Electric sails prove promising for propellant-less spacecraft propulsion

Electric sails (E-sails) are a proposed method for spacecraft propulsion. Similar to sailboats using wind flow on their sails to gain momentum, E-sails use a flowing plasma, like solar wind or Earth’s ionosphere. Using model E-sails in ground-based experiments, Goulden et al. obtained force measurements on E-sails to inform future applications.

They hung a tether — a fine copper wire about 35 centimeters long — on the ceiling of a vacuum chamber and measured its deflection each time they directed a plasma pulse to flow through the configuration. From this, they determined the force on the makeshift E-sail.

Their results were promising. As the negative voltage on the wire increased, so did the force on their E-sail from its surrounding plasma, greater than the expected drag on the system.

Though E-sails have been placed on small satellites, they have not yet been successfully deployed. However, this does not discourage author Lachlan Goulden.

“The current problems are engineering problems on deployment and general spacecraft engineering, and not with the physics of E-sails,” Goulden said.

In space-based applications, the wires will be much longer than those used here — for example, the NASA Heliopause Electrostatic Rapid Transit System proposed tethers 20 kilometers long — and bundled into sets to prevent breakage when hit with micrometeoroids. The voltages will also be higher, and spacecraft will require lighter wires, like aluminum or conducting polymer, rather than copper.

“This experiment was a very interesting and exciting one to work on, because it combines experimental laboratory plasma physics and theoretical modeling with direct, important spacecraft applications,” said Goulden. “There aren’t many spacecraft propulsion concepts that are propellant-less and, thus, could have significant impact on future spacecraft and space exploration.”

Source: “Measurements of the force produced by a negatively charged electric sail in a pulsed cathodic arc plasma,” by Lachlan Goulden, Joe Khachan, Iver H. Cairns, Jiongyu Liang, Kosta Tsoutas, and Marcela Bilek, Physics of Plasmas (2025). The article can be accessed at https://doi.org/10.1063/5.0274155 .