S2-2
Space Exploration Strategy with High Power Plasma Propulsions
大電力プラズマ推進による宇宙探査構想
Kiyoshi Kinefuchi, Yasuhiro Saito, Naoki Nagao, Koichi Okita,Ikkoh Funaki and Hitoshi Kuninaka
杵淵 紀世志，齊藤 靖博，長尾 直樹，沖田 耕一
船木 一幸，國中 均
Japan Aerospace Exploration Agency
2-1-1, Sengen, Tsukuba, Ibaraki 305-8505, Japan
宇宙航空研究開発機構 〒305-8505 茨城県つくば市千現2-1-1
Electric plasma propulsions are more effective device to propel spacecrafts than conventional chemical, orcombustion-based propulsions. It has been applied to numerous space missions so far because of their greatpropellant consumption efficiency. Recently, with improvement of performance, durability and reliabilityof them, the use of plasma propulsions has been expanding further. The expected future missions using
plasma propulsions include both satellite transportation to higher orbit and deep space exploration, andboth require high power thruster. Background of the future space exploration missions and R&D activitiesof plasma propulsions in Japan to contribute these missions will be discussed in this paper.

1. Introduction
Effective space transportation systems are needed
to expand the field of space activities beyond thelow earth orbit. Plasma propulsions, or electric
propulsions are promising technologies for theorbital transportation for future large-scale missions
due to their high specific impulse, that is, highpropellant consumption efficiency.
Electric propulsion is an energy conversion
device that convert electric energy into kinetic
energy of plasma jet through electrostatic,
electromagnetic or electrothermal acceleration thatpropel orbital spacecrafts. It has been used for
attitude control of GEO (geosynchronous orbit)
satellites like ETS series and for orbit transfer of
space exploration probes like Hayabusa asteroid
explorer in Japan so far. Nowadays, electric
propulsions begin to be applied to obit rising for
GEO satellites as well, i.e. all-electric satellites,
because they give great cost reduction to launch. A
great attention has been paid to electric propulsion
system especially high power, more than 5 kW
class systems.
TheInternationalSpace
Exploration
Coordination Group, ISECG, has been discussing
human space exploration toward the Moon, NEAs(Near Earth Asteroids), and Mars [1] as a following
activity after the retirement of International SpaceStation, ISS. They have been insisting on thenecessity of high power electric propulsion systems
for these missions as shown in Fig. 1.
Japan Aerospace Exploration Agency, JAXA,
has been contributing to the establishment andoperation of ISS for years, and now considering thecontribution to the future international space
exploration by Japanese own space technologies.
Electric propulsion is one of the candidates because
Japan has lots of heritage in this field.
In this paper, the future space exploration
missions discussed in ISECG will be introduced.
Then, R&D activities of electric plasma propulsions
in Japan toward to these missions will be explained.

Fig. 1 Critical technologies forhuman space exploration [1].

2. Future Space Exploration Missions [2]2.1 Asteroid Redirect Mission (ARM)
ARM will offer chances of human exploration ofan asteroid. In ARM, a robotic spacecraft with highpower electric propulsion such as Hall effectthruster to rendezvous with, capture and redirect anasteroid. The spacecraft will redirect it to a stableorbit around the moon. After that, astronauts aboard
a manned spacecraft, launched from a heavy rocket,will explore the asteroid around the moon.

2.2 Human Lunar Exploration
As a first step for the human lunar exploration, aplan to establish a space station around the moon is
discussed internationally. The promising location is
an Earth-Moon Lagrange point. To effectively
deliver supplies to the station, space cargo vehicle
with electric propulsion is favorable. The station
will play important role as a stepping stone to thelunar surface exploration as shown in Fig. 2.

Fig. 2 Image of human lunar surface exploration [2].

long period of time in orbit is a difficult problem.
JAXA has developed cryogenic propellant storagetechnologies as well as development of plasmathrusters.
Theactivities
willrealize
high-performance innovative space vehicles forefficient mass transfer. Figure 4 shows an arcjet
thruster operation with hydrogen propellant in thevacuum chamber in ISAS/JAXA.

Fig. 3 High power xenon hall thruster operation in
vacuum chamber in ISAS/JAXA.

2.3 Human Mars Exploration
The final destination described in ISECG/GER isMars. Very high power plasma propulsion on theorder of > 1 MW is the one of critical technology
needs and can more efficiently deliver cargo andcrew to beyond low Earth orbit destinations. The
candidates of the 1 MW class thruster would beMPD(Magnetoplasmadynamic)
andarcjetthrusters.
3. Electric Plasma Propulsion R&D in Japan
3.1 Hall Effect Thruster [3]Hall effect thruster produces thrust throughelectrostatic acceleration of ions and one of themajor candidates for the near term application ofhigh power electric propulsion. Hall thruster is
especially suitable for all-electric satellites because
it enables shorter trip time to GEO due to its higherthrust. JAXA is now promoting R&D activity ofHall thrusters with both universities and industries.
Figure 3 shows a snap shot of the high power hallthruster during operation in the vacuum chamber in
ISAS/JAXA.
3.2 MPD Thruster and Arcjet Thruster [4]MPD and arcjet thrusters are electromagnetic andelectrothermal
typeplasmaaccelerators,respectively. They are promising plasma thrusters
for very high power application. They can be easily
adapted to the high power operation due to theirhigher thrust density, or lighter system weight. The
performances of MPD thruster and arcjet areimproved by using cryogenic liquid hydrogen as apropellant. However, storing liquid hydrogen for aFig. 4 15 kW class hydrogen arcjet thruster operationin vacuum chamber in ISAS/JAXA.

4. Conclusion
High power electric plasma propulsions arestrongly required for next generation space
missions, such as all-electric satellite mission, andlarge scale space exploration beyond the earth orbit.
Hall, MPD and arcjet thrusters are candidates forthe high power operation, therefore, JAXA is now
promoting R&D activities of such thrusters.
References[1] International Space Exploration Coordination Group(ISECG): Global Exploration Roadmap (GER),
http://www.globalspaceexploration.org, 2013.
[2] N. Sato: Global Exploration Roadmap, Symposiumon International Space Exploration, Tokyo, 2014.
[3] N. Yamamoto, et al.: Developments of Robust
Anode-layer Intelligent Thruster for Japan In-space
Propulsion System, 33rd International Electric
Propulsion Conference, IEPC-2013-244, 2013.
[4] K. Kinefuchi, et al.: Preliminary Study of HighPower Hydrogen Electric Propulsion for the Space
Exploration, 50th AIAA/ASME/SAE/ASEE Joint
Propulsion Conference, AIAA-2014-3507, 2014.