The 35th International Electric Propulsion Conference, Georgia Institute of Technology, USA
October 8 – 12, 2017
1
The Technological and Commercial Expansion of Electric
Propulsion in the Past 24 Years
IEPC-2017-242
Presented at the 35th
International Electric Propulsion Conference
Georgia Institute of Technology • Atlanta, Georgia • USA
October 8 – 12, 2017
Dan Lev1, Roger M. Myers
2, Kristina M. Lemmer
3, Jonathan Kolbeck
4, Michael Keidar
4, Hiroyuki Koizumi
5, Han
Liang 6, Daren Yu
6, Tony Schönherr
7, Jose Gonzalez del Amo
7, Wonho Choe
8, Riccardo Albertoni
9, Andrew
Hoskins10
, Shen Yan11
, William Hart12
, Richard R. Hofer
12, Ikkoh Funaki
13, Alexander Lovtsov
14, Kurt Polzin
15,
Anton Olshanskii16
and Olivier Duchemin17
1Rafael – Advanced Defense Systems, Haifa, 3102102, Israel
2R Myers Consulting, LLC, Woodinville, WA, USA
3Western Michigan University, Kalamazoo, MI, 49009, USA
4George Washington University, Washington D.C., USA
5The University of Tokyo, Bunkyo-ku, Tokyo, 113-8654, Japan
6Harbin Institute of Technology, Harbin, China
7ESA/ESTEC, Keplerlaan 1, 2200 AG Noordwijk ZH, The Netherlands
8Korea Advanced Institute of Science and Technology (KAIST), Daejeon, South-Korea
9Airbus Defence and Space, Toulouse, France
10Aerojet Rocketdyne, Arlington, VA, 22209, USA
11Lab of Advanced Space Propulsion, Beijing Institute of Control Engineering, Beijing, China
12Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
13Institute of Space and Astronautical Science / JAXA, Sagamihara, Kanagawa, 252-5210, Japan
14Keldysh Research Centre, Onezhskaya st. 8, Moscow, 125438, Russia
15NASA Marshall Space Flight Center, Huntsville, AL 35812, USA
16EDB Fakel, Kaliningrad, 236001, Russia
17 Safran Aircraft Engines, Space Electric Propulsion Directorate, Vernon, 27200, France
The use of electric propulsion for commercial and research purposes has been gaining
terrain in the past few years. The focus of this paper is the technological and commercial
development of electric propulsion systems since 1993, the year when the first commercial
satellite with an EP system was launched. Since then, 248 satellites with EP systems have
been launched, showing the increased trust that operators have on this type of propulsion.
Over 70% of the 208 analyzed GEO satellites have either a gridded ion thruster or a Hall-
effect thruster, technologies that are replacing the arcjet systems. We report a strong
increase in the number of GEO satellites with EP systems, from an average of 8 satellites per
year to over 15 in the year 2016. For LEO applications, this technological development is not
only limited to the United States and Russia; countries such as China, Japan, South Korea,
and Israel have been aggressively penetrating the market with their own systems to a total of
18 spacecraft in LEO. Russia leads the LEO market with their SPT-series propulsion
systems. Since 1993, seven interplanetary spacecraft with EP have been launched, with the
USA and Japan leading these efforts. Small satellites and LEO satellites are not exempt from
this technological movement, with 15 small satellites launched in this time frame. Half of
them launched between 2015 and 2016, showing an accelerated growth and a large potential
for future developments. We report the technological and commercial development and
analyze the future potential of this technology.
The 35th International Electric Propulsion Conference, Georgia Institute of Technology, USA
October 8 – 12, 2017
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I. Introduction
N the hundred years since electric propulsion (EP) was originally conceived it has been developed by an
increasing number of research and industrial entities worldwide1. To date a myriad of technological subclasses of
EP exist2,3
, each at a different Technological Readiness Level (TRL), from basic notions of particle acceleration
techniques to space proven applications.
During the first decades, following the first operation in space of an EP system in 1964, most development
efforts have been invested in maturing five main types of EP technologies – ion engines, pulsed plasma thrusters
(PPT), resistojets, arcjets, and Hall thrusters.
The principle drivers supporting the research, development, and ultimately qualification of each of the five
technologies were government entities; either space agencies or different branches of the military. Most of the early
missions were technology demonstrators and served purely scientific or technological purposes such as the Vela,
Space Electric Rocket Test (SERT), Zond, Lincoln Experimental Satellite (LES) or ‘Meteor’ missions1,4
. With time,
as EP technologies matured, new and improved propulsion systems were implemented to enable new satellite
maneuverability and execute a variety of missions. The combination of mission requirements and commercial
incentives resulted in EP technology being used principally in GEO communication and in Earth observation
satellites. The lead players capable of developing and implementing EP technologies were the large geo-political
entities, namely the United States, Soviet Union, Japan, Europe, and China.
The first truly operational uses of electric propulsion were for spacecraft attitude control on the Russian Zond-2
in 19645, which used pulsed plasma thrusters, and by the U.S. Vela satellites, which in 1965 used resistojets
6. The
first U.S. use of PPTs was on the U.S. LES and NOVA satellites7,8
, which in 1968 started using pulsed plasma
thrusters for fine ephemeris control to achieve a “drag-free” orbit. The first commercial use of electric propulsion
was in 1981 with the launch of the Intelsat V series of GEO satellites, which used high power resistojets for North-
South Station-Keeping (NSSK), followed rapidly by their use on RCA’s Satcom19. Unfortunately, while the use of
high power resistojets continues successfully to this day on the original Iridium constellation (77 spacecraft) and
many geosynchronous satellites (over 20 to date)6, neither the use of PPTs nor resistojets precipitated a world-wide
adoption of electric propulsion, likely due to the incremental nature of the performance improvement they provide.
For this reason, resistojets are not included in the statistics in this paper.
In parallel to the commercial use of resistojets, considerable research and development as well as several
demonstration missions continued with the objective of increasing the capabilities and reducing the cost of space
missions. It was acknowledged that the use of these propulsion devices would thrive with the commercialization of
an increasing number of satellites10
due to the increased financial incentives in the commercial marketplace.
In 1993, 24 years ago, Martin Marietta’s communications satellite
Telstar 401 was launched and successfully operated using arcjet thrusters
for GEO orbit north-south station-keeping11
(Figure 1). While not the
first communications satellite to use EP for station-keeping, it marks the
point in time when EP technology changed the commercial satellite
marketplace and drove the broad, world-wide adoption of EP technology.
The use of arcjets for NSSK also demonstrated the crucial link between
the selection of in-space propulsion technology and launcher
requirements: the mass reduction enabled by arcjets resulted in a
significant reduction in launcher costs. The commercial success of the
Telstar 401 mission removed major barriers preventing private and
commercial satellite operators from harnessing EP technology.
Following Telstar 401, there was a rapid increase in the number of
satellite integrators implementing EP-based propulsion systems on their satellite platforms. To compete with the
strong advantages of arcjet technology, the additional primes adopted other forms of electric propulsion, such as
gridded ion and Hall-effect thrusters. Over time, EP technology has made great technological and commercial
progress. The main driver for the impressive advancement is the slow and steady commercialization of the space
industry led by a constant demand for an increasing number of communication satellites. In parallel, EP technology
demonstrated the capability to perform a variety of functions and is increasingly used in almost all space
applications, from tiny CubeSats, through Earth observation satellites in LEO, to remote interplanetary missions12
.
In this paper, we review the expansion process of EP in the last 24 years. To do so, we focus on four particular
spacecraft niches: (1) communication satellites in GEO, (2) satellites in LEO, (3) interplanetary or deep space
missions, and (4) small satellite platforms under 100 kg. For each niche, we present statistics showing the
chronological increase in the number of satellites carrying EP devices. Additionally, using a geo-political map of
I
Figure 1. Illustration of Telstar 401 -
the first commercial satellite to use
electric propulsion.
The 35th International Electric Propulsion Conference, Georgia Institute of Technology, USA
October 8 – 12, 2017
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international EP device manufacturers we show the steady expansion of EP technology to new countries that only
recently established space heritage for their devices, such as South Korea, China, Israel, and others.
II. GEO Communication Satellites
A. Missions in the Years 1993-2016
Commercial communication satellites in GEO saw the fastest growth in the past 24 years in terms of revenue and
number of satellites carrying EP systems. The increasing demand for telecommunication services, whether
commercial or military, serves as an incentive for the maturation of space-proven 1-5 kW electric thrusters.
Traditionally, EP is used to perform station-keeping maneuvers in order to maintain the spacecraft in its designated
slot in the GEO belt. Most GEO satellites carrying EP systems incorporated electric thrusters solely for north-south-
east-west station-keeping maneuvers. The propulsion systems consumed between 1.5kW and 4.5kW of electrical
power, depending on the type of electric thruster.
Despite years of successful use of EP for station-keeping, satellite primes and operators hesitated to use EP for
significant fractions of orbit raising because of the perceived elevated risk and financial penalties caused by the long
trip times to GEO. In addition to this, the benefits of EP were not always fully realized even for the NSSK
maneuvers since some satellite operators still required a three-year chemical propulsion contingency once on orbit.
Two missions played a key role in reducing the perceived risk of EP for orbit raising. In 2001 Artemis13
used RIT-
10 ion thrusters for a major fraction of the GTO to GEO transfer to compensate for a malfunction in the launch
vehicle’s chemical upper stage. The ion engines were fired over 18 months to reach GEO. The second key mission,
Smart-1, was launched in 2003 as a secondary payload to GTO, along with two commercial communication
satellites; and over the course of 13 months reached the Moon using a single 1.5 kW Hall thruster. The thruster
operated at maximum power of 1.2 kW due to power constraints of the small spacecraft. In fact, SMART-1 was the
first spacecraft to complete a full transfer from GTO to GEO – and beyond – using nothing but electric propulsion14
.
The combination of these missions, the successful experience with station-keeping, and the development of higher
power Hall thrusters led the US Air Force and Lockheed Martin to design the AEHF GEO spacecraft for EP orbit
raising, with an on-board bipropellant system designed to initially boost the spacecraft perigee over the van Allen
belts and 4.5 kW Hall thrusters operated two at a time provided the majority of the orbit raising from GTO to GEO,
an approach described conceptually in Ref.15. This orbit raising plan was complicated when AEHF Space Vehicle 1
(SV1) launched in 201016
and the on-board bipropellant system failed, forcing the use of the Hall thrusters for even
more of the orbit raising than planned17
. Over the course of a year the Hall thrusters were successfully used to reach
1st 5kW Hall thruster
(AEHF-1)
1st all-electric satellites
(ABS-3A, Eutelsat-115W-B)
1st planned GTO-GEO transfer
(AEHF-2)
1st GTO-GEO transfer
(ARTEMIS)1
st commercial Hall thruster
(Gals-1)
1st commercial ion thruster
(PAS-5)
1st commercial EP
(Telstar 401)
Figure 2. Number of EP-based GEO satellites launched in the years 1993-2016 (3-year running average),
divided into electric thruster subclasses.
The 35th International Electric Propulsion Conference, Georgia Institute of Technology, USA
October 8 – 12, 2017
4
GEO without compromising mission life. This was
followed by the launch of AEHF SV2 in 201218
and SV3
in 201319
, both which performed nominally with the Hall
thrusters boosting to GEO over 3 months following the
initial perigee raising using the bipropellant system.
Then in 2014 SPT-100 Hall thrusters were used aboard
the Express-AM5 and Express-AM6 satellites to perform
a planned 2,000 km orbit-raising maneuver to reach their
final orbit which started from a Proton-M launcher
super-synchronous insertion orbit20
. These EP orbit-
raising efforts culminated in early 2015 when Boeing
delivered the first all-electric satellites carrying XIPS-25
ion thrusters21
. These were the first satellites without on-
board chemical propulsion, and thanks to the great mass
savings of using a high specific impulse propulsion
system, the two satellites could be stacked and launched
together, the first time ever22
. In 2016, another all-
electric pair of satellites was successfully launched and
is operating as planned23
.
Figure 2 presents the number of EP-based GEO
satellites launched in the years 1993-2016. A 3-year
running average was used since the average variance in the order-to-launch time for GEO satellites is approximately
three years24,25
. Electric thruster subclasses are also presented for each year (resistojets are not included for reasons
given in the introduction). The presented values include all GEO satellites that incorporated EP systems, including
technological, and experimental satellites. It is assumed that technological and experimental GEO satellite missions
have the same significance as commercial satellites since they often serve as precursors to future commercial or
military GEO missions.
The figure shows a slight decreasing-increasing trend in the number of EP-based satellites launched between
1993 and 2016, with a relatively constant average of about 8 satellites per year. This number is a bit higher earlier in
the investigated period (the years 1999-2002) thanks to
several families of satellites (AMC, Echostar and NSS)
utilizing Lockheed Martin’s A2100 platform26,27
that were
launched in late 1990s and early 2000s. In addition, the
increase at the end of the investigated period (the years
2012-2016) is most likely due to the gained confidence in
EP technology and the slow entrance of newly developed
propulsion systems into the GEO satellite market, such as
the Chinese ion thruster (LIPS-20028,29
), European Hall
thruster (PPS-135030,31
) or the American 5 kW Hall
thruster (XR-532
).
Three subclasses of electric thrusters were used for
GEO station keeping and later for orbit raising maneuvers
– arcjets, Hall thrusters, and gridded ion thrusters. These
technologies were chosen for their power consumption,
thrust, specific impulse, and lifetime. Of the three, arcjet
technology was the most mature at the beginning of the
investigated period, making arcjet technology the most
prolific at that time (Figure 3). More than 95% of the 56
GEO satellites harnessing arcjet technology used Aerojet
Rocketdyne’s MR-510 aboard Lockheed Martin’s A2100
satellite platform33
. The first operational use of arcjets for
GEO satellites in Japan was also using Aerojet
Rocketdyne’s systems on the DRTS satellites16
.
In parallel with arcjet technology, and by virtue of its
higher specific impulse, ion thruster technology gained
acceptance. Hughes, later acquired by Boeing and most
SPT-10072
16
3
(Fakel)
XR-5(Aerojet)
1
11
KM-5(KeRC)
(1)
HEP-100MF + LHT-100(HIT & BICE) (LIP)
KM-45(KeRC)
2
SPT-70(Fakel)
HIT – Harbin Institute of Technology
BICE – Beijing Institute of Control Engineering
LIP – Lanzhou Institute of Physics
KeRC – Keldysh Research Centre
KM-60(KeRC)
PPS-1350(Snecma)
Figure 4. Number of GEO satellites using Hall
thrusters in the years 1993-2016, by Hall thruster
type and manufacturer (Ekspress-A4 carried both
SPT-100 and KM-5 thrusters. Stentor carried both
SPT-100 and PPS-1350 thrusters).
Figure 3. Relative fraction of each electric thruster
subclass for each six year period and the overall
breakdown for the years 1993-2016.
The 35th International Electric Propulsion Conference, Georgia Institute of Technology, USA
October 8 – 12, 2017
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recently by L-3 Communications, served as the leading ion thruster developer with the development of the XIPS-13
and XIPS-25 thrusters that were used on Boeing’s 601 and 702 satellite platforms34,35
. Of the 57 GEO satellites
incorporating ion thrusters in the investigated period, 31 satellites used the XIPS-25¸ 22 used the XIPS-13 and 4
satellites used thrusters developed and produced by other entities (European or Japanese RF ion thrusters).
Hall thruster technology migrated to the west during the 90’s and in the past 20 years was increasingly used by
Russian, American, and European companies. Hall thruster technology was found attractive because of its high
specific impulse, compared to arcjet technology, and because it produces a high thrust-to-power ratio relative to ion
thrusters, albeit the lower mass savings. The success of utilizing Hall thrusters aboard GEO satellites made the
technology the most used form of electric propulsion by the year 2016. As shown in Figure 4, the various types
Fakel’s SPT-100 Hall thruster36,37
have dominated the Hall thruster market with 72 of 95 satellites incorporating this
1.5 kW thruster. However, in recent years, new American, European, Chinese, and Russian Hall thrusters penetrated
the GEO satellite propulsion market12
, an indication of a trend shift in which a variety of different Hall thrusters will
be available for future missions.
Overall, during the years 1993-2016, a total of 208 GEO satellites incorporating EP systems, excluding high
power resistojets, were launched. The most used subclass to date is Hall thrusters, comprising approximately 46% of
all EP types, followed by ion thrusters (27%), and arcjets (27%).
B. Future Electric Thrusters and Platforms
Recent Hall thrusters such as Aerojet Rocketdyne’s XR-5, Fakel’s SPT-
140D38,39
or Safran’s PPS®-5000
31,40 produce a level of thrust significantly
higher than earlier generations, making it possible to consider full electric
orbit raising with significantly longer transfer durations, even for large
satellites. For instance, Airbus-built Eutelsat 172B (Figure 5), the first
European high power satellite to use EP for all maneuvers, is completing
its orbit raising to GEO within about four months after its June 2017
launch by Ariane 5 into a GEO standard transfer orbit and six more
satellites are currently under manufacturing using the Airbus E3000EOR
all-electric platform.
For the long-term goal of building all-electric GEO satellites, JAXA is
planning the Engineering Test Satellite 9 (ETS-9, scheduled launch 2021)
for testing suitable technologies for an all-electric bus. Two pairs of Hall
effect thrusters of up to 6 kW each are foreseen for orbit raising and NSSK42
. Mitsubishi Electric (MELCO) had
been selected as prime contractor for building the platform with two thrusters being manufactured by IHI Aerospace
with JAXA support and two SPT-140 Hall thrusters from Fakel43-44
.
Another direction in the development of Hall thrusters is increasing the thruster’s specific impulse, which
enables this technology to compete with ion thruster technology, without losing the benefit of its relative simplicity
and moderate voltage. Since the increase in specific impulse is achieved by increasing the discharge voltage, new
technological challenges must be solved to ensure adequate lifetime and stability of operation. The KM-60 thruster
developed at the Keldysh Research Centre (KeRC) is the world's first space-proven Hall thruster with a discharge
voltage of 500 V, and has been operated in orbit since 201445
. The average specific impulse of KM-60 exceeds 1850
s. Following the success of the KM-60 the next development step is the development of the KM-75 thruster with a
nominal discharge voltage of 810 V; resulting in specific impulse of over 2680 sec46
.
At this point, all major GEO platforms offer an electric propulsion option for partial or full electric orbit raising.
Lockheed Martin announced the extension of the use of XR-5 to their modernized A2100 platform47
. The first
commercial satellite to feature the XR-5 is HellasSat-4/SaudiGeoSat-1, which is scheduled for launch in 201848
.
Orbital ATK now offers the XR-5 system on their GEOStar-3 platform49
. The first two spacecraft to fly with this
bus are YahSat-3 to be launched in late 2017 and Hylas-4 to be launched in 201850
.
The PPS®5000 Hall Thruster system from Safran, while currently under qualification
31,40, has also entered
production of flight hardware with deliveries of several flight sets scheduled for late 2017 and early 2018. Its
detailed development status is presented in a separate paper at this conference40
. The operating domain under
qualification for the PPS®5000 ranges from 2.5 kW to 5 kW of discharge power, making it the highest-power Hall
thruster either qualified or currently under qualification. The voltage range for qualification is within 300 – 400 V.
Both voltage and power ranges correspond to current PPU limitations, and the thruster itself has growth potential for
higher power levels.
In China, during the past few years, electric propulsion has been developed with a specific road map51
in which
ion and Hall thrusters are firstly launched on experimental LEO and GEO spacecraft. The main purpose of these
Figure 5. Eutelsat 172B impression
in orbit41
.
The 35th International Electric Propulsion Conference, Georgia Institute of Technology, USA
October 8 – 12, 2017
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technological missions is to lay the groundwork for two future commercial GEO satellite platforms to utilize EP –
the DFH-5 and the all-electric DFH-4SP platforms. Both platforms will utilize the LIPS-300 ion thruster. In July
2017, the LIPS-300 ion thruster was launched aboard the Shijian-18 satellite which was lost due to launch failure52
.
In parallel, the Harbin Institute of Technology (HIT), in cooperation with Beijing Institute of Control
Engineering (BICE), has developed, and in late 2016 flight-tested53
, the magnetically focused Hall thruster (HEP-
100MF54
) which is a promising high-efficiency variation of conventional Hall thrusters. In this novel technology, by
using an unconventional magnetic field topology, the Hall thruster’s plume is focused and plume divergence
reduced; leading to a high thrust efficiency.
III. Low Earth Orbit (LEO) Satellites
LEO satellite platforms weighing over 100 kg, are designed to perform a variety of missions such as Earth
observation, atmosphere monitoring, rapid communication to Earth, or purely scientific missions55
. To do so,
different maneuver capabilities are required from the propulsion system – short periodic orbit maintenance
activations, long high impulse orbit raising operation, low thrust attitude control impulse bits, continuous operation
for drag compensation, or end-of-life disposal. Each mission requires a specific propulsion system tailored to meet
mission maneuverability needs. For this reason, the requirement diversity of LEO satellite propulsion systems is
greater than that of GEO communication satellites. The earliest successful operational use of electric propulsion on a
LEO small satellite was on the TIP/Nova small satellites, which used pulsed plasma thrusters for fine orbit control
starting in 19817,8
. However, developments in other satellite systems and small hydrazine thrusters reduced the
benefits from early electric propulsion systems and delayed further application. More recently, as EP technology has
matured and mission requirements have increased, use of EP systems on LEO small satellites has been revisited.
A key constraint on EP systems of LEO satellites is their power limitation. Unlike GEO comsats, LEO satellite
platforms typically have smaller, lower power payloads, enabling the small, lightweight low power platforms. Since
Table 1. List of all LEO satellites using electric propulsion and weighing over 100 kg that were launched in
the years 1993-2016 (excluding resistojets).
Name Purpose Launch
Mass, kg
Year of
Launch
Thruster
Type Thruster Application Comments
Venμs Technological/scientific 264 2017 HT IHET-300 (Israel)
Drag Compensation
Orbit transfer
Tech demo
Launched in
2017
X-37B OTV-4 Technological/scientific 5400 2015 HT XR-5 (USA) Tech demo
Vernov Technological/scientific 250 2014 PPT APPT-45-2
(Russia) Tech demo
Mission lost
before EPS
operation
Deimos-2 Earth Observation 310 2014 HT HEPS (S. Korea)
Attitude Control
Inclination Change
Debris Avoidance
EgyptSat 2 Earth Observation 1,050 2014 HT SPT-70 (Russia) Orbit Insertion
Orbit Maintenance
DubaiSat-2 Earth Observation 300 2013 HT HEPS (S. Korea)
Attitude Control
Inclination Change
Debris Avoidance
STSAT-3 Technological/scientific 175 2013 HT HEPS (S. Korea) Orbit Maintenance
Shinjian-9A Technological/scientific 790 2012
Ion
Thruster
& HT
LIPS-200 (China)
HT-40 (China)
Orbit raising
Tech demo
Kanopus-V 1 Earth Observation 473 2012 HT SPT-50 (Russia) Orbit Maintenance
Belka-2 Earth Observation 473 2012 HT SPT-50 (Russia) Orbit Maintenance
FalconSat 5 Technological/scientific 180 2010 HT BHT-200 (USA) Orbital Maneuvers
STSAT-2B Technological/scientific 100 2010 PPT (S. Korea) Orbit raising Lost in launch
STSAT-2A Technological/scientific 100 2009 PPT (S. Korea) Orbit raising Lost in launch
GOCE Technological/scientific 1,077 2009 Ion
Thruster T-5 (UK) Drag Compensation
TacSat 2 Technological/scientific 370 2006 HT BHT-200 (USA) Drag Compensation
Tech demo
Monitor-E Earth Observation 750 2005 HT SPT-100 (Russia)
EO-1 Technological/scientific 573 2000 PPT I_tot~1500 kNsec
(USA)
Attitude Control
Tech demo
AO-40 Technological/scientific 397 2000 Arcjet ATOS (Germany) Tech demo
Argos Technological/scientific 2,720 1999 Arcjet 26kW Arcjet
(USA) Tech demo
STEX Technological/scientific 693 1999 HT TAL-D55 (Russia) Tech demo
The 35th International Electric Propulsion Conference, Georgia Institute of Technology, USA
October 8 – 12, 2017
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smaller platforms are capable of generating merely hundreds of watts, due to partial exposure to the sun (in LEO)
and limited size of their solar panels, these platforms may usually accommodate low power electric propulsion
systems of no more than a few hundred watts56
.
Given the above-described propulsion system frame-of-work four types of electric thrusters have been used, not
including resistojets, in last 24 years: (1) PPTs, (2) arcjets, (3) low power Hall thrusters, and (4) low power ion
thrusters. All four types were incorporated onboard a total of 19 LEO satellites weighing over 100 kg. All satellites
are listed in Table 1. It is noteworthy that seven of the 19 satellites were technology demonstration missions, not
operational missions, enabled by the lower cost of LEO satellites.
While the missions in 1999 and 2000 included demonstrations of arcjet, PPT, and Hall thruster systems, Hall
thrusters became more dominant as mission heritage was gained and newer players, such as South-Korea, developed
their versions of electric thrusters57-59
.
It can also be observed in the table that only two
ion thrusters were launched on LEO platforms. The
first is the LIPS-200, a Chinese 1 kW thruster
operated in LEO28
to flight-test it as preparation for
future missions aboard GEO platforms60
. The
second thruster is the QinetiQ T5 Kaufman-type ion
thruster61
, which was chosen for the GOCE LEO
mission, where high specific impulse and low thrust
throttling capability were needed to reduce
propellant mass and allow for accurate continuous
drag compensation62
.
The relatively low number of satellites utilizing
electric thrusters is mainly due to the lack of
commercial incentives for LEO missions, which
have also prevented the industry from developing
and proving the suitable low power technology to
meet LEO satellite maneuverability demands. This
fact left low power thruster development in the
hands of the various governments that invested their
efforts to meet Earth observation needs (Figure 6).
Finally, because the required ∆V of LEO platforms is relatively low, for most LEO missions the advantage of
using electric propulsion is usually not that significant compared to chemical propulsion.
Several factors may change today’s picture and increase the usage of electric propulsion for LEO satellites:
1) Growing commercial incentives – In the past three years, there has been a fast-growing commercial using
LEO telecommunication satellite constellations to enable low-latency internet access to large parts of the
world63
. These satellites, which must be positioned above an altitude of 1,000 km64
, require performing an
energetically-costly orbit raising injection maneuver. The associated ∆V required to perform the maneuver
makes high specific impulse electric thrusters an attractive option for these satellite platforms, which is why
companies such as SpaceX and OneWeb are developing their own EP-based platforms65,66
.
2) Increased use of secondary launch opportunities – For many cases, even though launching as a secondary
payload reduces the cost of launch, the satellite is usually not placed in the desired operational orbit,
requiring the use of a higher performance on-board propulsion system for orbit placement.
3) Longer mission lifetime – As technology progresses, the average LEO satellite lifetime extends, requiring
additional propellant; therefore, making high specific impulse and long-lifetime electric thrusters an
attractive option.
4) Deorbit requirement – To reduce the amount of space debris, many countries require that each LEO satellite
be equipped with some means of propulsion which will enable the spacecraft to maneuver into a disposal
orbit. The deorbit requirement increases the overall required ∆V for the satellite platform, making electric
thrusters more attractive for LEO platforms.
5) New maneuvers – Low thrust high specific impulse capability allows for a variety of maneuvers that could not be performed in the past. Altitude change, plane change and phase change67
(to enable satellite servicing
or satellite re-positioning), drag compensation, and full attitude control (replacing the reaction wheels) to
name a few. The new potential applications open the door for new possible missions, increasing the overall
requirement for LEO satellites in general and electric propulsion in particular.
(2017)
Figure 6. Number of LEO satellites incorporating electric
propulsion systems (by thruster manufacturer nation and
by thruster type).
The 35th International Electric Propulsion Conference, Georgia Institute of Technology, USA
October 8 – 12, 2017
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IV. Planetary and Interplanetary Spacecraft
A. Missions in the Years 1993-2016
Electric propulsion stands out as an attractive choice for planetary and interplanetary missions thanks to its high
specific impulse compared with other types of propulsion. Of the various electric propulsion technologies, ion
thrusters possess the highest specific impulse and are able to deliver the total impulse required for these missions.
Therefore, ion thrusters are the most common form of electric thrusters used for interplanetary missions68,69
. In fact,
five of the seven EP-equipped interplanetary spacecraft utilize ion thrusters as their main means of propulsion.
The electrical power consumed by the electric thrusters depends on the mission needs and varies between several
watts (Electrospray thrusters on Lisa-Pathfinder) to over 2.5 kW (NSTAR thrusters on Dawn), and span a total
impulse range of 2×103 N-s to over 2×10
7 N-s depending on the mission requirements and technology capability.
Figure 7 and Table 2 list all
planetary and interplanetary
missions based on electric
propulsion technologies. It can be
observed that only seven
interplanetary missions included
electric propulsion in the past 24
years. The low figure is mainly due
to the high risk and cost associated
with interplanetary missions that
led to a natural tendency for
spacecraft designers to choose
well-based technologies with extensive in-flight operation history, such as chemical thrusters. However, over time
confidence in electric propulsion technologies grows and an increasing number of interplanetary spacecraft included
electric propulsion systems, as seen in the table.
The U.S., Japan, and the European Union are the present leaders to date with respect to planetary and
interplanetary missions that utilize EP systems for primary propulsion. It is expected that in the future, these nations
will fly an increasing number of EP-based interplanetary missions, continuing their leadership in this area. Many of
the proposed missions, as discussed in section IV-B (Future Missions), involve trips to asteroids, near-Earth objects,
and other bodies in the solar system. Some missions even go further, proposing to return samples from another body
back to Earth. Most of the proposed missions require the imparting of significant ∆V to the spacecraft to reach the
given destination. These missions, much like the past missions listed in Table 2, require high Isp propulsion systems
like those offered by EP to reach the proposed destinations and many of the missions could not be executed using a
lower Isp chemical propulsion system.
In addition to allowing spacecraft to reach a given destination, a high Isp EP system also offers the advantage of a
high degree of spacecraft maneuverability once the spacecraft is ‘on station’ at a destination. This has proven very
useful in the Dawn mission75,76
, for example, where the spacecraft entered orbit around Vesta and propulsively
Table 2. List of planetary and interplanetary missions using EP in the years 1993-2016.
Mission Name Destination Launch Year Prop. Sys. wet
(dry) mass, kg EP Technology Power, kW
Total Impulse, N-
sec
Deep Space 170 Asteroid 1998 129.5 (48) NSTAR
(Ion Thruster) 0.48-1.94
2.73×106
(qualified)
Hayabusa-171,72 Asteroid 2003 125 (59) µ-10
(Ion Thruster) 0.25-0.35
1×106
(space proven)
SMART-173,74 Moon 2003 113 (31) PPS-1350
(HT) 0.65-1.41
1.2×106
(space proven)
Dawn75,76 Protoplanets
Vesta & Ceres 2007 554 (129)
NSTAR
(Ion Thruster) 0.52-2.57
1.23×107
(planned)
>2×107
(space proven)
Hayabusa-272 Asteroid 2014 127 (61) µ-10
(Ion Thruster) 0.31-0.42
1.2×106
(space proven)
PROCYON69 Asteroid 2014 9.5 (7) (with cold gas system)
I-COUPS
(Ion Thruster) 0.038
2×103
(qualified)
Lisa
Pathfinder77 L-1 2015 - (Electrospray) 0.015 -
Dee
p Spac
e 1
1998
Hayabusa-1
Smart-1
2003
Daw
n
2007
Hay
abusa
-2
PRO
CY
ON
2014
Lisa Pathfinder
2015
Figure 7. Planetary and interplanetary missions utilizing electric
propulsion in the years 1993-2016.
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reduced altitude below 200 km (~125 mi) to obtain high-resolution low-altitude images and measurements of the
surface. Once it was finished at Vesta, the Dawn spacecraft still had enough ∆V capability to depart Vesta and
subsequently enter orbit around Ceres, where it again reduced orbital altitude to obtain high-resolution low-altitude
data. Another instance where use of a high Isp EP system afforded a high degree of spacecraft maneuverability was
the Hayabusa-1 sample return mission to the asteroid Itokawa71,72
. Not only was a large ∆V increment required to
reach the target asteroid and later return the spacecraft to Earth, but the maneuverability afforded by the propulsion
system was required to complete the mission. The high Isp system allowed first for the study of the asteroid’s
physical characteristics upon arrival and then enabled a powered landing on the surface and subsequent take-off to
return physical samples of the asteroid to Earth.
B. Future Interplanetary Missions
Given the fact that interplanetary missions require a relatively long development and preparation period, the
general spacecraft architecture of most missions for the next decade are delineated. Future known interplanetary
missions incorporating electric propulsion technologies include:
1) BepiColombo – The ESA Cornerstone mission to the planet Mercury,
BepiColombo78
(Figure 8) will use a high specific (>4000 sec), high
total impulse capability ion propulsion system. The BepiColombo
Solar Electric Propulsion Module will be propelled by a cluster of
high-power (in the 2.5-4.5 kW range) QinetiQ T6 gridded
ion thrusters79
providing a maximum thrust of 143 mN each. The
system will maintain one complete propulsion unit (Thruster, PPUs
and FCU) in cold redundant status. Over 3,000 hours of thruster
characterization tests using both a single and twin thruster
configuration have been performed. Thruster characterization with one
single neutralizer in twin thruster configuration and a test at high
temperature has also been performed. Analysis on the lifetime capability of the thruster (ion optics and
components) will provide suitable data for the improvement of the design and of the thruster reliability. A
lifetime test will also take place. The mission is forecasted to launch in 2018.
2) Solar Power Sail (SPS) – The SPS, now under Phase-A study at JAXA, is a Trojan asteroid sample return
mission80
. The mission is a strong candidate for strategic middle-class scientific mission at ISAS/JAXA.
During its cruising to a Trojan asteroid, SPS will use not only solar sail propulsion but also solar electric
propulsion. The flexible and lightweight feature of SPS was firstly demonstrated as JAXA's IKAROS
mission81
, and by scaling up IKAROS's solar power sail (14m x 14m) up to a larger 50m x 50m sail. High
electric power generation harnessing more than 5 kW is possible at 5.2 AU, and enables operation of a
high-Isp version of the μ-10 ion engine82
even at large distances from the Sun. If selected as ISAS's
strategic middle-class scientific mission, launch of the SPS spacecraft is planned for the early 2020s.
3) DESTINY+ – DESTINY+ is an asteroid flyby mission to the Phaethon asteroid83
. The spacecraft will first
be injected into an Earth's elliptical orbit, and then, the orbit is spiraled upward by employing the μ-10 ion
engine until the spacecraft goes into a Sun revolving orbit. Continuous ion engine operation is also required
in planetary space before conducting the asteroid flyby. DESTINY+ has several mission objectives,
including the demonstration and experimentation of space technologies for interplanetary voyage; the
investigation of the lifetime evolution of primitive celestial body; and the evolution process of meteor
shower dust. This small-class scientific mission, now under Phase-A study at JAXA, is tentatively
scheduled for launch aboard the Epsilon launch vehicle in 202284
.
4) Power and Propulsion Element (PPE) – The development of the proposed PPE was recently announced
as the first part of an evolvable human architecture to Mars that replaces the now cancelled Asteroid
Redirect Robotic Mission (ARRM) as a possible first application of the Advanced Electric Propulsion
System (AEPS)85,86
. AEPS leverages several NASA-developed technologies, including the 12.5 kW Hall
Effect Rocket with Magnetic Shielding (HERMeS)87
. This high-power EP capability, or an extensible
derivative of it, has been identified as a critical part of an affordable, beyond-low-Earth-orbit, human-
exploration architecture. AEPS will also find possible application to commercial missions and several
other robotic missions88
.
5) Psyche – Selected by NASA in January 2017 and slated for launch in 2022 as part of the latest Discovery
mission competition, the Psyche spacecraft89
(Figure 9) would investigate 16 Psyche, a large M-type
asteroid orbiting the Sun at roughly 3 AU. For Psyche, Arizona State University (ASU) and JPL have
partnered with Space Systems Loral, LLC (SSL), a commercial satellite manufacturer with extensive
Figure 8. Illustration of the
BepiColombo spacecraft.
The 35th International Electric Propulsion Conference, Georgia Institute of Technology, USA
October 8 – 12, 2017
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experience developing and flying high power SEP
spacecraft. The Psyche spacecraft conceptual design
leverages SSL's existing product line by multiple SPT-140
Hall Effect thrusters, each of which provides a maximum
thrust of approximately 250 mN. The SPT-140 thruster was
flight qualified by SSL for their commercial GEO
spacecraft product line in 2015, and is currently scheduled
to fly on an SSL spacecraft in 201790
. During early concept
studies, testing was conducted on the SPT-140 to extend its
throttle range and lifetime to match Psyche’s mission
requirements91,92
. In order to address the variation in peak
power voltage (65 to 100 V) over variable distances from
the Sun, the Psyche spacecraft concept design utilizes a power architecture in which discharge converters
from SSL's GEO heritage product line boost solar array voltage to provide 100V regulated power to the
Power Processing Unit. The research was carried out at the Jet Propulsion Laboratory, California Institute
of Technology, under a contract with the National Aeronautics and Space Administration.
6) DART – the Double Asteroid Redirection Test93
will use a 7.5 kW NEXT-C gridded ion thruster developed
by NASA and Aerojet Rocketdyne to deliver a spacecraft, being designed and built by APL, to the binary
near-Earth asteroid (65803) Didymos and demonstrate kinetic asteroid deflection for planetary defense by
crashing into the smaller body of the binary system and observing the change in its weak orbit around the
larger asteroid. The NEXT-C system can accommodate 80-160V input to the power processor and can
provide over 4100 s specific impulse at 235 mN thrust and is a candidate for several New Frontiers
missions. For the low cost DART mission, the NEXT-C thruster will operate at a single set point, with a
specific impulse of 3140s at 137mN thrust. Launch is forecast in early 202194
.
V. Small Spacecraft under 100 kg
Mini-satellites, Microsatellites95
, and CubeSats96
are a rapidly growing niche in the space industry. Since 2010,
the number of small satellites launched expanded by hundreds of percent to over a hundred spacecraft launched in
the year 2016. Moreover, it is estimated that in the next three years, this figure would increase to over 250 spacecraft
per year97
. Of all small satellites under 100 kg launched since the year 1993, only 15 incorporated electric thrusters.
This is due to the fact that most small satellites include a basic and minimal design, usually conducted by academic
institutions or space start-up companies. In many cases the mission design does not require the use of a propulsion
system. Additionally, most of the propulsion devices available to CubeSats are very expensive compared to the cost
of the satellite itself and are not affordable to academic institutions. Moreover, CubeSats launched from the ISS have
very strict requirements that limit the use of propulsion systems98
. Nevertheless, the increasing number of small
satellites, new applications found for these spacecraft, and the requirement to dispose of them at the end of mission
raise the demand for some means of propulsion.
Propulsion systems for small satellites must meet the following requirements:
1) Volume and Mass – Small satellites are volume-limited and subject to a stringent propellant mass
requirement, increasing the incentive for higher high specific impulse propulsion systems for higher V
missions. Depending on the size of the spacecraft, the available volume for the propulsion system ranges
from less than ¼ U99
up to about 1 U100
. Accordingly, the propulsion system’s wet mass can only have mass
up to several hundred grams. Note: A “U” of a satellite is a unit of measurement for CubeSats, which consist
of one or more 10 cm x 10 cm x 10 cm cubes. Thus, a “3 U” satellite consists of 3 cubes with lengths of
approximately 10 cm.
2) Total Impulse – The total impulse requirement is determined by the nature of the mission. Typical values
range widely since small satellite masses and mission requirements vary widely. Typical values range from
2 m/s for satellite de-tumble and attitude adjustments101
to 100 m/s for active attitude control and several
km/s for orbit changes and interplanetary missions. Impulse is generated by propulsion systems with
specific impulse between 30 and 3100 seconds.
3) Low Electromagnetic interference – Due to the compactness of small satellites, all their subsystems are
within close proximity from each other. Any electrostatic or electromagnetic interference caused by the
electric thrusters may harm on-board electronic components, thus hindering the mission.
4) Low power – One of the major limitations of electric thrusters on-board small satellites is the low available
electrical power due to the limited solar panel surface area of the small spacecraft. The typical value of the
Figure 9. Artist’s concept of the Psyche
Spacecraft.
The 35th International Electric Propulsion Conference, Georgia Institute of Technology, USA
October 8 – 12, 2017
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available electrical power
depends on the size of the
spacecraft and ranges between 5
W on a 1 U CubeSat and several
hundred watts on a 50-kg-class
satellite. In a typical 3 U CubeSat,
power is limited to around 10 W
unless the satellite has deployable
solar panels, which will
significantly increase available
surface area for solar cells. This
of course comes at the cost of
increased mass and increased
financial expense.
5) Cost-Effective – Most CubeSat
designers are either academic
institutes or small organizations
aiming at moderate satellite
capabilities. These entities have
small budgets and may be willing
to compromise on reliability as long as it drives down procurement costs. Additionally, the low cost of
CubeSats puts a limit on the total cost of the EP system – it cannot be larger than the cost of the satellite.
For these reasons electric thrusters for CubeSats should have a simple design and be made of low-cost
components; eventually lowering the end price of the propulsion system. Furthermore, many missions
simply do not require a propulsion system, mainly because attitude control can be done through other
means, such as magnetorquers or reaction wheels.
The list of small satellites launched with electric thrusters in the years 1993-2016
is presented in Table 3. The first small satellite to utilize electric propulsion (ION)
was launched in 2006 and used a Vacuum Arc Thruster (VAT). The satellite could
not be tested in orbit due to a failure of the Dnepr rocket which leads to a loss of
mission. Following the first CubeSat to be delivered with an electric thruster, three
other types of very low power thrusters were incorporated – Micro Pulsed Plasma
Thrusters (μPPTs), electrospray thrusters, and micro ion thrusters; Through 2016, 15
missions have been delivered with electric propulsion. The four types of electric
thrusters (VAT, μPPT, electrospray, and micro ion thruster) have been under
development for over a decade alongside other micro-electric propulsion devices102
which are yet to be used in space but may fly in future missions.
Vacuum arc thrusters103
and pulsed plasma thrusters104
are similar technologies
that create a quasi-neutral plasma discharge and do not require a neutralizer. The
former uses the cathode as propellant which is ablated during each discharge. The
ablated material is accelerated by means of magneto-hydrodynamics. In addition to
the VAT that was on the ION mission, George Washington University has developed
the the Micro-Cathode Arc Thruster (CAT), based on the vacuum arc thruster. The
CAT was flown on the BRICSat-P CubeSat, shown in Figure 10, in 2015. Pulsed
Plasma Thrusters rely on a discharge between two electrodes to ablate a non-
conductive propellant. PTFE is the most common propellant used for PPTs, and the only one to have been used for
space to date, although other materials have been proposed, such as PFPE, water or air106-108
. The MarsSpace &
ClydeSpace collaborative PPTCUP for CubeSat application (2 W) has been fully qualified, but awaits a flight
opportunity109
. The Austrian academic 2U CubeSat PEGASUS, launched successfully in June 2017 within the QB50
program, features µPPTs built by FHWN and supported by FOTEC to test delta-V capabilities for low-size
satellites110
.
For both VATs and PPTs, the amount of thrust developed is dependent on the amount of propellant ablated
during the discharge and the repetition rate of the discharge. For highly efficient thrusters, the amount of propellant
should not exceed the thruster’s capability to ionize the gas. This results in impulse bits that are on the order of tens
of microNewton-seconds. Therefore, achieving substantial thrust required for orbit/inclination change or exploration
Table 3. List of all small spacecraft (under 100 kg) using electric
propulsion that were launched in the years 1993-2016.
Name Launch
Mass, kg
Year of
Launch
Thruster
Type Application
AOBA-VELOX 3 2.00 2016 PPT Orbit Maintenance
AeroCube 8D 3.00 2016 Electrospray
AeroCube 8C 3.00 2016 Electrospray
Horyu 4 (AEGIS) 10.00 2016 VAT Attitude Control
Orbit Maintenance
BRICsat-P 1.90 2015 VAT Attitude Control
Orbit Change
AeroCube 8B 3.00 2015 Electrospray Tech demo
AeroCube 8A 3.00 2015 Electrospray Tech demo
PROCYON 67.00 2014 Ion Thruster Deep space travel
Hodoyoshi-4 64.00 2014 Ion Thruster
WREN 0.25 2013 PPT
CUSat 25 2013 PPT Attitude Control
Orbit Maintenance
STRaND-1 3.50 2012 PPT Attitude Control
PROITERES 15.00 2012 PPT
FalconSat 3 50.00 2007 PPT Attitude Control
Illinois Observing
Nanosatellite (ION) 2.00 2006 VAT
Figure 10. Fully assembled
BRICSat-P, showing the
side with VAT heads105
.
The 35th International Electric Propulsion Conference, Georgia Institute of Technology, USA
October 8 – 12, 2017
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missions requires several thrusters or high frequency
repetition rates, both of which are limited by low
power capabilities of small satellites and their ability
to dissipate the heat produced by the propulsion
system. Table 4 summarizes the various types of
missions to which each type of small satellite electric
thrusters is suited.
Electrospray thrusters for small satellites make
use of a strong electric field applied to a conductive
liquid to extract small charged droplets, ions, or
mixtures of both from the propellant reservoir. The
main benefit of electrospray systems relies on their
compactness, which is achieved by: (1) the lack of
pressurization in a relatively simple propellant
management system that uses propellants with zero
vapor pressure (ionic liquids), (2) the fact that no ionization volume
is needed to create charged particles and (3) the suitability of these
devices to be integrated in small packages using micromachining
techniques. The power required and the thrust available are
dependent on the number of emitter tips. As a result, electrospray
propulsion systems are very scalable, and they are suitable for all
types of small spacecraft missions. MIT has developed a number of
laboratory thrusters (Figure 11) and characterized their
performance111
. The current design is based on a 1 cm2 thruster
containing about 500 emitting tips that nominally produce 10-30
µN of thrust with a specific impulse of 700-1000 s. Flight versions
of these thrusters have been included in AeroCube8 satellites for
technology demonstration112-113
. Accion Systems Inc is creating TILE, which is a scalable version based on
clustering of arrays of these thrusters. It is envisioned that Accion’s TILE will be able to provide ~4000 N-s impulse
in a 1 U envelope114
.
Gridded ion thrusters are a technology that has simple scaling laws; therefore, they are relatively simple to
miniaturize. For most small spacecraft, there will be one gridded ion thruster as the main propulsion system. This
limits the scalability associated with electrospray thrusters, thus limiting their use in precision orbit maintenance and
formation flying. They produce a significant amount of thrust (on the order of 0.1 – 10 mN) with respect to a small
spacecraft, and therefore are ideal for exploration missions and orbit/inclination change. One limitation of gridded
ion thrusters is the requirement for beam neutralization, requiring increased power and mass requirements without
increased thrust. In this subclass of EP, the first small satellite that utilized micro ion thrusters was Hodoyoshi-4
equipped with an 8.1 kg miniature ion propulsion system, denoted MIPS115
. The spacecraft was launched in June
2014 and the ion thruster first operated in October 2014 where it showed a couple of successful operations during a
limited visible time in LEO. Another miniature ion thruster with the same design as MIPS was equipped on an
interplanetary micro-spacecraft, PROCYON116-118
, which was launched to an interplanetary orbit in December 2014
along-side Hayabusa-2. The ion thruster experienced 223 hours operation with an average thrust of 346 N119
. There
are several other small ion thrusters that have been developed but not yet delivered for a satellite mission. These
include Busek’s iodine-fueled 3-cm RF BIT-3, Giessen University’s 2.5-cm RF NRIT-4, and Airbus’s RIT-X.
It is interesting to note that about half of the EP-based satellites were launched in the years 2015-2016, hinting
on the growth potential that micro- electric propulsion has thanks to the small satellite market growing trend. It can
therefore be speculated that electric propulsion for the small satellite market will greatly expand in the upcoming
years.
VI. Conclusion
The last 24 years have shown an increased trust in electric propulsion systems from both satellite manufacturers
and operators. There has been a steady increase in the amount of launched satellites with electric propulsion systems
to a total of 248 spacecraft. Since 1993, 208 GEO satellites with EP technologies have been launched, with over
70% of them having either a gridded ion thruster or a Hall thruster on board, replacing the well-established arcjet
due to their higher specific impulse and proven reliability. The amount of EP-based satellites has had a steady
Figure 11. Picture of MIT’s electrospray
thruster, also operated aboard the
AeroCube8 nano-satellites.
Table 4. Electric thruster applicability to satellite mission
type.
Mission type VAT/
PPT Electrospray
Micro Gridded
Ion Thruster
Exploration X X
Orbit\Inclination
Change X X
Attitude Control X X X
Station Keeping X X X
Formation Flying X X
Precision Attitude
Control/Orbit
Maintenance
X X
Spacecraft
Detumble X X X
De-orbit X X X
The 35th International Electric Propulsion Conference, Georgia Institute of Technology, USA
October 8 – 12, 2017
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increase since the first commercial EP satellite was launched in 1993. The trend can be seen in Figure 12. Key
missions such as the European Space Agency’s SMART-1 mission in 2003 and the first conjoined GEO satellite
launch using Boeing’s 702SP fully electric bus in 2015 have shown the ability of EP systems to compete with
chemical propulsion systems when it comes to orbit transfers, despite the increased time it takes to get to the final
orbit. Satellite operators see the advantages of EP in terms of mass reduction on their spacecraft, and thus, lower
launch costs. Additionally, EP systems allow longer operation of the satellites given the same propellant mass.
Electric propulsion enabled missions that were unthinkable with conventional propulsion systems, such as NASA’s
Dawn mission, which has completed two successful orbit insertions around Vesta and Ceres. The Japanese mission
Hayabussa-1 showed the community how even against the greatest odds, the EP system was able to bring the
satellite back to complete the mission of returning samples to Earth.
The development of electric propulsion systems and the trend seen on geostationary satellites is not limited to
these and interplanetary missions. We also see a slow increase in the use of EP in small satellites, with an expected
impressive growth with the appearance of LEO satellite constellations. The increased usage of EP in LEO platforms
is augmented by a steady penetration to the market of new developers from countries other than the US and Russia.
We also see a strong increase in the small satellite sector, where CubeSat missions such as BRICSat-1 from the
US Naval Academy are paving new grounds when it comes to the usage of EP by these small missions. These EP
micro-propulsion devices enable brand new missions and allow universities and small organizations to perform
more and more complex missions. Additionally, having an EP system on board can allow them to continuously
compensate for drag, keeping the satellite in orbit for a longer period of time, making it easier to justify the initial
expense.
Future missions are currently underway and many will be ready to be launched within the next few years.
Missions such as Psyche and BepiColombo will further prove how EP technologies are the key to exploring our
solar system. On the commercial side, companies such as SpaceX with their upcoming Starlink network will
contribute to the trend seen in the previous 24 years, where operators have been slowly, but steadily transitioning to
electric propulsion systems for their satellites. If the trend from the previous 24 years is to continue, we can forecast
a very bright future for electric propulsion companies and we look forward to seeing this development unfold.
Acknowledgments
The authors thank Daniel Narviv (IAI), Mike Tsay (Busek), Paulo Lozano (MIT), Jonathan Paisley (Lockheed
Martin), Leonid Appel (Rafael), Jim Szabo (Busek), Dan Goebel (NASA JPL) and Cosmo Casaregola (Eutelsat) for
their advice, comments and help in shaping this paper.
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79 Stephen D. Clark, Mark S. Hutchins, Ismat Rudwan, Neil C. Wallace and Javier Palencia. "BepiColombo Electric
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104 Kenyon, Shaun, and Christopher Bridges. "STRAND-1: Use of a $500 Smartphone as the Central Avionics of a
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