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History and Prospects on Research, Development andApplication of Electric Rockets����������������������Hitoshi Kuninaka��� �Japan Aerospace Exploration Agency
Yoshinodai, Chuo, Sagamihara , Kanagawa, Japan����������� ��������������The electric propulsion, initiated by the founders in 1950’s, has achieved Geostationary Satellites forNorth-South Station Keeping in 1990’s and Deep Space Powered Flights in 2000’s as new eras in spacetechnology, where Japanese activities deeply contributed. EP will open a next new world: In-SpaceTransportation for human exploration and constructions of solar power satellite, and so on. Japanese R&D
efforts should be concentrated to realize 10-100kW electric propulsion.

1. History of Electric Propulsion
The electric propulsion (EP), initiated by thefounders such as Tsiolkovsky and Goddard in1950’s, has been researched on ground and tested inspace in 1960’s and 1970’s, enthusiastically as seenin Fig.1. The ion engine has progressed in theWestern world, and Hall thruster in the Eastern bloc.
These activities were shrunk at once in 1980’s
because R&D effort was concentrated to launchingrockets. In 1990’s various countries applied EP toGeostationary Satellites for North-South StationKeeping (GEO-NSSK) in order to prolong their lifein space and developed many series of satellite bus

installing EP in the standpoint of economy. In
2000’s NASA, ESA and JAXA succeeded the DeepSpace Powered Flights, independently, so that thenew era of space exploration was opened forexpansion of human intelligence to the solar system.
Japanese activities have deeply contributed toprogression of EP technology. In 2010 the largest EP
BPT4000 of Hall thruster with 4kW has just made adebut and lifts up 6-ton satellite to GEO. This is aprecursor of In-Space Transportation. Figure 2
shows chronology on EP growth in thrust, which
achieved 300mN, for the last few decades.

Fig.1. Flight Chronology of Electric Propulsion

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3. Proposed Approach in Japan
Japan has executed GEO-NSSK5 and Deep SpacePowered Flight 6 by EP leading the international
space community. JAXA and a space sector havedeveloped 35cm ion engine and 5kW Hall thruster
independently, which are candidates for In-SpaceTransportation in near term at Japanese local
activities. The author believes Japanese EP academy
and institutes should move on to develop 10-100kW
class EP for future In-Space Transportation ofinternational collaboration, gathering together ourintelligence. At this moment “selection” and“concentration” of our domestic activities are very
important7. Figure 3 shows the scenario to researchand develop high power EP in Japan.

Fig.2. Growth of EP in Thrust Force
2. World Trends on R&D
NASA had developed NSTAR ion engine1 rated
at 2.3kW since 1990 and succeeded Deep Space 1
and Dawn missions for space exploration, in 1998
and 2007 respectively. At beginning of 2000 they
started to develop NEXT ion engine with 6.9kW andperfected it in 20102. The Herakles Thruster with20-40kW was proposed in order to adapt space
nuclear power plant in Project Prometheus, which
was cancelled in 2003. In the latter half of 2000’s
the concept of In-Space Propulsion, in which EP
with high specific impulse makes spacecraft longreach and high maneuverability instead of larger
launch vehicle, has been now fully accepted. In 2010
President Obama announced the flexible path on thehuman approach to Mars through asteroids insteadof Moon. This idea stimulates to apply EP to300-700kW solar electric propulsion cargo for thehuman space exploration3 and construction of spacesolar power satellites and to research and develop
high power EP with 40-60kW in US. A US privatecompany has developed 1N Hall thruster with20kW4.
European Commission has funded several
institutes in Europe since 2008 to R&D on highpower EP as the program of HiPER (High PowerElectric propulsion Roadmap).
This world trend implies In-Space Transportation,
succeeding GEO-NSSK and Powered Flight in deep
space, a new frontier for EP in next few decades.

Fig.3. R&D Scenario of High Power EP in Japan
References
1M.J. Patterson and V.K. Rawlin, “Derated Ion Thruster
Design Issues”, IEPC 91-150
2D. Herman, “Review of the NASA’s Evolutionary
Xenon Thruster (NEXT) Long-Duration Test as of 632 kgof Propellant Throughput “, AIAA-2011-5658
3
N. Strange, R.G. Merrill, D. Landau, B. Drake, J.
Brophy, and R. Hofer, “Human Missions to Phobos andDeimos Using Combined Chemical and Solar Electric
Propulsion”, AIAA 2011-5663
4
http://www.busek.com/technologies__hall.htm
5
Mitsubishi Electric Corporation, “On-orbit operation
evaluation of ETS-6 ion engine subsystem operation”,NASDA-CNT-970004, 1998
6H. Kuninaka, K. Nishiyama, I. Funaki, T. Yamada, Y.
Shimizu and J. Kawaguchi, “Deep Space Flight ofMicrowave Discharge Ion Engines onboard Hayabusa”,
Journal of Space Technology and Science, Vol.22, No.1,
2007, pp.1-10
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