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ScienceDirect Procedia Engineering 185 (2017) 319 – 325
6th Russian-German Conference on Electric Propulsion and Their Application Development of KM-60 based orbit control propulsion subsystem for geostationary satellite
V. V. Vorontsov a, A. N. Kostin a, A. S. Lovtsov a, D. V. Volkov b, Yu. M. Ermoshkin b, E. N. Yakimov b, O. A. Gorshkovc, A. A. Ostapushchenkod, D. V. Udalovd, Yu. S. Arkhipove, S. A. Buldasheve a
Federal State Unitary Enterprise “Keldysh Research Center”, Onezhskaya str. 8, Moscow, 125438, Russian Federation b Scientific JSC “Academician M.F. Reshetnev “Information Satellite Systems”, Lenin str. 52, Zheleznogorsk, Krasnoyarsk region, 662972, Russian Federation c FSUE TsNIIMash, Pionerskaya str. 4, Korolev, Moscow region, 141070, Russian Federation d JSC SPC “POLYUS”, Kirov av. 56 c, Tomsk, 634050, Russian Federation e FSUE NIIMash, Stroiteley str. 72, Nizhnyaya Salda, Sverdlovsk region, 624740, Russian Federation E-mail:
[email protected] [email protected]
Abstract The paper contains the development results of an orbit-control electric jet propulsion subsystem intended for a geostationary satellite based on the EXPRESS-1000 family medium class platform. The subsystem is based on the newly-developed KM-60 thrusters featuring an increased specific pulse, and equipped with a Xenon storage tank made of composites, a small-sized Xenon feed unit, PPU and dedicated software. During the development stage, scientific and technical tasks were carried out to ensure thruster performance stability over the lifetime, to create a power processing system featuring increased output voltage, and a control unit operating through a multiplex data bus. As a result, a thruster subsystem significantly exceeding similar subsystems in main parameters was developed and implemented. © byby Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2017 2016The TheAuthors. Authors.Published Published Elsevier B.V. Peer-review under responsibility of the organizing committee of RGCEP – 2016. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the 6th Russian-German Conference on Electric Propulsion and Their Application Keywords: spacecraft, satellite, electric jet propulsion subsystem, thruster, flow control unit, Xenon feed unit, Xenon storage unit.;
1. Introduction Plasma thrusters have been used in national satellites since 1971 [1]. Since 1982, 45 satellites made by JSC ISS were launched and commissioned. These satellites were equipped with electric jet propulsion subsystems [2]. Employment of such type of propulsion subsystems have made it possible to improve satellite efficiency as a whole due to reduction of the mass of fuelled propulsion subsystems achieved thanks to the high efficient performance of plasma thrusters versus chemical thrusters. All these subsystems were based on plasma thrusters of M-70 and SPT100 types, with an accelerating voltage of 300 V [3] and equipment (storage and feed systems, power processing systems) manufactured to the technology level available at time of the propulsion subsystem creation. An analysis demonstrated that all these elements have essential resources both in terms of specific characteristics and mass. That is why on the cusp of 2000, a task was set to create updated elements of orbit-control electric jet propulsion subsystem for satellites, with
* Corresponding author. Tel.: +7(499) 158-0020; fax: +7(499) 158-0367. E-mail address:
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1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the 6th Russian-German Conference on Electric Propulsion and Their Application
doi:10.1016/j.proeng.2017.03.310
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the aim of further mass reduction. The relevance of this task was even enhanced with satellite life extension up to 15 years and more, the addition of new requirements for de-orbiting after satellite decommissioning, and satellite orbit raising to achieve the geostationary orbit. All these new requirements result in an increase of propellant volume required to generate the necessary total pulse and increase of propulsion subsystem mass. To make it reasonable, the JSC ISS set a task to develop a new thruster featuring an improved efficient performance, a newly developed PPU with improved output voltage and a lighter Xenon feed unit and Xenon storage unit made of composites. Such orbitcontrol propulsion subsystems were developed for medium-class satellites of 1000 to 1500 kg mass range (based on an EXPRESS-1000 platform) composing of a plasma thruster KM-60 (the Keldysh center), power processing unit PPU (SPC POLYUS), Xenon storage unit - XSU (NIIMash), Xenon feed unit - XFU (JSC ISS), and on-board software – OBSW (JSC ISS). This paper contains brief data on the above-mentioned subsystem components, problems solved at the component development stage, a comparison versus the similar previous generation components, and an assessment of the effects achievable thanks to the new subsystem. Such activities were continued, but with less intensity, at the Moscow Aviation Institute (MAI) only, and subsequently (since the end of 80-ies) – at the Research Institute of Applied Mechanics and Electrodynamics of MAI (RIAME MAI). With the purpose to increase efficiency of the first-generation APPT and to start development of APPT of the second generation, the necessary investigations were made, which were aimed at the increase of specific thrust impulse and thrust efficiency. The greatest attention was paid to the improvement of processes inside the discharge chamber. In the pulsed thrusters, in which the discharge period is 10–20 μs, high losses were explained by a wide scatter of masses in velocities and by the local-temporal mismatching between the plasma density distribution and the accelerating three-dimensional electromagnetic forces. The discharge-accelerating chambers characterized by relatively good matching of above distributions were developed by MAI [2, 3]. Magnetic fields varying in time and space were tested by magnetic probes, and plasma density by spectroscopic methods. The APPT laboratory models with thrust efficiency of about 20-30 % were designed as a result. 1. Orbit control propulsion unit An orbit control propulsion unit composes a thruster KM-60 and flow control unit (FCU). A thruster and FCU were developed and subjected to qualification tests by the Federal State Unitary Enterprise “Keldysh Research Center” (“Keldysh Center”) [4]. The KM-60 prototype is a KM-45 thruster equipped with a similar magnetic system, discharge chamber, and cathodes; by the beginning of KM-60 development activities, the KM-45 had passed more than 1000 hours of life tests [5]. The Keldysh Center also manufactured flight model propulsion units. The KM-60 Thruster has an improved specific pulse (versus an analog thruster of M-70 type developed by the OKB FACKEL) exceeding 2000 s at BOL. The KM-60 peculiarity is a long-term operation with high specific pulse at relatively low power capacity. Implementation of such requirements was a complicated scientific and technical challenge requiring dramatic efforts linked to thruster development. The main parameters of the KM-60 based propulsion unit are summarized in the Table 1. Table 1. Main propulsion unit parameters - thruster KM-60 and FCU
Main parameters of thruster KM-60 Thrust 42 mN Discharge voltage 500 V Discharge current 1.8 A Average specific pulse (over >1860 s lifetime) Total thrust pulse Current in magnet coil system (regulated)
>380 kN·s 1.5…2.5 A
Main parameters of flow control unit (FCU) Propellant Xenon Input working pressure 1.75 ·105 N/m2 Electric valve supply voltage: 6.3 V On firing (from 0.1 to 1 s) 2.2 V keeping mode
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Besides, a set of severe requirements were imposed to the thruster on the basis of its functions, including:
large quantity of firings (up to 8250);
high level of environmental effects (random vibration with rms deviation up to 25 g);
high level of single shocks achieving 2500 g.
To ease installation on a satellite, an orbit control propulsion unit was divided into two separate physical components, in particular, a thruster itself and a flow control unit (FCU). A view of propulsion unit components is given in Figure 1.
Fig. 1: View of components of KM-60-based propulsion unit (at the left - thruster KM-60, at the right– flow control unit).
For the qualification purposes, three orbit control propulsion units were manufactured. Within the qualification campaign, standard environment tests were carried out, as well as functional tests and measurement of thruster thrust vector positions. After that, each of three units was subjected to reduced life tests for at least 500 hours. To allow full-scale life tests, an additional KM-60 was manufactured, which successfully passed qualification tests prior to life tests. Thus, four KM-60 thrusters and four FCU’s were subjected to qualification tests. During life tests, significant atmosphere impacts on thruster specific parameters were detected when a chamber was opened to measure erosion profile. Therefore 4100 hour-long life tests were carried out without opening the vacuum chamber. High purity Xenon was used as a propellant. Gas was supplied from a test bench using a nominal FCU. FCU valves, and thermothrottle current were controlled by a test bench control unit. Thruster firing and operation were carried out as per a nominal cyclogram. As often as once 100 every hours, firing was performed using a redundant cathode. Specific pulse alterations versus operation time during life tests are shown in Figure 2. The plot demonstrates that a specific pulse achieves an approximately fixed level after 1500-hour running time. Details of test results are provided in a paper [4]. Approximately, after 1550 hours of thruster operation, after a protection coating was spread, an erosion of the end surfaces of the magnet system poles was observed. Tracks of thruster surface erosion observed after completion of life tests are shown in Figure 3. One can see that wear of an internal pole is symmetrical, though wear of an external pole is clearly seen, with maximum entrainment near a redundant cathode. At present, there are no surface erosion tracks initiating cathode electrode discharges located under floating potential. A nature of magnet pole erosion tracks demonstrates that they are mainly determined by return ion flux. Despite erosion of magnet system poles and ceramic insulators, at the life end a thruster still keeps its operability and parameters satisfying imposed requirements. The KM-60 total running time over all test campaigns was 4120 hours and 8357 firings, total thrust e at test completion was 41.8 mN. An analog, which is a thruster M-70 (manufactured by OKB FACKEL) with accelerating voltage of 300 V has a thrust of 40 mN and specific pulse of 1450 s [3]. So the KM-60 thruster, with a larger thrust and accelerating voltage of 500 V, has an advantage versus an analog thruster of about 28% in terms of specific pulse, thus allowing reduction of propellant volume.
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Fig. 2 : Alteration of a specific thrust pulse and average specific thrust pulse during 4100-hour life tests
Fig. 3 : Photo of a thruster end surface after 4100-hour tests
2. Power processing unit Power processing units (PPU) intended for propulsion subsystems used for satellites manufactured by JSC ISS are traditionally manufactured by SPC POLYUS [6]. SPC POLYUS also developed a power processing unit to ensure power supply for KM-60 based propulsion subsystem. Input voltage is 100 V, output voltage is 500 V. The Magnet power supply is independent, from a separate source; coil current is under stepped control. The PPU is capable of ensuring simultaneous operation of two out of eight thrusters, as selected. For the first time in SPC POLYUS practice, a control through a 1553 bus (Multiplex data bus = MDB) was implemented. Data is transmitted as per the standard GOST-R52070-2003 (analog to MIL STD-1553). Such approach gives exclusive flexibility to unit control versus direct command control approach. To improve reliability, PPU design is developed with deep redundancy and possibility of cross-links implemented. A functional PPU block-diagram is shown in Figure 4. Each thruster power channel is equipped with two power converters. The PPU ensures control of a thruster, flow control unit and Xenon feed unit.
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(УУП) CPU – control and power unit, (ИПК) VPS – valve power supply, (УП) IU – igniter unit (power source), (СТМК) MCS – magnet coil stabilizer (power source), (СНК) CHS – cathode heater stabilizer (power source), (ИПА) APS – anode power source, (СТА) ACS – anode current stabilizer (thermothrottle power source), (СОУ) ECS – exchange and control system, (УК) SU – switching unit, (БПК) XFU – Xenon feed unit, (БК) OCPU – orbit control propulsion unit. Команды – commands; ТМИ - TMI
Fig. 4. PPU view and functional block-diagram
To agree the electrical characteristics of the PPU with a relevant thruster, a dedicated filter is inserted between them. A system comprises an embedded microprocessor with PROM, and software responsible to check functions, and control function for MDB exchange. For the purposes of working out a unit, a laboratory/development model and qualification model were manufactured. Development models saw a full scope of environmental tests (including mechanical loads and thermal cycling) and functional tests. At the same time, to allow PPU stand-alone tests, a dedicated Electric Ground Support Equipment (EGSE) was developed comprising electrical thruster simulators. The PPU development model successfully passed firing coupling tests with the thruster development model used. QM PPU and PFM PPU saw acceptance firing tests, for which technological thruster models and PFM thrusters were used. 3. Propellant storage and feed system A functional block-diagram of a propellant storage and feed system is shown in Figure 5.
Fig. 5 : Functional block-diagram of a propellant storage and feed system (ГЗ) FP – filling port, (ГП) COP – check-out port, (БХК) XSU – Xenon storage unit, (ДД) PT – pressure transducer, (ПК) PV – pyro valve, (БПК) XFU – Xenon feed unit, (БУР) FCU – flow control unit, (ДК) – OC thruster
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The Xenon feeding unit (XFU) was developed by JSC ISS [7]. It is based on a high-precision mechanical reducer and contains two channels, each of which equipped with high-pressure valve, reducer, receiver, low-pressure valve. The unit input and output is equipped with filters and small-sized check-out ports to supply technological gas during checks. The unit also contains high- and low-pressure transducers. Input pressure is up to 250 •105 N/m2, output pressure is up to 1.75 •105 N/m2. The unit ensures gas flow rate within a range of 1.5 to 12 mg/s. At the development stage, a XFU and QM XFU laboratory model were manufactured. Development models underwent a full scope of environmental tests in line with the relevant specification and functional tests, the positive results of which allowed design requirements to be validated. The XFU is controlled by the PPU and ensures Xenon supply to two operating thrusters. A peculiarity of a new XFU is a high accuracy of output pressure maintained by a mechanical reducer, thus enabling to exclude a two-step pressure regulation scheme. The new XFU mass is 8.9 kg less than the previous unit mass. A Xenon storage unit was developed by FSUE NIIMash, as per the technical specification provided by JSC ISS, and is intended to store propellant. The main component is a tank comprising a lining made of titanium alloy and a pressure shell made of the synthetic fiber Armos. Domestic materials are only used to fabricate XSU. Working pressure is 140•105 N/m2, fracture pressure is 250 •105 N/m2. Tank capacity is 71 kg Xenon. In addition to a tank, XSU also comprises fixation elements (supports) to facilitate its installation on a satellite, a filling port, pressure transducer and pyro valve set. At the development stage, several development models were manufactured which saw a full scope of ground development test campaigns, including mechanical loads, thermal cycling, storageability and fracture tests. The Xenon storage unit is flight proven and is successfully used for several satellites. Its mass is 4.3 kg heavier than the mass of its previous analog unit built as a pressed spherical tank made of titanium alloy; however, its capacity is 40 kg larger. The tank factor (ratio of a tank mass to maximum capacity) is 0.126 as opposed to 0.3 of its previous analog unit; that means a significantly better perfectness of its design. 4. On-board software 5. During the exploitation phase, all propulsion subsystems used for ISS satellites are controlled by dedicated software which is a functional component of the subsystem. For the KM-60 based subsystem, JSC ISS also developed a dedicated software program implemented in the on-board computer which is a part of the satellite onboard control subsystem (OCS). The program task is to deploy a thruster firing cyclogram, monitoring of subsystem parameters at each stage, thruster cut-off in case of abnormal situations, generation of reports and statistic data. To debug the on-board software program and to ensure operation of the satellite simulator, a dedicated propulsion subsystem model was created to simulate propulsion units operation accompanied with generation of full set of telemetry parameters in accordance with issued control commands, operation logic of units and specified abnormal situations. The on-board PS control software program demonstrated positive results during full cycle of stand-alone and complex debugging activities. It was also used during ground electrical tests of the propulsion subsystem at the satellite level. The developed program ensures reliability, ease and flexibility of PS control. 6. Propulsion subsystem integration To create a KM-60 based propulsion subsystem, a satellite manufacturer followed the approach of compiling the subsystem from separate functionally completed units. Such approach allows achieving notable advantages versus a concept of complete propulsion system delivery, thanks to the flexibility in structure formation, price and quality. However such approach requires special attention to be paid to validate capability of mutual operation at the unit level, and subsystem integration in a satellite. Within the frame of propulsion subsystem integration activities performed in the Keldysh Center, development models of propulsion units and PPU were subjected to firing coupling tests. Acceptance firing tests for flight models of propulsion units, PPU and XFU were performed in the JSC ISS using a dedicated test bench GVU-60 (Figure 9) [8]. Chamber length is 8030 mm, diameter is 3380 mm. A venting system ensured oil-free vacuum of 10-4 mm Hg for operation of SPT-100 type thrusters. In the course of tests gas flow rate was measured, telemetry and technological parameters were recorded. After successful completion of firing tests, complex electrical tests of propulsion unit, XFU, PPU, OBSW were carried out at the satellite level. To this end, technological gas (nitrogen) was supplied to the system, and release of electrical valves was verified. Instead of actual thrusters, the PPU was loaded with electrical simulators provided by PPU EGSE. Software was delivered for electrical tests after being tested at the On-board software test environment level. Successful complex tests completed process of propulsion subsystem integration sequence.
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Flight tests confirmed the main design parameters of the subsystem, including thruster thrust values, power consumption. To evaluate effect achieved through using new KM-60 based propulsion subsystem, one can compare its mass with a design mass of analog M-70 based subsystems and other components used previously, under the similar requirements in terms of quantity of simultaneously running thrusters (main mode assumes simultaneous operation of two thrusters) and total pulse. The KM-60 based subsystem equipped with new Xenon storage and feed units is 91 kg lighter than the subsystems based on M-70 thruster and previous generation units. Such noticeable advantage is mainly achieved due to less Xenon filled, tanks quantity and mass, that is, due to efficient performance of a KM-60 thruster. Released mass can be used to increase quantity of payload transponders or additional propellant aimed to prolong satellite lifetime. In both cases, satellite mission efficiency is improved. 7. Conclusion Cooperation of Russian companies with the JSC ISS as a prime player completed the development of an orbit control propulsion subsystem intended for medium class geostationary satellites based on the EXPRESS-1000 platform. The subsystem is based on KM-60 plasma thrusters featuring an accelerating voltage of 500 V and specific pulse increased by 28% (efficient performance) versus previous generation thrusters. For plasma thrusters with power less than 1 kW now in use, such results were achieved for the first time and no equals are known throughout the world. To ensure operation of the propulsion subsystem, a dedicated power processing system with improved output voltage, multilevel redundancy and control through a multiplex data bus was created. A small-sized twochannel Xenon feed unit based on a mechanical reducer with a small flow rate and high accuracy of output voltage retention was developed. The Xenon storage unit with a tank made of composite materials was developed. With only a few exceptions, the propulsion subsystem is built using Russian materials and components. The on-board SW program was created ensuring easy and flexible control of the subsystem. At the satellite manufacturing company, a dedicated test bench intended for firing integration tests of plasma thrusters was commissioned. The KM-60 based propulsion subsystem successfully passed ground tests and achieved flight qualification. Its main performances were confirmed during flight tests. For the first time since 1994, Russian geostationary satellites are equipped with electric jet propulsion subsystems featuring essentially improved performance characteristics. New subsystem mass is 91 kg less versus the previous generation subsystem. Its implementation is a new step forward in evolution of national space propulsion subsystems and allows improving characteristics of medium class geostationary satellites due to reduction of portion of PS mass in the total satellite mass. References [1]. Khodnenko V.P. Activities of VNIIEM in EPT field. History, our days and prospects. - 33rd International Electric Propulsion Conference, The George Washington University, D.C. US, October 6-10, 2013, IEPC-2013-65. [2]. Volkov D.V., Ermoshkin Yu.m., Yakimov E.N. Usage of electric jet thrusters for ISS satellites. – Electrojet thrusters. History. Our days. Prospects. Abstracts for international scientific and training conference devoted to 60th anniversary of OKB FACKEL, Kaliningrad, October 5-7, 2015. [3]. Murshko V.M., Kozubsky K.N. New Russian space technologies: Electrojet propulsion subsystems in space. Devoted to 55th anniversary of OKB FACKEL – Electrojet systems developed by OKB FACKEL. Book of reports and articles. Kaliningrad, 2010, pp. 25-37. [4]. Kostin A.N., Lovtsov A.S., Vasin A.I., Vorontsov V.V. Development and qualification of Hall thruster KM-60 and the flow control unit. - 33rd International Electric Propulsion Conference. The George Washington University, USA, October 6-10, 2013. IEPC-2013-055. [5]. Gorshkov O., BelIkov M., Muravlev V., Shagayda A.,et al. Development and qualification test of Electric Propulsion System based on the HET KM45 for GSAT-4 Spacecraft. - 58th IAC, Hyderabad, India, September 24-28, 2007. IAC-07-C4.4.01. [6]. Galayko V.N., Gordeev K.G., Ermoshkin YU.M., Mikhailov M.V., Yakimov E.N. Current status and perspectives of development of power processing units intended for electrojet plasmic thrusters. – Electronic and electromechanical systems and devices. XIX scientific and technical conference, Tomsk, April 16-17, 2015, SPC “POLYUS”, pp. 3-5. [7]. Ermoshkin Yu.M.., Zhitnik Yu.N., Ladygin A.P. Activities of ISS related to development of propellant storage and feed units for electrojet thrusters. Reshetnev readings. Proceedings of XIX international scientific and training conference devoted to 55th anniversary of Reshetnev Siberian State aerospace university, in two parts, Part 1, under the general editorship of Yu.Yu. Loginov. Siberian State aerospace university, Krasnoyarsk, November 10-14, 2015, pp. 153-156. [8]. Simanov R.S., Nikipelov A.V. Improvement of satellite propulsion subsystem firing test working place, using GVU -60. - Reshetnev readings. Proceedings of XIX international scientific and training conference devoted to 55th anniversary of Reshetnev Siberian State aerospace university, in two parts, Part 1, under the general editorship of Yu.Yu. Loginov. Siberian State aerospace university, Krasnoyarsk, 2015. pp. 173-175. [9]. Lazurenko A., Vial V., Kim V., Kozlov V., Skrylnikov A., Bouchoule A. Investigation of the SPT operation under high discharge voltages. - 28th International Electric Propulsion Conference, Toulouse, Fr., March 17-21 2003. IEPC-2003-211. [10]. Gorshkov O.A., Muravlev V.A.,Shagaida A.A, Hall effect and ion plasmic thrusters intended for satellites (under editorship of RAS academician A.S. Koroteev), - M., Mashinostroenie, 2008. 280 pp. [11]. Vial V., Cornu N., Coulaud E., Arrat D. PPS NG: Hall Effect thruster for next generation spacecraft. - The 32nd International Electric Propulsion Conference, Wiesbaden, Germany, Sept. 11-15, 2011. IEPC-2011-120.
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