payload mass and power consumption is mainly given by the presence of TWTAs which present about % of the total mass and from 0% to 0% of the overall DC power consumption [1]. Figure depicts the EPC power distribution scheme with CAMP and TWTA. The EPC and TWTA performance merits for 0V satellite bus voltage with 0% CAMP, % EPC and % TWTA efficiencies respectively are given in Table. 1 Both CAMP and EPC have limited contribution to power dissipation budget compared with amplification tubes. The power dissipation for C and Ku-band output passive equipment after TWTAs can be calculated using following equation.

9 = () The power dissipation budget is utilized to manage design process of heat pipes network through telecom satellite platform and determining temperature zones on payload panels. The power dissipation values for given EPC and TWTA performance merits are presented in Table As the TWTA power dissipation values are calculated, overall payload power dissipation and consumption values can be determined. Payload power merits carry particular importance since platform performance such as thermal handling and electrical power subsystem specifications (solar panel and battery aspects) are concretized respect to these values. An arbitrary telecom satellite including 1 Ku-band TWTAs with nominal/ redundant channels and C-band TWTAs with nominal/1 redundant channel generates the power consumption and dissipation values given in Table. Subsequent to calculation of power consumption and dissipation values of required payload equipments, the thermal zones on platform panels are optimized in order to cautiously accommodate payload equipments. Spacing between sequent equipment must be optimized to diminish connection mismatches and cabling RF losses. The optimized panel layout of major payload equipment is depicted in Figure. The mass budget of the panel is examined in Table excluding switch, RF harness, waveguide and coaxial match masses. The mass uncertainty of active units is estimated as % whereas the passive units such as IMUX, OMUX and filters have uncertainty of %. 1 In Figure, Ku-band and C-band payload equipment are colored with green and yellow respectively. Head pipe network is illustrated with brown where o area is blued and o

10 area has no color. The panel power dissipation merits regarding equipment specification is given Table.. Conclusion Telecom satellite manufacturing procedures restrain costly design steps of not only PDR and CDR but also initial proposal process. Proposal preparation typically lasts for several months and causes high waged man-hour cost. Afterwards telecom satellite design strictly depends on the payload performance requirements with evaluation of compatible platform and launcher options. In conclusion, payload and platform design tools avoiding higher man-hour save both satellite design time and cost. Since the PDR and CDR utilize detailed design functions, satellite optimization tools yield rapid and accurately estimated performance merits. TPAT acquires necessary payload performance merits such as RF losses, EIRP and G/T. Also power consumption and dissipation values which perform a vital role on satellite panel optimization in terms of equipment assembly and heat pipe network design are computed regarding payload performance. This yields design engineers to rapidly prepare commercial telecom satellite proposals. 1 References 1 [1] Elbert BR. Introduction to Satellite Communications. nd ed. Norwood, MA, USA: Artech House,. 0 1 [] Roddy D. Satellite Communications. th ed. New York, NY, USA: McGraw-Hill, 00.

11 [] Dunbar N. Trends in communications satellite platform design. In: IEEE Colloquium on Communication Opportunities Offered by Advanced Satellite Systems Conference; 1 October, London, UK. New York, NY, USA: IEEE. pp.1-. [] Chaumon JP, Gil JC, Beech TW, Garcia G. SmartRings: advanced tool for communications satellite payload reconfiguration. In: IEEE Aerospace Conference; - March 00; Big Sky, MT, USA. New York, NY, USA: IEEE. pp.-1. [] Jian L, Cheng W. Resource planning and scheduling of payload for satellite with genetic particles swarm optimization. In: IEEE Congress on Evolutionary Computation; 1- June 00; Hong Kong, China. New York, NY, USA: IEEE. pp [] Kieffer E, Stathakis A, Danoy G, Bouvry P, Talbi EG, Morelli G. Multi-objective evolutionary approach for the satellite payload power optimization problem. In: IEEE Symposium on Computational Intelligence in Multi-Criteria Decision-Making (MCDM); -1 December 01; Orlando, FL, USA. New York, NY, USA: IEEE. pp [] David A. CNES Space Technology Course Space Techniques and Technology Volume: Platforms, Tolouse, France: CNES, [] Wang CC, Nguyen TM, Goo GW. Satellite payload architectures for wideband communications systems. In: IEEE Military Communications Conference Proceedings; 1 October - November ; Atlantic City, NJ, USA. New York, NY, USA: IEEE. pp [] Nguyen TM, Wang CC, Kumar R, Goo GW. Signal processing techniques for wideband communications systems. In: IEEE Military Communications Conference Proceedings; 1 October - November ; Atlantic City, NJ, USA. New York, NY, USA: IEEE. pp. -.

12 [] International Telecommunications Union. Handbook of Satellite Communications. rd ed. New York, NY, USA: Wiley, 00. [] Gokten M, Yagli AF, Kuzu L, Yanikgonul V, Sanli E, Gulgonul S. Preliminary design of TUSAT satellite communication payload. In: IEEE First AESS European Conference on Satellite Telecommunications (ESTEL); - October 01; Rome, Italy. New York, NY, USA: IEEE. pp. 1-. [1] Demirel S, Sanli E, Gokten M, Yagli AF, Gulgonul S. Properties and performance comparison of electrical power sub-system on TUSAT communication satellite. In: IEEE First AESS European Conference on Satellite Telecommunications (ESTEL); - October 01; Rome, Italy. New York, NY, USA: IEEE. pp [1] Kuzu L, Yagli AF, Gokten M, Yanikgonul V. Reliability analysis of TUSAT satellite communication payload. In: IEEE First AESS European Conference on Satellite Telecommunications (ESTEL); - October 01; Rome, Italy. New York, NY, USA: IEEE. pp [1] Demircioglu E, Nefes MM. Reliability-based TT&C subsystem design methodology for complex spacecraft missions. In: CISS 00. nd Annual Conference on Information Sciences and Systems. -1 March 00; Princeton, NJ, USA. New York, NY, USA: IEEE. pp [1] Gulgonul S, Koklukaya E, Erturk I, Tesneli AY. AYA:Haberleşme Uydusu Faydalı Yük Sistemi Akıllı Yedekleme Algoritması. J Fac Archit Gazi Uni 01; : [1] Ceruti L, Gambarara M, Viganó D. New generation EPC for medium power TWTs. In: Proceedings of the Fifth European Space Power Conference (ESPC). 1- September ; Tarragona, Spain. New York, NY, USA; IEEE. pp

13 Figure 1. Architectural design methodology of a telecom satellite Figure. Practical service areas covering Turkey, Europe and Mid-Asia 1

14 Figure. Proposed payload analysis tool flowchart Figure. Snapshot of the design environment 1

15 Figure. Post TWTA signal flow chain Figure. EPC power distribution scheme 1

16 Figure. Optimized panel configuration for major payload equipment Table 1. Satellite design requirements and antenna specifications Antenna Performances Payload Specifications Ku-Band West Coverage Rx (dbi). G/T (db/k). Tx (dbi). EIRP (dbw) 0 Ku-Band East Coverage Rx (dbi) 0. G/T (db/k) 1. Tx (dbi) 0 EIRP (dbw) Ku-Band Turkey Coverage Tx (dbi) EIRP (dbw) C-Band Turkey Coverage Rx (dbi). G/T (db/k) 1 Tx (dbi) 0. EIRP (dbw) 1

17 Table. Typical output losses for a telecom satellite Equipment WG Length (m) WG Loss (db/m) Component Loss (db) Waveguide wg HPI 0.1 Waveguide wg R-switch 0.0 Waveguide wg R-switch 0.0 Waveguide wg R-switch 0.0 Waveguide wg C-switch (db) 0.0 Waveguide wg OMUX 0. Waveguide wg Test coupler 0.0 Waveguide wg Worst case. m 1.1 db Nominal.0 m 1.1 db Table. Repeater power output for satellite coverage areas Coverage Area BOL (dbw) EOL (dbw) West (Ku-Band) East (Ku-Band) 0.0. Turkey (Ku-Band) 1.0. Turkey (C-Band).. Table. EPC and TWTA performance merits Frequency Band Bus Current (Amps) EPC Input (Watts) TWTA Output (Watts) EPC Dissipation (Watts) Ku-Band C-Band Table. Power dissipation of output passive equipment after TWTAs Coverage Area Worst Case Dissipation (W) Nominal Dissipation (W) West Ku-Band..1 East Ku-Band Turkey Ku-Band Turkey C-Band

18 Table. Total payload power dissipation and consumption values Equip. Name Nominal C- band TWTA Redundant C-band TWTA Nominal Ku-band TWTA Redundant Ku-band TWTA Ku-Band Receiver C-Band Receiver Ku-Band TTC Receiver Ku-Band TTC Transmitter Ku-Band Beacon Num. of Equip. Power Dissipation Unit Dissip. (W) Total Dissip. (W) Num. of Equip. Power Consumption Unit Cons. (W) Total Cons. (W) Total Payload Dissipation:.1 W Total Payload Consumption:. W Table. Panel mass budget including uncertainties Unit Quantity Unit Mass with Uncertainty (g) Total Mass (g) Ku-band CAMP. Ku-band TWTA 1 Ku-band EPC 1. 1 Ku-band HV Cable Ku-band Power Isolator 0 Ku-band OMUX ( Ch) 0 0 Ku-band OMUX ( Ch) 1 C-band CAMP C-band TWTA 1 C-band EPC C-band HV Cable

19 C-band Power Isolator C-band OMUX ( Ch) 1 Ku-band TTC Receiver 1 Ku-band TTC Transmitter 1 Ku-band TTC Beacon 1 Table. Panel power dissipation merits Temperature Panel 1 Panel Total Power Dissipation Zone o W W 0W/m o 0W W 0W/m