1. Mariano Andrenucci Professor, Department of Aerospace Engineering, University of Pisa, Italy Chairman and CEO, Alta S.p.A, Via A. Gherardesca 5, 56121 Ospedaletto, Pisa, Italy e-mail: m.andrenucci@alta-space.com Advanced Course ”Electric Propulsion Concepts and Systems” ESA/ESTEC, Noordwijk, September 15-19, 2008 Hall Thrusters Historical Overview

2. Slide 2 Hall Thrusters - Historical Overview Advanced Course: Electric Propulsion Concepts and Systems M. Andrenucci ESA/ESTEC, Noordwijk, September 15-19, 2008 Early Hall Thruster Studies in the USA In the early sixties the Hall ion accelerator was investigated at Lewis and Langley Research Centers, AVCO/Everett, EOS, United Aircraft, and Curtis Wright. All of the devices were annular in geometry in order to produce a radial magnetic field throughout the acceleration region with the electric field applied along the axis. There were some differences in the methods used to preionize the flowing gas and in the power level of operation.

3. Slide 3 Hall Thrusters - Historical Overview Advanced Course: Electric Propulsion Concepts and Systems M. Andrenucci ESA/ESTEC, Noordwijk, September 15-19, 2008 One serious attempt to design a competitive Hall ion accelerator in which the losses were minimized was done with an experimental study by United Aircraft. The accelerator was originally designed to operate with surface contact ionization; however, it was found that with cesium essentially complete ionization could be obtained near the anode by electron bombardment. Early Hall Thruster Studies in the USA Hall thruster research was completely abandoned in the USA in the late ’60s in favor of other concepts.

4. Slide 4 Hall Thrusters - Historical Overview Advanced Course: Electric Propulsion Concepts and Systems M. Andrenucci ESA/ESTEC, Noordwijk, September 15-19, 2008 At the beginning of the 1990s access to the EP technology heritage of the former Soviet Union was opened to the western countries. This triggered a real revolution in the EP world. Despite initial skepticism, the HET technology developed by the Russians proved exquisitely suited for a variety of space applications Exempt from dissipative phenomena and instabilities characterizing MPD thrusters Higher thrust densities, easier scalability at comparable efficiencies with respect to Ion thrusters How had this been achieved? Hall Effect Thrusters

5. Slide 5 Hall Thrusters - Historical Overview Advanced Course: Electric Propulsion Concepts and Systems M. Andrenucci ESA/ESTEC, Noordwijk, September 15-19, 2008 1961 : the Birth of the TAL On the basis of research activities carried out in the late 1950s A.Zharinov proposed the TAL scheme, obtaining the USSR “Invention Author Certificate” #24371 ( priority date 23.12.1961).

6. Slide 6 Hall Thrusters - Historical Overview Advanced Course: Electric Propulsion Concepts and Systems M. Andrenucci ESA/ESTEC, Noordwijk, September 15-19, 2008 1967 : the Double Stage TAL Zharinov ideas were not supported by IAE management, and in 1962 he left to TsNIIMash. In 1967 the first powerful double stage TAL model was successfully operated. Later on, performance levels of interest for space operations were achieved for such TAL models TsNIIMASh shared its activity on TAL with the Rockets and Space Corporation Energia and with Bauman High Tech School (BHTSc), Kharkov Aviation Institute (KhAI) and Dnepropetrovsk State University(DSU).

7. Slide 7 Hall Thrusters - Historical Overview Advanced Course: Electric Propulsion Concepts and Systems M. Andrenucci ESA/ESTEC, Noordwijk, September 15-19, 2008 1970s : the Single Stage TAL At the end of the 1970s, under the guidance of TsNIIMASh scientist E.Lyapin, a low-power single stage TAL model Isp lower than 3000 s was developed. The specific features of the single stage TAL is the usage of a deep hollow anode and low magnetic induction inside the accelerating channel (0.01-0.03Tesla) very close to the typical level realized earlier in SPTs. Study of this thruster’s operation showed that the discharge deeply penetrates into the anode cavity and that ~90% of the propellant flow ionization takes place within the cavity.

8. Slide 8 Hall Thrusters - Historical Overview Advanced Course: Electric Propulsion Concepts and Systems M. Andrenucci ESA/ESTEC, Noordwijk, September 15-19, 2008 1965 : Morozov and the Thermalized Potential Morozov did not like TAL concept His main ideas were: - the creation of the electric field within an extended plasma volume with the help of the magnetic field - use the magnetic field lines for ion flow focusing during acceleration To obtain the ion flow focusing it was necessary to have a relatively low electron temperature. This implied the use of a dielectric discharge chamber whose walls could “cool” the electron gas with a high secondary electron emission. In 1965 Morozov had published a paper describing the principle of such focusing and the equation for the plasma potential distribution along the magnetic field line (the so-called “thermalized” potential) which was the base for his ideas on the ions focusing.

9. Slide 9 Hall Thrusters - Historical Overview Advanced Course: Electric Propulsion Concepts and Systems M. Andrenucci ESA/ESTEC, Noordwijk, September 15-19, 2008 1964 : the E-accelerator By 1964 the team under Morozov’s guidance, including Yu. Esipchuk, Yu. Sharov and some others from IAE laboratory headed by German Shepkin had created the 1st so-called E-accelerator, which was preliminarly characterized in 1964.

10. Slide 10 Hall Thrusters - Historical Overview Advanced Course: Electric Propulsion Concepts and Systems M. Andrenucci ESA/ESTEC, Noordwijk, September 15-19, 2008 1968 : Towards the First SPT Flight Test In 1968 the State Committee on Atomic Energy decided to carry out a flight test of an SPT on board the Meteor satellite This idea had been proposed by Morozov and supported by the academicians Lev Artsimovich, head of the IAE Plasma Research Division, Anatoly Alexandrov, IAE president and Andronik Iosiphian, president of the All-union Institute of Electromechnics (VNIIEM) and chief designer of the Meteor type satellites It was decided also that IAE would supervise the test, that the future Design Bureau Fakel would develop the experimental propulsion system, the Design Bureau Zarya would develop the PPU, VNIIEM would be responsible for the integration of the propulsion system and would carry out the test with attendance of all others. It was also decided to involve in the SPT studies the Moscow Aviation Instutute (MAI) and Central Institute of the Aviation Motor Building During 1969-1970 the mock-up of the experimental propulsion system (EPS) was developed, manufactured, tested at IAE and transferred to FDB Fakel. During 1970-1971 the EPS flight version was developed, manufactured by FDB Fakel and DB Zarya, and tested at FDB Fakel with attendance of IAE, DB Zarya representatives. Then it was transferred to VNIIEM and integrated In December 1971 the Meteor satellite with SPT was launched and in 1972 the EPS was tested in flight, operating for about 200hours.

11. Slide 11 Hall Thrusters - Historical Overview Advanced Course: Electric Propulsion Concepts and Systems M. Andrenucci ESA/ESTEC, Noordwijk, September 15-19, 2008 1971 : the First SPT Flight Test The mock-up developed at IAE in 1969 by Yu.Sharov(left side) and the first SPT flown on the Meteor Satellite (right side) developed at Fakel by V.Bryzgalin et al.

12. Slide 12 Hall Thrusters - Historical Overview Advanced Course: Electric Propulsion Concepts and Systems M. Andrenucci ESA/ESTEC, Noordwijk, September 15-19, 2008 1972 - 1974 : Continuing Research Activities In a series of experiments carried out at MAI in 1972-1974, V. Kim and A. Bishaev were able to obtain local plasma parameters distributions inside the accelerating Channel. The sputtering yield of ceramics under bombardment by the accelerated ions generated by an SP-like plasma source was determined at MAI by a team of scientist led by I. Shkarban

13. Slide 13 Hall Thrusters - Historical Overview Advanced Course: Electric Propulsion Concepts and Systems M. Andrenucci ESA/ESTEC, Noordwijk, September 15-19, 2008 1974 : Second Flight Test During 1972-1974 the propulsion system functional scheme and propellant storing and management units designs were also improved by the Fakel team under management of the Fakel chief designer R.Snarsky and leadership of the principal designer K.Kozubsky; the same was done for the power processing unit by the leading designer of the first PPU’s, L.Novoselov and others at SPhTI. As a result of such activities, the second SPT flight test Eol-2 was made in 1974 (over 600 hour s) on board of Meteor type satellite by VNIIEM and others

14. Slide 14 Hall Thrusters - Historical Overview Advanced Course: Electric Propulsion Concepts and Systems M. Andrenucci ESA/ESTEC, Noordwijk, September 15-19, 2008 Further steps of the SPT development During 1969-1972 by IAE experts V.Mikhailichenko and E.Petrov had discovered that SPT thrust efficiency could be significantly improved by creating the magnetic field with great gradient in the direction from anode to the accelerating channel exit. This was in correspondence with theoretical analysis of the accelerated ion flow stability in the ExB fields made by A.Morozov At the same time the cathode design which prototype was developed at IAE was significantly improved at Fakel by B.Arkhipov and others. The life time tests of the first flown SPT models were made at Fakel showing that one of the main these thrusters elements wearing processes is the discharge chamber wall erosion. It was found also that erosion rate is reduced in time and this is the opportunity to get large enough SPT life time (Yu.Kondakov from Fakel had derived the semiempirical law for this erosion rate variation in time).

15. Slide 15 Hall Thrusters - Historical Overview Advanced Course: Electric Propulsion Concepts and Systems M. Andrenucci ESA/ESTEC, Noordwijk, September 15-19, 2008 1974 : the Magnetic Screens Another important step was the development of a magnetic field topology ensuring the highest thrust efficiency, but under increased discharge chamber wall thickness to increase thruster life time. This was achieved for the first time in 1973-1974 by V. Kim and A. Bishaev by means of the magnetic shunts (or magnetic screens). The first laboratory models with magnetic screens surrounding the discharge chamber were developed and tested at MAI.

16. Slide 16 Hall Thrusters - Historical Overview Advanced Course: Electric Propulsion Concepts and Systems M. Andrenucci ESA/ESTEC, Noordwijk, September 15-19, 2008 1978 : the SPT-100 The next important step was the development of a thruster design featuring a very large increase in life time capability (thruster with “shifted accelerating layer”). This idea was first proposed and tested at Fakel by V. Kozlov and was then more carefully studied and implemented in the SPT-100 laboratory model by V. Kozlov (as PhD student) and V. Kim at MAI during 1975-1978 The SPT-100 lab model was fully tested at MAI and IAE and through an accelerated test methodology it was shown that thruster lifetime could exceed 5000 hours

17. Slide 17 Hall Thrusters - Historical Overview Advanced Course: Electric Propulsion Concepts and Systems M. Andrenucci ESA/ESTEC, Noordwijk, September 15-19, 2008 Preparing for Success Before 1980, a large number of thrusters of different sizes and schemes had been developed and tested at IAE, MAI and Fakel At the top of the range, the powerful SPT-290 model for primary missions was developed at Fakel under leadership of V. Murashko. This model was able to operate with high efficiency at powers levels up to 35kW and specific impulse values over 3000s. The outstanding success of the SPT concept, technology and science was achieved through the combined effort of IAE, Fakel, MAI, TsIAM, MIREA, MSU, KhAI, BHTSc and others.