In Orbit Operation of 20mN Class Xenon Ion Engine for ETS-VIII

Transcription

1 Orbit Operation of 20mN Class Xenon Ion Engine for ETS-VIII IEPC Presente at the 30 th ternational Electric Propulsion Conference, Florence, Italy Toshiyuki Ozaki *, Yukikazu Kasai, an Takafumi Nakagawa Mitsubishi Electric Corporation, Kamakura, Kanagawa, , Japan Takashi Itoh, Kenichi Kajiwara **, an Masafumi Ikea Japan Aerospace Exploration Agency, Tsukuba, Ibaraki, , Japan The Engineering Test Satellite VIII (ETS-VIII) of Japan Aerospace Exploration Agency (JAXA) uses a 20mN class xenon ion engine subsystem (IES) for North-South Station Keeping (NSSK). The IES was moifie for a larger satellite with longer lifetime base on the former IES. ETS-VIII, a three-ton class geosynchronous satellite with 10 years bus lifetime, was launche 18 Dec JST; it reache the planne an all bus systems were checke out. The IES showe goo results an is now uner normal operation. The accumulate operation time of the IES in was about 1100 hours for the half year. g Ia Ib Ick I k M m MHC m MPF m NHC Ptrs q T Va Vb Vck V Vnk η u η T Nomenclature = gravity acceleration = acceleration gri current, ma = beam current, ma = main hollow cathoe keeper current, A = ischarge current, A = neutralizer keeper current, A = mass of xenon = main hollow cathoe flow rate, SCCM = main propellant feeer flow rate, SCCM = neutralizer flow rate, SCCM = thruster power consumption, W = electric charge = thrust, mn = accelerator voltage, V = beam voltage, V = main hollow cathoe keeper voltage, V = ischarge voltage, V = neutralizer keeper voltage, V = propellant utilization efficiency = thruster efficiency * Senior Engineer, Space Systems Department, Kamakura Works, Ozaki.Toshiyuki@r.MitsubishiElectric.co.jp Engineer, Space Systems Department, Kamakura Works, Kasai.Yukikazu@ma.mee.co.jp Engineer, Space Systems Department, Kamakura Works, Nakagawa.Takafumi@p.MitsubishiElectric.co.jp Deputy Project Manager, ETS-VIII Project Team, Office of Satellite System ** Manager, Spacecraft Propulsion Engineering Group, stitute of Aerospace Technology Associate Senior Engineer, ETS-VIII Project Team, Office of Satellite System 1

2 I. trouction The first-generation IES was applie for NSSK to two JAXA satellites, ETS-VI an Communications an Broacasting Engineering Test Satellite (COMETS), a two-ton class geosynchronous satellite with 6 years bus lifetime. ETS-VI an COMETS were launche respectively in 1994 an in Although both satellites unfortunately faile to be inserte into their planne s, the thrusters were successfully operate in an the thruster characteristics agree with the groun test results Base on the first-generation IES results, the IES was moifie to exten the lifetime 12. The objective of the moification was to apply for NSSK propulsion of a very large geosynchronous satellite. Development of the ETS-VIII was initiate on The satellite was a three-ton class geosynchronous satellite with 10 years bus lifetime; its main mission objective was to verify the mobile satellite communication an multimeia system technology by using a large-scale eployable reflector (LDR). The ETS-VIII image in is shown in Figure 1. The satellite is 2.45 m wie, 2.35 m eep an 7.3 m high. The with of the eploye solar pales is 40 m. The LDR size is 37 m. The regulate bus voltage is 100 V. The satellite use the IES for NSSK maneuver because the moest low thrust level of electric propulsion was suitable for a flexible structure such as LDR as well as propellant mass reuction attributable to high specific impulse. The IES successfully complete all groun tests incluing the thruster life test 20. Figure 1 ETS-VIII image in II. 20mN class ion engine subsystem A. Main specific parameters an construction The main specific parameters of the IES are presente in Table 1., the north an south ion thrusters will fire for about 5-6 hours, 11 times each two weeks for NSSK alternately. Thrust Metho Average Thrust from BOL to EOL Average Isp from BOL to EOL Total mass of IES Total Impulse Total Operation Time Total Number of Firing Power consumption uring beam firing Thrust vector changing range Table 1 The Main Specific Parameters Kaufman-type xenon ion thrusters >= 20 mn >= 2,200 sec 96 kg N-sec 16,000 hours 3,000 cycles <= 880 W +/-5 eg The ETS-VIII IES comprises five components; two Ion Engine Controllers (IEC), two Power Processing Units (PPU), one Propellant Managing Unit (PMU), one Ion Engine Driver (IED) an two Ion Thruster Units (ITU). A block iagram of the IES is portraye in Figure 2. The IEC controls the operation of PPUs an IED in accorance with sequence logic. The IEC has a comman an telemetry interface with ETS-VIII interface unit. The PPU has seven power supplies for operating thrusters. The output of one PPU is switche to north or south thrusters by internal relays. The PMU stores pressurize the xenon propellant an supplies regulate xenon gas to the ITUs. The PMU consists of two xenon storage tanks (TKX), two pyro valves, one Pressure Regulation 2

3 Moule (PRM), some pressure transucers, an some latching valves. The IED supplies electrical power to actuate the latching valves in both PMU an ITUs an to actuate the gimbal stepping motors. One ITU consists of two thrusters (TRSs) flow control moules (FCMs) an ion thruster gimbal (ITG). The TRS generates thrust for NSSK uner the supply of electrical power from PPU an xenon propellant from PMU via FCM. The FCM is constructe with four orifices, incluing an aitional orifice, which increases the flow rate for the neutralizer ignition, an two latching valves. It controls the mass flow rate of three routes to TRS inepenently. The ITG controls thrust vector by mechanical gimbaling uner the supply of electrical power from IED. Each ITU is mounte on north an south eges of the anti-earth panel of ETS-VIII. The ITU on the north ege an ITU on the south ege are respectively calle the ITU-N an the ITU-S. The PMU is mounte on the lower eck panel of the satellite. The IEC, PPU an IED are installe in the satellite bus moule. Note : IED/PMU have an internal reunancy Figure 2 ETS-VIII IES Block Diagram B. Operational moe of the IES The IES has several operating moes for hollow cathoe conitioning, beam firing, gri cleaning an thrust vector ajustment. 1. Iling Moe (IDLG moe) IDLG moe, low power is supplie to hollow cathoe heaters (both the Main Hollow Cathoe (MHC) an the Neutralizer Hollow Cathoe (NHC)) for egassing. 2. Neutralizer Moe (NEUT moe) NEUT moe, NHC is supplie xenon propellant, the cathoe is heate by the heater an the keeper is supplie electric power. The NHC keeper ischarge is ignite an maintaine. 3. Discharge Moe (DISC moe) DISC moe, the MHC an main ischarge chamber are supplie xenon propellant, the cathoe is heate by the MHC heater an the MHC keeper an the anoe are supplie electric power. After the MHC is ignite, the main ischarge between the MHC an anoe is ignite an maintaine. Then plasma is generate. 4. Beam Moe (BEAM moe) BEAM moe, after NHC, MHC an the main ischarge are ignite, the gri system of the thruster is supplie electric power an the ion beams are extracte. The NHC supplies electrons uring ion extraction in orer to maintain electrical neutrality. The IES generates thrust for NSSK maneuvering. 5. Gri Cleaning Moe (CM moe) During long perios of TRS operation, a short circuit might be create between gri plates by metal flakes. CM moe, PPU supplies electric power to gri plates to release a short circuit between gri plates. 6. ITG Operation Moe The center of mass of the satellite will move as the propellant is consume. this moe, ITG moves the cant angle of TRS to aim the thrust vector at the mass center. 3

4 C. Operation For the NSSK maneuver, one thruster on the south ege generates thrust in the south irection uring the require perio at the escening noe an one thruster on the north ege generates thrust in the north irection at the ascening noe. The control in the IES is performe by the software logic installe in IEC an the harware logic installe in PPU. Major functions of PPU harware logic are the high-spee control for the protection of the PPU circuits an TRS critical parts. (e.g., High voltage break own in the thruster s beam extraction system occurs.) The total control of the IES is execute by the sequential commans from IEC to PPU an IED. For practical NSSK maneuvers by the IES, the IES is operate in BEAM moe. The control sequence is presente in Figure 3. The IES starts its operation when the IEC receives the operation start comman, IES TRS START from the Remote terface Moule (RIM) after receiving the thruster selection (primary or seconary an North or South) comman, IES A/B SEL an ITU-N/ITU-S SEL, uration time of beam firing setting comman, IES TMR an operating parameter setting comman, IES PARA SET SEL. Then the IEC sens the comman to the IED for opening necessary latching valves of both the PMU an FCM an to PPU for supplying electric power to the TRS. Accoring to each PPU operating status signals, the ON/OFF control an output level control for proper power supplies are performe by the IEC. After the uration time reaches the setting perio, the IES operation is terminate. Every power supply of the selecte PPU is turne off an every latching valve of PMU an FCM is close. A. Start up sequence IES A/B SEL ITU N SEL or ITU S SEL IES TMR IES PARA SET SEL IES TRS START PPU A or B ON,IED A or B ON Select North Unit or South Unit SET Duration Time SET "BEAM MODE" SET Reference Values, VB REF, ID REF, ICH REF, INH REF PPU CONTROL FLOW PS 4, 6&7 ON NHC Discharge ON PS 6 OFF PS 3 & 5 ON MHC & Main Discharge ON PS4 OFF PS 1/2 ON Thrust Generation IED CONTROL FLOW OPEN LVs Propellant supply to TRS CLOSE LV for NHC ignition DURATION TIME UP B. Shut off sequence PS 1/2, 3, 5 & 7 OFF PPU A&B OFF IED OFF PS1: Beam Power Supply PS2: Accelerator Power Supply PS3: Main Discharge Power Supply PS4: MHC Heater Power Supply PS5: MHC Keeper Discharge Power Supply PS6: NHC Heater Power Supply PS7: NHC Keeper Discharge Power Supply Figure 3 Control sequence (Beam moe) III. Operational Results in progress of the Ion Engine in ETS-VIII (Figure 4) was launche from Tanegashima Space Center on 18 Dec JST using H-IIA booster rocket, as shown in Figure 5. The satellite successfully reache the planne geosynchronous. 4

5 Before normal operation, satellite bus systems were checke out for function an performance. The IES was checke out for function moes an performance from 22 Jan JST to 29 Jan JST. All thrusters showe goo operational results. Subsequently, normal operation of the NSSK starte from 3 March. To ate, both the thruster NA an SA are running smoothly. Seconary thruster operation has not occurre. Figure 4 Photograph of ETS-VIII on groun Figure 5 Photograph of the launch A. Operation of IES uring check out Four thrusters of the IES were checke out for function moes such as IDLG, NEUT, DISC, CM an BEAM moe. Total beam firing time an high voltage break own number are shown in Table 2. High voltage break own occurs between gri plates with egassing at the beginning of life. Even if a break own occurre, the IES automatically starte to fire. The number of high voltage break owns was much smaller than we expecte. The ignition times of NHC an MHC are about 1.5 minutes. Table 2 Total firing time of each thruster at check out Thruster NA Thruster NB Thruster SA Thruster SB Total firing time 11 hours 36 minutes 7 hours 51minutes 11 hours 53minutes 8 hours High voltage break own number As an example, the BEAM moe telemetry ata for Vb, Ib, Ia, V, I, Vck, an Vnk of the thruster SA are shown in Figure 6. Because the ischarge current change from 3.25A to 4.0A, the beam current an keeper voltage of the MHC change. On the other han, acceleration gri current, ischarge voltage, an keeper voltage of NHC were almost fixe. Figure 6, Vb an Ib were zero when the break own occurre. B. -Orbit Performance Evaluation of Thrusters A comparison of the performance values in an those of the groun test are shown in Table 3. The values in are the telemetry an esign parameter. T, Isp an Ptrs were calculate using the following equations. The esign values of Va, Ick, k, mmhc, mmpf, an mnhc are, respectively, -500 V, 0.5 A, 0.5 A, 2 sccm, 6.5 sccm, an 0.6 sccm. The value of η T is assume as Results of the check out inicate that all thrusters of the IES showe goo operation an performance. T=η T Ib (2M Vb/q) 1/2 Isp=η T η u /g(2q Vb/M) 1/2 η u =M Ib/(q(m MPF +m MHC +m NHC )) Ptrs=Vb Ib+ Va Ia+V I+Vck Ick+Vnk k 5

6 Figure 6 Operational parameter telemetry example of thruster SA 6

7 Table 3 Operating parameter comparison of in- an groun tests Parame Thruster NA Thruster NB ter BEAM1 BEAM2 BEAM3 BEAM4 BEAM1 BEAM2 BEAM3 BEAM4 Vb, V Ib, ma Va, V (-500) (-500) -506 (-500) (-500) (-500) (-500) (-500) (-500) Ia, ma V, V I, A Vck, V Ick, A (0.5) (0.5) (0.5) (0.5) (0.5) (0.5) (0.5) (0.5) Vnk, V k, A (0.5) (0.5) (0.5) (0.5) 0.5 (0.5) (0.5) (0.5) (0.5) mmhc (2) 9.38 (2) 9.42 (2) 9.38 (2) 9.4 (2) 9.36 (2) 9.36 (2) 9.36 (2) 9.36 mmpf (6.5) (6.5) (6.5) (6.5) (6.5) (6.5) (6.5) (6.5) mnhc, (0.6) (0.6) (0.6) (0.6) (0.6) (0.6) (0.6) (0.6) sccm T, mn Isp, sec Ptrs Parame Thruster SA Thruster SB ter BEAM1 BEAM2 BEAM3 BEAM4 BEAM1 BEAM2 BEAM3 BEAM4 Vb, V Ib, ma Va, V (-500) (-500) (-500) (-500) (-500) (-500) (-500) (-500) Ia, ma V, V I, A Vck, V Ick, A (0.5) (0.5) (0.5) (0.5) (0.5) (0.5) (0.5) (0.5) Vnk, V k, A (0.5) (0.5) (0.5) (0.5) (0.5) (0.5) (0.5) (0.5) mmhc (2) 9.48 (2) 9.46 (2) 9.44 (2) 9.46 (2) 9.3 (2) 9.28 (2) 9.28 (2) 9.28 mmpf (6.5) (6.5) (6.5) (6.5) (6.5) (6.5) (6.5) (6.5) mnhc (0.6) (0.6) (0.6) (0.6) (0.6) (0.6) (0.6) (0.6) T, mn Isp, sec Ptrs

8 C. Normal operation status The IES has functione smoothly an continuously uring 3 March - 15 August. Attitue isturbance attributable to firing is sufficiently low by ajusting the thrust vector by ITG in comparison with that attributable to natural factors. An example of the thrust level of the thrusters is shown in Figure 7. The accumulate beam firing time an number are shown in Table 4. Figure 7 Example of thrust in normal operation (14-16 May, 2007) Table 4 Beam firing time an number in normal operation (22 Jan.-15 Aug.) Accumulate beam firing time Accumulate beam firing number Thruster NA Thruster NB Thruster SA Thruster SB 480 hours 83 hours 559 hours 8 hours 88 times 15 times 98 times 2 times IV. Conclusion The IES on ETS-VIII is now uner normal operation on geosynchronous. All thrusters showe goo operational results at the check out an primary thrusters are firing for NSSK. The beam firing time of the IES in accumulate about 1100 hours uring roughly a half year. We expect to use the 20mN class ion engine with a gri to the wie application such as aeroynamically rag free an eep space exploration. References 1 Shimaa, S., Takegahara, H., Gotoh, Y., Satoh, K., an Kajiwara, K., Ion Engine System Development of ETS-VI, AIAA/ASME/SAE/ASEE 25th Joint Propulsion Conference, AIAA , Monterey, CA, USA, Shimaa, S., Takegahara, H., Gotoh, Y., Satoh, K., S. Kitamura, an Kajiwara, K., Ion Thruster Contamination Evaluation, AIAA/ASME/SAE/ASEE 25th Joint Propulsion Conference, AIAA , Monterey, CA, USA, Shimaa, S., Gotoh, Y., Nishia, E., Takegahara, H., Nakamaru, K., Nagano, H., an Teraa, K., Evaluation of Ion Thruster Beam Neutralization, AIDAA/AIAA/DGLR/JSASS 22 n ternational Electric Propulsion Conference, IEPC , Viareggio, Italy, Shimaa, S., Gotoh, Y., Takegahara, H., an Nagano, H., Mass Flow Controller of Ion Engine System, AIDAA/AIAA/DGLR/JSASS 22 n ternational Electric Propulsion Conference, IEPC , Viareggio, Italy, Shimaa, S., Satoh, K., Gotoh, Y., Nishia, E., Takegahara, H., Nakamaru, K., Nagano, H., an Teraa, K, Ion Engine System Development of ETS-VI, AIDAA/AIAA/DGLR/JSASS 22 n ternational Electric Propulsion Conference, IEPC , Viareggio, Italy,

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