Electric sail

Electric sail (also called electric solar wind sail) is a proposed form of spacecraft propulsion using the dynamic pressure of the solar wind as a source of thrust. It is similar to the magnetic sail except that it uses an electric field instead of a magnetic field for deflecting solar wind protons and extracting momentum from them.

Principles of operation and design

The electric sail consists of a number of thin, long and conducting tethers which are kept in a high positive potential by an onboard electron gun. The positively charged tethers repel solar wind protons, thus deflecting their paths and extracting momentum from them. Simultaneously they also attract electron from the solar wind plasma. The arriving electron current is compensated by the electron gun. A way to deploy the tethers is to rotate the spacecraft and have the centrifugal force keep them stretched. Potentiometers between each tether and the spacecraft can be used to fine-tune the tether potentials and thus the solar wind force individually and thus control the attitude of the spacecraft.

Intrinsic limitations

The electric sail probably cannot be used inside planetary magnetospheres because there is no solar wind there, only slower plasma flows and magnetic fields. While modest variation of the thrust direction can be achieved by inclining the sail, the thrust vector always points more or less radially outward from the Sun.

Applications

• Fast mission (>50 km/s or 10 AU/year) out of the Solar system and heliosphere for small or modest payload
• As a brake for small interstellar probe which has been accelerated to high speed by some other means such as laser lightsail
• Inward-spiralling mission to study the Sun at closer distance
• Two-way mission to inner Solar System objects such as asteroids
• Off-Lagrange point solar wind monitoring spacecraft for predicting space weather with longer warning time than 1 hour

See also

• Magnetic sail
• Solar sail
• Spacecraft propulsion

References

• Janhunen, P., Electric sail for spacecraft propulsion, Journal of Propulsion and Power, 20, 4, 763-764, 2004.
• Janhunen, P. and A. Sandroos, Simulation study of solar wind push on a charged wire: basis of solar wind electric sail propulsion, Annales Geophysicae, 25, 755-767, 2007

External links

• Electric Sailing at Kumpula Space Centre/ Finnish Meteorological Institute/Space Research