Nano-Electric Impulse Engine: Specific Impulse Adjustable from 100s to 10,000s

This nanotech electric impulse thruster is scalable for use with energy ranges from watts to megawatts power.

Termed the nanoparticle field extraction thruster – nanoFET – this highly integrated propulsion concept is a high efficiency, variable specific impulse engine type that can be readily scalable for a large range of future space science and exploration missions ("Nanoparticle Electric Propulsion for Space Exploration"; pdf download, 460 KB).
The nanoFET utilizes highly scalable MEMS/NEMS structures to feed, extract and accelerate nanoparticles through micron-sized thrusters. The nanoparticles to be used as propellant can be of various geometries and materials.

....Here is how it works: Conductive nanoparticles would be transported to a small liquid-filled reservoir by a micro-fluidic flow transport system. Particles that come into contact with the bottom conducting plate would become charged and pulled to the liquid surface by the imposed electric field. If the electrostatic force near the surface can cause charged nanoparticles to break through the surface tension, field focusing would quickly accelerate the particles through the surface. Once extracted, the charged nanoparticles would be accelerated by the vacuum electric field and ejected, thus generating thrust.

....Another advantage of this system is that it affords a much broader set of missions with a single engine type – nanoFETs have an unprecedented thrust-to-power ratio for electric propulsion systems; they can adjust specific impulse over a large range from 100s to 10,000s; they show a high efficiency range of over 90% over the entire specific impulse range; they do not have the life-limiting factors common in ion thrusters.

The system is also very flexible with regard to the size and type of particles that can be used. Almost any conductive nanoparticle, such as carbon nanotubes, fullerenes, as well as metal nanospheres and nanowires could be used. Currently, the researchers are experimenting with silver, nickel and copper nanoparticles ranging in size from 5 nm to 70 nm.

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This thruster lacks the thrust needed to launch a craft from Earth to orbit. But once in orbit, its high efficiency would enable a wider range of missions per payload weight.