2012. № 60

Design and ballistic optimization methods of spacecraft missions with electric propulsion thrusters are considered. The results of different spacecraft trajectory optimization are presented.

Keywords: spacecraft; electric propulsion; thrust; optimal control; approximate methods; geocentric maneuvers; interplanetary transfer

There is common agreement within the scientific community that in order to understand our local galactic environment it will be necessary to send a spacecraft into the region beyond the solar wind termination shock. Considering distances of 200 AU for a new mission, one needs a spacecraft traveling at a speed of close to 10 AU/yr in order to keep the mission duration in the range of less than 25 yrs, a transfer time postulated by European Space Agency (ESA). Two propulsion options for the mission have been proposed and discussed so far: the solar sail propulsion and the ballistic/radioisotope-electric propulsion (REP). As a further alternative, we here investigate a combination of solar-electric propulsion (SEP) and REP. The SEP stage consists of six 22-cms diameter RIT-22 ion thrusters working with a high specific impulse of 7377 s corresponding to a positive grid voltage of 5 kV. Solar power of 53 kW at begin of mission (BOM) is provided by a light-weight solar array. The REP stage consists of four space-proven 10 cm diameter RIT-10 (radio-frequency ion thruster) that will be operating one after the other for 9 yrs in total. Four advanced radioisotope generators provide 648 W at the beginning of mission (BOM). The scientific instrument package is oriented at earlier studies. For its mass and electric power requirement 35 kg and 35 W are assessed, respectively. Optimized trajectory calculations, are based on our «InTrance» method. The program yields a burn out of the REP stage in a distance of 79.6 AU for a usage of 154 kg of Xenon propellant. With a hyperbolic excess energy C3 = 45.1 km2/s2 a heliocentric probe velocity of 10 AU/yr is reached at this distance, provided a close Jupiter gravity assist adds a velocity increment of 2.7 AU/yr. A transfer time of 23.8 yrs results for this scenario requiring about 450 kg Xenon for the SEP stage, jettisoned at 3 AU. We interpret the solar and SEP/REP as a competing alternative to solar sail and ballistic/REP. Omitting a Jupiter fly-by even allows more launch flexibility, leaving the mission duration in the range of the ESA specification.

Keywords: radio-frequency ion thruster; solar electric propulsion; interstellar heliopause probe; mission strategy; radioisotope-electric propulsion

Reliability issues are becoming increasingly important during the development and operation of modern products, thus increasing the flow of information that helps to identify various reliability aspects for products differing in complexity substantially: from elements to large systems. This includes new scientific and mathematical approaches, engineering methods, analysis of statistical and logical data, etc. However, there still remains a serious problem of increasing the reliability of various elements, thousands and thousands of which are used in real designs. A large number of theoretical, numerical and experimental works is conducted, which are generalized in [1, 2], for example, but to date there are no reliable enough and convenient methods for the evaluation of reliability of different elements, especially when their own parameters and operating conditions are changing. In most cases, either empirical coefficients for simple linear relationships or results of numerous time-consuming test studies are used for such assessments.

Keywords: calculation of reliability; statistical ensemble; Boltzmann's law; the probability of failure

The article describes the technologies developed and introduced into production at the Joint Stock Company «Avionics and Communication System» to increase the reliability and the specific performance of the power and control equipments of the stationary plasma thruster.

Keywords: calculation of reliability; statistical ensemble; Boltzmann's law; the probability of failure

The tasks of actively removing space debris and deflecting asteroids are greatly simplified by the use of contactless actuation, in which linear and angular momentum is transferred to a target without a direct mechanical interaction. The recently proposed ion beam shepherd (IBS) concept enables contactless actuation in a very efficient way by using the beam momentum of an ion engine or space plasma thruster pointed towards the surface of a target. This article summarizes the main aspects of the IBS technology and its applicability to the space debris removal and asteroid deflection problems.

Keywords: ion beam shepherd; asteroid deflection; space debris

The general performance of the spacecraft from the space segment «Meteor MP», and basic requirements for spacecraft corrective propulsion system are presented.

Keywords: stationary plasma thruster; corrective propulsion system; spacecraft

The results of the development of highly efficient electric propulsion of low power for small spacecraft are presented. The parameters and performance of the new scheme thruster PlaS-40 (average diameter of acceleration channel is equal to 40 mm) with small power consumption 200…650 W are investigated at discharge voltage from the following range 100…500 V.

Keywords: electric propulsion; small spacecraft; hybrid plasma thruster

The article describes the work on creation electric propulsion, conducted at the Keldysh Research Center. An overview of the achievements in the development of the Hall and ion thrusters, as well as studies of the basic physical processes occurring in the thrusters of this type. A brief description of the experimental framework to carry out full cycle of tests of electric propulsion systems at the stage of ground tests.

Keywords: spacecraft; electric propulsion; ion thruster; Hall thruster

The article describes the work on creation electric propulsion, conducted at the Keldysh Research Center. An overview of the achievements in the development of the Hall and ion thrusters, as well as studies of the basic physical processes occurring in the thrusters of this type. A brief description of the experimental framework to carry out full cycle of tests of electric propulsion systems at the stage of ground tests.

Keywords: spacecraft; electric propulsion; ion thruster; Hall thruster

APCON has developed and manufactured Radio Frequency Generators (RFG), since 2001 for Astrium Space Transportation and in cooperation with research projects with University of Giessen. The design is based on Design Reference Project of Satellite Artemis (RITA-10). The space qualified RITA-10 Radio frequency ion propulsion system has an operating life in excess of 20,000 hours and a nominal specific impulse of 3058 s. Until then APCON realized the following types of RFG's: RFG-900W for RIT−22/ ASTRIUM (thrust is 250 mN) (The thruster has achieved a nominal specific impulse of 6,400 seconds and has been operated in ground testing facilities for more than 10,000 hours); RFG-600W for RIT-15 (thrust is less than 180 mN); RFG-200W for RIT-10 (thrust is less than 80 mN); RFG-40W for RIT-3.5 (thrust is from µN to 4.0 mN). These thrusters ware not built for aerospace application. The experiences with this unit have encouraged further and comprehensive design refinements which were applied in the following development of the ion thrusters next generation.

Keywords: Radio Frequency Ion Thruster (RIT); Electric Propulsion Power Systems; Radio Frequency Generator (RFG); RFG-Power Supply Control Unit (RFG-PSCU); Beam Current Control Unit (BCCU); Positive High Voltage Converter (PHVC), Negative High Voltage Converter (NHVC); Power System; Serial Command Interface (SPI); Analog/Digital Converter (A/D 12 Bit); Digital Analog Converter (DAC 12 Bit)

Chemical and cold gas thruster plume flow and plume spacecraft interaction are subject of research and application at the German Aerospace Center, DLR, Germany, since about three decades. DLR is extending these activities in Göttingen to cover electric space propulsion testing and thruster investigation. For this purpose a new high vacuum facility, named STG-ET, has been built especially for electric propulsion testing. The vacuum chamber measures 12.2 m in length and 5 m in diameter. The design focus is on plume interaction with spacecraft components and on long-term tests. The facility will be equipped with advanced measurement methods for plasma analysis and thrust and thrust vector measurement. Inauguration of the facility took place in October 2011. This paper describes the facility, special design features, and first tests performed in the vacuum chamber.

Keywords: vacuum chamber; electric space propulsion; xenon; thruster; cryopump

Sputtering is an important process in the application of electric propulsion devices. For instance, the extraction grids of gridded ion thrusters are subject to grid erosion by charge-exchange ions, which works towards an increase of the accelerator grid hole diameter and limits the thruster lifetime, or the acceleration channel walls of Hall Effect ion thrusters are suffering from strong erosion by ions from the discharge plasma itself. One of the challenges facing further application of electric thrusters for space missions is the establishment of valid lifetime predictions. For the modelling, reliable sputter yield data are required, which, however, are often not available in the required energy and angular dependency for the ion-material combination under consideration. Especially sources of errors in sputter yield measurements like the influence of the background pressure, the roughness of the starting surface and the role of knowledge of the primary ion beam properties will be discussed in this short paper. Beside this an idea to surface modification of Titanium is given and assessed. Measurement strategy for isolating material like BN is short outlined and preliminary data are announced. More complete descriptions for metals and isolator sputter yield measurements of the Leibniz-Institut für Oberflächenmodifizierung (IOM) group are given in special papers [1, 2, 3].

Keywords: sputtering; electric propulsion; Xenon low energy sputtering; titanium; carbon-carbon; BN; gridded ion thruster; Hall effect thruster; silver connectors; low energy broad beam ion sources

With the success of the asteroid explorer mission “Hayabusa”, and increasing availability of high electric power in space, Japan is moving to develop a high-power electric propulsion system in the 10 to 100-kW class. With a decades-long expertise in various electric propulsion systems, several concepts are studied to yield the best possible design while enabling new mission types for scientific and commercial application.

Keywords: high-power electric propulsion; Hall thruster; Space Solar Power System (SSPS); Solar Electric Propulsion Systems (SEP)

We set up an advanced diagnostic system for in-situ characterization of electric propulsion thrusters. The system uses a high precision 5-axis positioning system and several diagnostic tools, such as a telemicroscope, a laser head, a pyrometer, a Faraday probe and a plasma monitor, for gathering a comprehensive set of performance parameters of electric propulsion thrusters, including, for instance, erosion of lifetime limiting mechanical parts, surface temperature of selected thruster parts, current density distribution, ion energy distribution and beam composition. The capabilities of the system are, exemplarily, demonstrated for a gridded ion thruster and a Hall-effect thruster.

Keywords: electric propulsion; in-situ diagnostics; telemicroscope; laser head; pyrometer; Faraday probe; plasma monitor; gridded ion thruster; Hall effect thruster

This paper presents the activities of Astrium Space Transportation in the field of electric propulsion. Astrium ST is an electric propulsion provider for propulsion systems, components and test services. The Radio Frequency Ion Thruster family "RIT" is described and a presentation of the pressure regulation device XRFS is given. Additionally, electric propulsion system aspects are included in this paper. Astrium has a broad knowledge in test conduction for life & endurance tests, environmental tests and sophisticated tests like dual firing or solar radiation for electric propulsion. The description of Astrium ST's test activities and services is complemented with the history of EURECA and ARTEMIS. Both missions mark milestones for electric propulsion in Western Europe. Both missions were equipped with Astrium ST's RIT-10 thruster assemblies RITA 10.

Keywords: electric propulsion system; radio-frequency ion thruster; thruster family; RITA 10 flight heritage; test services; electric propulsion components

A large RF-ion thruster “RFIT-45”, having an ionizer diameter of 48.6 cm and consuming 35 kW of power, is described. It is scheduled to generate a thrust of 760 mN at a specific impulse of 7000 s and a lifetime of more than 50,000 hours. The beam current will be 7.0 A, the positive high voltage 4.5 kV. A 1 MWe nuclear power plant could supply up to 30 clustered thrusters. At lifetime penalty, a thrust-enhanced single engine may generate 1.08 N at nearly 50 kW of power. To keep the lifetime specification, an enlargement of the rf-thruster (65 cm ionizer diameter and 70 kW or 80 cm and 105 kW) may reduce the number of clustered engines, too. The RFIT-45 engine has been designed in accordance with smaller RIT-devices. A set of technical drawings is available. The scheduled performance data were derived from scaling laws of the RIT-family.

Keywords: radio frequency ion thrusters; thruster design; scaling laws; high power; high specific impulse; lunar cargo ferry; Mars excursion ship; nuclear power plant

A large RF-ion thruster “RFIT-45”, having an ionizer diameter of 48.6 cm and consuming 35 kW of power, is described. It is scheduled to generate a thrust of 760 mN at a specific impulse of 7000 s and a lifetime of more than 50,000 hours. The beam current will be 7.0 A, the positive high voltage 4.5 kV. A 1 MWe nuclear power plant could supply up to 30 clustered thrusters. At lifetime penalty, a thrust-enhanced single engine may generate 1.08 N at nearly 50 kW of power. To keep the lifetime specification, an enlargement of the rf-thruster (65 cm ionizer diameter and 70 kW or 80 cm and 105 kW) may reduce the number of clustered engines, too. The RFIT-45 engine has been designed in accordance with smaller RIT-devices. A set of technical drawings is available. The scheduled performance data were derived from scaling laws of the RIT-family.

Keywords: radio frequency ion thrusters; thruster design; scaling laws; high power; high specific impulse; lunar cargo ferry; Mars excursion ship; nuclear power plant

It is considered application of electric propulsion (EP) module based on radiofrequency ion thruster RIT-22, as a main propulsion system of InterhelioProbe solar orbiter. It is presented comparison of RIT-22 option with stationary plasma thruster SPT-140D and bipropellant propulsion options. Carried out mission analysis shows the RIT-22 option is preferable for InterhelioProbe spacecraft.

Keywords: electric propulsion system; spacecraft radiofrequency ion thruster; InterhelioProbe mission; mission analysis

It is considered application of electric propulsion (EP) module based on radiofrequency ion thruster RIT-22, as a main propulsion system of InterhelioProbe solar orbiter. It is presented comparison of RIT-22 option with stationary plasma thruster SPT-140D and bipropellant propulsion options. Carried out mission analysis shows the RIT-22 option is preferable for InterhelioProbe spacecraft.

Keywords: electric propulsion system; spacecraft radiofrequency ion thruster; InterhelioProbe mission; mission analysis

The state of the Stationary Plasma Thruster (SPT) development in Russia and directions of their further development are considered in this paper. It is shown that development of thrusters of different power is reasonable nowadays including development of the medium power SPT with increased specific impulse and life time. The problems appearing in the different directions of development are considered also.

Keywords: stationary plasma thruster (SPT); spacecraft (S/C)

The state of the Stationary Plasma Thruster (SPT) development in Russia and directions of their further development are considered in this paper. It is shown that development of thrusters of different power is reasonable nowadays including development of the medium power SPT with increased specific impulse and life time. The problems appearing in the different directions of development are considered also.

Keywords: stationary plasma thruster (SPT); spacecraft (S/C)

Upgraded SPT-100 thruster model performances at low discharge voltage are presented. The thruster operation parameters region for spacecraft insertion into the target orbit are determined.

Keywords: electric propulsion; stationary plasma thruster; spacecraft; thrust; specific impulse

Research and development of high power electric propulsion at the S.P. Korolev RSC Energia have more than semi centenary history. Main steps are the development of lithium-fed magnitoplasmodynamic thrusters are presented, which resulted in the creation of large engines (500 kW) with high specific characteristics and long life. 500-hour testing of such thruster and space experiment with its model are conducted. A newly developed radiation-cooled thruster with anode layer tested at TsNIIMASH with bismuth at the power of 34 kW demonstrated specific impulse of 5200 s and efficiency of 70 %. An alternative propellant (iodine) is proposed for high power engines with closed electron drift and testing of iodine SPT has been started.

Keywords: electric propulsion; magnitoplasmodynamic thruster; thruster with closed electron drift; anode; cathode; specific impulse; efficiency

Resolution No. 220 of the Russian Federation Government “On measures for attracting leading scientists to Russian educational institutions of higher professional education” opened the door to new forms of international scientific cooperation. Moscow Aviation Institute became the winner of competition and received a grant for the foundation of the «Radio-Frequency Ion Thruster Laboratory (RF IT Laboratory)» under the leadership of Prof. Horst Wolfgang Loeb for the execution of the R&D work “Research and development of space high-impulse high-frequency electric ion thrusters” for the period of 2010-2012. The history of cooperation between MAI and universities of Germany in the field of electric propulsions and results of the RF IT Laboratory activities as of a new form of Russian-German cooperation in this field are presented in the paper.

Keywords: rf-ion thruster; electric propulsion; Russian-German cooperation

A power supply system (PSS) of spacecraft, using electric propulsion in particular, is always comprising a primary and a secondary power supply units, the latter providing PSS operation in the shadowed path of the trajectory or compensating the lack of power from the primary power supply unit. Solar panels are generally used as the primary power supply units, and storage batteries of various types are used as the secondary ones. The state-of-the-art of such panels and batteries and prospects for their improvement are considered by the example of developments of the JSC «Saturn».

Keywords: power supply system; spacecraft; solar panel

Basic trends in the development of electric propulsion (EP) based propulsion systems (PS) of spacecraft (SC) designed for scientific studies and practical use of space may be conditionally divided into five main groups. Such division is stipulated by the PS power level and, correspondingly, by the EP power level and type. The first group is intended for securing operation of small satellites (50…500 kg) during the missions aimed at the remote Earth sensing, meteorology, mapping, etc., which are as a rule realized in the low earth orbits. Electric propulsion systems (EPS) of this group are characterized by relatively low power of up to several hundred Watt. The second group based on the EPS with low- and medium-power EP (1…2 kW) is intended for securing operation of the orbit correction and maintenance systems of SC with the mass of several tons. Primary task of the third group is to secure maneuvers for heavy (5 tons and over) interorbital platforms (4…6 kW EP). The fourth group comprises propulsion systems with nuclear reactors (NPP) and EP of 20…30 kW in power for the near-earth and lunar transportation missions. The fifth group comprises super-power PS of MW class with the EP power of 50…100 kW for the deep space exploration, transportation and interplanetary missions.

Keywords: thruster; Hall thruster; plasma thruster; electric thruster; thrust; specific impulse; power; propulsion unit; interorbital

Up-to-date R&D works in the field of ablative pulsed plasma thrusters are reviewed, as well as application of such thrusters in Russia. A set of flight models of electric propulsion systems based on the next-generation ablative pulsed plasma thrusters with the discharge energy from 8 J up to 155 J is developed by the RIAME MAI. The Research Center “Kurchatov Institute” studies physical processes in high-power APPT and develops technology for modifying surface layer of constructional materials under the influence of intense plasma flows.

Keywords: ablative pulsed plasma thruster; small spacecraft; plasma; electric discharge

History and application of stationary plasma thrusters (SPT) (Morozov thrusters) on board Russian and foreign spacecraft are reviewed. The review covers events beginning from the first space tests of SPT on board the Meteor spacecraft up to the current SPT application on board Russian and foreign satellites. The following new challenges for SPT in the twenty first century are considered: high specific impulse, long operational lifetime, high and low power levels.

Keywords: stationary plasma thruster; spacecraft; electric propulsion unit

Elaboration of principles for constructing test facilities for the investigation of electromagnetic (EM) radiation of electric propulsion (EP) under ground conditions is considered. Based on the analysis of the available domestic and foreign test facilities, general requirements are identified and new approaches to the design of modeling stands, intended to solve practical problems in order to ensure electromagnetic compatibility of electric propulsion, were proposed. The recommendations on the arrangement of such facilities are given and options of engineering implementation of the next-generation test complexes to be used to investigate EM radiation of EP of various types are presented.

Keywords: spacecraft; electric thrusters; electromagnetic compatibility

The ESA Propulsion Laboratory (EPL) is located at ESTEC, the European Space Research and Technology Centre of the European Space Agency. ESTEC, sited in Noordwijk, The Netherlands, is the largest ESA establishment, a test centre and hub for European space activities. It has responsibility for the technical preparation and management of ESA space projects and provides technical support to ESA’s satellite, space exploration and human space activities. EPL provides test services to the ESA Propulsion and Aerothermodynamics Division of ESTEC, which is responsible for R&D activities and support to ESA projects in the areas of chemical propulsion, electric and advanced propulsion and aerothermodynamics. This paper will describe the EPL organization, facilities and activities.

Keywords: spacecraft propulsion; electric propulsion testing; cold gas testing

By European Space Agency (ESA) subcontract, the University of Giessen investigated a 10 cm diameter Radio Frequency (RF) ion thruster RIT-10 operated with atmospheric gases. Such «RAM-EPs» will be used for air drag compensation of very low orbit satellites which take the propellant from the ambience. The performance tests have been carried out in the large Giessen test facility «Jumbo» with Nitrogen, Oxygen, and with a mixture of both, without and finally with 10 % of Xenon additive. The discharge characteristics showed the known graphs. Also in accordance with theory, the generated thrust at a given beam current was about a half compared with xenon operation. Maximum thrust was found to be 8 mN. A 500 hours endurance test showed no degradation effects.

Keywords: radio frequency ion thruster; test power supply; flow control unit; thrust; efficiency; discharge characteristics

The present paper takes a fresh look at future Mars Sample Return Mission including electric propulsion (EP) for the transfer. The standard mission scenario includes two spacecraft (S/C) launched separately from Earth: an orbiter and a lander. The lander sets down on the red planet together with an ascent vehicle to collect samples. The ascent vehicle would then take off from the Martian surface into Mars orbit with traditional chemical propulsion to transfer the samples to the orbiter waiting there for the return trip to Earth. The results of the system analysis identify EP for the orbiter as most beneficial in terms of launch mass, enabling a launch into Geostationary Transfer Orbit (GTO) by a relatively modest launch vehicle like the Soyuz-Fregat. Concerning the lander, a separate transfer with chemical propulsion appears more advantageous compared to an electrical one. Such a hybrid version of the sample return mission could be conducted within 1150-1300 days. In an advanced scenario, the lander could even ride the electric orbiter, piggy-back style, to the Red Planet.

Keywords: low thrust electric propulsion; mars sample return

On January 1, 2012 an «excellence initiative» within the «Loewe» program started with the aim of continuation of the research and development of rf-ion engines of the RIT type. The grant comprises 3.77 million EUR for three years, and it is given by the Minister of Science and Art of the Federal Country of Hessia, Wiesbaden. The R&D work will be mainly done by Giessen University with the assistance of 4 other German scientific institutions.

Keywords: radio frequency ion thruster

Since a couple of years, scientific European Space Agency missions like «Post Goce», «NGGM», and «LISA» are being prepared which need a very precise micro-thrusting in the range of 50 to 2500 μN. Thus, in 2004, Giessen University started a scaling-down program of the standard RIT-10 engine. Three mini-thrusters have been built and tested, whereby the 2.5 cm device, called μN RIT-2.5, reached the status of an advanced breadboard model. Following extensive optimization tests at Giessen, the thruster was operated at the Nanobalance Facility of Thales Alenia, Torino/Italy under ESA/ESTEC contract. Thrust range and linearity, thrust resolution, thrust noise, and response time have been measured showing that the μN RIT-type would be a good candidate for micro thrusting on the above mentioned satellites and spacecrafts.

Keywords: spacecraft; radio-frequency ion thruster (RIT); electric propulsion (EP)