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[S]pacecraft that use these thrusters all require a neutralizer to ensure that they remain “charge-neutral”. This is necessary since conventional plasma thrusters generate more positively-charged particles than they do negatively-charged ones. As such, neutralizers inject electrons (which carry a negative charge) in order to maintain the balance between positive and negative ions. [T]hese electrons are generated by the spacecraft’s electrical power systems, which means that the neutralizer is an additional drain on power. The addition of this component also means that the propulsion system itself will have to be larger and heavier. To address this, the York/École Polytechnique team proposed...

A novel propulsion concept under study at the University of Washington, Seattle, with NASA funding. M2P2 would use the solar wind to accelerate a spacecraft by pushing on a miniature version of Earth’s magnetosphere generated by the craft. The injection of plasma from the Sun into an artificially generated magnetic field would drag the magnetic field lines out and form a bubble some 30-60 km in diameter, depending on the strength of field that the spacecraft produced. An engine using this technology is estimated to be 10-20 times more efficient than the Space Shuttle Main Engine. With a bottle of...