IEPC-97-002
ELECTRIC PROPULSION TN EUROPE: DEVELOPMENT AND APPLICATIONS
Giorgio Saccoccia
Head of Electric Propulsion Unit ESA Technical and Operational Support Directorate ESTEC, Keplerlaan 1, 220 AG, Noordwijk, The Netherlands phone: +31(0)71565 4688 fax: +3I (0)71565 5421 e-mail: [email protected]
ABSTRACT The second step in the use of electric propulsion on the big GE0 telecoms will imply the performanceof full orpartial The paper shows the current status of development of Cl3 by means of high thrust electric electric propulsion systems in Europe, with a p‘articular propulsion engines and the use of electric thrusters for the emphasis posed on the programmes which already foresee remaining in-orbit onerationg. This will eventually get to the use of electric thrusters in the short and medium term. disembark completely the chemical propulsion system, The industrial involvement in Europe in the development therefore optimising the platform for a full use of electric of electric propulsion systems is also presented. As a result propulsion and maximising the mass savings. Studies and of years of activities in this field, Europe has a very large development in this direction have been already initiated inventory of electric thrusters, and now that electric pro- in the USA and in Europe. pulsion is recognised as a key technology for modem Other applications today foreseen for electric propulsion spacecraft, these European thrusters can be used for all the in the field of telecommunication satellites include differ- applications currently envisaged for this rechnology. Some ent mans on constellatio anfq orbit of these thrusters have been fully developed ‘and
2. ELECTRIC PROPULSION FOR TELECOM the two Primes for ESA in 1996’s’, the choice on SPT was SPACECRAFI- mainly dictated by the qualification status, the thruster performance and by system considerations. In the last three years and after a long period of discussion The SPT-100 thruster (see Fig.2), is commercial&cl in on this subject, the major US manufacturers of GE0 Europe by So&C Euro#enne de Propulsion (SEP) of telecoms (Hughes, Lockheed-Martin and Loral) have pro- Villaroche 0. Since 1993 SEP is part of an international posed new platforms based on the use of electric propul- company called ISTI (International Space Technology sion forNSSK operations. This decision was also favoured Inc.) formed by Space Systems Loral (USA), Fake1 by the new market scenario for such satellites, which Enterprises(Russia),RIAMEInstitute(Russia)andAtlan- envisages large platforms (4 tons launch mnss) with pow- tic Research Corporation (USA), for the development and erful payloads (more than 10 kW) and long life duration commercialization of the SPT thrusters. In addition to this, (15 years). Under this scenario, it appeared clear that, with SEP is collaborating with Fake1 for the development of an a mass saving of several hundreds kilograms with respect advanced version of the WI’-100 thruster, called PPS to a satellite using chemical propulsion for NSSK, electric 1350,which will be produced by SEP. Both SPT-100 and propulsion is the key technology to enhance the compefi- PPS-1350 technologies will be space qualified on the tiveness of aGE0 commercial satellite, making possible a French technology satellite STENTOR. large increase in revenues for the satellite operators. The The other two electric propulsion technologies candidate choice made by the US manufacturers could create a for NSSK application on GE0 telecoms are the competitiveadvantage for these companies with respect to Radiofrequency Ionisation Thruster (RIT-IO), developed Europe in the telecom market. The two European GE0 by Daimler Benz (D) and the Electron Bombardment telecom Primes, Aerospatiale and Matra Marconi Space, Thruster (UK-lo), developed by Matra Marconi Space had to react quickly to this threat and, therefore, engaged (UK). A flight test of these two technologies is planned on in the design and development of a new generation of the ESA technology satellite ARTEMIS (see Fig.3). The platforms, compatible with the use of electric propulsion performance range of these two thrusters was optimised for NSSK. This effort has generated the two new European by the producers at a time when the requirement of the platforms “Spacebus 3000” (Aerospatiale) and “Eurostar telecom platforms in terms of mass and electrical power 3000” (MMS), which foresee the use of Hall Effect thrust- were different by the current ones. In order to make more ers (SPT-100) for the NSSK. For flexibility, the two acceptable these two thrusters by the new satelliteproduc- platforms still offer the option of using chemical thruster crs, advanced commercial version of the RIT- 10 and UK- for NSSK. As it was highlighted in a study performed by 10 thrusters are being evaluated’.
i>. m R&D .c_- ____._--__----_.__/ _.-I.. -_-.-.__“...-.. .,_” ._. -...-.._~ . .~_ _._ . ..__ .~_.~..._‘_.- _..,. __~._,__‘_ _.._ _. _ ~~~~~~~_~~~_~~.~~~- Ultru-Jim Drug compcrrsutrnn Cnnslellul,lrons Sfdmn Keepplng Pnmmy propulwn ard positioning (Scirncc, in LEO (T&con,) GTO-GE0 bwrsfer (Science) Earth observntwn) (T&corn) (Science, Telecom)
Field of application
Fig. 1 Field of Application of European Thrusters IEPC-97-002 11
the development of a propulsion system which will be capable of being used, at least for the main components, on either the future Aerospatiale or Matra platforms. Following the subdivision of duties for the satellite devel- opment, the PPS is being developed under Aerospatiale responsibility, and it is composed by the following mod- ules: - Thruster module - Gas Module - Electric module.
The thruster module, based on the SPT-100 and the PPS- 1350 engines, is under the responsibility of SociCte Europeenne de Propulsion (SEP) of Villaroche (F). 2SPT-lOOand2PPS1350thrustersareplannedtobeused on Stentor. This module will include also an orientation Fig. 2 SPT-100 Schematic (courkvy ISTf) mechanism developed by Aerospatiale. The gas module for Stentor will include a xenon storage 2.1 Stationary Plasma Thrusters for STENTOR assembly, based on a new tank develop4 by Aerospatiale, with a pressure capability up to 310 bars, and a xenon The French technology satellite Stentor, being sponsored distribution assembly. by the French Space Agency CNES, will be jointly devel- In the framework of the electric module for Stentor, a new oped by Alcatel Espace and Aerospatiale, both of Paris (F) Power Processor Unit (PPU) is being developed by ETCA and Matra Marconi Space of Velizy (F) as prime contrac- of Belgium’; this unit is supposed to be interfaceble in the tors. Among the other technologies to be tested, the satel- future with the new MatraMarconi ad Aerospatiale buses. lite, currently scheduled for launch aboard an Ariane Thruster Switching Units (TSU) are used inside the PPU, vehicle in late 1999, will use SPT Thrusters for North in order to save mass. The development of the PPU is co- South Station Keeping during the 9 years mission. fundedbyESAandtheBelgiangovemment.Qualification The Plasma Propulsion System (PPS) for Stentor is the is expected for 1998. subject of a special collaboration between Aerospatiale The mass of the complete Plasma Propulsion System for and Matra Marconi Space, being the scope of this activity Stentor is expected to be around 60 kg.
Fig. 3 The Artemis Satellite (courtesy Alenio) IEPC-97-002 12
2.2 Ion Engines for ARTEMIS sion on the new European platforms and to prepare the field for the next generation of telecoms, fully based on The ESA Artemis technology demonstration satellite is electric propulsion systems. The full use of electric pro- being developed by Alenia Spazio (I), for a launch in the pulsion for both station keeping, attitude control and year2000 with thea Japanese H-2Alauncher maiden flight uansfer from GTO to GEO, in fact, could be the most and for 10 years of operational life. rewarding improvement forfutureGEOcommerciaIspace- Ion propulsion was originally introduced on Artemis as a craft, leading to increawd payload mass capabilities. A technology demonstration and support to the mission, due leading USA Prime has recently assessed that the increase to the large payload mass and the limited spacecraft size. in the number of operational transponders can be up to 100 When recently, for budget reason, it was decided to use an %: from 45 to 90 transponders. This implies a doubling of H-2 rocket instead of an Ariane, ion propulsion has been the revenues as from the first day of operation. Further- elevated to fully operational status, due to the evolution of more the lifetime of the s/c is effectively extended thus the Artemis mission profile. securing further profits. Both the German RIT-10 and the British UK-10 gridded On the other hand, extending the usage of electric propul- ion propulsion technologies will be used on Artemis as a sion for these new operations has direct consequences on fully operational and redundant system for the NSSK other subsystems and the implications on the commercial operations s. The Artemis Ion Propulsion Package (IPP) is aspects of the mission itself deservecareful consideration, being developed by Daimler Benz Aerospace of Mtinich in pnrticular for what concemes the time required to (D) and Matra Marconi Space of Portsmouth (GB), with perform the GTO-GE0 transfer. the German company acting as responsible for the com- plete IPP. Under a recent ESA initiative, the basis for a truly Euro- The IPP for Artemis is composed by the following main pean effort for the procurement of competitive comrner- elements: cinl platforms based on the use of electric propulsion is - RITA (Radiofrequency Ion Thruster Assembly) being created, in agreement between Industry, National - EITA (Electronbombardement Ion Thruster Assembly) Space Agencies and Satellite and Launcher Operators. - ITAA (Ion Thruster Alignment Assembly) This initiative will complete current national activities, - PSDA (Propellant Supply & Distribution Assembly). like the French programme called “Stentor Fertilisation”, created with the aim of develop ‘and qualify on ground The main characteristics of the IPP are shown in the items which are not covered by the Stentor activities, in following list: view of the use of electric propulsion on the future Euro- Thrust level RITA 15mN pean buses. Thrust level EITA 18mN In a progressive approach, the following areas should be IPP total impulse 1.2 x 106 Ns covered: IPP power consumption (max) 607w IPP dry mass 85 Kg Mastering of current electric propulsion technology for Propellant loading capacity 40 Kg lhe NSSK of Current GE0 platforms Total lifetime per thruster lOOOOh(+50%cont.) - Coordination and improvement of existing R&D on EP Operation cycle 3 h every 12 h (not in - In-flight assessment of EP (Artemis, Stentor, others) eclipse), RIT or UK - Set-up of centralised EP testing facilities
On Artemis 2 RIT thrusters will be mounted together with Development of new electric propulsion technologiesfor 2 UK-10 thrusters on the Ion Thruster Alignment Assem- the next generation of GE0 platforms (full electric pro- bly (ITAA), developed by Daimler Benz and ORS (A). pulsion spacecraji) The Power Supply and Control Unit for the RIT assembly - Future platforms/missions conceptual studies for Artemis is being developed by FIAR (I). - Development and testing of high thrust EP engines The Neutralizer for the RIT system has been developed - Development of new EP system components and qualified by LABEN/Proel Tecnologie(1) - Satellite system optimisation (AOCS, thermal, etc.) The development and qualification of the UK-10 6 baqed EITA are being carried out by Matra Marconi Space (UK), Full use of new electric propulsion technologies on the with the support of DRA and AEA Laboratory (UK). next generation of GE0 platforms - EP-based platform demo mission - Industrialisation of equipment. 2.3 Electric propubion for future GE0 Telecoms
The need for a faqt implementation of electric propulsion 2.4 Electric Propulsion for Satellite Comtellation.. on the future commercial telecoms is today recognised by companies and space operators in Europe. For this reason, In addition to the current and future application of electric additional, coordinated activities are being initiated, in propulsion on GE0 telecoms, the field of application of order to speed-up the implementation of electric propul- electric propulsion for operations of satellites belonging to IEPC-97-002 13 constellation in Low Earth Orbit is very important and installed on the satellite. The development of the arcjet, constantly growing. Electric propulsion can be used on called ATOS (ArcjetThrusteronOscarSatellite),isfunded these satellites to perform operations such a$: by the German Space Agency DARA and it is a coopera- - Drag compensation tion between the Institut fiir Raumfahrt Systeme (IRS) of - Sunsyncronous orbit maintenance Stuttgart, acting as project leader, and tbe Institut fiir - Gap filling maintenance ThermodynamikundTechnischeGebBludeaustistung(ITIJ - Deorbi ting. of Dresden ‘. The 750 W arcjet will use Ammonia propel- Furthermore, electric propulsion can be used to perform lant for safety reasons on ground and will be used to also the orbit transfer from the initial orbit where the perform the following operations: launcher delivers the satellite and the insertion into the - final inclination change (Av req.: 300 m/s) final orbit. - orbit control (Av req.: 180 m/s/year). Many satelliteconstellations are under study/development The planned duty cycle envisages one 40-60 min. thruster today, which can adopt electric propulsion for part or all of firing every 3rd-4th day, depending on power, orbit and their manoeuvres, Teledesic being the most interesting attitude control constraints. The P3-D electric propulsion example. system main parameters are shown in the following lisr In Europe, studies on these types of applications have just - Propelkant mass: 52 Kg ammonia in two tanks begun, and potentialities exist that European thrusters, - Operational life: 600 h of thruster operations such as SPT, FEEP, small arcjets or other thrusters will be - Achievable Av: 1200 m/s (i.e. 5 years of used on future satellite constellations for different opera- orbit control) tions. - Thruster mass: 480 g Selection of electric thrusters from the world market for - Power supply: 2500 g these applications will be based on characteristics, some- - Other componena: 1200 g. how different from the ones for classical applications, such as: On the satellite, a diagnostic package is foreseen for the - Mass production capabilities observation and control of the thruster performance. - Simplicity of design A schematic of the P3-D satellite is shown in Fig.4. - Low system cost - Low integration cost - Low system mass 3. ELECTRIC PROPULSION FOR SCIENTIFIC - Low system volume SPACECRAFT - Low propellant mass requirement - Low electrical power requirement. The use of electric propulsion for scientific spacecraft is today recognised in the USA as well as in Europe as an The attractiveness of this new market segment for electric important step forward in this field of space applications propulsion is enormous and Europe will play a role in it and projects are proposed to validate in the short term the with its thrusters. use of this technology in this area. For interpkanetary probes, replacing chemical propulsion with electric thrusters for primary propulsion operations 2.5 Arcjets for small telecoms (AMSAT P3-D) will minimise the operation costs of the mission and will increase the payload delivered in the final orbit. An addi- As an example of application of European electric propul- tional benefit comes from the fact that electric propulsion sion on a small telecom satellite, an OSCAR satellite P3- trajectories are almost free from launch window con- D (Orbital Satellite Carrying Amateur Radio) of the intcr- straints, which instead affect classical gravity-assisted national organisation AMSAT (AMateur SATellite Or- missions. Time of flight is often reduced, with respect to ganisation) will be launched with the second ARIANE 5 the use of chemical propulsion with planetary fly-by. test flight and on this mission a thermal arcjet will be The very low and highly controllable thrust levels pro-
Ix--.-_ Fig. 4 The P?-D Satellite (courtesy AMSAT) IEPC-97-002 14 vided by some electric propulsion technologies, have ESA_xx: a 26 cm ion engines developed on the basis of a opened the door to a new category of missions, othenvise European cooperation involving Germany, the United impossible. Kingdom and Italy, currently under ESA’s Technology In the following paragraphs, a review of the most impor- Research Programme (TRP) funding. The thruster will be tant missions currently considered in Europe and the the design product of both German and British experience envisaged electric propulsion technologies are presented. accumulated in this field, the ideabeing to make use of the radio-frequency electrodeless discharge of the RIT-35 concept (Daimler Benz and Giessen University) together 3.1 Solar Electric Propulsion for Planetary Missions with the simple and reliable grid system developed for the UK-25 (AEA Technology); Italy (Proel) will provide the Solar Electric Propulsion (SEP) can be successfully used neutralizer devices and the high-power electronics will be as primary propulsion systems of spacecraft for interplan- also built in Italy. The FSA-xx is capable of thrusts up to etary missions and orbit transfer. A proper use of SEP may 200 mN (6 kW of power) *. - offer the possibility of flight time reduction w.r.t chemi- RIT_15: this thruster is a larger version of the RIT-10. and cal propulsion (reduction in mission operation costs) makes use of most of the components already developed - allow application ofsmall/medium launch vehicles(sub- for the smaller engine. For this reason, the complete stantial launch cost savings) development of this thruster requires not a major effort. - allow increase in net maSs deliverable, depending on Daimler Benz is currently receiving fundings from the SEPspecific mass (enabler of missions otherwise impos- Gcrmrln Space Agency (DARA) for activities on this sible) thruster.TheRIT-15iscapableofthrustsupto50mN(1.5 - remove the launch window constraints imposed by corn kW of power). plex gravity assisted missions, therefore enlarging the scientific objective of the missions (in particular for the The current ESA missions which foresee the use of SEP small bodies rendez-vous missions). for prim,ary propulsion ;LTehere presented.
In the USA, the potentiality of SEP for this type of application will be tested soon on the first New Millen- The Mercury mission objective will be the complete nium spacecraft, which will use the ionengine technology. determination of the planet chemical composition, mag- In Europe, similar technologies exist already, or are close netic field, mass distribution, topography and ephemeris. to their final development, but only recently efforts have A spacecraft of more than 500 kg dry mass is planned to been dedicated to a careful assessment of the use of SEP to be placed in a low Mercurian orbit. Electric propulsion interplanetary missions. may be used in all or some of the three phases of the In ESA, in particular, a mission to Mercury with SEP is mission trajectory which are: being considered and a small technology demonstration - escape from Earth gravity field satellite for science, based on electric propulsion, may be - transfer trajectory to Mercury developed in the next few years. In addition, the evaluation - Mercurian orbit injection and circularisation. of a SEP based option for the comet rendez-vous Rosetta Evaluations performed so far’ have demonstrated that the mission is being performed. Also for the LISA mission time of flight for an electric propulsion based mission is in (seelater) the possibility of using SEP for tbeorbit transfer the order of 1.4 to 2.7 years, which is shorter than the time phase will be considered. needed using chemical ballistic trajjectories with multiple The electric thrusters which will be used on these missions gravity assists (4.3 to 5.5 years). Therefore the use of will have been very probably already developed for the electric propulsion will minimise the operation costs of GTO-GE0 transfer of commercial telecoms (see before), the mission together with an increment of payload in orbit and will require only delta-qualifications for the scientific due to the high specific impulse of this technology. An missions. With this approach, consistent development cost additional benelit comes from the fact that electric propul- savings will be performed, and an additional push for the sion trajectories are free from launch windowsconstraints, use of electric propulsion on scientific missions will come which instead affect the gravity assists missions. from the commercial applications of electric propulsion. The spacecraft currently considered is a three axis stabi- lised satellite with a 15 kW solar array. The actuators The candidate European electric thrusters which will pos- during the cruise phase could be provided by proper sibly be used on missions of this type are: throttling of the electric propulsion thrusters. The impact of electric propulsion on the mechanical, SPT-14Q: The development of this thruster, capable of thermal and power systems must carefully be taken into thrust levelsof280mN forapowerconsumptionof4.5 kW account. Gimbal platform, thermal dissipation, power hs been started by ISTI, in the fmmework of a NASA/ allocation and distribution are only some of the aspects to Air Force sponsored activity. As part of ISTI, SEP(F) will be accounted for. An industrial study on this mission is take part to this development. An high thrust version of the planned to start in autumn 1997. PPS-1350 thruster can also be envisaged, with full French/ This mission is currently being studied in the framework European effort. of the ESA Horizon 2000 plus programme. IEPC-97-002 15
SMART-I Alternative propellants to Cesium are currently being The SMART-l mission is cutTently investigated by ESA studied in order toea5y the handling and operation require- to demonstrate innovative technologies relevant to future ments. scientific missions, especially planetary missions, where Furthermore, another field emission concept using Indiurn, the use of electric thrusters as primary propulsion is based on a technology developed by the Austrian Research mandatory. The mission currently proposed will go to the Centre Seibersdorf for space charge compensation and Moon and beyond employing innovative trajectory, com- already proven in space many times, is being studied as bined with solar electric propulsion. The small spacecraft microthruster in the few w range 12. will be launched by an Ariane 5 as piggyback into a geostationary transfer orbit. Small SEP thrusters will be As regard the applications to scientific missions, FEEP is used, as demonstrator of larger thrusters to be adopted for currently considered as the key enabler for a series of bigger spacecraft in the future. Also FEEP thrusters (see missions being studied in ESA and elsewhere, where later) are currently being considered as part of the attitude FEEP will be the actuator in sophisticated control systems. and control system. This mission is studied in the frame of A short overview of the most important of these is shown the ESA scientific programme and can be realised in the here. early future using a complete different approach trying to minimise the design, manufacture and testing time sched- Loser 1nterfemmeterSslac;e Ante- ules. The goal for this mission is to be realised with a The primary objective of the LISA mission is to detect and budget one order of magnitude lower than a typical ESA observe gravitational waves from massive black holes and Cornerstone scientific mission. galactic binary stars in the frequency range lo4 to 10-l Hz. Useful measurements in this frequency range cannot be made on ground because of the unshieldable background Field Emission Electric Propulsion (FEEP) for Mis- of local gravitational noise. The mission, which is cur- sions with Ultra-tine pointing Requirements rently proposed in the framework of the Horizon 2000 plus programme of the European Space Agency”, consists of 3 FEEP technology is being developed in Europe for a range spacecraft forming a lruge equilateral triangle in space (see of applications in different fields, requiring performance Fig.S). The length of each side of the triangle is 5xlo6km, such as: defining the length of the ‘arm of three laser interferomerers - very low thrusts in the range l+lOOO~ (fine pointing, on the s‘arne pkane. The spacecr‘aft at each vertex of the low disturbances) triangle Serve as a light source and be‘amsplitter for the - very fine modulation capability interferometer. At the heartofeachspacecraftisavacuum- - fast response time in control loops enclosure containing a proof mass which serves as an - very low propellant consumption (no need for complex optical reference for the light beams. When agravitational feeding systems) wave passes through the system it causes a strain distortion - simple system design of space, which, in turn, causes fluctuations in the separa- - compact envelope (no problem of location on the S/C). tion of the proof masses, detected by the fluctuation in the optical path of the interferometer. Great care must be taken The Cesium FEEP concept was originally conceived by to ensure that the optical paths are not disturbed by other the European Space Agency (ESAIESTEC), and means. Centrospazio (I) has developed the concept at the present FEEP thrusters are used to enable the spacecraft to follow level of engineering lo. The same organisation is today its proof mass precisely, without introducing disturbances dealing with the design of the flight h‘ardware and the in the bandwidth of interest (drag-free control). assessment of the use of FEEP for candidate missions. In Six clusters of four thrusters each will be mounted on each 1996, an agreement was finalised between Centrosp‘azio spacecmft equipment panel. The maSs allocated to the and Laben (I) for the creation of a structure capable to complete FEEP system is 27 kg (including all electronics develop and industrialise the complete FEEP system. and structure), and the power allocated for normal opera- The FEEP system consists of: tions id 28.5 W. Requirements on the thrust levels for the - Emitter/accelerator LISA missions are between 1 and 50 @V, with thrust noise - Neutraliser below 0.1 @J. An hri‘ane 5 or a Soyuz launcher will deliver - Sealed Thruster Container the spacecraft to the required Earth escape trajectory, from - FEEP Electronics Unit (FEU). which each of the three spacecraft will be transferred to its Laben is responsible for the design and development of thl: individual orbit by means ofjettisonable propulsion mod- commercial FEEP Electronics Unit. ules. In the case of a launch with Soyuz, primary electric The FEEP system is today ready to undergo a full develop- propulsion might be used to reach the desired final orbit. ment and qualification programme. The current set of activitiesfortbeF’EEPdevelopmentenvisagesalsoaflight Free Fiver Inrerfemmefer UlMWINl test on a Shuttle Get Away Special to be performed in 1999 The case for increased angukar resolution in the study of to validate in space in severe working conditions the main the Universe is very strong, and interferometry techniques system components *I. represent the next step in this respect, to support future IEPC-97-002 16
astronomy missions. The use of aperture synthesis is, in fact to replace a large diameter monolithic instrument by The GAIA mission main objective will be the detennina- a set of smaller telescope which, combined together, tion of astrometric parameters with 10 wsec accuracy. would give the same resolution performance. ESA sup- Direct distance determination of objects from the galactic ports this position and currently supports the study of a center and information on gravitational light bending will Free Flyer Interferometer as a proposal for its Horizon be achieved.The proposed GAL4 project is a “super- 2000 plus progmmme I’. A constellation of spacecraft (7 in Hipparcos” astromebic mission employing a scanning the configuration proposed in Fig.6) will form the interfer- satellite, a fixed baseline optical interferometer, and an ometer (the central spacecraft serves as a hub for the advanced detection system (Fig.7). GAIA will employ others), the level of resolution for the observation being three small (3-meters baseline) interferometers to measure related to the number of “legs” of the interferometer distances and motions of tens of millions of stars through- configuration. The interferometer spacecraft only rely on out our Galaxy. In order to obtained the stated astrometric electric propulsion to perform orbit and attitude control precision, the individual mirrors in each interferometer and reconfiguration of the observatory (change ofbaseline must becorrectly positioned with respect to the underlying length and direction). In particular, FEEP thrusters will bc 3m telescope. Relativity, stellar and galactic structure and used to perform AOCS and orbit phasing distance (OPD) evolution will benefit from the results obtained with this control, with the following requirements: mission. The spacecraft will be launched by Ariane 5. - max thrust: about 20 pN with 1 pN quantkation step Electric propulsion thrusters are currently being consid- - repeatability on thrust force: 10 % ered as possible actuators for the attitude andorbit control - duty cycle 100 % modulated at 100 Hz system which requires minimum impulse bits of less than - consumption: 10 g/year per thruster. lo” Nsec. For the higher thrust applications (lO+SOmN), the use of This mission is also studyed in the frame of the ESA ion engines or SPT is currently envisaged. Horizon 2000 plus programme
\ e orbits
Fig. 5 ‘he LISA Mission Concept Fig. 7 The GAlA Mission
Fig. 6 The Free Flyer Interferometer Mission (DARWIN) Fig. 8 The Galileo Galilei Mission Concept IEPC-97-002 17
Gravitv and Oc_an Circulation (m Galileo Galilei (GG) is a small mission currently under The Gravity and Ocean Circulation Explorer (GOCE) study by eight research institutions in Italy, with approval mission is one of the selected candidates for the next phase and funding by the Italian Space Agency I’. The mission of EOPP16 and might not be feasible without using electric concerns a small, low altitude, Earth satellite (I 150 kg, propulsion. GOCE is designed to measure the Earth’s total mass and 520 km altitude) with the objective of gravitational field to the accuracy of 2 mgal. This mission testing the Equivalence Principle formulated by Einstein, is unique, in that it aims at the sustained operation of a generalising Galileo’s and Newton’s work, to one part in complex spacecraft at an altitude where re-entry would 1016,four orders of magnitude better than the best ground normallybeexpectedwithinaveryshortperiodoftime.At results. In comparison to similarmissionsproposed for the this altitude, between 250 and 300 km, the residual air drag same scope, the satellite is much less massive, non cryo- will be very significant, therefore a continuous thrust must genic (simpler), only one axis stabilised and does not beappliedalong tbevelocityvectortocounteractthis drag. require active pointing. Two concentric test bodies with 4 Simultaneously, thrust must be applied in the twomutually capacitance masses in between form the experiment: were perpendicular directions to counteract any drag caused by the two bodies attracted differently by the Earth (i.e. were asymmetry of the vehicle in order to establish a drag free theproportionalitybetween inertial and gravitational mass environment. Two parallel studies on the GOCE design of test bodies violated), a signal would appear at the have been performed by Daimler Benz @) and Alenia spinning frequency. Theexperiment is schematically shown Spazio (I), which have proposed different options for the in Fig.% The spacecraft will be equipped with FEEP spacecraft, with different requirements for the propulsion thrusters, located on the outer surface of the rotating body, system. One of the options proposed (Daimler Benz) is in order to largely compensate the low effect of air drag. shown in Fig.9. About 5 g of caesium will be used ‘as propellant for the The low thrust technology (up to 10 mN) today discussed complete mission (6 months) and only about 1 W of in greatest demil for GOCE is electrostatic propulsion, electrical power. The capabilities of FEEP of operating in specifically the gridded ion engine concepts currently pulsed mode will be used in this mission. under development or qmalitication in Europe and FEEP”. The gridded ion engines considered are the RIT-10 and the UK-10 as developed for Artemis (see before), but with 4. ELECTRIC PROPULSION FOR new electronics, and another low thrust ion engine being EARTH OBSERVATION SPACECRAFT developed in Italy by LABEN/Proel Tecnologie ‘*. This thruster,calledRMT(lZadiofrequencywitbMagneticField Electric propulsion will very likely open new mission Thruster) is specifically being developed for thrust levels opportunities in the field of Earth Observation, enabling in the 2+12 mN range, for applications on small satellites. the satisfaction of mission requirements otherwise Currently RMT prototypes have been successfully manu- imposssible. In particular, the advent of satellites in very factured and characterised under contract of the Italian low Earth orbit has open the door to a sophisticated use of Space Agency (ASI). electric thrusters. Electric propulsion will be used on these missions to The main characteristics/features of the RMT thrusterare: perform tasks, sometimes different from the ones of Thrust: 2+12 mN conventional telecommunication spacecnft: Specific impulse 2300+3700 s - actuators in sophisticated control systems (precise thrust Thruster efficiency 0.5+0.65 control) Expected lifetime >lOOOO h. - drag compensation for orbit maintenance - drag-free environment enabling. Due to the different requirements imposed by these mis- sions to electric thrusters w.r.t. conventional applications, SUN SENSaAS assessment of existing European electric propulsion tech- nologies (thrusters and peripherals) are currently being performed, to identify the best candidates for these appli- cations.
4.1 Ion Engines for EOPP FLIGHT Several missions proposed in the framework of the Earth Observation Preparatory Programme (EOPP) at ESA high- light the great potential of Electric Propulsion for applica- ION THR”SlERS tions on low Earth orbiting satellites. The first European Earth Observation missions interested in the use of electric propulsion are here presented. Fig. 9 - Concept of GOCE (cnurk~y Doimler Benz) IEPC-97-002 18
nE_ Modelling in the field of electric propulsion covers at least Another mission selected for the new phase the EOPP is the following subjects: the Radiation Explorer spacecraft19. This mission will help - Thrusters/spacecraft interaction (plume/beam impinge- to understand climate variability and change, and thus ment,ElectromagneticCompatibility/ElectrostaticDis- radiative processes that play a key role in climate. The chnrge (EMCYESD), plasma environment, etc.) satellitewillbeinasun-synchronousorbitatabout500+600 - Lifetimeforeca5tofcriticalcomponents(dischargecham- . km, where the atmospheric drag is still significant. This bers, grids, electrodes..) orbit has been selected taking in consideration the insfru- - Thruster performance evaluation ments requirements and the size of the propulsion system - Ion/plasma beam characterisation (ion optics, etc.). in charge of the drag compensation and the compensation of external and internal torques. The spacecraft configura- Activities on these subjects are currently carried out at lion concept will be constrained by the accomodation of different levels in many European companies/organisa- the instruments which required unobstructed Earth view. (ions working in electric propulsion or involved in the A classical configuration basedon the existing SPOTlERS application of this technology on spacecraft. The most bus concept would satisfy these needs and at the same time important of these developments are presented in what reduce the development risks. follows. Ion engines might be used to Frform the drag compensa- tion operations for orbit maintenance. The use of electric propulsion requires the assessment of potential consequences on the spacecraft performances. 5. OTHER ELECTRIC PROPULSION The specificity of an electric thruster is to use high electri- ACTIVITIES AND DEVELOPMENTS cal power, with either high currents (Arcjets) or high voltages (Ion Thrusters), leading to the production of 5.1 Testing of Electric Propulsion Systems charged p‘articles ejected as a plasma plume. Due to the presence of neutrals, even in the case of high velocity A very important subject related to the development of primary ions (ion thrusters), charge-exchange collisions electric propulsion systems is the assessment ‘and qunlifi- wit1 give rise to a cold plasma which accumulates around cation testing of electric thrusters and peripherals. Because the spacecraft. of the long operational time of electric thrusters (in pnrticu- For optimised system design, Matra-M‘arconi Space (F) is lar for applications on commercial satellites) money and involved in the development of powerful simulation tools time consuming tests are necessary to qualify systems for for the analysis of plume impingement and contamination space applications. In addition, large and complex facili- risk on spacecraft, and EMC/ESD problems. The PIONIC ties must be employed, not always available to the thruster and TDAS-EMC frameworks are the result from this developers. For this reason, the tendency in Europe is to try effort to identify a restricted number of test centres where, if Simikar development are being carried out by CERT- constraints of intellectual properties and competition can Onera (F), Aerospatiale (F), Proel Tecnologie (I), some- be removed, test activities can be performed on different times on the basis of modification and adaptation of systems as a service for different electric propulsion sys- existing tools (i.e. from Russia) to current sateIlite/thrust- tems producers. ers configurations. The main subjects for testing activities in this field are: Ageneralised lackofexperimental/operationaldatawhich - Life qualification tests of thrusters and complete systems can be used to validate models has been identified. In - Characterisation of thruster performances particular, many problems arise when data are tentatively - EMC/EMI tests of thruster/PCUlhamess collected in test facilities. For this reason, the need exists - Plume impingement and sokar army cont‘amination tests for a comprehensive programme of validation in space (development of models and definition of a realistic test An example of the illustrated global approach for testing is case based on a satellite using E.P., integration on the the performance characterisation and life-time test of the satellite of necessary data acquisition devices, detailed RIT-10 thruster, as a p‘art of the qualification activities for reduction of data collected during the flight, validation of Artemis. Such tests are performed in the ESA/ESTEC the models developed by means of these data). JZSA and Electric Propulsion Laboratory, in Noordwijk (NL) 20. National Agencies will support the development of diag- nostic packages to collect data from satellites which use electric propulsion systems, like Artemis, Stentor and 5.2 Modelling for Electric Prop&ion Russian spacecraft (Express, Gals).
Modelling activities in the field of electric propulsion &f rrLnecofCriricoIu‘r represents an important tool and a subject of growing Qualificatio: tests of electric thrusters are expensive and importance which goes in pamlIe to the fast increase in time consuming. Modelling can be used to extrapolate interest in electric propulsion and to the application of this short test on critical components (cathodes, discharge technology to spacecraft. ch‘ambers, grids, etc.) for the evaluation of thrusters’ life IEPC-97-002 19 time. For this purpose, the need exists for the definition of 8. H.Bassner, R.Bond, K.Groh, “The ESA-XX Ion standard qualification procedures, accepted by the cus- Thruster”, paper A2/4,2nd European Spacecraft Pro- tomers. pulsion Conference, May 1997 (Prmeedings: ESA- Many models are currently available or under develop- SP-398) ment in Europe for ion engines and arcjets, while the 9. G. Racca: “Mercury Orbiter Mission with Solar Elec- availability is not at the same level for SPT. tric Propulsion”, ESA Future Science Projects Study In particular, AEATechnology (UK) ha developed a code ESA/PF/1440.97/GR, April 1997 (called SHAPPIRE) 2’, which has been used to model the 10. S.Marcuccio. A.Genovese, M.Andrenucci, “Experi- grid erosion of the UK-10 and to optimise the UK-10 mental Characterisation of FEEP Emitters”, paper extraction grid system, leading to agrid configuration with A2/3, 2nd European Spacecraft Propulsion Confer- extended lifetime. Similar codes are being developed by ence, May 1997 (Proceedings: ESA-SP-398) IOM @) for thrusters of the RIT family. 11. S.M,arcuccio, A.Genovese, M.Andrenucci, “FEEP One important area where reliable models are still missing Thrusters: Development Status and Prospects”, paper is the one of ion engine cathodes. B l/5, 2nd European Spacecraft Propulsion Confer- ence, May 1997 (Proceedings: ESA-SP-398) 12. M.Fehringer, F.Rtidenauer, “Space-proven Indium 5.3 Other Activities on Electric Propulsion Liquid Metal Ion Emitters for Microthruster Applica- tions”, paper A2/6,2nd European Spacecraft Propul- R&D activities on electric propulsion are performed in sion Conference, May 1997 (Proceedings: ESA-SP- Europe also on the following subjects: 398) - Low, medium and high powerarcjets (BPD, IRS, DASA, 13. “LISA: Laser Interferometer Space Antenna for the Centrospazio) Detection and Observation of Gravitational Waves. A - MPD thrusters (Centrospazio, IRS) Cornerstone Project in ESA’s Long-term Space Sci- - SFT physics investigation (CNRS, Centrospazio) ence Programme Horizon 2000 plus”, Pre-phase A - Electric propulsion spin-offs, such as: Report, Max-Planck Institut fiir Quantenoptik, Aerothermodynamics Plasma sources (IRS, Feb. 1996 Centrospazio), Plasma contactors (Lnhen/ProelL 14. Matra Marconi Space, “Moon BaqedfFree Flyer Op- tical Interferometer”, A proposal for ESA AO/l- 2918/94/NL/CC, Nov.1994 REFERENCES 15. A.Nobili et al., “Galileo Galilei Flight Experiment on the Equivalence Principle with Field Emission Elec- 1. “Assessment of European Electric Propulsion Sys- tric Propulsion”, The Journal of the Astronautical tems for Telecom Platforms”, Final Report of Sciences, ~01.43, No.3, July-Sept. 1995, pp.219-242 Aerospatiale study for ESA Contract 162005, De- 16. “Gravity Field and Steady-State Ocean Circulation cember 1996 Mission”, ESA-SP-1196(l), April 1996 2. “Assessment of European Electric Propulsion Sys- 17. A.Tobias Galicia, M.Aguirre, M.Schuyer, “Propul- tems for Telecom Platforms”. Final Report of Maua sion System for the Gravity and Ocean Circulation Marconi Space study for ESA Contract 162002, De- Explorer Mission”, paper B2/1,2nd European Space- cember 1996 craft Propulsion Conference, May 1997 (Proceed- 3. KBohnhoff, H.Bassner, “Commercialised Ion Pro- ings: ESA-SP-398) pulsion for NSSK of Communication Satellites”, pa- 18. M.Pessana, G.Noci, “Low-Thrust Ion Propulsion for per B 1/2,2nd European Spacecraft Propulsion Con- OrbitMaintenanceandDrag-freeControloftheGrav- ference, May 1997 (Proceedings: ESA-SP-398) ity Explorer Mission”, paper B2/3, 2nd European 4. B.Thiard, G.BeaufiIs, H.Declerq, “SPT Electrical Spacecraft Propulsion Conference, May 1997 (Pro- Module Development”, paper A2/1, 2nd European ceedings: ESA-SP-398) Spacecraft Propulsion Conference, May 1997 (Pro- 19. “Earth Radiation Mission”, ESA-SP-1196(3), April ceedings: ESA-SP-398) 1996 5. H.Renault, M.Silvi, K.Bohnhoff, H.Gray, “Electric 20. G.Saccoccia, J.Gonzalez, R.Kukies, H.Miiller, “Life- Propulsion on Artemis: aDevelopment Status”, paper time Test Set-up at ESTEC for RIT-10 Thruster B111, 2nd European Spacecraft Propulsion Confer- Qualification for ARTEMIS”, AIAA-95-2519, 31st ence, May 1997 (Proceedings: ESA-SP-398) Joint Propulsion Conference, San Diego (USA), July 6. D.Mundy,“CharacterisationoftheUK-1OIonThrusIer 1995 for the Artemis Programme”, paper A2/2, 2nd Euro- 21. R.Bond, P.Lath,am, “Ion Thruster Extraction Grid pean Spacecraft Propulsion Conference, May 1997 Design andErosionModelling Using Computer Simu- (Proceedings: ESA-SP-398) lation”, AIAA-95-2923, 31st Joint Propulsion Con- 7. D.Zube, A.Dittman, E.Messerschrnid, “System Veri- ference, San Diego (USA), July 1995 fication and Integration of the ATOS Ammonia Arcjet”, AIAA-96-2716,32nd Joint Propulsion Con- ference, Lake Buena Vista (USA), July 1996