esa standard documentemits.sso.esa.int/emits-doc/estec/ao6337_rd4.pdf · the document is produced...

a

TD_Electrical Motors_V2-2.doc

D O C U M E N T

document title/ titre du document

EUROPEAN SPACE TECHNOLOGY HARMONISATION

TECHNICAL DOSSIER

LECTRICAL OTORS

prepared by/préparé par Gerard Migliorero reference/réference TEC MMM/2007/224 issue/édition 2 revision/révision 2 date of issue/date d’édition 16 April 2008 status/état Document type/type de document Technical Note Distribution/distribution

Electrical Motors issue 2 revision 2-

page ii of iii

A P P R O V A L

Title titre

Electrical Motors issue issue

2 revision revision

2

author auteur

Gerard Migliorero Date date

16 April 2008

approved by approuvé by

date date

C H A N G E L O G

reason for change /raison du changement issue/issue revision/revision date/date

C H A N G E R E C O R D

Issue: 2 Revision: 2

reason for change/raison du changement page(s)/page(s) paragraph(s)/paragraph(s)

Electrical Motors issue 2 revision 2-

page iii of iii

T A B L E O F C O N T E N T S

1 INTRODUCTION ..................................................................................................1

2 EXECUTIVE SUMMARY......................................................................................3

3 TECHNOLOGY STATUS OVERVIEW.................................................................4 3.1 Technology Overview........................................................................................................................4 3.2 Areas Covered by this Technology Dossier.......................................................................................6 3.3 Rationale for Harmonisation of the Technology................................................................................7 3.4 Technology State of the Art .............................................................................................................10 3.5 Competitiveness and Benchmarking................................................................................................11 3.6 Technology Trend ............................................................................................................................12

4 MISSION NEEDS AND MARKET PERSPECTIVES..........................................14 4.1 Application to Missions ...................................................................................................................14 4.2 Market Perspectives .........................................................................................................................16 4.3 European Strategic Interest ..............................................................................................................18 4.4 Technology Requirements ...............................................................................................................19

5 ROADMAP .........................................................................................................20 5.1 Summary of the Mapping Meeting ..................................................................................................20 5.2 Development Approach ...................................................................................................................20 5.3 Schedule ...........................................................................................................................................29 5.4 Costs................................................................................................................................................30 5.5 Statistics ..........................................................................................................................................31 5.6 Roadmap Implementation Status .....................................................................................................32

6 CONCLUSIONS .................................................................................................35 6.1 Status................................................................................................................................................35 6.2 Conclusions......................................................................................................................................36

APPENDIX A – TECHNICAL DETAILS .......................................................................................38

APPENDIX B – LETTER FROM ETEL ON ELECTRICAL MOTORS FOR SPACE APPLICATIONS 47

Electrical Motors issue 2 revision 2

page1 of 46

1 INTRODUCTION This document is the Technical Dossier of Electrical. This Technical Dossier is issue number 2 and represents the 2nd visit to this Technology subject for Harmonisation: previous harmonisation was held in Second Semester 2002. The reference of the 2002 Electrical Motor technical dossier is: TOS-MMM/2002/341 issue 1 r 0 dated on 27th August 2002. This Technical Dossier is the output of a consultative process that involved National Space Agencies, European Space Industry and the European Space Agency. This consultative process, known as Harmonisation of European Space Technology, aims to define an overall technology plan that is synergic among the stake holders and that can be used as reference for implementing R&T plans. The document is produced incrementally throughout the Harmonisation process. The revisions of the document will follow the lifecycle as explained below and summarized in Table 1-1 Revision Index:

Revision 0: First release of the Document. The document is issued for the preparation of the Mapping Meeting. The chapter Roadmaps contains only the proposed future developments.

Revision 1: Released for the preparation of the Roadmap Meeting. The document is

reviewed to take into consideration the outcome of the Mapping Meeting and to include the proposed roadmap

Revision 2: Released after the Roadmap Meeting. The chapter Roadmap is updated to

include the comments received at the meeting with Eurospace and with the THAG at the Roadmap Meetings. The Executive Summary is also added to the document. This chapter will also be used to compile the section of the European Space Technology Master Plan.


page2 of 46

Revisions Contents of the Technical Dossier Rev. 0 Rev. 1 Rev. 2

1. Introduction 2. Executive Summary (1) 3. Technology Status Overview R 4. Mission Needs and Market Perspectives R 5. Roadmap (2) R R 6. Conclusions Symbols: Compiled Section R: Section Reviewed (1): Section also appears in the ESTMP (2): Contains only the proposed future developments.

Table 1-1 Technical Dossier Lifecycle


page3 of 46

2 EXECUTIVE SUMMARY Introduction An electrical motor is the combination of an electromechanical converter and its controller. It performs the function of providing elementary motion along one axis within a mechanism. This harmonisation addresses the following types of motors: Electromagnetic motors

• Brushed DC motors (incl. brush equivalent concepts) • Brushless DC motors • Stepper motors • Voice Coil motors

Non electromagnetic motors

• Piezo-electric motors and other (often non-magnetic) working principles, including those used in micro-technology

Harmonised Roadmap The development approach foresees activities along 4 aims: Aim A: Generic Motor Activities Aim B: Brushless Motor Aim C: Stepper Motor Aim D: Other Motor Technologies For each of these aims, activities have been identified during the THAG process. Following the decision of Etel (CH) to stop supplying the European industry with electrical motors for space applications, it has been decided to add two activities aiming at replacing Etel motors.


page4 of 46

3 TECHNOLOGY STATUS OVERVIEW

3.1 Technology Overview The commonly named Electrical Motor is a device capable of providing elementary motion along one axis within a mechanism. This device is a complex assembly of many components. Each of these components has its own particular technology, but the more fundamental, covered in this document, is the frameless electrical motor, highlighted in red in the here-after chart. Details concerning the constitution of an electrical motor can be found in the boxed text below. The chart above identifies the most common Electrical Motor components. An electrical motor is the combination of an electromechanical converter and its controller. The electromechanical converter is composed of a motor integrated to a speed reduction device to provide motion along one axis with the required energy and speed. This motion can be rotational or linear. The main components of an integrated motor are typically a frameless electrical motor mounted in its housing, a bearing assembly and a shaft. A phase commutation device or a position measurement sensor might also be necessary. The frameless electrical motor comprises a fixed stator and a moving rotor. The rotor may be internal or external. Other variants are also possible, such as an axial gap with disk shape rotor and stator. The most common motor is nevertheless the configuration with an external stator with windings, combined with a rotor equipped with magnets, which are mounted on the output shaft of the motor. The shaft rotation is guided by the bearing assembly, which is most commonly achieved by a pair of preloaded ball bearings.

Position Sensor

Preload & Lubrication

Ball Bearings

Control Electronic

Magnetic Bearings Hydrodynamic Suspension

Bearing Assembly Motor Housing & Shaft

Stator Rotor

Frame Less Electrical Motor

Integrated Motor Speed Reduction Device

Electromechanical Converter

Power Supply Signal Electronics

Controller

Electrical Motor


page5 of 46

Different types of bearing assemblies can be used for space applications: ball bearings, magnetic and hydrodynamic suspensions. Each of these requires specific tribological solutions, consistent with space requirements. One of the major motor cost drivers and one of the main trade off parameters for the space mechanism designer is the motor controller. It provides the motor windings with the required current in order to generate the motion. The controller can be a simple DC voltage provider, usually including a current limiter, or a complex and expensive electrical power provider, comprising numerous functionalities. Depending on the technology used, these may include:

- position sensor processing electronics, - power bridge and commutation functions, - current measurement, - galvanic insulation device between the power line and the signal/command lines, - bridge sequencing logic, - current shape setting, - motor position, speed or torque control loop, - interface function between the mechanism and the spacecraft or launch vehicle.

The controller also includes all the software required by the mechanism movement during the release and operational mission phases. To simplify the architecture of a motor controller, it is possible to consider it as being composed of two different parts: the high power part (the power supply) and the low power part (the signal electronics). The latter covers the commutation, sensor and command signals, while the power stage provides the current and hence the power to the motor with the appropriate phase (e.g. 2- or 3-phase). The power stage of the controller interfaces with the motor windings (in most cases, with the stator). The fundamental and specific electrical motor know-how is the capability to design a frame-less motor and identify the associated power supply requirements. The remaining motor technologies are encountered in any mechanism and are therefore not necessarily specific to electrical motors. These include: bearings, tribology, electronics design. Because of this complexity, it is a real challenge for the space mechanism designer to select and procure the appropriate technology, optimal in terms of motor concepts, performances, reliability, material adequate for space applications and compatible with the application schedule and overall costs. Depending on the motor magnetic concept, the way in which an electrical motor brings about mechanical motion to a mobile payload can be radically different. To simplify the understanding of these differences, it can be stated that some motors are intended to provide forces, while others provide positioning as a function of time. The brushless DC motor is a typical example of the first category, while the stepper motor falls under the second.


page6 of 46

There are also other types of electrical motor technologies, such as the variable reluctance stepper motor or the induction motor, as well as other varieties of motors that produce linear instead of rotational motion. Additional details concerning these motor technologies are presented in the Appendix A

3.2 Areas Covered by this Technology Dossier The above introduced Appendix A also contains a brief overview of emerging motor technologies, such as the piezoelectric or the micro electromechanical systems (MEMS), which are not classically considered as electrical motors. Nonetheless, these technologies are important because they support the miniaturisation of space motors, which in turn permits the reduction of payload mass and volume, and consequently a decrease in mission costs.

Electric motors for space, within motor technology in general, comprise the following operational principles

Electromagnetic motors

- Brushed DC motors (incl. brush equivalent concepts)

- Brushless DC motors

- Stepper motors

- Voice Coil motors

Non electromagnetic motors

- Piezo-electric motors and other (often non-magnetic) working principles, including those used in micro-technology

Of these 2 main families of electric motors and actuator, the most important and most familiar are the electromagnetic group of devices. However the rapid development in piezo systems into diverse terrestrial applications means that they must be considered, especially as some of their characteristics make them attractive for space applications. In this vein we mention magneto-strictive devices in passing, which are similar in characteristics in many ways to piezo systems. There is a strong trend of development and diversity in piezo electric motors and piezo actuators. Motors ranging from nano-scale to several cubic centimetres in volume are available in a wide variety of shapes and configurations. The industrial demand for small, lightweight motors in portable technologies will continue to stimulate research and development of new piezo motor designs, although adaptation and qualification will be required before the technology can be used for space applications. Piezo actuators seem ideally suited to sub-


page7 of 46

miniature mechanisms, which is a niche of space applications. However piezo motors have much lower efficiency, and shorter lifetime than electromagnetic counterparts, and space missions require a highly integrated motor concept. Low mass and high efficiency are key design drivers that require very advanced motor materials, highly powerful permanent magnets associated with an appropriate design, but still guaranteeing the high reliability that can be achieved only through repeatable, controlled, fully qualified and robust manufacturing processes. Furthermore, piezo actuators are not seen as a replacement for small electromagnetic motors, but as solution to specific small-scale actuator applications. In view of the above, piezo-electric motors shall be considered at a later stage of this Electrical Motor Harmonisation exercise. Nevertheless and resulting from the disengagement of manufacturer of the space qualified piezo actuator ceramic material, an activity for evaluating other sources took place within CNES in collaboration with the Cie CEDRAT. Further short term actions concerning piezo-electric motors are therefore necessary. The full technological control of all of these electromagnetic motors is essential in order to guarantee the independence of European space activities. It is therefore of the utmost importance to support the European space motor developments

3.3 Rationale for Harmonisation of the Technology When the Electrical Motors were subject to harmonisation in 2002, the main objectives were to set-up a new European Supplier for Space Brushless motor technology and to reinforce the competitiveness of the European suppliers of the other types of Space Electromagnetic Electrical motors. CNES in cooperation with ESA experts has initiated an activity in open competition for European companies for which 13 companies from various countries have been solicited as potential candidates. SOTEREM, supported by its sister company SERMAT, has been selected to cover the brushless and brush DC motor development and procurement. In this framework, several ESA and CNES programs have been initiated with the company SOTEREM:

- a sealed brush DC motor for deployment mechanism - a redundant high torque brushless DC motor - the Pleïades Control Momentum Gyro motor - application of the sealed DC motor to a gear motor for mechanism deployment for

satellites and platforms ( on going) Further Space Electromagnetic Electrical motors ESA programs have been supported, for which ITT in open competition are currently under preparation for developing:


page8 of 46

- a stepper motor for space actuator applications - a voice coil motor engineering model

The main achievement and results are in line with the first objective of the Electrical Motors Harmonisation Road Map:

- adaptation of industrial know-how and processes towards space standards - space qualification of a new family of high torque brushless DC motors - delivery of a first set of FMs for Pleïades program

It is proposed to revisit this subject to update the roadmap and complement it with today status and needs. The steps addressed during this revisit exercise were:

- 1 - extension of the existing space qualified family of specific electromagnetic motors, covering:

- Brushed DC motors (incl. brush equivalent concepts)

- Brushless DC motors

- Stepper motors

- Voice Coil motors

- 2 - Adaptation of Industrial Motor Technologies for Space Applications

Looking more specifically at space applications, the electromagnetic electrical motor technology landscape can be divided in two main industrial categories:

- -Category 1: Custom design and special-purpose motors for key spacecraft equipment, often in mission critical applications (e.g. solar array drive mechanisms, antenna and electric propulsion thrusters pointing, SAR antenna deployment mechanisms, etc.) on which previous R&D efforts were focus in priority

- -Category 2: Adapted general-purpose (industrial/commercial) motors in local and decentralised applications, often for actuation tasks in scientific instruments and other payloads (e.g. for miniature rovers and robotic arms, instrument mirror and aperture door actuation, internal scanning motion, etc.)

Although both categories were addressed during the first Electrical Motor harmonisation exercise in 2002, more emphasis was put on the first category, due to the critical situation resulting from the closure of the space department within the company ETEL (CH).

Regarding this first category, continuous efforts shall be dedicated to maintaining, re-establishing and extending European capabilities, e.g. with the companies


page9 of 46

SERMAT/SOTEREM (F), SAGEM (F). However, the spectrum of space qualified motors presently available in Europe is limited. For various ESA projects, motors have been procured from US suppliers. A long-term European independence in the area of space motors appears feasible and desirable. However, any major support by ESA needs to be assessed against realistic business opportunities on the space equipment market.

On the other side, there is a steadily growing interest in the second category of electric motors. Recent examples for using adapted industrial motors include projects like Rosetta (e.g. Midas & Rosetta Lander), Mars Express (e.g. MEX-PFS & Beagle-2), Venus Express (e.g. VEX-PFS), Expose and Biopan. The motors for these applications are supplied by companies like e.g. Faulhaber/Minimotor (D/CH) and Maxon (CH), which are well known for their industrial motor product lines in an impressive variety of motor performance, sizes, optional features, etc.

Modern industrial electric motors are the result of high and long-term investments into the development, targeted at the optimisation of the product performance itself as well as large-volume production processes. Therefore, the underlying technical maturity and quality standards are generally high.

Taking above-mentioned factors into account, there is a very good basis for adapting industrial motor technology in a more systematic and consistent way than previously, for the benefit of the European space community. Especially academic/scientific entities will rely on such further consolidation; affordability in terms of cost, delivery time, internal manpower allocation, etc. might be a main driver.

However, the use of industrial electric motors for space implies a series of dedicated investigations relating to:

- General compatibility with the relevant space environment, with emphasis on vacuum and extended temperature range

- Adequate performance of potentially life limiting components like e.g. shaft bearings, and commutators in brushed DC motors


page10 of 46

3.4 Technology State of the Art Electrical motors are currently present in a very large number of terrestrial applications: their annual production is in the order of magnitude of millions of units, while electrical motors flown in space are around some hundred units per year. Therefore, it is clear that the main technology developments in this field come from terrestrial developments, and that space has to follow those trends. However, some specific product development has to be made to fulfil the needs of particular space applications. It is for the abovementioned reasons that currently in Europe the number of companies active in this field for space is relatively small. Table 3 reports the major European actors in Electromagnetic Electrical Motors for space applications:

Table 3- Industries involved in the Electromagnetic Electrical motors Technologies

At the Mapping Meeting, Eurospace stated that although the Cie ETEL (CH) has decided to stop their activities in motors for space application mid 2000, they continue to supply the electrical motors for the SADM Oerlikon products, such a the Galileo SADM. The situation has been clarified with ETEL, who confirmed their decision to abandon space business (see Annex B). It is thus necessary to ensure the development and emergence of a new European company for space electrical motors to fill the gap left by ETEL

Company/Institution – Nationality Name of Item RemarksSAGEM / SAFRAN (F) Category 1 Mainly for stepper motorsSERMAT SOTEREM (F) Category 1 & Category 2 Mainly for sealed brush and brushless DC motors

Soterem, closely supported by its sister company Sermat (aeronautical motors), is open for new motors development

CSEM (CH) Category 2 controlled motor solutions; frameless motor subcontractedEPFL (CH) Category 1 Supporting laboratoryRoboDrive (D) Category 1 Robotic ApplicationsFAULHABER / MINIMOTOR (D/CH) Category 2 All kind of motorsFAULHABER / MPS (D/CH) Category 2 All kind of motorsMicroBeam (CH) Category 2 All kind of motorsMAXON (CH) Category 2 All kind of motorsRUAG (CH) Category 2 All kind of motorsMuirhead (UK) Category 2Phytron Launchers Stepper motorsKollmorgen-Artus (F) Launchers Mainly for sealed brush DC motors P > 700 WThales AEM Launchers motors for VEGA TVCArtus (Pacific Scientific) Launchers motors for Ariane 5 upper stage TVC pumpParvex Launchers motors for Ariane 5 TVC valvesSABCA Launchers controlled motor solutions; frameless motor subcontracted


page11 of 46

3.5 Competitiveness and Benchmarking The following table highlights the expertise in Electromagnetic Electric Motors outside of Europe

Major drivers in Far East are high efficiency motors for hybrid cars, and for solar powered applications. Appears to be a long term view based on perceived future needs.

Varied, Automotive, motors for light and heavy industry

Stepper motors, various motors

Mitsubishi Electric JapanLiterature only (no response to approaches)

Competitor to AeroflexAwaiting responseAwaiting responseMOOG Components Group USA, Phil Prosser & David Marks (telephone)

‘Cogless’ brushless technology is a primary differentiator in the market. Improvements largely incremental. Key drivers are extreme temperatures for Mercury & Venus (500°C) applications, and cryomotors for the outer planets. ITAR not seen as an issue except for China. Heritage seen as a major market issue – sales include major European contractors EADS, AAS Contraves etc.

80% of the market is space, rest is defence & civil aerospace. Missions:Telecoms, EO, Interplanetary, Surface rovers. Solar array motors, antenna motors, reaction wheels, instrumentation –anything that moves on a spacecraft

DC motors for spacecraft mechanisms, Stepper, Brushless, Cogless(ZeroCog), Limited angle actuators, Voice coils. Space qualification (Performance life, TV, EMI, vibration) engineering & test is in-house. Also gear-heads and gimbals

Aeroflex Motion Control Systems USAPhone: (661) 799 9363 Karl Anderson (telephone), Mike Dandy (visit)

Development of new materials for EM motors, improvements on future EM designs.

Study funded by the US DoE with the intention of improving operating and design efficiency of all EM motors

Characterisation techniques for electric steels

Clarkson University USADr Pillay

Key Trends & driversTarget MarketPrimary developmentsEntity

Major drivers in Far East are high efficiency motors for hybrid cars, and for solar powered applications. Appears to be a long term view based on perceived future needs.

Varied, Automotive, motors for light and heavy industry

Stepper motors, various motors

Mitsubishi Electric JapanLiterature only (no response to approaches)

Competitor to AeroflexAwaiting responseAwaiting responseMOOG Components Group USA, Phil Prosser & David Marks (telephone)

‘Cogless’ brushless technology is a primary differentiator in the market. Improvements largely incremental. Key drivers are extreme temperatures for Mercury & Venus (500°C) applications, and cryomotors for the outer planets. ITAR not seen as an issue except for China. Heritage seen as a major market issue – sales include major European contractors EADS, AAS Contraves etc.

80% of the market is space, rest is defence & civil aerospace. Missions:Telecoms, EO, Interplanetary, Surface rovers. Solar array motors, antenna motors, reaction wheels, instrumentation –anything that moves on a spacecraft

DC motors for spacecraft mechanisms, Stepper, Brushless, Cogless(ZeroCog), Limited angle actuators, Voice coils. Space qualification (Performance life, TV, EMI, vibration) engineering & test is in-house. Also gear-heads and gimbals

Aeroflex Motion Control Systems USAPhone: (661) 799 9363 Karl Anderson (telephone), Mike Dandy (visit)

Development of new materials for EM motors, improvements on future EM designs.

Study funded by the US DoE with the intention of improving operating and design efficiency of all EM motors

Characterisation techniques for electric steels

Clarkson University USADr Pillay

Key Trends & driversTarget MarketPrimary developmentsEntity

Aeroflex Motion Control Systems Incorporated specialise in motors and actuators for space applications. These are primarily DC motors for spacecraft mechanisms, and include stepper motors, brushless motors, (especially their ‘ZeroCog’ version which they regard as an important market differentiator), limited angle actuators, and voice coils. 80% of their market is space, and the rest is defence & civil aeronautical. Aeroflex perform in-house space qualification including performance testing, life testing, thermal vacuum and outgassing, electromagnetic interference and compatibility testing, and vibration testing) engineering & test is in-house. They also manufacture matching gear-heads and gimbals. Mission types addressed include; telecommunications, Earth Observation, Interplanetary and Surface rovers and robotics. Mechanisms addressed include Solar array motors, antenna motors, reaction wheels, instrumentation – anything that moves on a spacecraft. Key development drivers are high temperatures for Mercury & Venus (up to 500°C) applications including BepiColombo, and cryomotors for the cold regions and outer planets. Aeroflex sell to European contractors such as EADS Astrium, ThalesAleniaSpace and Oerlikon Space etc. They do not see ITAR as an issue except for China. Heritage of involvement in mission is seen as a major market issue. Aeroflex are keen to increase their sales into Europe. Aeroflex regard Moog Incorporated as their main commercial rival in the US. Clarkson University have received a grant from the US Department of Energy to develop more efficient motors. The primary goal of the project is to characterise the losses in laminated cores used in electric motor construction. The aims are given more specifically in the following areas:


page12 of 46

- To understand the principles governing core losses in laminations, particularly at high frequencies and with a non-sinusoidal driver; - To develop an instrument capable of accurately measuring the core losses of motor laminations exposed to non-sinusoidal and/or high frequency excitations; - To measure the core losses of laminations when exposed to high frequency sinusoidal and non-sinusoidal excitations; - To develop models to categorise core losses as a function of frequency, lamination thickness, resistivity, peak flux density and wave shape; - To test the models using prototype motors, measuring the improvements in efficiency Generally, it can be stated that European technologies for electrical motors for space are at the same level, and in some cases even better, than non-Eu ones. However, Europe is currently lacking in industrial capabilities to develop new products: this situation is causing substantial dependence on US supplier, which have bigger industrial capabilities and can therefore offer a broader range of products.

3.6 Technology Trend The classical electrical motor technologies are currently well developed and there are not any major breakthroughs envisaged in the forthcoming years. The only evolutions should arise from the space environment constraints and standard, on-going improvements of the technology should aim to: Increase power/mass and power/volume ratios; Improve efficiency; Reduce noise/vibrations; Increase speed ranges; Increase reliability; Any exceptions to this should come from the developments required for specific applications, such as extreme temperature motors, motors operating in corrosive environments, etc. Nevertheless, new industrial applications of electrical motor, like the following one’s, might authorise motor improvements in new technology areas, for which space applications could take benefit and be considered in the electrical motor Technology Road map. - Environmental and climate concerns are stimulating resurgence in interest in electric motor design. Particular interest is being shown in designs for solar powered vehicles and electric and hybrid cars. The electric motor is being viewed as a system, in which the controller electronics, the motor efficiency, and the matching of the load to the motor must all be improved and optimised to increase system efficiency.


page13 of 46

- One of the newest and most vigorous trends is in motor controller electronics for permanent magnet motors, switched reluctance motors and hybrid systems, which allows huge flexibility of both speed of operation and frequency of operation. - Advances in high purity steels, new permanent magnet materials, soft magnetic materials and conductors and insulation are making possible many new construction geometries and designs. - Superconducting motors are becoming practically feasible thanks to new fabrication methods for making high-temperature superconductors (HTS) into flexible wires suitable for winding coils. With transition temperatures now up to ~90K, cooling is within the range of liquid nitrogen and cryocoolers. - There is a trend to smaller, high speed motors, exploiting power = torque x speed. This is becoming evident in domestic appliances such as Dyson vacuum cleaners and cordless drills, which use small motors running at 100,000 rpm, with appropriate gearing. - Fault-tolerant motor systems are developing well, mainly driven by the needs of the aviation industry and the military. MTBFs of motor systems e.g. for aircraft flap control are believed to be ~105 hours (i.e about 12 years). - In this respect there is a trend to replace hydraulic systems such as flap control in the aviation industry with fault tolerant electric motors in order to save weight and increase reliability. - There is a trend to develop high-temperature motors. This allows the use of electric motors actually inside jet engines, and in hot areas of e.g. car engines. Continuous operation at above 350°C is required for in-engine applications in aviation. - There is steady progress in low temperature motors, although issues remain regarding bearings, lubricants and materials.


page14 of 46

4 MISSION NEEDS AND MARKET PERSPECTIVES

4.1 Application to Missions Electrical motors can be found in some equipment in every Space Mission:

- Attitude control (reaction wheels) - Solar panel orientation and deployment - Satellite/lander ejection - Hold-down & release systems - Door opening mechanism - Antenna pointing and deployment - Scanning - Shutters - Filters and samples wheels - Boom deployment - Rovers - Fans - Valve control - Pumps - Small motors for robotics - Exploration support motors (drilling, ..) - Refocusing mechanism for mirrors - Launcher thrust vector control - Launcher Re-entry vehicle flap control mechanisms.

Pending application, electrical motors might perform for short, very short or long operational lifetime. Such requirements have a significant impact on motor bearing and its lubrication, but not on the frameless electrical motor design in most of the cases. Same remark applies for harsh condition application like with dust environment (Space exploration, …) This is not the case regarding the temperature environment of the application. Specific efforts remind to be spent in developing category 1 motor winding and magnetic circuit and adapting category 2 motors for extreme temperatures. Most of the Electrical motors are on-board Spacecraft and only few motors units are, for the time being, used on launcher applications. The situation might slightly change due to recent Electrical Thrust Vector Control development for the VEGA launcher and the foreseen electrical flap control mechanisms for envisaged Re-entry vehicles In fact, when considering the power distribution of space motors (which is representative of their applications), it can be observed that the larger part lies in the low power range, which corresponds to typical satellite applications. The current application needs, classified in terms of


page15 of 46

power, can be identified by the regularity with which motors fall into the following power ranges:

Power Range Application Examples Regularity

Below 1 W Experiments in the infrared range, prohibiting

mechanism heat generation: ISO, instruments on Cassini or Rosetta lander.

Occasionally

Between 5 and 15 W General spacecraft applications, i.e. both payloads and services in medium sized satellites for commercial and

scientific use. Commonly

Between 200 and 3000 W MELFI - 80° C freezer for ISS, EDEN astronauts centrifuge flown on Neurolab. Occasionally

Up to 10 kW Bio-mechanic experiments working against human power – MARES for ISS Exceptionally

Up to 100 kW Thrust Vector Control Electro Mechanical actuator for VEGA, Ariane MPS and Ariane evolution New developments

The following typology of Electrical motors highlights the key specifications and performances domains for some typical applications of electrical motors


page16 of 46

4.2 Market Perspectives No specific space motor market survey has recently been carried out. Nevertheless, in the frame of the overall space business inquiry, performed by Euroconsult at the request of ESA in 1998, some information concerning motors can be highlighted. Although not very recent, this survey can still be considered valid as the electrical motors market has not changed significantly. According to the report, it has been established that the European annual motor production for satellites was approximately 300 units. The few extra units produced for manned space applications and for launchers will certainly not change this number significantly. When considering the future market evolution in terms of power, there are two distinct trends. From the telecom market there should be an increase in demand for more powerful motors, as these satellites tend to become larger in size and complexity. Also the new very high power market for electrically powered thrust vector control and re-entry vehicle flap control mechanisms should emerge. On the other hand, payloads (especially for scientific applications) tend to become smaller, so there should also be an increase in demand for less powerful motors, including those using micro technologies. The Space market is not self sustainable, European motor suppliers selected for space activities must also have activities in the non space sectors • Spin-in technologies should be supported and long term procurement shall be ensured • Industrial motor suppliers should consider the specific space aspects and should be capable to quickly adapt an industrial motor for space by application of space materials and processes • Motor developments for dedicated space requirements (very long lifetime) should be initiated with established pump developers At the time of the market survey study, ETEL and SAGEM were identified as the only European motor manufacturers. Their joint market share was evaluated at 160 motors per year, although, as the new comer company SOTEREM has not yet reached the equivalent market level than previously covered by ETEL, part of this Category 1 motor has been certainly transfer in Category 2 with the CIE Faulhaber/Minimotor (D/CH) and Maxon (CH). Refer to the previous paragraph 3.3. In the case of small series of recurrent mechanisms, some other industries manufactured their own motors, which were of a unique design or specific application. A typical example was Teldix and their production of attitude and control wheels.


page17 of 46

The motor price range was reported for both brushless and stepper technology to be in the order of 10 to 15 kEuros, although specific high performances / medium power motors, such as for the ERA or MARES ISS applications are in the range of 100 to 300 KEuro per unit and about 500 KEuro for development. No motor price drop was expected in the future, mainly due to the important motor production for military and civil applications, estimated at several thousand units per year. When comparing the then market position with the situation today, the main change results from Etel’s mid 2000 decision to stop their activities in motors for space application. Historically, Sagem was active in a specific area of the space electrical motor market, providing hybrid stepper motors derived from similar available products, and particularly when synergy with other applications was possible. Since the Etel decision, Sagem’s (now Safran) attitude with regard to the space market does not appear to be very different and that will most likely remain the case. It can be anticipated that the result of an updated European motor market survey would confirm the order of magnitude of the above numbers, which shows that the size of the Electromagnetic European space motor business is limited and does not guaranty the return of investment. The small size of the European motor market explains the low level of motor business and reinforces one of the main drawbacks of the European produced motor, which is its procurement time, mainly due to long lead item components. When compared to U.S. motors, European motors require a much longer procurement time and are available only at a higher cost. Although these factors are secondary when compared to the full mechanism assembly costs and schedule, even European customers will tend to buy their motors in the U.S. There is, however, a very significant advantage that European motors have over their American counterparts: U.S. motors are provided without generic qualification and without documentation. European motors, by comparison, are developed with a full range qualification status, due to the few but diverse applications. Consequently, when procuring a U.S. motor, projects do not perform a qualification at motor level, but mostly only at mechanism or subsystem level. In this way, project development risks are increased significantly and, whenever a failure is encountered, there is a significant impact on the costs and schedule of the project. Finally, European motors might provide a cheaper overall solution than a U.S. procured equivalent, although it require an apparent significant investment The small market, without any major growth prospects, together with Etel’s decision to abandon their space business, reinforces the generally accepted view that for a company to be able to supply the European space motor market, it has to be subsidised. In addition, it must find synergies with other motor applications, especially those with strong similarities in motor research, technology improvement and in motor industrialisation aspects.


page18 of 46

The above statement is certainly valid for the Electromagnetic European space motor, which fall into the Category 1. R&D investment in Category 2 Electromagnetic European space motors might result in a better situation regarding the return of investment.

4.3 European Strategic Interest Electrical motors are key components in a broad range of space applications. From the smallest scientific payload, up to the high power electrical actuators in launchers, all these require some means of transforming electrical energy into mechanical motion. All knowledge is essential in this very complex technological field. Such knowledge can only be gained from an industry active in industrialisation of electrical motors. It is essential for Europe to be in the forefront of technological development, because a downgrading of European technology would be very difficult to restore in the future. The alternative to this would be to procure space motors outside Europe, with all the risks that such a decision would involve. Europe would no longer be able to carry out its missions independently and would always be constrained in terms of cost and schedule by poor or non-existent technical support. Procuring a motor is far from straightforward, mainly due to the interaction between all the motor components. There is always a development risk present, which can be minimised with the involvement of an established and recognized European motor supplier, able to assist and advise in selecting a motor and to inform mechanism designers. Procuring a fully integrated actuator and electronics might reduce the mechanism development risk, mainly due to the relatively simple interface and responsibility share between the overall mechanism and the device in charge of providing the mechanism motion. Nevertheless, this approach increases the difficulties for the mechanism leader and its design office to control fully all the technical aspects of the motor and motor components. A very close industrial partnership between the mechanism and motor suppliers might overcome this difficulty. The technology transfer constraints, the confidentiality aspects, and the U.S. limited quantity of technical information, are factors that do not lend themselves to a collaboration between European mechanism developers and U.S. motor suppliers. Therefore, the existence of European motors is a mandatory strategic aspect to guarantee European space independence Currently, space industry has proven that it is capable to procure motors for space application from standard suppliers either by in-house modification or by specifying accordingly Preferably, the knowledge about the space specific aspects of a motor should move from space industry into selected motor suppliers The fully integrated actuator and electronics shall not be addressed in this dossier


page19 of 46

For all applications, the close industrial partnership (Electro-Mechanisms prime/Motor supplier) is a key factor and has already been applied in the past

4.4 Technology Requirements The following table contains the ESTER requirements related to this technology dossier on Electrical Motors. ID Title TRT ROM Cost Priority T-7850 Development of a family of Brushless

DC motors to cover the range 0,1 to 1 Nm (3 sizes)

2010 M M

Table 4-1 Ester Electrical Motor related Technology Requirements


page20 of 46

5 ROADMAP

5.1 Summary of the Mapping Meeting The mapping meeting took place the 5 September 07 resulting in an overall agreement on the presented ESA views. Industry supports the need to have European space motor suppliers with recognised and significant involvement also in the Non Space sector. Current space industry experience of adapting non space motors to space needs should be more systematically exploited to find the common approach related to the different types of motors. The outcome could be generalized specifications for materials, processes and testing at supplier level and a list of companies that are willing to produce according to those specifications. Disruptive technologies for new types of motors are to be assessed regarding micro motors, piezo motors, magnets material, etc… The industry comments and concerns have been addressed, resulting in the revision 1 of this document. European electrical motor know-how needs to be protected and the technical content of this widely distributed document is considered enough and appropriate. Other technical issues, which have no direct impact on Electrical Motor design and development, have been highlighted during these discussions. Need for technology enhancement tribology / bearing for long lifetime applications and motor-associated-sensors (Optical encoder, Hall effect sensors and potentiometer) were shared by the participants, but considered out of the scope and to be addressed separately.

5.2 Development Approach The proposed development approach foresees activities along 4 aims: Aim A: Generic Motor Activities Aim B: Brushless Motor Aim C: Stepper Motor Aim D: Other Motor Technologies


page21 of 46

Activities overview

A1 Sub activity of reaction sphere for attitude control The purpose of this activity is to demonstrate the feasibility of a new promising concept of a Reaction Sphere for advanced AOCS, because one Sphere might be able to replace four Reaction Wheels or Control Momentum Gyros, resulting in potential mass and cost saving. Among several Reaction Sphere innovative techniques and challenges, one is concerning the “spherical shape” of the Electrical Motor for which a demonstrator is under development by the Company MAXON (CH) in the frame of this activity. A2 Sub activity of reaction sphere Engineering Model (EM) Referring to the above description, the purpose of this Sub-activity is to develop an Engineering Model of an Electrical Motor for Reaction Sphere, pending the demonstration of the Reaction Sphere feasibility. A3 Enhancement of cryogenic motor performances and technologies EM Possible Science Missions selected in Cosmic vision may require cryogenic motors. The purpose of this activity is to identify the technical constraints linked with the cryogenic environment, which will impact the electrical motor design and performances, such as: - Electrical motor design tolerances compatible with the thermoelastic effects - Materials compatibility in term of magnetic performances and mechanical, thermal and electrical robustness in the cryogenic environment. - …others

2007 Electrical Motor Harmonisation proposed activitiesAIM A: Generic motor activities

A1 Sub activity of reaction sphere for attitude control Reaction Sphere for AOCS XA2 Sub activity of reaction sphere engineering model Reaction Sphere for AOCS XA3 Enhancement of cryogenic motor performances and technologies. EM Generic Cryogenic XA4 Electric motor design and MAIT process for high temperature environment. EM Generic High temperature XA5 Adaptation of cryogenic temperature industrial motor technologies for space applications Generic Cryogenic XA6 Adaptation of hot temperature industrial motor technologies for space applications Generic High temperature X

AIM B: Brushless motorB1 Sub activity. New size of brushless DC motor for the mini CMG generation. Control Momentum Gyro XB2 Adaptation of industrial motor technologies for space applications. Generique XB3 National CNES activity for space qualification for DC Brushless motors (France) Control Momentum Gyro XB4 Sub activity: High torque brushless DC motor for pointing systems Pointing Systems XB5 Redundancy and outgassing design enhancement of Brushless motor Robotic X

AIM C: Stepper motorC1 Stepper Motor for Space Actuator Applications Generic Steerable Mechanisms XC2 Solar Array Drive Mechanism Stepper Motor Generic Steerable Mechanisms XC3 Thrust Orientation Mechanism Stepper Motor Generic Steerable Mechanisms X

AIM D: Other motor technologiesD1 Development of a EM Sealed Gear Motor for Deployment Mechanism Telecom Solar Array Deployment XD2 Development of a QM / FM Sealed Gear Motor for Deployment Mechanism Telecom Solar Array Deployment XD3 Development of a QM Sealed Gear Motor family Generic Appendage Deployment XD4 Voice Coil Motor Engineering Model Earth Observation GMES / MTG XD5 Voice Coil Motor Qualification Model Earth Observation GMES / MTG XD6 Activity pending identification of the need for linear actuators for cryogenic temperature applications Generic Cryogenic tbc ? ?D7 Piezo new sources materials, piezoceramics motor qualification Generic High precision, Low stroke XD8 Adaptation of industrial micro motor technologies for space applications Generic mini Mechanisms XD9 Electrical motor technology survey for advanced / next generation motor technology breakthrough Generic X X

Leading Application Category 1 Category 2


page22 of 46

Based on Electrical motor concept trade-off, this activity shall result in a design and manufacturing an Engineering Model of an optimum Electrical Motor design for demonstrating the achievable performances of an Electrical Motor in cryogenic environment. A4 Electric motor design and MAIT process for high temperature environment. EM Future missions, like Bepi Colombo, Solo … would require high temperature electrical motors. The purpose of this activity is to identify the technical constraints linked with the high temperature environment, which will impact the electrical motor design and performances, such as:

• Electrical motor design tolerances compatible with the thermoelastic effects • Materials compatibility in term of magnetic performances and mechanical, thermal and

electrical robustness in high temperature environment, especially concerning the resin, resin outgassing, adhesive, wire insulation, wire fretting process, …)

• …others • The quantification of the high temperature achievable limits for electrical motor

components will result in: • The quantification of the achievable high temperature requirements, compatible with the

future mission expectations. • Possible Electrical Motor concepts and performances.

Based on Electrical motor concept trade-off, this activity shall result in a design, manufacturing and test of an Engineering Model of an optimal Electrical Motor for demonstrating the design feasibility and the achievable performances in high temperature environments for future missions like Bepi Colomo, Solo, and equivalents. A5 Adaptation of cryogenic temperature industrial motor technologies for space

applications Following the “Adaptation of industrial motor technologies for space applications” activity and the other activity regarding the “Enhancement of cryogenic motor performances and technologies”, which might result in an optimum Electrical Motor design, and in a better knowledge of the space specific constraints of the cryogenic environment, the purpose of this activity is to apply the practical and cost competitive experience of successful transition from Industrial to Space motor for cryogenic application. This activity will identify existing industrial motors compatible with cryogenic environment, implement the necessary design and process adaptation to fulfil the space requirements and validate the adapted design by means of the Manufacturing, Assembly, Integration and Test of an Engineering Model. A6 Adaptation of hot temperature industrial motor technologies for space applications Following the “Adaptation of industrial motor technologies for space applications” activity and the other activity regarding the “Electric motor design and MAIT process for high temperature


page23 of 46

environment EM, which might result in an optimum Electrical Motor design, and in a better knowledge of the space specific constraints in high temperature environment, the purpose of this activity is to apply the practical and cost competitive experience of successful transition from Industrial to Space motor for cryogenic application. This activity will identify existing industrial motors compatible with high temperature environment, implement the necessary design and process adaptation to fulfil the space requirements and validate the adapted design by means of the Manufacturing, Assembly, Integration and Test of an Engineering Model. B1 Sub activity New size of brushless DC motor for the mini CMG generation Based on previous European ITAR free brushless DC motor for Control Momentum Gyro (CMG), which has been developed by the Cie Soterem following an Open Competition, this new activity is to develop a smaller size of a brushless DC motor with the same challenging performances. This brushless DC motor is a key component of the Control Momentum Gyro foreseen to be validated in the frame of activity by means of the Design, Manufacturing, Assembly, Integration and Test of an Engineering Model. This activity is an ESA activity in preparation / synergy with all the internal ASTRIUM activities for Space missions requiring CMG equipments. B2 Adaptation of industrial motor technologies for space applications The proposed activity is aimed at creating a procedure concerned with selection, characterisation, modification, testing and supply of low-cost Commercial-Off-The-Shelf devices for general and specific space applications. The scope of the activity would be to identify, screen, propose upgrades and test procedures for COTS motors with the aim of offering end users (e.g. application or development engineers) space suitable components. The present approach would be viewed favourably as a means of enabling wider use of COTS devices in space and associated cost savings and availability of a wider range of motor types and capabilities, better suited to specific applications. The activity's feasibility was already proven in different space projects (e.g. ROSETTA LANDER, EXPOSE, BIOPAN, Beagle 2, MIDAS, etc.). A significant cost/performance improvement at component level is considered as being the main objective. Subsequent to this first part of this activity (focussing more on the feasibility of the approach) a hardware oriented demonstration of the proposed motor upgrade initiative shall be performed via a test programme jointly defined and agreed with the Agency's PA/QA representatives. In this phase of the activity a statistically relevant number of motors of each type (brushed, brushless, stepper, piezo) shall be selected, screened, upgraded, inspected, tested in the frame of a test campaign defined on solid and unanimously accepted basis, with clear test objectives and pass/fail criteria such as to establish a clear and unambiguous procedure to upgrade COTS equipment to space standards, with full traceability, and confirmed performances. B3 Improvement of DC Brushless motors (France)


page24 of 46

In the frame of all the Cie Soterem activities in developing Space DC Brushless motors, this National CNES activity aims to identify and reinforce as needed the Soterem Design and Manufacturing processes of these DC Brushless motors for it’s to fulfil the Customer needs according to Space requirements. Regarding the budget and the activity schedule, please refer to the output of the Road Map meeting action to the French Delegation B4 Sub activity High torque brushless DC motor for pointing systems ESA and the THAG Electrical Motor team support the ASD- Eurospace proposal to enlarge the European ITAR free brushless DC motor family by developing a high torque brushless DC motor for pointing systems. The targeted performances, which have been identified during the Road Map meeting preparation should be in the order of magnitude of the following data: - Peak torque: 7Nm - Motor constant : Km = 1.0 Nm/sqrt(W) - Iron/cobalt technology to be studied in order to optimise the mass/power - Lifetime: 7-10 years The purpose of this activity is to consolidate the specifications and targeted applications of this high torque brushless DC motor and validate its feasibility by means of the Design, Manufacturing, Assembly, Integration and Test of an Engineering Model. B5 Redundancy and outgassing design enhancement of Brushless motor RoboDrive has already developed a brushless DC motor with interesting performances, which has already been used. A new activity is proposed in view to enhance this brushless DC motor: Implementation of prime and red winding Reduction outgassing by means of materials selection. C1 Stepper Motor for Space Actuator Applications ITAR free European Space Actuators have been developed in the last few years to fulfil the need for deployment mechanisms for various spacecraft appendix, for Antenna pointing, for Electric Propulsion Pointing mechanisms, for Solar Array Drive mechanism and other various mechanisms. Most of these actuators are equipped with a high performance stepper motor minimising the torque ripple, which is an important requirement in some cases. For others deployment or pointing mechanism applications involving significant flexible harness, such as the Electric Propulsion Pointing mechanisms, Antenna with RF cables / flexible waive-guide, Deployable radiator with flexible tubing, ..etc, the actuator shall be able to provide a significant un-powered detent torque in view to avoid the implementation of complex and costly breaking or detent break system, while avoiding step loss. This is to develop, manufacture and test a Breadboard Model and an EQM (Engineering and Qualification Model) of a frameless stepper motor offering a typical ratio between its Nominal


page25 of 46

Torque and Detent Torque in a range of 20 to 30 % with I/F compatible with existing European Actuator for space applications. This development consists in adapting existing stepper motor and qualified material and process. The targeted FM motor recurrent price is the half of the existing high performance stepper motor, resulting in competitiveness improvements. C2 Solar Array Drive Mechanism Stepper Motor and C3 Thrust Orientation Mechanism Stepper Motor These new activities for developing EQMs (Engineering and Qualification Models) of electrical motors similar to the existing ETEL motors is a consequence of the Road Map meeting actions to the French and Swiss Delegation regarding the Cie ETEL. At this occasion, ETEL has officially stated that they won’t supply electrical motors for space applications anymore. D1 Development of an EM Sealed Gear Motor for Deployment Mechanism The activity objective is to develop an Engineering Model of a brush gear motor to fulfil an appendage deployment function in the following context. Brush Gear motors are often used to motorise and regulate the speed of large solar arrays for telecommunication applications. Today, most of actuators are coming from US with the associated ITAR regulation constraints. One of the major concerns of this technology is the very poor electro-mechanical behaviour of the brushes under high vacuum that has lead in the past to many on ground and in orbit failures. In the frame of a previous ESA contract, Soterem (F) has successfully developed a breadboard of a sealed brush DC motor. This particular configuration offers the benefit of avoiding all electro-tribological issues relating to the operation of brushes under vacuum (wear and contact resistance issues). This motor has been identified as a solution to fulfil an appendage deployment function. For that purpose the existing motor design has to be slightly adapted and a gearbox must be developed to reach the targeted speed and torque. The first application foreseen is the deployment motorisation and speed regulation of a high power solar array from Alcatel Space (F) for Spacebus spacecraft family. D2 Development of a QM / FM Sealed Gear Motor for Deployment Mechanism Following the “Development of an EM Sealed Gear Motor for Deployment Mechanism” activity and based on the achieved results, the purpose of this activity is to consolidate this development towards the QM and Flight application model by means of optimising the industrial organisation compatible with the market needs and Design, Manufacturing, Assembly, Integration and fully Testing, including life test a Qualification Model, according to contractual Long Term Agreement between Prime and the Sealed Gear Motor supplier Ruag (CH)


page26 of 46

D3 Development of a QM Sealed Gear Motor family Following the technical and commercial successes of the new concept of Sealed Motor and Sealed Gear Motor, the purpose of this activity is to identify further applications for which the absence of costly drive electronic associated with a brushed Electrical Motor, while all the drawbacks due to the brushes behaviour in space environment are not anymore a constraint in this Sealed Motor. From the results of this market assessment, this activity will result in a new size and a new technical specification for a certainly “smaller”(tbc) type of Sealed Motor and Sealed Gear Motor, for which an adaptation of the existing design will be validated by a BM (Breadboard Model) follow by the Design, Manufacturing, Assembly, Integration and fully Testing, including life test of a EQM (Engineering and Qualification Model). D4 Voice Coil Motor Engineering Model Voice Coil Motors have been used in several instruments and offers an accurate positioning capability. Although the Voice Coil Motor is simple, there's no manufacturer of space qualified Voice Coil Motors in Europe. The Swiss Cie ETEL has stopped its designing activity in 2000. Since then, several breadboards of instruments have been built in Europe using US manufacturer Voice Coil motors. The activity aims at having an European source of Space Voice Coil Motors that are intended to be used for a pointing mechanism, like the ones for Meteosat Third Generation (MTG). A special emphasis will be on the Parts, Materials and Processes, as those actuators are generally used close to the optics and shall be ready to be used in Phase C/D program. An EM will be designed, built and tested, with the goal to reach at least a minimum set of specifications. A first effort is to establish the Parts, Materials and Processes (PMP) for the VCM technologies (in relation in particular, with the coils and the magnetic parts). Although not necessary for the identified need, coil redundancy will be addressed. The second effort is to realize an EM allowing an assessment of the feasibility of the specific VCM MTG need. The goal is to achieve the required force with the allocated electric power. The required moving mass will results from the design. The EM functional performance will be checked. The force at different currents will be measured versus position. A lifetime test will be performed in TV conditions. D5 Voice Coil Motor Qualification Model Following the “Voice Coil Motor Engineering Model” activity and based on the achieved results, the purpose of this activity is to consolidate this development towards the QM and Flight application Model by means of the Design, Manufacturing, Assembly, Integration and fully Testing, including life test a Qualification Model for the identified project(s) and application(s)


page27 of 46

D6 Activity pending identification of the need for linear actuators for cryogenic temperature applications

Refer to the output of the Road Map meeting action to the French Delegation D7 Piezo new sources materials, piezoceramics motor qualification Referring to the CNES presentation during the mapping meeting, this activity concerning Piezo motor has been proposed in the following context:

• In the past decade, CNES and ESA work together to qualify a piezo source and number of flight applications were developed (characteristics so appreciated for high precision instruments)

• ESA also funded piezo rotating motor study at CEDRAT company (F) • Years of CNES R&D activities at CEDRAT company make piezo actuators solutions

available for space applications (amplified actuators, lot evaluation process…) • Good complementarity with NOLIAC (NW) as European ceramic supplier

=> Need to prolong lot evaluation work performed under CNES funding by an ESCC standard at ESA level… The purpose of this activity is to Design, Manufacturing, Assembly, Integration and fully Testing, including life test of an EQM (Engineering and Qualification Model) based on the new material identified and validated by the CNES. D8 Adaptation of industrial micro motor technologies for space applications Following the “Adaptation of industrial motor technologies for space applications” activity, the purpose of this activity is to apply the practical and cost competitive experience of successful transition from Industrial to Space mini and / or micro motors, which might offer to the Space mechanisms alternative, compact or innovative mechanism concepts. This activity will identify existing mini and / or micro industrial motors and, from the background gained during the “Adaptation of industrial motor technologies for space applications”, identify and implemented motor design adaptation validated by means of Manufacturing, Assembly, Integration and Test of an Engineering Model. Like for all the other activities aiming to adapt industrial motor technologies for space applications, this activity will cover all industrial motor potential candidates including the one’s which integrate reducers or gear boxes. Therefore the adaptation for space will address also that reducer aspects, such as bearings, lubrication, gear material, … D9 Electrical motor technology survey for advanced / next generation motor

technology breakthrough Although Electrical Motor markets assessment, Benchmark identification and in a general term, space electrical motors activities performed since the 2002 THAG has not resulting in


page28 of 46

identifying any real technology breakthrough, but technology enhancements like, for example, the sealed motor technique. The 2007 THAG electrical motor team has considered appropriate to set-up this cost limited technology survey activity aiming to perform a dedicated and worldwide survey of a maximum types or concepts of electrical motor, within the objective to identify new technologies and / or breakthrough technologies, which might be applicable for advanced / next generation of space electrical motors.


page29 of 46

ID rmonisaReferenc

Task Name

1 AIM A: Generic motor activities2 A1 Sub activity of reaction sphere for attitude control3 A2 Sub activity of reaction sphere engineering model4 A3 Enhancement of cryogenic motor performances and technologies. EM5 A4 Electric motor design and MAIT process for high temperature environment. EM6 A5 Adaptation of cryogenic temperature industrial motor technologies for space a7 A6 Adaptation of hot temperature industrial motor technologies for space applicat8 AIM B: Brushless motor9 B1 Sub activity. New size of brushless DC motor for the mini CMG generation.10 B2 Adaptation of industrial motor technologies for space applications.11 B3 National CNES activity for space qualification for DC Brushless motors (Franc12 B4 Sub activity: High torque brushless DC motor for pointing systems13 B5 Redundancy and outgassing design enhancement of Brushless motor14 AIM C: Stepper motor15 C1 Stepper Motor for Space Actuator Applications16 C2 Solar Array Drive Mechanism Stepper Motor17 C3 Thrust Orientation Mechanism Stepper Motor18 AIM D: Other motor technologies19 D1 Development of a EM Sealed Gear Motor for Deployment Mechanism20 D2 Development of a QM / FM Sealed Gear Motor for Deployment Mechanism21 D3 Development of a QM Sealed Gear Motor family22 D4 Voice Coil Motor Engineering Model 23 D5 Voice Coil Motor Qualification Model24 D6 Activity pending identification of the need for linear actuators for cryogenic tem25 D7 Piezo new sources materials, piezoceramics motor qualification26 D8 Adaptation of industrial micro motor technologies for space applications27 D9 Electrical motor technology survey for advanced / next generation motor techn

Half 2, 2006 Half 1, 2007 Half 2, 2007 Half 1, 2008 Half 2, 2008 Half 1, 2009 Half 2, 2009 Half 1, 2010 Half 2, 2010

5.3 Schedule


page30 of 46

P(U) P (C)(H,M,

L)(H,M

,L) Appr. Addit. Type Company Current TargetAIM A: Generic motor activities

A1 Sub activity of reaction sphere for attitude control 400 GSTP DN CSEM / Maxon CH motor activity. 2 3A2 Sub activity of reaction sphere engineering model M H 900 GSTP DN CSEM / Maxon CH motor activity. Cont'd. 3 5A3 Enhancement of cryogenic motor performances and technologies. EM M M 250 GSTP OC Space specific cryogenic motors 3 6A4 Electric motor design and MAIT process for high temperature environment. EM H H 350 GSTP OC Space specific hot temperature 3 6A5 Adaptation of cryogenic temperature industrial motor technologies for space applications M M 250 GSTP OC Industrial cryogenic 3 6A6 Adaptation of hot temperature industrial motor technologies for space applications H H 250 GSTP OC Industrial hot temperature 3 6

AIM B: Brushless motorB1 Sub activity. New size of brushless DC motor for the mini CMG generation. 250 GSTP Brushless motor family 3 6B2 Adaptation of industrial motor technologies for space applications. 223 GSTP OC Competitiveness improvements 3 6B3 Improvement of DC Brushless motors (France) M H ? CNES DN Soterem Competitiveness improvements 5 6B4 Sub activity. High torque brushless DC motor for pointing systems M H 300 GSTP Pointing Systems 3 6B5 Redundancy and outgassing design enhancement of Brushless motor M M 100 GSTP DN RoboDrive Cie Performances enhancement 6 7

AIM C: Stepper motorC1 Stepper Motor for Space Actuator Applications 100 GSTP OC Competitiveness improvements 3 5C2 Solar Array Drive Mechanism Stepper Motor H H 100 GSTP OC Replacement of the Etel motor 3 6C3 Thrust Orientation Mechanism Stepper Motor H H 100 GSTP OC Replacement of the Etel motor 3 6

AIM D: Other motor technologiesD1 Development of a EM Sealed Gear Motor for Deployment Mechanism 265 ARTES 5 DN Soterem Brush DC equivalent motor. 3 6D2 Development of a QM / FM Sealed Gear Motor for Deployment Mechanism H H 168 ARTES 4 DN RUAG / Soterem

qCont'd 6 7

D3 Development of a QM Sealed Gear Motor family M H 200 GSTP DN RUAG / Soteremq

Cont'd 6 7D4 Voice Coil Motor Engineering Model 120 GSTP OC European linear motor 3 6D5 Voice Coil Motor Qualification Model H H 150 GSTP DN tbd European linear motor. Cont'd. 6 7D6 Activity pending identification of the need for linear actuators for cryogenic temperature applications ? M ? CNES ? European linear motor cryogenic 3 ?D7 Piezo new sources materials, piezoceramics motor qualification M H 400 GSTP OC Piezo motors 3 6D8 Adaptation of industrial micro motor technologies for space applications M M 200 GSTP OC Micro nano motors 3 6D9 Electrical motor technology survey for advanced / next generation motor technology breakthrough M M 50 tbd OC Other motor technologies 1 2

Breakdown per programme KEYTRP 0 0 Green Funded and running

GSTP 1093 3550 Orange Funded and in planningCTP Red New funding request

ARTES 265 168OTHER tbd + CNES 50 + ? Blue

TRL levelRemarkBudget (kEuro) Programme

Proc. PolicyProposed Programm

e5.4 Costs

Remarks: For most of the on-going, approved and for some foreseen activities, the Electrical Motor activity is only a fraction of the highlighted budgets.


page31 of 46

0

500

1000

1500

2000

2500

2007 2008 2009

Electrical Motors: Budget per year and per aim

AIM D: Other motor technologiesAIM C: Stepper motorAIM B: Brushless motorAIM A: Generic motor activities

0

500

1000

1500

2000

2500

3000

k€

H M LPriority

Requested Budget Per Priority (Criticality)

0

500

1000

1500

2000

2500

3000

k€

H M LPriority

Requested Budget Per Priority (Urgency)

5.5 Statistics


page32 of 46

5.6 Roadmap Implementation Status At the time when the Etel Cie has announced that their production of electrical motors for space is discontinued, Europe was lacking a local supplier willing to cope with all the variety of technical specifications and the limited demand of the space sector. The 2002 Electrical Motor Harmonisation has resulted in the decision to urgently select a new European Electrical Motor provider company. This company was expected to fulfil the following requirements:

1. The company should have a technical background in the field of electrical motors. 2. The company should be willing to adapt existing designs or to develop new designs to

custom defined specifications. 3. The company should have a QA system (ISO 9000, AQAP) 4. Delivery time for custom-made motors should be within 18 months of order, with the

aim of reducing this to 12 months. 5. For what concern the recurrent and non-recurrent costs, the situation did not allow the

identification of products and prices to be used as reference, because US suppliers have often more competitiveness in term of price, and the modest visibility in their design prevent to identify significant recurrent and non-recurrent costs benchmarking..

CNES in cooperation with ESA experts has initiated an activity in open competition for European companies resulting in the selection of the Cie SOTEREM, supported by its sister company SERMAT. Several ESA and CNES programs have been initiated with the company SOTEREM and further Space Electromagnetic Electrical motors ESA programs are currently under preparation, although in Open Competition. The main achievement and results of this strategy were the selection of this new European electrical motor and the achievement of the following first objective of the Electrical Motors Harmonisation Road Map:

- adaptation of industrial know-how and processes towards space standards - space qualification of a new family of high torque brushless DC motors - delivery of a first set of FMs for space sensitive program

The following table presents the activity of the previous roadmap of Electrical motors with its implementation.


page33 of 46

ACTIVITY COMPLETION DETAILS HRM_A: Generic motor activities A01: (ch-1) : motor source in CH Covered GSTP activity: Study of a reaction sphere for

attitude control using H-Brisc 2 A02: (te-1) : Teldix motor support Covered TRP activity: Control Momentum Gyro

Breadboard. GSTP activity: Qualification of a Magnetic Bearing Momentum Wheel. NATIONAL activity: Reaction Wheels (Germany)

A03: (gm-1) : Market assessment Covered Corporate effort A04: (gm-2) :Benchmark identification

Covered Corporate effort

HRM_B: Brushless motor B01: (bl-1) CNES EQM low torque

Covered National activity: Brush-Less and Linear Motors (France)

B02: (bl-2) : Bruhless motor family

Covered National activities (France) New activities needed to continue this line

B03: (bl-3) : Competitiveness improvements

Partially covered

TRP activity: Adaptation of industrial motor technologies for space applications (Phase 1) – On hold. GSTP activity: Adaptation of industrial motor technologies for space applications (Phase 2). NATIONAL activity: Space qualification for DC Brushless motors (France) New activities needed to continue this line

HRM_C: Stepper motor C01: (st-1) : Competitiveness improvments

Covered TRP activity:Adaptation of industrial motor technologies for space applications (Phase 1) - On hold. GSTP activity: Stepper Motor for Space Actuator Applications

HRM_D: Other motor technologies

D01: (be-1) EM brush equivalent motor

Covered ARTES 5 activity: Development of a Sealed Gear Motor for Deployment Mechanism EOEP activity: Development of a Sealed Brush DC Motor

D02: (be-2): FM / QM brush equivalent motor

Partially covered

Not yet FM/QM activities in approved plan, but the need is confirmed

D03: (be-3): Brush equivalent motor improvments

Partially covered

Not yet FM/QM activities in approved plan, but the need is confirmed


page34 of 46

D04: (li-1) : European linear motor

Covered GSTP activity: Voice Coil Motor Engineering Model

D05: (pi-1) : Piezo technology evolution

Covered TRP activities: Rotary Piezo Actuator; Piezo Valve for Space Applications; Rotating Piezo Motors for High Precision Positioning GSTP activity: Rotary Piezoelectric Motor - Prequalification National activities: Novel piezoelectric actuators; Novel piezoelectric actuators (France)

D06: (mn-1) : Micro nano technology improvments

Not pursued

D07: (ot-1) : Other motor technologies

Not pursued Not pursued because of extensive work in other areas.


page35 of 46

6 CONCLUSIONS Extract from Conclusions of the 2nd Semester 2007 Meetings, ESA/IPC(2008)31, endorsed by IPC at its 243rd meeting on 2-4 April 2008.

6.1 Status The main objectives of the 2002 Electrical Motors harmonisation activity were to improve commercial conditions for European Supplier of Space Brushless motor technology and to strengthen the competitiveness of the European suppliers of the other types of Space Electromagnetic Electrical motors. Generally, it can be said that the strategy chosen at the time of the first Harmonisation has proven to be correct, however the desired targets in terms of schedule could not be achieved since the level of funding was lower than expected. It is not possible to provide exact figures on coverage of the previous Roadmap due to lack of detailed budget figures specified at the time. Because of these delays, products which were identified for specific projects could not be used: these projects had therefore to resort to US motors, with the difficulties which usually occur when non-European products are procured. Electrical motors are currently present in a very large number of terrestrial applications: their annual production is in the order of magnitude of millions of units, while electrical motors flown in space are around some hundred units per year. Not surprisingly therefore in Europe the number of companies currently active in this field for space is relatively small. Electrical motors are key components in a broad range of space applications. It is therefore of strategic interest for Europe to maintain at least 2 sources for Category 1 motors in order to:

- Maintain and further develop the existing high level of expertise - Ensure the technology timely availability for all missions - Avoid any dependency on non-European sources


page36 of 46

Approved Additional

Breakdown per programme

TRP 0 0GSTP 1093 3550

CTPARTES 265 168

Other ESA 50

Total ESA 1358 3718

OTHER (National)

Budget (k€)

0

500

1000

1500

2000

2500

3000

k€

H M LPriority

Requested Budget Per Priority (Urgency)

0

500

1000

1500

2000

2500

3000

k€

H M LPriority

Requested Budget Per Priority (Criticality)

0

500

1000

1500

2000

2500

2007 2008 2009

Electrical Motors: Budget per year and per aim

AIM D: Other motor technologiesAIM C: Stepper motorAIM B: Brushless motorAIM A: Generic motor activities

6.2 Conclusions The Roadmap (Issue 2, Rev. 2), as updated following the Roadmap Meeting, is supported by THAG. The Roadmap addresses 4 main (Aims) based on the approach to have an extension of the existing space qualified family of specific electromagnetic motors and adaptation of Industrial Motor Technologies for Space Applications: Aim A: Generic Motor Technologies Aim B: Brushless Motor Aim C: Stepper Motor Aim D: Other motor technologies (sealed gear motor, piezo, …) The Roadmap indicates 3.72M€ of new funding request in addition to the already approved 1.36M€ for this technology area. Distribution per priority, per programme and over time (date of expected CA) is provided below.


page37 of 46

The following points were highlighted:

- It was agreed that technical emphasis should be put on materials for frameless motors regarding long time duration missions, particularly for harsh environment including high speed.

- The small space market, without any major growth prospects, together with ETEL’s decision to abandon their space business(*) reinforces the generally accepted view that for a company to be able to supply the European space motor market, institutional support is key.

- It is necessary to ensure the development and emergence of a new European company for space electrical motors to fill the gap left by ETEL.

- Synergies should be sought with other motor applications, especially those with strong similarities in motor research, technology improvement and in motor industrialisation aspects.

- The need for a common ECSS standard on Electrical motors was recognised. However, going beyond guidelines/information already provided in the Technical Dossier was very challenging, mainly due to industrial confidentiality issues.

- R&D investments are needed for both Category 1 and Category 2 motors. - Future missions require high temperature electrical motors and may require cryogenic

electric motors. - It was agreed that a harmonisation on Position Sensors should be conducted as soon as

possible.

(*) Since the THAG restricted meeting of the 13th February, and following further exchanges between ESA, the Swiss Delegation and ETEL, ETEL has sent (28th February) a letter (Annex 1) to the Swiss Delegation clarifying that: “.., since the change in the company ownership in 1999, ETEL has decided to withdraw from defence and aerospace projects to focus on the industrial sector exclusively. As a consequence, no new aerospace projects are accepted since then. However, ETEL was conscious that some customers were depending on ETEL technology. In those cases, ËTEL has met its commitment by supporting on going applications and by delivering products according to all signed contracts that were not yet ended. Today, the company orientation towards the industrial sector is fully realized. ETEL's aerospace R&D capacity, dedicated production equipment and tooling as well as the number of aerospace-trained and qualified workers has been reduced to the minimum, in fact just enough to fulfil our commitment since a few contracts are not finished yet. ETEL is fully aware that as a consequence of its decision, ESA will look for an alternative motor supplier and ETEL will be de facto disqualified for any new project.”


page38 of 46

APPENDIX A – TECHNICAL DETAILS There are a number of physical phenomena that can be used to convert electrical energy into mechanical energy. Of these, the two most common are:

Lorenz Force. The interaction between magnetic fields and current-carrying conductors generates mechanical forces. This, for instance, is the working principle of the Permanent Magnet Synchronous Motor: the permanent magnets mounted on the rotor (motor rotating part) generate the magnetic field that interacts with the current-carrying windings in the stator (motor fixed part). The force that is generated causes the relative motion of the rotor with respect to the stator.

Minimal Reluctance Principle. A magnetic circuit always tends to a configuration that minimises its overall reluctance. A more intuitive way of presenting this principle can be observed in Figure 1. When two pieces of a ferromagnetic material are immersed in a magnetic field, forces are exerted on the two pieces that tend to bring them into an aligned position. This minimises the magnetic flux path length and, at the same time, the reluctance. This is the working principle of the Reluctance Stepper Motor.

Figure 1 – Minimal reluctance principle.

Some motors use a combination of both of these phenomena. The Hybrid Stepper Motor is such an example. Other phenomena, such as the piezoelectric effect, are also used for electromagnetic energy conversion and are addressed in the A3. Emerging Technologies subsection. Considering the type of motion produced, electrical motors can be grouped into two categories: linear and rotational, of which the latter is the most common. A brief description of the different motor technologies and the corresponding electronic drive requirements is presented in the following subsections.


page39 of 46

A1. Rotational Motors A.1.1. PM Synchronous Motors (Brushless DC) PM synchronous motors can be split into three categories: Torque Motors. These usually have a large outside diameter and short axial length; are typically used for low speed, high precision applications such as: antenna pointing, robotics, motors for valves, scanning mechanisms, reaction wheels, precision control of instruments. A 100 Nm / 80 rpm torque motor was used for an astronaut centrifuge flown on the space shuttle (EDEN - Neurolab). Also a 10 Nm / 100 rpm motor forms part of an Ariane launch vehicle servo-command. High-Speed Motors. Used for pumps, gyroscopes, valves. Toothless Motors. These are well suited to high or low speed applications that require a smooth speed/torque characteristic. A study conducted under ESA/ESTEC contract identified the guidelines necessary to design an efficient low noise motor. A toothless permanent magnet synchronous motor was built and tested in order to consolidate the study output. The brushless DC motor requires a position sensor and an electronic driver, capable of providing a polyphase system of currents/voltages.

Performances Speeds range from 0 to in excess of 200 000 rpm; typically between 250 and 5000 rpm. Speeds above 15 000 rpm can be considered high speeds, not due to motor technology limitations but due to bearing issues. The torque for the slotted designs can range from less than 0.001 Nm to over 10 000 Nm. There is no limit as far as space applications are concerned. For classical toothless designs, torques range from less than 0.001 Nm to approximately 5 ~ 10 Nm. The torque can be increased when considering other industrial concepts. These, however, still have to be developed in order to comply with the space environment loads (vibration, temperature, vacuum). Power can exceed 40 kW. No power limitation is expected as far as space applications are concerned. A.1.2. Stepper Motors The key advantage of the stepper motor technology is the simplicity of the electronic driver, which results in an incremental stepping motion, satisfying many mechanisms requirements without the need of a position sensor. It provides a simple and efficient brushless solution. There are three configurations of the stepper motor that are most commonly used in space: The hybrid stepper motor. In space, this is the most widely used stepper motor. Its applications include: solar panel and antenna pointing, guidance of ionic thrusters, cover opening, positioning of samples and calibration units, mechanical switches, scanning, deployment mechanisms, etc. This type of stepper motor has the following characteristics: relatively low working speeds, high torque/volume or torque/mass ratios, and small stator to rotor mechanical air gap.


page40 of 46

The reluctance stepper motor. Having a very simple and robust mechanical design, it is used mainly in very low temperature applications (e.g. cryogenic valves). It has a low cost and relatively high torque/weight capability when loaded, but a low efficiency (close to 50 %), which makes it suitable only for low temperature applications where the copper losses are greatly reduced. In these conditions, the drawbacks of low efficiency are limited, and are further compensated by the ease of the design/manufacturing processes for extreme temperatures. Its main drawback is poor noise behaviour, both in terms of torque ripple and vibrations. The electromagnetic stepper motor, which can be regarded as a PM synchronous motor with a large number of poles. The advantage of this configuration lies in its use of PMSM technology in open loop, with a good torque/power capability and an increased working speed. A particular configuration of the electromagnetic stepper motor has a thin disc rotor, being characterized by a very low inertia and a high specific torque. It is used in antenna pointing and ionic thrusters mechanisms. The electronic driver is in general simple. In its simplest form, it operates in an open loop, full step and unipolar working mode. A more complex design, still in open loop, is a micro-stepping driver that controls the motor acceleration and deceleration profiles (micro-stepping is a driving method that allows for a stepper motor to hold a position between the full-step positions). On the other hand, the classical electronic driver for stepper motors works in open loop and consequently the electronic processing of a position sensor is not required.

Performances The performances reached with hybrid stepper motor technology are: Speed: speeds under 10 step/s are considered very low speeds; low speed: 10 ~ 200 step/s; high speed: above 200 step/s. Torque exceeding 5 ~ 10 Nm are unusual for a stepper motor. Step accuracy: ± 5 ~ 10 % of a step is obtained with an unloaded motor, due to both the machining inaccuracies and hardware imperfections. When a load is applied, a position error appears that is caused by the holding torque angular stiffness. The worst case is one in which the load torque equals the holding torque, resulting in an error of a full step. A.1.3. Brush DC Motors Brush DC motors were the first motors to be developed more than a century ago. Indeed, at that time, the only available source of energy was DC batteries and the motor had to be able to cope with such an electrical constraint. The idea of the ‘mechanical brushes’ came and exists to this day, but a competing technology has recently emerged in the form of electronic power bridges, capable of performing electrically precisely what the brushes do mechanically. Finally, the use of DC batteries is also a typical space constraint and, for this reason, the brush DC motor is definitely worth considering for space applications. Although they are structurally different, the brush DC motor is magnetically identical to a brushless DC motor. The structural difference lies in the fact that the windings of the brush motor


page41 of 46

are in the rotor and the permanent magnets are in the stator. Because of this, there has to be some kind of mechanical commutation to energise the windings, which is achieved via the use of brushes and a collector. In space conditions (low temperature, vacuum) the life of these components is sometimes very short. For this reason, the use of brush motors in space applications is unadvisable. On the other hand, the advantages of low mass, ease of use and low purchase price (in addition to performances that are identical to those provided by brushless motors) make the brush DC motor very attractive for applications with a limited life cycle. Application examples include the deployment of antennas and solar arrays (Hubble, polar platform), and their use in scientific experiments, including ejection mechanisms (Rosetta lander). When choosing a brush motor, however, the initial economical gains might be outweighed by the necessary development and qualification tests, resulting in a design more costly than that of a brushless type. In some cases, the contact materials prove to be inadequate and must be replaced, necessitating long and unpredictable development tests. In order to overcome the problems arising from the use of brushes, an alternative technology was developed under ESTEC contract that combines the benefits of both brush and brushless technologies. This new type of motor, called a smart motor, was developed with the aim of behaving as a typical brush DC motor, but with only two feeding leads. In fact, the smart motor consists simply of a brushless DC motor with the required driving electronics integrated into a single housing. Another development under way is the design of a sealed brush motor. It consists of a brush motor enclosed in a tight envelope filled with nitrogen. This design minimizes the temperature and vacuum effects on the brushes and collector, thus increasing the reliability, and still maintaining the low cost and ease of use of the brush motors. The power is transmitted to the shaft outside the envelope through a magnetic hysteresis coupler. Brush motors are supplied by DC voltage or current drivers. These electronic systems can be unipolar or bipolar for double rotation directions. The motor speed is variable, nearly proportional to the voltage. No position sensor is needed for the motor commutation, ensured by the commutation brushes.

Performances Speeds range from 30 ~ 20 000 rpm, with a standard working range of 250 ~ 10 000 rpm. Speeds higher than 10 000 rpm are considered high speeds, due to bearing and brushes/collector mechanical issues. Torque, range from 0.01 Nm ~ 1000 Nm. There is no maximum, as far as space applications are concerned. No power limitation is expected, as far as space applications are concerned. Efficiencies of 90 % or higher can easily be achieved.


page42 of 46

A.1.4. Induction Motor One of the key advantages of the induction motor (also called ‘asynchronous’ motor) is the fact that it does not require an electronic driver. The precondition for this is that an AC power distribution is available and further that the motor can be connected directly to the AC lines, without introducing additional devices, such as a starting current limitation or an EMC filter. If the motor speed needs only to be roughly controlled, then the use of a position sensor can be avoided. Thus, under such conditions, the induction motor provides a very suitable solution. In space, the potential of the induction motor technology is restricted by several key drawbacks, which lead ultimately to the selection of other complementary technologies, such as permanent magnets synchronous motors. These key drawbacks are most often: the fact that a straightforward connection to an AC power line is not available, necessitating the use of drive electronics; the availability of technologies having a similar working range and higher overall performances, such as higher efficiencies. The use of induction motors in space is consequently relatively marginal. Applications include pumps and ventilators. In terms of torque / speed performances, the following can be expected from the electronics which feeds an induction motor: The driver must be able to generate a polyphase system of currents / voltages (DC-AC converter if only a DC supply is available); If a speed or position loop is expected, the electronic driver must be able: (1) to process a position sensor; (2) to be able to adjust the supply voltage or frequency for the control of the torque – speed characteristics.

Performances

The following performances are typically attainable with induction motor technology: Speeds range from zero to in excess of 100 000 rpm. The standard working range is between 500 and 10 000 rpm. Speeds higher than 15 000 rpm are considered as high speeds, not due to motor technology limitation but due to bearing issues. Torque and power: no limitation is expected as far as space applications are concerned. Efficiency of induction motors is currently below 60 % within standard power ranges. A.1.5. Hysteresis Motor For performance reasons, the hysteresis synchronous motor is rarely selected by mechanism designers, yet it is well known in space applications. Indeed, most gyroscopes make use of this technology.


page43 of 46

Due to their working principle, hysteresis motors are limited to power below a few hundreds of a Watt, delivered at high speed but with low torque. Efficiencies above 70 % are commonly reached. This technology is a good alternative for high speed / low power applications, when an AC voltage source is available. Since 1992, due to the existence of integrated electronic drives for low power brushless DC motors, the latter technology becomes more preferable, due to its higher efficiency and / or better mass & compactness. A.1.6. Limited Angle Torquers In some applications, a motor is required to rotate through a specific angle. If this angle is limited, the structure of the motor can be simplified to that of a single-phase system. These motors are often called ‘Limited Angle Torquers’ and they can be driven very easily with a single DC driver. A position sensor can return a position signal if needed, but the LAT can also simply function as an ON /OFF latch, in open loop. More common applications include high debit valves, laser ray interrupters and stellar orientation systems. A2. Linear Motors The linear motor appears in a wide range of different designs and is more and more used in industrial applications. In space, the use of linear motors is attractive for both very small strokes (a few millimetres) and medium strokes (a few centimetres), but for long strokes the overall mass of the linear motor principle is usually higher than a rotary motor with a mechanical transmission. Linear motors for Space applications are not designed for high speeds and high dynamics, which are not usually required for space payloads. The growing space interest for linear motors comes indeed from the direct drive principle, allowing very high precision position control, as well as very smooth position transitions. Additionally, in some cases, the suppression of either the ball screw or the mechanical transmission is very attractive (lubrication issues and wear) but the inherent drawbacks of the direct drive principle should not be overlooked. Most linear motors work in closed loop and they require a good linear position feed-back (encoder). The main types of electric linear motors are presented hereafter. A.2.1. Moving Coil Linear Motors This technology already exists and has been used extensively in industrial applications (eg. reading head of computer hard discs). Its key advantages are a good dynamic behaviour (small motor moving mass) and a straightforward linear mechanical guidance. Its linearity is also beneficial, provided that the motor is adequately designed. The moving coil actuator is the only motor totally free of magnetic hysteresis and detent force or torque.


page44 of 46

Finally, even if relatively heavy, this technology is often the preferred choice in space applications, due to its smooth and linear behaviour. Space programs that have used such technology include GOMOS, CALU and IASI. A.2.2. Moving Magnets Linear Motors Compared to the moving coil actuator, this technology offers a significantly higher force / mass ratio (indeed it is 2 to 3 times lighter for a given power and force) and is consequently often preferred when dimensions / mass are key parameters. Its good overload capability and in particular its better thermal behaviour, often make it the preferred choice. Its dynamic limitations include a potentially highly non-linear force / stroke / current characteristic (which can be avoided by design) and a more complex mechanical guidance (strong magnetic effects to be withstood). These limitations restrict the number of potential industrial applications. Indeed, its limited dynamic performance increases the competition with more classical solutions. A.2.3. Electromagnets An electromagnet operates in open loop, to perform a single action, such as opening or closing, with no intermediate control between extreme positions. This type of actuator is normally capable of only limited strokes, typically between 1 and 10 mm. Examples of space applications include: release of the ISO infrared space telescope launch cover; unlocking of an arm on the Huygens / Saturn probe; locking of an optical mechanism during launch on the SAX mission. The market potential of this technology is considerable and has been so for many years. Electromagnets generally make use of the reluctant principle. They contain no magnets, but a coil (often redundant) and an iron structure. They work on the principle of the variable air gap and are normally of cylindrical geometry. The force that reluctant motors develop is proportional to the square of the current (provided it is not saturated) and thus always acts in the same direction, irrespective of the current direction. A spring returns the shaft to its original position, once the power is switched off. Due to the local saturation of the pole piece, the design is not straightforward and the optimisation of the actuator is difficult. If a redundant winding is present by means of two separate coils, the output force will generally be less than the sum of those for the two coils separately, due to the local saturation of the iron pieces. Such devices are robust and can function across a very large temperature range. An extension of this technology is the bi-stable electromagnet, in which an additional magnet provides a second stable position in non-powered state. Such actuators are used, for example, to drive valves (ATV) that can stay in both open or closed positions, once the power is switched off. Alternatively, an additional magnet can also be used to increase the electromagnet force / power characteristics, without creating a second stable position.


page45 of 46

A3. Emerging Technologies In order to decrease mission costs, payloads are becoming smaller and lighter. The miniaturization of their different components is therefore necessary. This subsection briefly summarises some of the developing technologies that are related to the miniaturisation of space motors. A3.1 Piezoelectric actuators and motors The piezoelectric effect (the deformation of certain types of crystals when a voltage is applied across them) is also used to convert electrical energy into mechanical energy. The deformations obtained are small, but the forces developed can be quite considerable. Furthermore, the amplitude of the motion can be amplified with the aid of mechanical assemblies. There are several configurations of piezo-electrical motors, capable of producing both linear and rotational motion. This technology is currently used in several space instruments, such as VIRGO, the sun observation satellite SOHO, and the MIDAS experiment aboard Rosetta and in the DIMAC sensor aboard of FOTON M3 mission, as few examples. A3.1.1 Piezoelectric actuators Piezoelectric actuators are using piezoelectric materials (crystals or ceramics) that deform under an electrical field. The obtained strain is small, but the generated force is large. Sometimes, piezo actuators are amplifying the motion through an elastic coupler or an hydraulic amplifier. Piezo actuators do not have any moving parts and display an almost infinite life. Piezoelectric actuators are therefore interesting for rapid and/or precise motion. They display some advantages against electromagnetic actuators when a miniaturized function is necessary. They increasingly used in scientific payloads, such as SOHO/VIRGO, ROSETTA/MIDAS and Micro-Gravity payload like the DIMAC sensor for FOTON M3 mission. Several other instruments due for flight (LISA-PF/LMU, PICARD/SODISM, MARS-MSL/SAM) are also using piezoelectric actuators. Performances Stroke between some microns and about 1 mm can be obtained. To get a static displacement, the piezo actuator should be continuously energized, but the power consumption is in the range of milli-watts. Forces between 50 N and 5000 N can be obtained. A3.1.2 Piezoelectric motors Piezoelectric motors are also using piezo materials to convert electrical energy into mechanical deformations. This limited strain is thus converted into a large motion through friction. Piezoelectric motors can be either linear or rotating and display a force/torque at rest without any power supply. They represent also a unique solution to provide a fully non magnetic motion.


page46 of 46

Piezoelectric motors have been used in Rosetta/Midas and SWARM/magnetometer as COTS Commercially Of The Shelves components. Precise positioning function can be realized. Performances Piezoelectric motors are limited to low power motor (below 10 watts) and offer relatively high torque at low speed, which can avoid the use of a gear box. Speed between some rpm to 1000 rpm can be obtained. Torque below 1 N.m can be obtained. Speed up to 1 m/s can be obtained. A3.2 Other emerging technologies Some very small motors (typically a few millimetres in diameter) use the same electromagnetic energy conversion principles described in the previous subsections. The main technological challenges in the development of these motors are the bearings and the manufacturing tolerances. Other miniaturized mechanical devices (called micro electromechanical systems, MEMS) are produced with the same fabrication processes that are used for integrated circuits. Interrupters, accelerometers, gyroscopes, or valves can be derived from this technology. The required electronics can also be integrated into the same substrate. These devices have low mass and power requirements, and their small size make them less sensitive to the dynamic environment of launch as well as to cosmic radiation. It is forecast that a complete satellite, comprising exclusively MEMS devices, could weigh as little as one quarter of a kilogram.


page47 of 46

APPENDIX B – LETTER FROM ETEL ON ELECTRICAL MOTORS FOR SPACE APPLICATIONS


page48 of 46

esa standard documentemits.sso.esa.int/emits-doc/estec/ao6337_rd4.pdf · the document is produced...

Documents