PPU MK 3 FOR 5 KW HALL EFFECT THRUSTERS 11 TH EUROPEAN SPACE POWER CONFERENCE

Thales Alenia Space Belgium (ETCA) has developed and qualified the PPU Mk3, dedicated to 5kW Hall Effect Thrusters, to reply to the market demand of full electric satellites performing the Orbit Raising with Electrical Propulsion. The PPU Mk3 is based on the PPU Mk2 heritage (itself derived from the PPU Mk1) but features additional optimizations to reduce cost and take advantage of the single cathode configuration and independent magnet of most 5 kW class thrusters. The PPU Mk3 anode supply was first consolidated by a successful coupling test of the 5kW Anode supply and Filter Unit breadboards in October 2014. Then, a Demonstration Model (DM) of the PPU Mk3, fully representative of the EQM, has been built and has been successfully validated by coupling test with the SPT140-D thruster from Fakel in May 2015, with the PPS-5000 thruster from Safran in October 2015 and with the XR-5 thruster from Aerojet in December 2015. The PPU Mk3 EQM has undergone its qualification tests which have included thermal vacuum tests, pressure increase test (corona) and a full EMC test campaign. After the Qualification Review successfully held in March 2016, the PPU Mk3 EQM has been already coupled with a SPT140-D thruster, in May 2016. Next coupling test is planned with the PPS-5000 thruster in October 2016. In August 2016, the three first PPU Mk3 flight models have been delivered from a total of fifteen PPU Mk3 flight models already ordered by two customers. After the presentation of TAS-B experience in Electric Propulsion, the PPU Mk3 product is described, with its development, coupling tests and qualification. 1. TAS-B EXPERIENCE IN ELECTRIC

The PPU Mk3 is based on the PPU Mk2 heritage (itself derived from the PPU Mk1) but features additional optimizations to reduce cost and take advantage of the single cathode configuration and independent magnet of most 5 kW class thrusters.The PPU Mk3 anode supply was first consolidated by a successful coupling test of the 5kW Anode supply and Filter Unit breadboards in October 2014.Then, a Demonstration Model (DM) of the PPU Mk3, fully representative of the EQM, has been built and has been successfully validated by coupling test with the SPT140-D thruster from Fakel in May 2015, with the PPS-5000 thruster from Safran in October 2015 and with the XR-5 thruster from Aerojet in December 2015.The PPU Mk3 EQM has undergone its qualification tests which have included thermal vacuum tests, pressure increase test (corona) and a full EMC test campaign.After the Qualification Review successfully held in March 2016, the PPU Mk3 EQM has been already coupled with a SPT140-D thruster, in May 2016.Next coupling test is planned with the PPS-5000 thruster in October 2016.
In August 2016, the three first PPU Mk3 flight models have been delivered from a total of fifteen PPU Mk3 flight models already ordered by two customers.
After the presentation of TAS-B experience in Electric Propulsion, the PPU Mk3 product is described, with its development, coupling tests and qualification.

TAS-B EXPERIENCE IN ELECTRIC PROPULSION
Since 1996, Thales Alenia Space Belgium (ETCA) designs, develops and produces Power Processing Unit (PPU) to supply Hall Effect Thrusters.
The first PPU Mk1 qualification model (Fig. 1), developed for the 50V bus Stentor program, has supplied during 8900 hours an SPT-100 thruster in a vacuum chamber simulating space environment.In the frame of AlphaBus extension program and in partnership with ADS and TAS-F, TAS-B has developed the PPU Mk2 product (Fig. 2).The PPU Mk2 addresses PPS1350-G, PPS1350-E, SPT-100 and Hall Effect Thrusters up to 2.5kW for 100V platforms.
Taking benefit of the flight experience of the PPU Mk1, the PPU Mk2 provides 1.6 times more output power (1.5kW AE 2.5kW) and more flexibility to thrusters and platforms, with reduced manufacturing cost.Qualified in July 2014, the PPU Mk2 EQM was successfully coupled with the PPS1350-G at 1.5kW, the PPS1350-E at 2.5kW and the SPT-100.The first PPU Mk2 flight model is delivered from a total of ten PPU Mk2 flight models ordered by two customers.

PPU MK3 DESCRIPTION
The PPU Mk3 features all the supplies required to operate a Hall Effect Thruster which features a single cathode and a magnet coil independent from the discharge.It also features a switching function which enables to operate one out of two thrusters.It communicates with the satellite platform through a 1553 bus and receives its power from a 100V bus.downstream the TSU.This filter enables to limit the voltage ripple at PPU output due to the thruster noise.Indeed, when the thruster is fired, it generates significant noise.A telemetry providing an image of the thruster noise RMS current value is implemented.
The PPU Mk3 is robust to abnormal pressure increased inside satellite up to 1Pa, by mechanical design.
The mass of the PPU Mk3 that includes TSU and two FUs is 18.6 kg.Its dimensions are 390 x 315 x 263 mm³ (LxWxH).
The PPU Mk3 most dissipative functions are located as close as possible to the baseplate for cooling purpose.
The two anode modules include the input switch protections and the main transformer and inverter.The HI module features the heater and ignitor supplies and the MT module contains the magnet and thermothrottle supplies.These four modules are plugged into the Backplane module which features the sequencer, including the communication to the platform and the DCDC.The TSU/FU module comes on top and includes the switching relays necessary for thruster selection and the filter units.

PPU MK3 DEVELOPMENT
The PPU Mk3 development started in 2013, with a Study Phase, to issue and review PPU Mk3 specification with the thruster manufacturers and the primes.The PPU Mk3 architecture was optimized and new packaging was selected to reduce the number of modules and sub-assemblies in order to propose more competitive product.This phase was concluded in January 2014 with the issue of the Technical Requirement Document which is the input for the following phase, the PPU Mk3 Development Phase.
During this phase, a 5kW anode and FU breadboard were coupled with a SPT140-D thruster, in Fakel facilities, at Kaliningrad, Russia, in October 2014, in order to secure the interfaces with the thruster.By powering the thruster up to 400V and 4.7kW, the anode supply output characteristics and output impedance were validated.The implementation of the FU inside the PPU Mk3 was also validated by testing different harness lengths between PPU, FU and thruster.With these results, the PDR was successfully closed in November 2014.
After the PDR, the PPU Mk3 Demonstration Model (Fig. 5), representative of future flight model (fit, form and function) was developed, manufactured and tested with representative load simulating the thruster and XFC.

Figure 5: PPU Mk3 DM
The modules of the DM were first tested independently and then assembled.The objective of the DM was to validate the design, including the PCB routing, in a mechanical assembly representative of the flight models.This was important to validate as early as possible that there were no internal EMC issues.The testing of the DM also enabled to validate the FPGA which controls and monitors all the PPU supplies.
The DM was tested in hot and cold conditions at ambient pressure to validate the good operation of all functions within a wide temperature range as well as to validate the thermal management of the unit.The dissipations in different representative conditions were also measured to check that they were inferior to the worst case computations.The efficiency was measured typically above 95% (Fig. 6).The anode supplies of the PPU Mk3 DM were tested up to 5.2 kW to demonstrate margin on the maximum output power  In May 2015, the PPU Mk3 DM has been successfully coupled with a SPT140-D thruster at Aerospazio facilities, in Italy, in partnership with ADS.During that test, the PPU also operated the XFC and its FPGA efficiently regulated the discharge current by controlling the thermothrottle current.This validation test launched the definition and manufacturing of the PPU Mk3 EQM which was anticipated before the CDR, successfully closed in September 2015, in order to reduce the development planning.
In October 2015, the PPU Mk3 DM was also successfully coupled with a PPS-5000 thruster at Pivoine facilities in CNRS Orléans, France.
In December 2015, the PPU Mk3 DM was also successfully coupled to an XR-5 thruster (without XFC) in the frame of an ESA contract led by European Space Propulsion (ESP) as well, at QinetiQ facilities in Farnborough, UK.This test involved experts from ESP, Aerojet Rocketdyne, Mars-Space and TAS-B.

PPU MK3 QUALIFICATION AND FM's
The PPU Mk3 EQM (Fig. 7) was submitted to a full qualification campaign.In August 2016, the three first PPU Mk3 flight models have been delivered from a total of fifteen PPU Mk3 flight models already ordered by two customers.

Figure 1 .
Figure 1.Stentor PPU Mk1 EQM Qualified for the 100V Spacebus 4000 platform, the 100V PPU Mk1 and Filter Unit (FU) EQM have cumulated 6300 hours ground operation with a PPS1350-G thruster.Thirty three PPU Mk1 flight models were delivered to Airbus DS, ESA, IAI, OHB, Safran, TAS-F.In October 2005, the Smart-1 spacecraft reached the Moon after 4958 hours of cumulated operation of the PPU and its PPS1350-G thruster.Eighteen PPU Mk1, currently in flight for North South Station Keeping on nine telecom satellites, have cumulated more than 32 400 hours flight operation in March 2016.For the SmallGEO platform, TAS-B has developed and qualified an External Thruster Selection Unit (ETSU) to select one out of four thrusters.Two ETSU flight models were delivered, associated with the PPU flight models.

Figure
Figure 2. PPU Mk2 EQM 2. PPU MK3 OBJECTIVES The objective of the PPU Mk3 development was to capitalize on the PPU Mk2 product to propose a costoptimized solution with a reduced time to market to drive 5 kW-class thrusters.These high power thrusters will enable an electrical orbit raising of telecom satellites.The PPU Mk3 objectives were: -Competitive product, -Dedicated to PPS-5000, SPT140-D, XR-5 thrusters.-Dedicated to SpaceBus Neo, Eurostar 3000, NeoSat and Electra platforms.o Bus voltage: 100V regulated o MIL-STD-1553B interface -Qualification and first flight models in 2016

FigureFigure 3 .
Figure 3. PPU Mk3 Functional Diagram The main functions of the PPU are: -1553 data bus interface to communicate with the satellite.-DC/DC converter which enables to supply the lowlevel circuits of the PPU.This DC/DC must be fused protected.-Sequencer, which is implemented by a FPGA and which controls and monitors all the PPU supplies.The sequencer features an automatic mode where the sequencing of all the supplies is managed to start-up the thruster and operate it in steady mode.Telemetry based protections are also implemented in the FPGA.The sequencer includes a PROM which contains default values and valid ranges to operate different types of thrusters.Standard start-up or soft-start start-up sequence where the cathode is ignited and kept in sustain before applying the anode voltage to reduce inrush current may be selected.The sequencer also implements the regulation loop of the discharge current by controlling the setting of the thermothrottle supply.-Input switch protections (one for each discharge supply) which enables to avoid any failure propagation to the satellite 100V bus in case of an internal failure.-Two inverters with their transformer provide the insulated voltages required for the thruster.The inverter is a resonant topology in order to optimize the efficiency.-Two discharge supplies operate in parallel with their outputs summed by diodes.They provide the anode voltage which is commandable from 100V up to 400V.The discharge supplies implement a power limitation: once the knee-current is reached, the voltage drops linearly as the current increases as presented in figure 4 which shows the anode supply characteristic.The short-circuit current is commandable up to 22A.The anode supply, based on two modules of 2.5kW connected in parallel,

Figure 4 .
Figure 4. U-I characteristics of the Anode Supply

Figure 6 :
Figure 6: PPU Mk3 DM Efficiency Another objective of the DM was to provide a representative equipment to validate the Automatic Test Equipment and its test sequence code.The development phase indeed included the implementation of automatic test sequences to implement production tests.

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UK.The test setup included a Thruster simulator reproducing the Discharge current, allowing to test the Discharge current regulation control through the PFCV.The coupling test was successfully carried out.The digital model used for regulation study and optimization was thereby validated.The Discharge current stability, accuracy, response time and overshoot were within required performances.Thanks to this pre-development and the coupling test of PPU Mk3 DM with XR-5 thruster, the development of a PPU Mk3 variant for XR-5 thruster is secured.TAS-B has designed, developed and qualified a new PPU Mk3 product dedicated to 5kW-class Hall Effect Thrusters and 100V satellite platforms.The PPU Mk3 took advantage of a strong heritage with the already qualified PPU Mk2 to ensure a short time to market.Cost reduction measures were implemented in the design, mainly in terms of mechanical packaging.The development started in 2013 and the equipment was successfully qualified in March 2016.Coupling tests were successfully performed with the PPS-5000, the SPT140-D and the XR-5 thrusters.Up to now, a total of 37 PPU (Mk1, Mk2, Mk3) flight models have been delivered by TAS-B from a total of 60 PPU flight models ordered by our customers: Airbus DS, ESA, IAI, ISS, OHB, Safran, TAS-F.