in 1911 predicted that electricity may some day propel vehicles. Traditional
rocketry has dominated
aerospace propulsion in the 20th and early 21st centuries. Conventional rockets achieve motion by expelling mass, most commonly the
combustion output from
chemical propellants to generate thrust via
Newton's third law, which is the familiar
rocket launch with
explosive flame and smoke beneath it. Electric propulsion developed as a parallel track for spacecraft propulsion, focusing on electrical and electrostatic methods of accelerating propellant rather than relying solely on chemical combustion.
1900s to the 1950s (center), with (l-r)
Ernst Stuhlinger,
Holger Toftoy,
Wernher von Braun, and
Robert Lusser at
Marshall Space Flight Center. Oberth is credited with defining electric propulsion concepts as a "serious and worthy pursuit in astronautics". Early antecedents of electric propulsion emerged by the early 20th century.
Konstantin Tsiolkovsky writing in 1911 included an early published statement of the basic electric-propulsion idea: using electricity to increase the velocity of ejected particles. Tsiolkovsky wrote: Early work on electrostatic acceleration dates to
Robert H. Goddard, whose 1917 patent application (granted 1920)
Edgar Choueiri has described in
Journal of Propulsion and Power as the first documented electrostatic ion accelerator intended for propulsion. In his 1918-1919 manuscript
"To whomsoever will read in order to build",
Yuri Kondratyuk discussed electric propulsion in the context of
cathode rays and described thrust from electrically discharging and repelling material particles, alongside a schematic that Choueiri noted may be the "first conceptualization of a
colloid thruster".
Hermann Oberth's 1929 book
Wege zur Raumschiffahrt defined, in
Edgar Choueiri's assessment, 'for the first time publicly and unambiguously' that related propulsion concepts were 'a serious and worthy pursuit in astronautics'. During the interwar period, early electric-propulsion work began moving from theory toward experiment.
Valentin Glushko joined the
Gas Dynamics Laboratory in
Leningrad in 1929, and by 1933 with staff developed an early electric thruster prototype, an
electrothermal approach intended for spacecraft propulsion. The device was likely the first electric thruster to ever be studied on a thruster stand, and was the first electrothermal thruster ever built. According to Choueiri, early thinking and experimentation in related propulsion research focused mainly on electrostatic concepts, but the first laboratory electric thruster was electrothermal and the first electric thruster to fly in space was a mostly electromagnetic pulsed plasma device. After the 1930s, related electric-propulsion research reached a lull in public published activity for over a decade through and after
World War II. The postwar period saw growing institutional interest in electric propulsion within both military and civilian research programs. The first clear postwar reappearance of these propulsion concepts in open scientific literature was in December 1945, in the
Journal of the American Rocket Society, where the term "
ion rocket" was first coined by Herbert Radd. In 1947 at
Fort Bliss,
Wernher von Braun encouraged
Ernst Stuhlinger to investigate his spacecraft propulsion ideas, telling Stuhlinger, "I wouldn't be a bit surprised if one day we flew to Mars electrically!"
1960s-1970s During the 1960s through the 1970s, electric and electromagnetic propulsion matured experimentally, with some systems flying in limited operational roles. Electric propulsion research during this period expanded across multiple countries and institutional settings. was the first
ion engine NASA spacecraft, launched on July 20, 1964. In
West Germany, electric-propulsion development also proceeded from 1960 at
German Aerospace Center (DLR) institutes in
Stuttgart and
Braunschweig and at the
University of Giessen. At Gießen, Horst Löb's group began development of radio-frequency ion thrusters of the RIT type, which use
radio frequency fields rather than physical
electrodes to ionize propellant, starting with the conception, laboratory model, and first tests of the RIT-10; the prototype was further improved through the 1960s and transferred to industry for qualification in 1970. A June 1960 decree of the
Central Committee and
Council of Ministers (No. 715-296), declassified after the Soviet period, directed the development of "space electric rocket engines". This included ion and electroplasma thrusters with target specific impulse of 5,000-10,000 seconds, a measure of propellant efficiency, assigning work to
OKB-1,
the Kurchatov Institute, and other named bureaus as part of a broader 1960-1967
Soviet Union space development plan. In 1964, Ernst Stuhlinger published
Ion Propulsion for Space Flight, characterized by Choueiri as the first comprehensive book on electric rocket technology, marking the field's transition into a serious engineering discipline. On 20 July 1964, two electrostatic ion engines were tested in space in the
Space Electric Rocket Test (SERT I), and the
mercury electron-bombardment engine produced thrust in flight. SERT I was the first spacecraft to incorporate electric propulsion; its mercury electron bombardment
ion engine, which ionizes mercury vapor by bombarding it with electrons and then accelerates the resulting ions electrically, ran for 31 minutes, becoming the first electric engine to operate in space. A 1966 NASA
Lewis Research Center overview stated that electric-propulsion spacecraft then under study could not be expected to take off from Earth and therefore would need to be launched to Earth orbit by chemical rockets before beginning low-thrust operation. The 30 November 1964
Zond 2 mission to
Mars from the Soviet Union marked the first planetary use of electric propulsion. Following the Zond 2 demonstration, pulsed plasma thruster development was transferred from the Kurchatov Institute to
OKB Fakel, whose "Globus" pulsed propulsion unit flew in 1968. The follow-on
Space Electric Rocket Test II (SERT II), launched on 3 February 1970, was the first long-duration operation of ion thrusters in space; its two mercury electron-bombardment engines accumulated over 5 months and 3.5 months of continuous operation respectively, and after intermittent restarts, one thruster logged over 11 years of total operation through 1981. Alongside ion engine development, a distinct line of electromagnetic thruster research was advancing in the Soviet Union. In the 1960s, A. I. Morozov proposed the
stationary plasma thruster (SPT), a Hall-effect device that accelerates ionized propellant using perpendicular electric and magnetic fields. Within decades, hundreds would fly in space. The first SPT was tested in orbit aboard a
Meteor spacecraft in 1972, with corrective propulsion units operating on further Meteor missions through 1980.
1980s Commercial electrothermal propulsion entered operational satellite service during this period. Hydrazine
resistojets, electric thrusters that heat propellant before expelling it, began commercial
geostationary north-south
orbital station-keeping, used to maintain orbital position, with
Intelsat V in 1980.
1990s firing its
ion thrusters in space. The end of the
Cold War opened access to previously restricted Soviet electric propulsion technology. U.S. electric propulsion specialists traveled to Russia in 1991 to evaluate the Russian SPT-100 at the
Scientific-Research Institute of Thermal Processes in Moscow and at Fakel in
Kaliningrad using U.S. instrumentation. Brophy's subsequent JPL report said the measured performance appeared close to the advertised values, and noted claims that more than fifty lower-power SPT units had already flown on Russian spacecraft. The report laid out a second program phase in which thrusters would be brought to the United States for testing toward possible Western use. That work fed into the later
Ballistic Missile Defense Organization Russian Hall Electric Thruster Technology (RHETT) effort to move Hall thruster technology toward Western operational use. Electric-propulsion work matured across the decade.
Hydrazine-based
arcjet rockets were deployed in 1993 on
Telstar 401, extending electrothermal electric propulsion into higher-performance commercial geostationary use. Alongside these experimental programs, electric propulsion was also entering routine commercial service. Commercial electric propulsion also entered Western geostationary satellite operations in the 1990s, as
Hughes Boeing 601HP communications satellites began using gridded xenon ion thrusters (XIPS) for station-keeping in 1997. After initial Russian usage from the 1970s, beginning in the 1990s qualified SPT units entered service on American and European spacecraft as well. European electric propulsion programs reached similar milestones in the years that followed. The Gießen RIT line later reached flight application on the
European Space Agency's
Artemis satellite, launched in 2001, which carried two German RIT-10 thrusters for station-keeping. By the late 1990s, ESA was already positioning solar electric primary propulsion as a key technology for future deep-space missions through
SMART-1, whose
PPS-1350-G Hall thruster was later developed in the
CNES Stentor satellite program and adapted from a geostationary station-keeping design. By the late 1990s, electric propulsion had moved from experimental and military programs into routine commercial satellite operations, particularly for geostationary station-keeping, orbit raising, and related orbit-control maneuvers.
Deep Space 1 became the first U.S. space mission to use an ion thruster as its primary means of propulsion through 1998, validating NASA's
NSTAR solar electric propulsion system in long-duration flight.
21st century mission. SMART-1, launched in 2003, demonstrated solar electric primary propulsion in flight for ESA and carried the Hall thruster system that had been developed from late-1990s European work on commercial electric-propulsion applications and deep-space mission preparation. While electric-propulsion research and deployment continued, new systems were also launched into space.
Hayabusa was launched by the
Japan Aerospace Exploration Agency in 2003, propelled by
electrodeless plasma thruster technology. By 2012, more than 270 Hall-effect SPT units had operated on over 60 Russian spacecraft. NASA's
Dawn became the first spacecraft to orbit an object in the main
asteroid belt at
Vesta in 2011, and the first to orbit a
dwarf planet at
Ceres in 2015. Its
ion propulsion system made Dawn the only spacecraft ever to orbit two extraterrestrial destinations. ESA's
GOCE in 2009 and JAXA's
Super Low Altitude Test Satellite "TSUBAME" (2017-2019) marked later electric-propulsion milestones by demonstrating continuous drag compensation and ion-engine-supported super-low-altitude operations in
very low Earth orbit. ESA and JAXA's
BepiColombo, launched in 2018, marked a later major milestone in solar electric propulsion when its Solar Electric Propulsion System began in-flight commissioning in November 2018, in what ESA described as the first in-flight operation of the most powerful and highest-performance electric propulsion system flown on any space mission to date. In November 2023,
Psyche became the first spacecraft to use Hall effect thrusters in interplanetary space, beyond the Earth-Moon system. The spacecraft uses its electric thrusters for both primary propulsion and momentum control and carries no chemical propulsion system. It is scheduled to enter orbit around the asteroid
(16) Psyche in 2029. ==Definitions==