TECHNOLOGY HEMP-Thruster concept
Figure 1 shows the system context diagram of an EPS with the delimitation of the H2020 HEMPT-NG scope. The system is comprised of four main parts, the thruster module (HTM) which includes the thruster itself (THR) and the neutralizer (NTR), the flow control unit (FCU) that supplies the thruster module with the propellant gas, and the power processing unit (PPU) that supplies the thruster with electric power and controls the FCU and the thruster module. The FCU is connected to the propellant tank on the satellite by the pressure supply assembly (PSA) which reduces the tank pressure down to the working pressure of the FCU. The tank itself is not part of the H2020 HEMPT-NG scope. The PPU is connected to the electronic systems of the satellite which are also not part of the H2020 HEMPT-NG scope.
The thruster module is developed by TD. The FCU is contributed by TAS-D with the micro-FCU from AST. The PPU for LEO applications is developed by TAS-B, and the PPU for Telecom./Navigation by Airbus. TD as design authority will handle the system aspects.
State of the art Functional Principle of the HEMPT technology
HTA The HEMP-Thruster Electric propulsion system
The core of the HEMPT Electric Propulsion System (EPS) – also called HEMP Thruster Assembly (HTA) – is formed by the HEMP thruster module (HTM), that consists of the thruster (THR) and the neutralizer (NTR). The system consists further of the Flow Control Unit (FCU), the Pressure Supply Unit (PSA) and the Power Processing Unit (PPU).
The present HTA system architecture is shown in the figure below. It consists of two main elements - the PSCU (Power Supply and Control Unit) = PPU, which supplies the HEMPT modules (four in the figure) with power and controls their operation, and the HEMPT module itself.
The HEMPT module itself in the current design is composed of a thruster, a neutralizer compensating the resulting electric charge of the spacecraft, the Flow Control Unit (FCU) controlling the propellant flow and therefore thrust and the mechanical and thermal structure including the radiator. Thrust control can be achieved by control of the propellant throughput only. This is done by the Flow Control Valve (FCV), which provides the capability to regulate the flow and therefore the anode current by adjusting the control current through the valve which is done by the PSCU internal regulator.