TECHNOLOGY HEMP-Thruster concept

The HEMP-Thruster concept is an ion propulsion technology that is based on the use of permanent magnets for plasma confinement. Through this confinement there is no discharge channel erosion and the technology provides excellent lifetime of the thruster which is a unique feature of the HEMP technology. The plasma is generated in a DC field applied by one single electrode and accelerated at the magnetic cusps created by the alternating polarity of the permanent magnets. This concept allows high acceleration voltages enabling a high specific Impulse (ISP) and in consequence a drastic reduction of propellant consumption.
Since the HEMPT-NG-concept has minimal complexity it provides an excellent basis for economic competitiveness. In the past the market of small satellites in LEO using electric propulsion and electric orbit raising for telecom and navigation satellites in GEO and MEO has been introduced. In order to address these new fields, the development of EP systems for LEO satellites and for telecom satellites in GEO is proposed. It is expected, that the system for GEO can also be exploited for space transportation using clustering techniques.
System context diagram

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

A HEMP thruster generates its thrust by the acceleration of gas ions in an electric field formed as a result of an electrical potential between the anode and the cathode of the neutralizer.
A HEMP thruster generates its thrust by the acceleration of gas ions in an electric field formed as a result of an electrical potential between the anode and the cathode of the neutralizer. The ions are generated in a dielectric plasma discharge channel and are confined by a system of periodically arranged permanent magnets. The magnetic field topology efficiently minimizes electron losses on the discharge channel walls and therefore erosion phenomena with the result of enhanced lifetime. The anode with the propellant gas inlet is mounted at the upstream end of the discharge channel, and the neutralizer cathode for ignition and neutralization of the ion beam is placed at the downstream end.

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.