Electric Propulsion for Station Keeping and Electric Orbit Raising on Eutelsat Platforms

Transcription

1 Electric Propulsion for Station Keeping and Electric Orbit Raising on Eutelsat Platforms 2015-b/IEPC-97 Presented at Joint Conference of 30th International Symposium on Space Technology and Science 34th International Electric Propulsion Conference and 6th Nano-satellite Symposium, Hyogo-Kobe, Japan C. Casaregola 1 Eutelsat, Paris, 75015, France Abstract: With a fleet of 34 geostationary satellites and more than 30 years of service from space, Eutelsat is today Europe s most long-standing satellite operator and one of the world s leading satellite operators. The first two platforms using Electric Propulsion procured are SESAT-1 (EUTELSAT 16C) and KA-SAT, for which Electric Propulsion is limited to on-station operations. The successful demonstration of sustained capability of Electric Propulsion for these two platforms in addition to the extensive flight heritage with no significant anomalies demonstrated in the last decades on both commercial and scientific platforms, prove the high level of maturity reached by Electric Propulsion systems. Based on that and due to new attractive launch options, one full-electric platform - EUTELSAT 115 West B has been procured and launched in March The launch of EUTELSAT 115 West B is a key milestone for telecom platforms as it makes Eutelsat the first Operator to use Electric Propulsion for a complete electric orbit raising. Two additional platforms EUTELSAT 117 West B and EUTELSAT 172 B - are under procurement and will perform complete electric orbit raising as well. An overview of Eutelsat platforms using Electric Propulsion for station keeping and electric orbit raising is given in the paper. ADSL CPS EP EOR ESA E/W FAA FU GEO GPS GTO Isp MMH NTO N/S PPS SPT Nomenclature = Asymmetric Digital Subscriber Line = Chemical Propulsion System = Electric Propulsion = Electric Orbit Raising = European Space Agency = East West = Federal Aviation Administration = Filter Unit = Geostationary Orbit = Global Positioning System = Geostationary Transfer Orbit = Specific Impulse = MonoMethylHydrazine = Nitrogen TetraOxide = North South = Plasma Propulsion System = Stationary Plasma Thruster 1 Spacecraft Propulsion Mechanical and Thermal Systems Engineer, Department of Engineering; Eutelsat, ccasareg@eutelsat.com 1

2 SSTO TOM TMA XIPS XFC XPC WAAS = Supersynchronous Transfer Orbit = Thruster Orientation Mechanism = Thruster Module Assembly = Xenon Ion Propulsion System = Xenon Flow Control = XIPS Power Controller = Wide Area Augmentation System I. Introduction ITH more than 30 years of service from space, Eutelsat is the Europe s longest-standing satellite operator. WCreated as an international organisation in 1977, Eutelsat took shape in order to operate the first generation of communications satellites ordered by the European Space Agency (ESA) and to reflect Europe s ambition to develop an industry able to build, launch and operate satellites. From its first satellite launched in 1983, today Eutelsat's fleet of 34 satellites covers Europe, Africa, the Middle East and large parts of the Asian and American continents. Additional six satellites are to be launched by Eutelsat s in-orbit resources are positioned in geostationary orbit between West and 172 East. From these premium orbital positions, the Eutelsat satellite fleet is able to serve two thirds of the globe, users in 150 countries in Europe, Africa, Asia and the Americas, from the East Coast of North and South America through to the Asia-Pacific coast. Eutelsat experience and quality of service have gained the confidence of a broad and growing portfolio of customers that include broadcasters, pay-tv operators, telecom operators, Internet service providers and government agencies. The procurement of the first Eutelsat telecom platforms using Electric Propulsion (EP) dates back on mid-90s with SESAT-1. Then, a second platform - KA-SAT was procured and launched in Both these two platforms were put in their orbital slot by using either direct GEO insertion or by on-board chemical propulsion. Then Electric Propulsion has been used on both platforms only for on-station operations. Their records of operational and flight performance data have shown up to date satisfactory results with respect to Eutelsat requirements. Furthermore, in some cases, flight performances have been even better than the expected ones. However, for next years the use of Electric Propulsion on telecom platforms will be increased. Electric Propulsion used for full or partial orbit raising is becoming more and more frequent justified by the high level of maturity reached by EP systems and by the specific economics of the overall mission. With the launch of EUTELSAT 115 West B in March 2015, Eutelsat opened the door to a new era. Eutelsat is in fact the first operator that has launched a full-electric telecom platform performing a complete Electric Orbit Raising (EOR). Moreover, two additional platforms that will perform complete EOR EUTELSAT 117 West B and EUTELSAT 172 B are under procurement and will be launched in the fourth quarter of 2015 and in second quarter of 2017 respectively. II. Electric Propulsion for On-Station Operations on Eutelsat Platforms A. The SESAT-1 (EUTELSAT 16C) Spacecraft Procured at the end of 90s from ISS-Reshetnev (former NPO-PM) with payload manufactured by Thales Alenia Space (former Alcatel Alenia Space), SESAT-1 (Siberian-European SATellite) was designed to provide 18 Ku channels to satisfy the telecommunications needs in Central and Eastern Europe for a minimum operational lifetime of 10 years. SESAT-1 whose commercial name is today EUTELSAT 16C - was launched from Baikonour in April 2000 and was placed directly into geostationary orbit by a Proton K-BlockDM launcher. Figure 1 shows SESAT-1 in the stowed configuration. The propulsion subsystem is composed of a Xenon SPT Propulsion system for station keeping and orbit control and of hydrazine thrusters for attitude control. All components of the propulsion subsystem are Russian built. In detail, the Electric Propulsion system is composed of 4 tanks for Xenon storage, a pressure regulation unit able to deliver the Xenon to the thrusters and 8 SPT assemblies. A power supply provides the power to the subsystem, controlling the propellant feed lines as well as the selection of the operating thrusters. Each thruster assembly is composed of a Xenon flow control unit and a Hall effect thruster SPT 100 manufactured by Fakel. This 1.5 kw thruster is Figure 1. SESAT-1 satellite in the stowed configuration (Courtesy of NPO-PM) 2

3 able to provide a nominal thrust of 83 mn at an Isp of 1520 s (anode voltage of 300 V) for a total impulse of 670 kns equivalent to more than 2200 hours at nominal thrust. Each thruster is equipped with 2 redundant cathodes that are periodically cycled in accordance with the NPO-PM and Fakel recommendations. The SESAT-1 satellite in its in-orbit configuration with solar panels and communications antennas deployed is shown in Figure 2. After separation from the Proton-BlockDM and direct insertion in GEO, SESAT-1 station acquisition was performed by using the 4 SPTs (2 prime + 2 redundant) mounted on the E/W faces. Regular station keeping maneuvers to keep the satellite within its allocated orbital slot, i. e. ±0.1 degree N/S and E/W, are performed by other 4 inclined SPTs, 2 mounted on the North face and two mounted on the South face. Nominal on-station operations are performed by using 1 thruster at a time and no thruster operation during eclipse period ±1 hour for EW thrusters is possible. As regards the station keeping profile, 1 maneuver per day is generally performed 7 days out of 7. During Equinox, 2 maneuvers per day are performed. Typically, maneuvers near equinox are longer than the ones near solstice period. Spacecraft attitude control is performed by using hydrazine thrusters, a pair of thrusters for each axis. However, a low level pulsing is required by these thrusters as main attitude control requirement is during initial acquisition, station keeping burns and wheels unloading. To date, SESAT-1 has accumulated a total firing duration of almost 5600 hours, in which the most used SPT 100 thruster has been firing for almost 2000 hours and the most used cathode for almost 1000 hours. SESAT-1 was designed for 10 years lifetime and after 15 years of service it is still operating properly as expected. B. The KA-SAT Spacecraft KA-SAT was manufactured by Airbus Defence and Space (former EADS Astrium), based on the Eurostar E3000 platform, with a total weight of about 6.1 tons. It was launched from Baikonour by Proton Breeze M in December 2010 and was positioned at 9 East for a design lifetime of 15 years. KA-SAT is a high throughput telecommunications satellite able to provide broadband Internet access services across Europe and some parts of the Middle East and North Africa. KA-SAT s revolutionary concept is based on a payload with 82 Ka-band spotbeams connected to a network of ten ground stations. This configuration enables frequencies to be reused, taking total throughput to beyond 90 Gbps and making it possible to deliver Internet connectivity for more than one million homes, at speeds comparable to ADSL. In Figure 3 the KA-SAT spacecraft in deployed configuration. KA-SAT propulsion system is composed of both Chemical Propulsion System (CPS) and Plasma Propulsion System (PPS). The CPS is used for all transfer orbit maneuvers including the final deorbiting, E/W station keeping maneuvers, attitude control and wheels off-loading as necessary. The PPS is used for Figure 2. SESAT-1 satellite in the deployed configuration (Courtesy of NPO-PM) Figure 3. Artistic view of KA-SAT satellite in the deployed configuration (Courtesy of Airbus Defence and Space) N/S station keeping maneuvers, orbit inclination and eccentricity control. The KA-SAT CPS is based on the generic EUROSTAR 3000 design with 4 propellant tanks (2 NTO + 2 MMH), a Helium tank to provide pressurization, a 450 N apogee engine and fourteen 10 N reaction control thrusters. The PPS is mainly composed of a Xenon storage tank, an electronic pressure regulator, two 2-axis gimbaled thruster module assemblies (TMA) and 2 power processing units along with their associated pipework and harness. Each TMA comprises 2 SPT-100s manufactured by Fakel, an associated Xenon Flow Controller (XFC), a pointing mechanism (TOM) bearing and canting the SPTs with its associated thermal hardware and 2 filter units (FUs) one per thruster. The use of TOM can guarantee a thrust 3

4 axis excursion of ±12 with respect to the nominal position. The PPU controls the selected SPT and its associated XFC on the basis of programmed procedures and commands received from the on-board computer. After separation form the launcher in GTO, KA-SAT has performed its orbit acquisition by means of 4 apogee burns using the chemical system. During spacecraft operational life, N/S station-keeping maneuvers are performed by means of Electric Propulsion whereas E/W maneuvers and spacecraft attitude control are performed with chemical propulsion. A typical station keeping profile of KA-SAT for a cycle of 7 days consists of 5 days in which combined inclination/eccentricity control is done with 5 pairs of N/S maneuvers by using Electric Propulsion. The 6 th day is used for longitude drift control done with chemical pulses for E/W maneuver and to offload residual pitch angular momentum with chemical pulses as well. The final day of the cycle is for assessment and planning. The N/S stationkeeping phase duration lasts approximately 120 minutes but this duration could vary depending on the period of the year. As for SESAT-1, different constraints need to be respected while executing the N/S and E/W station-keeping maneuvers. After 4.5 years of service, KA-SAT has accumulated a total firing duration of more than 3500 hours. The most used SPT 100 thruster has been firing for almost 1800 hours and the most used cathode for about 900 hours. The system is working as expected. III. Electric Propulsion for Electric Orbit Raising on Eutelsat Platforms The extensive flight heritage reached by EP systems in the last decades with successful results and the growing on-board power available on telecom platforms have pushed the developments of Electric Propulsion systems towards higher power levels. In addition, since SpaceX Falcon 9 burst on the scene, a renewed competition in the launch services has started aimed at offering lower launch costs. In particular, the launch cost reduction due to the reduced launch mass of a full-electric spacecraft has raised the debate about the benefits that each operator can gather by considering a complete EOR. And as preliminary result of the overall mission cost equation, the bigger is the launch cost reduction, the longer is the time to orbit that in principle could be acceptable by an operator during EOR. As consequence, during the last few years, new design of telecom platforms have been proposed by all major spacecraft manufacturers in which Electric Propulsion has assumed a primary role. Moreover, new launch and operational strategies to perform the complete EOR and on-station operations only by using Electric Propulsion have been extensively investigated. Eutelsat has been monitoring with great interest all these developments and today, three Eutelsat satellites EUTELSAT 115 West B, EUTELSAT 117 West B and EUTELSAT 172 B - have Electric Propulsion on-board performing complete EOR and on-station operations. A. The EUTELSAT 115 West B Spacecraft Manufactured by Boeing Defense and Space and based on 702SP platform, EUTELSAT 115 West B (former Satmex 7) is part of a groundbreaking procurement agreement involving the manufacture and delivery of four all-electric satellites featuring a revolutionary design that significantly reduces launch mass while keeping payload performance. Equipped with 12 C-band and 34 Ku-band transponders connected to four service areas, EUTELSAT 115 West B will extend reach of the Americas to markets in Alaska and Canada. It will focus in particular on serving clients providing data services, including broadband access, cellular backhaul, VSAT solutions and social connectivity. EUTELSAT 115 West B is due to enter service late Launched on 1 March on a Falcon 9 in a dual configuration, EUTELSAT 115 West B and its co-passenger are the first-ever allelectric propulsion telecom satellites to perform a complete EOR. The 2.2 tons spacecraft was delivered in a Supersynchronous Transfer Orbit (SSTO) and - after three days - EUTELSAT 115 West B s Electric Propulsion system was prepared for the EOR that will take more than seven months. The spacecraft is 3-axis stabilized with momentum wheels, solar arrays are able to provide up to 8 kw to the Payload for a contractual life of 16 years. In Figure 4 the EUTELSAT 115 West B Figure 4: EUTELSAT 115 West B stacked with its co-passenger (courtesy of Boeing) 4

5 spacecraft in stacked configuration with its co-passenger. The Electric Propulsion System is based on the Boeing Xenon Ion Propulsion System (XIPS) and it is composed of four gimbaled 25 cm ion thrusters and two XIPS power controllers (XPCs). Each thruster and therefore each XPC - is capable to operate in two modes, low-power mode at 2.2kW for attitude control (79 mn thrust, Isp=3400 s) and high-power mode at 4.4kW for orbit transfer (165 mn thrust and Isp=3500 s) 1. Each XPC is connected to a diagonal pair consisting of one north and one south thruster. While both XPCs are used in nominal operation, one XPC and diagonal thruster pair are capable of performing all maneuvers for the required spacecraft life. The platform is full-electric (no chemical propulsion mounted on-board), therefore all major functions - EOR, N/S and E/W Station-Keeping, wheels offloading, station relocation and final re-orbitation for disposal are performed by the XIPS. At the time the paper has been written, EUTELSAT 115 West B has already performed about 30% of the overall EOR with nominal XIPS performance. The EOR phase is expected to be concluded at the end of September Once the spacecraft has reached its final orbital position in GEO and all in-orbit tests have been completed, station keeping operations will be performed four times a day involving all 4 XIPS every day of the year. B. The EUTELSAT 117 West B Spacecraft Scheduled to be launched in the third quarter of 2015, EUTELSAT 117 West B (former Satmex 9) is also based on the 702SP platform developed by Boeing. It will be co-positioned at 117 West with the EUTELSAT 117 West A (former Satmex-8) satellite to offer expanded capacity across more than 45 nations and territories in the Americas, notably for video, telecommunications and government sectors with 40 Ku band and hosted payload. Following the agreement concluded with Raytheon payload that will enhance the availability and accuracy of Global Positioning System (GPS) signals for the Federal Aviation Administration (FAA), the Wide Area Augmentation System (WAAS) payload will provide coverage to reference stations in Canada, Mexico and Puerto Rico, as well as the continental United States and Alaska, improving GPS signal accuracy to seven meters from 100 meters. Commercial airline and general aviation pilots can use this extremely accurate information for more direct flight paths and precision approaches to airports and remote landing sites. Electric Propulsion system is Boeing XIPS, the same as Figure 5: Artistic view of EUTELSAT 117 West B (Courtesy of Boeing) for EUTELSAT 115 West B. The Eutelsat 117 West B is a 1.9 tons platform, it will be mounted in the upper position of the stacked configuration and will be launched with its co-passenger on a Falcon 9 in SSTO. After separation from the launch vehicle, the EOR phase will take about 7 9 months. C. The EUTELSAT 172 B Spacecraft EUTELSAT 172 B is based on an evolution of the Eurostar E3000 platform from Airbus Defence and Space specifically designed for the EOR. The spacecraft will host 17 C-band and 44 Ku-band transponders. It will also host a High Throughput ku-band payload specifically designed for in-flight broadband, featuring multiple user spots optimised to serve densely-used Asian and trans-pacific flight paths and interconnected to gateways operating in the Ka band. This new payload will be the first customised for in-flight connectivity over the Pacific Ocean Region, delivering an overall throughput of 1.8 Gbps to an underserved market Figure 6: Artistic view of EUTELSAT 172 B (courtesy of Airbus Defence and Space) 5

6 forecast to enjoy sustained growth over the coming years. In addition to Electric Propulsion for the orbit raising, EUTELSAT 172 B will be Eutelsat s first satellite equipped to dynamically distribute power between beams connected to its High Throughput payload. This facility will enable Eutelsat to respond to traffic variations across the eight time zones covered by the payload s 11 beams that span from the Western seaboard of North America to South-East Asia. Despite such a three distinct payloads, the use of Electric Propulsion for orbit raising and for all station-keeping maneuvers allows a significant spacecraft mass reduction. In fact, EUTELSAT 172 B is a 3.5 tons spacecraft and this will enable this powerful satellite to be launched in GTO with the Ariane 5 lower position, offering lower launch costs. The solar array is composed of two deployable wings able to provide up to 13 kw to the payload. The EUTELSAT 172 B Plasma Propulsion System (PPS) will be used to perform all major spacecraft functions such as complete EOR, N/S and E/W station-keeping, wheels offloading, station relocation and final re-orbiting for disposal. The EP thrusters mounted on-board are the Fakel SPT-140D 2 able to provide a nominal thrust of 270 mn and an Isp of about 1850 s at 4.5 kw (anode voltage of 300 V) and the Snecma PPS able to provide a nominal thrust of 320 mn and an Isp of 1700 s at 5 kw (anode voltage of 300 V). The EOR for EUTELSAT 172 B will take about 4 months. IV. Conclusion The successful in-flight experience of SESAT-1(EUTELSAT 16C) and KA-SAT and the extensive flight heritage of EP systems demonstrated on telecom and scientific platforms confirm the high level of maturity reached by EP systems for commercial applications. In addition, thanks to the recent developments of Electric Propulsion systems for higher power levels and due to the attractive options given by new launchers that burst on the scene, Electric Propulsion is assuming a primary role for telecom platforms. With the launch of EUTELSAT 115 West B, Eutelsat has in fact opened the door to a new era for Electric Propulsion. For the first time, a full-electric telecom platform has been procured and launched to perform the complete orbit raising and all in-flight operations by the use of Electric Propulsion. The launch of EUTELSAT 115 West B and the on-going procurement of other two full-electric platforms to be launched by 2017 EUTELSAT 117 West B and EUTELSAT 172 B prove once again Eutelsat s commitment to innovation that contributes to increasing competitiveness and improving customer service. Acknowledgments The author wishes to thank Eutelsat Department of Engineering (DIN) and Department of Exploitation (DEX) for the support provided. Special thanks to Vladimir Chechik (Flight Dynamics Engineer in Eutelsat) for the precious help given in providing spacecraft operational data. Many thanks to Vanessa O Connor (Director of Corporate Communications in Eutelsat), Andrew Lindley (Director of Engineering in Eutelsat) and Pierre Timmerman (Head of Quality and Spacecraft Platform in Eutelsat) for their comments, suggestions and corrections received that have been highly appreciated. References 1 K.-R. Chien, S. L. Hart, W. G. Tighe, M. K De Pano, T. A. Bond and R. Spears, L-3 Communications ETI Electric Propulsion Overview, IEPC , 29 th International Electric Propulsion Conference, Princeton, New Jersey, J. J. Delgado, R. L. Corey, V. M. Murashko, A. I. Koryakin and S. Y. Pridanikov, Qualification of the SPT-140 for use on Western Spacecraft, AIAA , 50 th Joint Propulsion Conference, Cleveland, Ohio, O. Duchemin, P. Dumazert, N. Cornu, D. Estublier, F. Darnon, Stretching the Operational Envelope of the PPSX000 Plasma Thruster, AIAA , 40 th Joint Propulsion Conference, Fort Lauderdale, Florida,