A feasibility study of implementing a MicroPropulsion Subsystem (MPS) based on the RIT technology in place of the FEEP for the LISA Pathfinder mission was performed. The mission imposes stringent requirements on the MPS thrusters in terms of thrust range and dynamics, thrust accuracy, thrust noise and stability. In addition, the mission application brings significant constraints for integration on a spacecraft that is reaching the end of its development, not only in terms of mass and power, but also in terms of mechanical and electrical integration without impacting what has already been build and verified at system level. Previous tests performed on a miniRIT thruster operating at higher thrust levels showed the capability to comply with those requirements and constraints. A number of RIT thrusters were designed, built and tested to verify compliance to the major LISA Pathfinder MPS specifications. The system implications of using a RIT MPS have been studied. Restrictions on power and mass budgets, use of existing interfaces had to be taken into account. Existing FEEP MPS equipment and units, e.g. PCUs and Neutralizers, were re‐used as far as possible. Different RIT MPS architectures were considered. Finally, to minimise the impact on the already built platform, the RIT MPS was designed as a form fit replacement of the Slit FEEP MPS. 1 Electric Propulsion Engineer, Directorate of Technical and Quality Management, Mechanical Department, Propulsion and Aerothermodynamics, TEC-MPE, davina.maria.di.cara@esa.int 2 Lisa Pathfinder Senior System Engineer, Directorate of Science and Robotic Exploration, SRE-PNS, stein.strandmoe@esa.int 3 Lisa Pathfinder Thermal Engineer, SRE-PNS, jose.antonio.romera.perez@esa.int@esa.int 4 Lisa Pathfinder Spacecraft and AIV Manager, Directorate of Science and Robotic Exploration, SRE-PNS, luca.stagnaro@esa.int 5 Electric Propulsion Team Leader, Hans.Leiter@astrium.eads.net 6 System Engineering Team Leader, Rainer.Killinger@astrium.eads.net 7 Head of EP-Group, University of Giessen, davar.feili@uni-giessen.de 8 Physicist, EP-Group, University of Giessen, benjamin.lotz@physik.uni-giessen.de 9 LISA Pathfinder Micropropulsion S/S Program Manager, aldo.polli@selexgalileo.com 10 LISA Pathfinder Micropropulsion S/S System Engineer, luca.ceruti@selexgalileo.com

The Laser Interferometer Space Antenna project (USA) is a co-operative program between ESA and NASA to detect gravitational waves by measuring distortions in the space-time fabric. NASA Pathfinder is the precursor mission to LISA designed to validate the core technologies intended for LISA One of the enabling technologies is the micro-propulsion system based on field emission thrusters necessary to achieve the uniquely stringent propulsion requirements.A consortium consisting of Astrium GmbH and the University of Applied Sciences Wiener Neustadt (formerly AIT) was commissioned by ESA to develop and qualify the micro-propulsion system based on the Indium Needle FEEP technology. Several successful tests have verified the proper Needle Field Emission Electric Propulsion (FEEP) operation and the thermal and mechanical design of subcomponents of the developed system. For all functional tests, the flight representative Power Control Unit developed by SELEX Galileo S.p.A (also responsible for the Micro-Propulsion Subsystem (MPS) development) was used. Measurements have shown the exceptional stability of the thruster. An acceptance test of one Thruster Cluster Assembly (TCA) over 3600 h has shown the stable long term operation of the developed system. During the acceptance test compliance to all the applicable requirements have been shown such as a thrust resolution of 0.1 mu N, thrust range capability between 0 and 100 mu N, thrust overshoot much lower than the required 0.3 mu N + 3% and many others. In particular important is the voltage stability of the thruster (+/- 1% over the duration of the testing) and the confirmation of the very low thrust noise. Based on the acceptance test the lifetime of the thruster is expected to exceed 39,000 h generating a total impulse bit of 6300 Ns at an average thrust level of 50 mu N. A flight representative qualification model of the Needle FEEP Cluster Assembly (DM1) equipped with one active TCA has performed a qualification program consisting of acceptance, vibration, shock, and thermal vacuum test. During the last test, the thermal vacuum test (TVT), a performance decrease was observed. According to a preliminary analysis, this performance decrease is not linked to the thermal conditions simulated in the TVT but might be rather linked to secondary effects of the TVT set-up. (C) 2011 Elsevier Ltd. All rights reserved.

The Laser Interferometer Space Antenna project (LISA) is a co-operative program between ESA and NASA to detect gravitational waves by measuring distortions in the spacetime fabric. LISA Pathfinder is the precursor mission to LISA designed to validate the core technologies intended for LISA. One of the enabling technologies is the micro-propulsion system necessary to achieve the uniquely stringent propulsion requirements. Two competing systems, a cesium slit emitter (Alta, Italy) and the indium needle emitter technology (AIT, Austria) have been commissioned to develop this micro-propulsion system. At this point, the cesium slit emitter was chosen by ESA as baseline. The indium needle emitter technology was chosen as back-up solution and its development and test are still proceeding and the obtained results are documented in the present publication.

The Laser Interferometer Space Antenna project (LISA) is a co-operative program between ESA and NASA to detect gravitational waves by measuring distortions in the spacetime fabric. LISA Pathfinder is the precursor mission to LISA designed to validate the core technologies intended for LISA. One of the enabling technologies is the micro-propulsion system necessary to achieve the uniquely stringent propulsion requirements.

The following paper describes the test activities performed at AEROSPAZIO during a 3000 h endurance test carried out on the RIT-22 thruster. In particular, the paper describes the vacuum data and the beam diagnostics test results. The test activities were aimed at performing a continuous firing of the RIT thruster at the selected nominal operating point corresponding to 175 mN of thrust. Characterisation tests (Perveance, Electron Back Stream) were performed at selected operating times. Beam diagnostics was performed approximately each 100 h of thruster operation. The test activities were performed in the new Aerospazio large Vacuum Test Facility. The vacuum conditions were better than 6 x 10 -6 mbar during all thruster operations.

To demonstrate and promote North/South station keeping (inclination control) using ion propulsion, ESA on July 12, 2001 onboard Ariane 510 launched its most advanced telecommunication satellite: ARTEMIS. Due to a launcher failure the satellite was injected into a useless too low elliptic orbit.The ARTEMIS mission was salvaged by an Alenia Spazio/Astrium/ESA team at Telespazio (Fucino) using in novel modes to operate the on-board chemical and ion propulsion systems provided by Astrium.Using the chemical propulsion system provided by Astrium GmbH-Lampoldshausen - the inital orbit, having an apogee of half the targeted altitude. was quickly upgraded to a safe circular parking orbit at 31000 km altitude. The Liquid Apogee Engine was fired in total 8 times to achieve apogee as well as perigee raising.The final Orbit raising to geostationary altitude is being performed by means of the ion propulsion system (IPP) applied in a newly designed spacecraft attitude control mode. Alenia Spazio and Astrium, in close cooperation, quickly redesigned all control and data handling software modules affected since the original spacecraft configuration was designed for inclination. control only and not to generate thrust with the ion engines in a direction tangential to the orbit.The flexibility of the IPP system consisting of 4 thruster assemblies, provided in its totality by Astrium including the 2 alignment mechanisms for precision thrust direction control, had proven invaluable.To demonstrate the technologies available in Europe and to enhanced reliability, Astrium implemented two different technologies: a Kaufmann type system (EITA) provided by Astrium Ltd. - Portsmouth, and a Radiofrequency Ion Thruster Assembly (RITA) provided by Astrium GmbH - Ottobrunn. Two ion engines of different technology were mounted side by side on one ITAM (Ion Thruster Alignment Mechanism) provided by Austrian Aerospace. Artemis, after EURECA launched on 31 July 1992 and retrieved on I July 1993, is the second European satellite equipped with electric propulsion.This paper, after a brief description of the ion propulsion system and the results of the qualification life testing will summarize as well the special testing to support the orbit rising. The core part however will address the IPP performance on ARTEMIS in orbit during activation, inclination control and orbit raising operations. In a prominent chapter the 3-axis attitude control used during the orbit raising phase with the ion thrusters is described. In addition a principle maneuver strategy of the ARTEMIS Salvage Mission is shown. (C) 2003 Elsevier Science Ltd. All rights reserved.

Ion propulsion (IP) enables for a significant higher specific impulse than conventional chemical systems and most other electric propulsion concepts. The strict separation between the ionization of the propellant and the acceleration allows for an optimization of the thruster to specific mission requirements. In the past, the application of IP was mainly focused on North South Station Keeping (NSSK) of geo satellites. Nowadays IP should be also suitable for extended orbital maneuvers as spiral-up and de-orbiting of Geo-satellites satellites. The specific impulse for these commercial applications is typically in the range of 3000-5000s. Regarding future interplanetary missions significant higher specific impulse is from growing interest. Thus EADS Space Transportation GmbH has undertaken pre-cursor tests to demonstrate the possibilities of high specific impulse applications using existing hardware. Base on the modular designed RIT-XT engine the operation with specific impulse of more than 6000s has been successfully performed. The tests underlined also the benefits of the potential free radio frequency (rf) ionization principle. Especially working in the high specific impulse regime the rf ionization demonstrates an unbeaten flexibility in design combined with highest reliability. After a short introduction into the advantages of IP a brief explanation of the thruster’s function principle is given and the components of RIT-XT are described. The test setup is explained and the test results of the high specific impulse pre-cursor demonstrator are presented.

Based on the Radiofrequency Ion Thruster (RIT10_ART) built and successfully qualified for ARTEMIS [1] the astrium GmbH - Space Infrastructure, formerly DaimlerChrysler Aerospace AG started to develop two improved ion thrusters for low to medium thrust (RIT10_EVOlution), and high thrust (RIT_XT) applications. After an initial description of the RIT operational principle this paper will summarize the RIT10_EVO test results that were used to demonstrate the performance of the new high performance grid for the RIT_XT. Finally the test results of the RIT_XT development testing will be provided.

In order to qualify Astrium's RIT10 thruster for ESA's ARTEMIS satellite a 15,000 hour lifetime test was started in July 1998. The test, dedicated to the thruster only, is being performed at ESTEC's vacuum test facility. But to test the thruster as flight like as possible and to investigate potential interactions with the electronics or the feed system Astrium decided to test the complete subsystem. This includes the EQM models of all other components of the Radiofrequency Ion Thruster Assembly (RITA) which are the Radiofrequency Generator (RFG), the Power Supply and Control Unit (PSCU), and the Flow Control Unit (FCU). RITA is based on the Radiofrequency Ion Thruster RIT10, with an 8.7 cm diameter ion beam and a 10cm discharge vessel, providing a nominal thrust of 15 mN. It is part of the Ion Propulsion Package (IPP) that will provide the Deltav for North-South-Station-Keeping (NSSK).Purpose of this paper is to give a report on the status of the lifetime test. As an introduction we will briefly describe the IPP, with special emphasis on the RITA. In the main part, exceeding the scope of previous papers a detailed status report of the thruster's lifetime test, including a description of a test anomaly, will be given.

The Gravity Field and Ocean Circulation Explorer (GOCE) is a mission for implementation in the "Earth Explorer" line of research oriented ESA-Earth observation missions. The objective of the mission is to produce high-accuracy, high resolution, global measurements of the Earth's gravity by satellite, leading to improved gravity field and geoid models for use in a wide range of applications.GOCE will fly on a near-circular, sun-synchronous dawn-dusk orbit with 96.5 degrees inclination. The measurement orbit will be at an altitude of around 250 km. During measurement the satellite will be maintained at constant altitude and the nongravitational accelerations, mainly due to atmospheric drag, will be actively controlled by onboard thrusters.The dominant component of the drag is aligned with the mean direction of motion and will be balanced by an ion propulsion system. Two ion thrusters of the electric propulsion system, one in operation and one in redundancy, must provide continuos thrust to counteract the air drag force in a wide frequency band in the range from 1 to 12 mN at a resolution of 25 muN and of 20 mN for orbit raising after long-eclipse seasons.The RF-ion thruster RITA as qualified for N/S stationkeeping for the mission on Artemis with improvements in the grid system for higher thrust level has been investigated for this application. Changes in the beam current controller and associated electronics shall allow the resolution of the thrust level of 25 muN and the use of an analogue flow controller developed by DERA, England shall enable the propulsion system to fulfil the GOCE requirements.Special tests have been performed to demonstrate the ability of RITA for GOCE application.

The present paper details some of the test conducted during the manufacturing of the Indium needle emitters. Furthermore, it presents the series of qualification tests conducted with the flight representative units. Final verification of the present design and the needle FEEP technology will be obtained by an extended lifetime tests.