Institutsleiter

Prof. Dr.-Ing.
Stefanos Fasoulas

Stellvertreter

Prof. Dr.-Ing. Sabine Klinkner

Prof. Dr. rer. nat. Alfred Krabbe

Sekretariat
Prof. Fasoulas

Larissa Schunter

Sekretariat
Prof. Klinkner

Annegret Möller

Sekretariat
Prof. Krabbe

Barbara Klett

Administration

Dr. Thomas Wegmann

 


Institut für Raumfahrtsysteme
Pfaffenwaldring 29
70569 Stuttgart

Tel. +49 711 685-69604
Fax +49 711 685-63596

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About PPTs

What is a PPT?

A Pulsed Plasma Thruster (PPT) or Pulsed Magnetoplasmadynamic Thruster (iMPD) is an electric space propulsion system. It works with help of electromagnetic forces and is hence grouped together with the stationary MPD Thruster, the Hall Thruster and the Inductive Thruster.

Figure 1: ADD SIMP-LEX developed at IRS.

A PPT consists of four main parts. First, a capacitor is needed to store the energy for the pulse. Electrodes are connected to the capacitor to establish an electric potential. The propellant necessary is situated between the electrodes. To ignite the pulse, a spark plug is installed.

Once the capacitors are charged the spark plug triggers and forms a short-time arc discharge. This discharge ionizes propellant along the surface causing a discharge of the main circuit. The ablated and ionized propellant forms a conductive plasma sheet. This circuit forms a current loop that creates a magnetic field. The magnetic field perpendicular to the plasma current leads to a Lorentz force accelerating the plasma. Hence an impulse is achieved by the thruster. One pulse ends when the entire energy stored in the capacitor is discharged.

The moving plasma between the electrodes adds a time dependent resistance and inductance to the circuit of the thruster, thereby influencing the oscillation behavior.

The energy stored in the capacitor bank does not have to be provided by the pulse power unit continuously but may be supplied in between the pulses. This reduces the power requirements of the thruster on the on-board power supply, allowing for more flexibility in power management.

 

Figure 2: Conceptual model of unsteady electromagnetic acceleration by a self-induced magnetic field.

Why use a PPT?

Pulsed Plasma Thrusters are developed and investigated due to their low mass and flexible power consumption compared to other electric or chemical alternatives. They may hence be used on small satellites providing limited mass, space and energetic capacities. Further, they form a robust, easy-to-handle, and reliable system with reproducible performance. Ablative PPTs (PPTs using solid propellant, e.g., Polytetraflourethylene) stick out by their simple handling of the propellant. Storage or injection problems as found in usual chemical thrusters, i.e., hydrazine based systems, do not play a role in PPTs.

Why is it interesting to do research on PPTs?

Due to their very flexible design, PPTs allow to investigate variations in design and to perform parametric studies in all aspects of the thruster.
Concerning the geometry of the electrodes, their width, their length, their thickness, the gap between them, their shape (rectangular, tongue, coaxial), and their inclination to each other - the flare angle - can be investigated.  For the propellant, the question of material, its density, its configuration, either breech-fed or side-fed, and if side-fed the angle and gap between them is occurring. From an energetic point of view, the capacitance and the applied voltage play an important role, but also the inductance and resistance of the whole electric circuit is relevant. Therefore the material’s decision and the design of the connecting and current carrying parts influence the performance of the thruster tremendously. The possibilities for research seem unlimited.
Most studies are conducted to determine the performance characteristics of the thruster, i.e., the impulse bit achieved, and the mean exhaust velocity and the thrust efficiency respectively. Further, the determination of the plasma physics require intensive research work. Hence, the ability to characterize thrusters and to understand better the physical processes during the discharge is given.