Hans Leiter

RIT-22 Ion Engine Development - Endurance Test and Life Prediction

Electric Propulsion based on gridded ion thruster technology is the key for several upcoming missions. Namely the European Space Agency ESAs corner stone mission BepiColombo to the Suns nearest planet mercury is a representative for these type of missions. Beside harsh thermal and radiation environment the required total impulse and engine lifetime is a challenge for the electric propulsion system. EAD Space Transportation GmbH proposes its new ion thruster RIT-22 based on cathodless radiofrequency technology for this mission. A 3,000h Endurance test demonstrates the engine is compliant with the mission requirements. This paper describes the ion engine, the test setup and the test facility. One section is devoted to the control software which bases on the flight proven architecture for ARTEMIS. Test results are given and the life time prediction is presented.

Sputter investigation of ion thrusters grid materials

We performed angle and energy dependent sputter yield measurements of various ion thruster grid materials under xenon ion incidence in the energy range 200..1400eV and at normal and oblique incidence up to 70°. Materials investigated are metals as molybdenum and titanium and carbon materials as high-dense graphite of various grain sizes, CarbonCarbon material and pyrolytic graphite. No significant difference between the various carbon materials w.r.t. sputter yield was found. The reduction of the sputter yield of the metals by nitriding was proven but it seems to be not useful as material for ion thruster grid.

RIT-µX - High Precision Micro Ion Propulsion System based on RF-Technology

RIT-µX is a radio frequency ion engine for micro propulsion applications. The ionization of the propellant by electro magnetic fields offers inherently highest thrust control, -stability and resolution. The function principle of the engine and the specific advantages are explained and the layout of a propulsion system is presented. Potential missions are described and selected test results are given.

RIT-22 Ion Propulsion System: 5,000h Endurance Test Results and Life Prediction

§** †† ‡‡ §§ Electric Propulsion based on gridded ion thruster technology is the key for several upcoming missions. Namely the European Space Agency ESAs corner stone mission BepiColombo to the Suns nearest planet mercury is a representative for these type of missions. Beside harsh thermal and radiation environment the required total impulse and engine lifetime is a challenge for the electric propulsion system. Astrium GmbH BL Equipment and Propulsion proposes its new ion thruster RIT-22 based on cathodless radiofrequency technology for this mission. In 2006 a successful 3,000h test was extended for another 2,000h. The 5,000h Endurance test demonstrates the compliance between egine performance and mission requirements. This paper describes the ion engine, the test setup and the test facility. One section is devoted to the control software which bases on the flight proven architecture for ARTEMIS. Test results are given and the life time prediction is presented.

Note: An advanced in situ diagnostic system for characterization of electric propulsion thrusters and ion beam sources

We present an advanced diagnostic system for in situ characterization of electric propulsion thrusters and ion beam sources. The system uses a high-precision five-axis positioning system with a modular setup and the following diagnostic tools: a telemicroscopy head for optical imaging, a triangular laser head for surface profile scanning, a pyrometer for temperature scanning, a Faraday probe for current density mapping, and an energy-selective mass spectrometer for beam characterization (energy and mass distribution, composition). The capabilities of our diagnostic system are demonstrated with a Hall effect thruster SPT-100D EM1.

Laser Induced Fluorescence Spectroscopy on Neutral Xenon: Two-Photon Cross Sections and Measurements in an Ion Thruster Plume

Two-photon absorption laser induced fluorescence (TALIF) measurements in neutral xenon are presented both in a cold gas cell and in the plume of the radiofrequency ion thruster RIT-10. Measurements in the cold gas cell concentrate on the characterization of TALIF schemes involving levels of the 6p and 6p multiplets with respect to natural lifetimes, collisional deactivation coefficients and two-photon absorption cross sections. The feasibility of two TALIF schemes including the 6p[1/2]0 and 6p [3/2]2 levels has been demonstrated in the plume of the RIT-10. Relative particle densities have been measured at a distance of 12 cm downstream the acceleration grid in the center of the plume axis.

In Situ Thermal Characterization of the Accelerator Grid of an Ion Thruster

hole diameter, distance between holes, or grid shape. These parameters are also measured in situ with a telemicroscope for high-resolution optical imaging and a triangular laser head for surface profile scanning. The distance between grid surface and pyrometer optics are precisely monitored with the support of the triangular laser head, for which the position is fixed with respect to the pyrometer. The distance measurement allows for correcting the measurement spot size of the pyrometer. The temperature profiles at three different beam power levels (1250, 2250,and4000W),andwarm-upandcool-downphases demonstrate thecapabilities ofthe complexequipment.Itis found that thermal steady state is reached after 4 h of thruster firing. Furthermore, it is shown that the accelerator grid surface temperature increases almost linearly with increasing beam current.

Photon Laser-Induced Fluorescence of Neutral Xenon in a Thin Xenon Plasma

Two-photon absorption laser-induced fluorescence (TALIF) measurements of relative ground state densities of neutral xenon on the plume axis of the radio-frequency ion thruster RIT-10 are reported. ATALIF scheme involving excitation of the 6p0 1=2 0 was applied. TALIF signals have been analyzed both in the cold gas flow and during thruster operation. Results show the principle feasibility of the investigated TALIF scheme, which seems to be a useful extension to formerly applied TALIF transitions for diagnostics in a thin xenon plasma.

Development of a Miniaturized RF Ion Engine System for Commercial and Scientific applications

The typical advantages of electric propulsion are known for long and and an increasing number of spacecrafts is equipped with EP for North-South-Station Keeping, orbit transfer or as primary propulsion system in case of interplanetary probes. An new and emerging field is the high precision positioning and orbit control of spacecrafts. Especially formation flying benefits from the high accuracy in thrust of EP systems. Challenging missions and their demands for the propulsion system are described. The description highlights the need of miniaturised electric propulsion systems. Amoung all the different EP concepts, radiofrequency ion thrusters show excellent scalability,also for down scaling. Astrium, University of Giesen and their partners have been working in the field of radio-frequency propulsion technology for long. Their approach, bases on a flight proven technology is presented. The basic principle is explained together with the technologys heritage. Test results complete the publication.

Ion analytical characterisation of the RIT 22 ion thruster

We present the energy-selective mass spectroscopy (ESMS) as a very useful tool for the characterisation of the discharge chamber plasma and the ion beam. The beam composition, particularly the content of multiply charged ions and contaminations can be studied. From the energy distributions, information on the plasma properties and processes occurring in the plasma and the beam can be obtained. Modification of the spectrometer to allow the analysis at higher ion energies (up to 5 keV) is described. First results of the characterisation of the RIT-22 ion thruster are presented. The basics of radio-frequency ionisation are well understood. Nevertheless, more detailed knowledge of the discharge processes would allow for further performance improvements. Therefore, fast non-intrusive diagnostic methods are from growing interest. Optical methods like LIF and OES were successfully established for plasma monitoring of ion engines and plasma thrusters. In contrast to Langmuir probe measurements, optical diagnostics give access to neutral particles also. Although these methods offer many advantages their implementation is challenging. In respect to measurements on flight-hardware the above methods have one decisive disadvantage: hardware modifications (e.g. optical viewports or windows) are required. Here, we present an interesting non-intrusive approach to the plasma properties - the energy selective mass spectrometry (ESMS) or, as it is sometimes called plasmamonitor. Observing the ionic species, their densities and energy distributions in the beam gives meaningful insights into the discharge chamber. For that the ion thruster to be examined remains as is. Besides the access to discharge parameters this beam diagnostic delivers detailed information of the ion beam too. The angular distribution of ion emission and their energy can be investigated not only from beam ions, but also from secondary ions. The divergence angle can be deduced. These results are from crucial interest with respect to thruster-spacecraft interaction, e.g. the impact of energetic ions on solar cells.