PPU Developments at Thales Alenia Space in Belgium: PPU Mk4 and Low Power PPU

Since 1996, Thales Alenia Space in Belgium designs, develops and produces Power Processing Unit (PPU) to supply Hall Effect Thrusters (HET). Several generations of PPU's were developed and qualified with the ESA support, leading to more than 130 PPU Flight Models delivered up to now. The first generation, the PPU Mk1 was dedicated to 1.5 kW HET (PPS-1350, SPT-100) used on geostationary telecom satellites to perform North-South Station Keeping. The second generation, the PPU Mk2, powered HET up to 2.5 kW. In order to perform the Electrical Orbit Raising of geostationary telecom satellites and Station Keeping, the PPU Mk3 was developed and qualified in 2016 to power 4.5 kW HET's (PPS-5000, SPT-140D). Then, the PPU Mk3 has been upgraded in PPU Mk3 EVO to offer more flexibility, more output power (up to 5kW), more robustness to radiation environment and less dependency on export control regulations by implementing European parts. Capitalizing on this strong heritage, TAS-B has initiated, on one hand, the development of a highly competitive PPU capable of operating HET up to 7 kW in a wider operating voltage range. On the other hand, TAS-B extends its PPU portfolio to PPU's for lower power thrusters (700W - 1kW) answering to the current space market with growing interest in LEO constellations. The LEO spacecraft's are smaller, have less available power and require higher competitiveness. The development of the PPU Mk4 started in the frame of the European Union's Horizon 2020 Strategic Research Cluster (SRC) on Space Electric Propulsion with the CHEOPS project. After a successful coupling test of a functionally representative PPU Elegant Breadboard with the 7kW HET and its Fluidic Management System (FMS), the PPU EM modules were developed, manufactured and tested thanks to ESA support and successfully coupled with the 7kW HET and its FMS in December 2024. The development is continued to reach qualification in 2026. In order to produce a highly competitive product, a design-to-cost approach was followed and several key technologies have been used: new converter topology, planar magnetics including a dedicated configuration for high power, innovative thermal management means, GaN transistors, digital control implemented in a rad-hard TAS-B Digital Processor Controller (DPC) designed specifically for space applications. This microcontroller based on a multi-core architecture provides useful resources for monitoring and controlling power supplies. It implements low voltage functions such as Data Bus interface, thruster start-up sequencing and regulation of the thruster discharge current via propellant pressure regulation. The development of the Low Power PPU's was initiated as part of the EPIC H2020 HEMPT-NG project with the design, manufacturing and successful coupling test of a functionally representative Low Power PPU breadboard with the HEMPT EVO thruster. Then, a fit, form and function representative Low Power PPU HEMPT EM was developed with the ESA support. It was successfully coupled with the HEMPT EVO thruster and its Flow Control Unit in October 2023. Looking for a highly competitive product, a design-to-cost approach was followed and the following key technologies were selected: use of COTS components, planar magnetics, GaN transistors, digital control implemented in a rad-hard TAS-B DPC. The development is continued to reach qualification and delivery of Flight Model's in 2025 according to the first commercial order of Low Power PPU awarded to TAS-B. Building on the legacy of the Low Power PPU for 700W HEMPT, the development of a Low Power PPU EM optimized for 1kW HET was performed in the frame of the EPIC H2020 CHEOPS Low Power project. The anode supply topology was adapted to optimize efficiency for higher output power at lower output voltage and the HET specific supplies were implemented. A fit, form and function representative Low Power PPU HET EM was developed, manufactured and successfully coupled with the PPS X00 thruster and its FMS in February 2025. After a brief introduction of TAS-B heritage in Electric Propulsion, this paper presents the ongoing developments of the PPU Mk4 and the Low Power PPU as well as the key results obtained during the coupling test campaigns.