The history of electric space propulsion begins a few hundreds of kilometers from Moscow. Constantin Tsiolkovksy (1857-1835), a nearly deaf and self-taught schoolteacher inspired by Jules Verne’s stories of space travel, dreamed about interplanetary spaceflight. He is considered today as one of the three fathers of modern rocketry who laid the theoretical groundwork that became the basis for aerospace engineering. He is also one of the first scientists who ever mentioned electric propulsion in his early publications, in 1911, although he remained highly sceptical about its feasibility. In 1924, he even declared: “the force of electricity is unlimited and can, therefore, produce a powerful flux of ionized helium to serve a spaceship. However, we shall leave these dreams for a while and return to our prosaic explosives.” Electricity was poorly known at the time, and therefore electric propulsion was still considered a dream.

     On the other side of the Pacific, Robert Goddard (1882-1945), one of Tsiolkovksky’s contemporaries, was working on both electricity and propulsion. Although he often is identified as another father of modern rocketry, no historical evidence has showed a direct connection between both visionaries. Being naturally drawn to the topic, Goddard mentioned electric propulsion in his notebook as early as 1906 and came up with the basic principles for the acceleration of electrons, which kept him busy for another decade. In 1917, he patented an important method for producing electrified jets of gas, the first documented electrostratic ion accelerator in history. And yet, as the United States entered World War I, scientists focused their efforts on practical and well mastered chemical propulsion solutions that better fitted military needs at the time.

     A few years later, Hermann Oberth (1894-1989) took the propulsion community by storm. In 1922, his doctoral research proposal on rocket science labelled as “utopian” was turned down by the University of Heidelberg. He was then invited to defend his thesis a year later at the University of Cluj in Romania and published a controversial book called The Rocket Into Planetary Space that he further developed and republished in 1929. This publication, describing all practical considerations associated with the design of an electricity-powered spacecraft, rapidly became an immense source of inspiration for a whole generation of upcoming rocket scientists and science fiction writers that brought spaceflight even closer to reality. But many fields still needed to be better understood for electric propulsion to eventually blossom.

     Waiting for their moment of glory, electric propulsion concepts were left on dusty shelves for a long time as jury was still out on whether it even could become an effective solution for spacecraft. In the context of growing geopolitical tensions, the United States and the Soviet Union took two different technical research trajectories for electric propulsion: the Americans focused on gridded ion thrusters, or ion drives, while Soviets put an early emphasis on Hall effect thrusters. This can be explained by scientific breakthroughs in both countries at the same time.

     In the United States, Ernst Stuhlinger (1913–2008), who was familiar with Oberth’s ideas, gave electric propulsion research a new impulse and became a leading figure in the field, proactively supported by Wernher von Braun (1912-1977) himself. He gathered all available research findings at the time and his efforts helped to turn electric propulsion science into a legitimate area of research, anchoring it into reality once and for all. In doing so, he shaped the American approach to electric propulsion at an early phase and his legacy can still be seen today. This newfound curiosity for electric solutions led to a handful of experiments such as SERT-1, the SNAPSHOT and ATS programmes that were conducted throughout the 1960s although they never led to the launch of an operational electricity-powered satellite. Unresolved technical challenges such as contaminations and low lifetimes eroded the promising future of electric propulsion and nurtured skepticism on their practicality for another 30 years.

     In the Soviet Union, scientists started working on electric propulsion at a very early stage. At the Soviet design bureau OKB-1 under the leadership of no other than Sergei Korolev (1907–1966), the heirs of Tsiolkovsky focused on the development of Hall effect thrusters, catalyzed by the growing mastery of plasma physics. Cutting edge research was conducted from the 1960s onwards as well, from research lab to research lab, leading to the creation of FDB Fakel, now Fakel Industries which is still producing hall thrusters today.

     Not only the United States and the Soviet Union pursued these ambitions: Japan, Germany and France carried out similar research to find the ideal thruster and turn in-orbit mobility into reality.

     

The history of electric propulsion (EP) definitely changed its course after the collapse of the Soviet Union. The licensing of Soviet proven Stationary Plasma Thruster (SPT) technology led to the diffusion of electric propulsion to Europe and the United States, creating subclasses of EP across the world. In 1991, Kaliningrad and Moscow, American propulsion scientists came to test SPT in Kaliningrad, where Fakel sits, and Moscow and their findings confirmed that STP performances were promising for the commercial industry. First considered mostly for stationkeeping, these Soviet thrusters were progressively used for other applications such as orbit raising.

The new millennium also was a turning point for space exploration as many advanced concepts were demonstrated during this period, debunking the myths about electric propulsion.

The Deep Space 1 mission in 1998, was a technology demonstrator designed for interplanetary travel that produced NASA’s first close-up pictures of a comet nucleus. It is one of the key missions that contributed to this shift of perception as electric propulsion proved to be a strong contender for missions requiring a high degree of maneuvarability. This proven technology supported the Dawn mission launched in 2009, the first NASA exploratory mission to use ion propulsion for the study of two protoplanets in the asteroid belt: Vesta and Ceres. The mission was terminated only in 2018 and the spacecraft was left orbiting around Ceres. 

In Europe, the quest for capable thrusters gained momentum with the SMART-1 mission launched in 2003. Four years after Deep Space-1 and six years before the Dawn mission, the European Space Agency launched its first lunar probe, SMART-1, who studied the chemical composition of the soil and tested critical capabilities for navigation and control maneuvers along the way. It reached operational lunar orbit in 2005 before crashing into the Moon a year later at a speed of 2 kilometers per second, creating a huge cloud of dust that could be seen from Earth. The same year, the Japanese Hayabusa spacecraft, also powered by ion engines, landed on the 25143 Itokawa asteroid, and returned samples to Earth in 2010. 

This period of impressive technological innovation was a paradigm shift for the industry. Electric propulsion repeatedly demonstrated its potential for demanding missions, building trust in their reliability and performances. After decades of being considered impractical and unreliable, electric propulsion supported some of the most innovative missions in deep space exploration and marked the birth of the electric age for spacecraft. The commercial availability of some of the most advanced EP thrusters coming from the Soviet Union combined with successful technology demonstrations favourized their adoption on the commercial telecom market. Operators recognized their value for high-precision maneuvers and set at the same time a new standard for years to come. Between 2000 and 2010, the number of electricity powered satellites more than doubled, and the commercialization of EP thrusters started gaining momentum ever since.

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