Electric sail

An electric sail (also called electric solar wind sail or E-sail) is a proposed form of spacecraft propulsion using the dynamic pressure of the solar wind as a source of thrust. It creates a "virtual" sail by using small wires to form an electric field that deflects solar wind protons and extracts their momentum. It was invented by Pekka Janhunen in 2006 at the Finnish Meteorological Institute.

To test the technology, a new European Union-backed electric sail study project was announced by the FMI in December 2010. The EU funding contribution was 1.7 million euros. Its goal was to build laboratory prototypes of the key components, it involved five European countries and ended in November 2013. In the EU evaluation, the project got the highest marks in its category. The technology could enable faster and cheaper access to the Solar System, and in the longer run may enable an economic utilisation of asteroid mining. An attempt was made to test the working principles of the electric sail in low Earth orbit by Estonian nanosatellite ESTCube-1 (2013-2015), but the piezoelectric motor failed to turn the reel. In subsequent ground-based testing, a likely reason for the failure was found in a slipring contact which was likely physically damaged by launch vibration. With the expected launch time of May 2016, the Finnish Aalto-1 nanosatellite will test the electric sail.

An international research team that includes Janhunen received funding through a 2015 NIAC Phase II solicitation for further development at NASA's Marshall Space Flight Center. Their research project is called 'Heliopause Electrostatic Rapid Transit System' (HERTS).

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 deflect solar wind protons, thus extracting momentum from them. Simultaneously they attract electrons from the solar wind plasma, producing an electron current. The electron gun compensates for the arriving electric current.

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