A ROCKET motor in which THRUST is produced by the ejection of charged atomic particles (IONS) accelerated by an electric field, rather than by the expulsion of hot gases generated by chemical reactions as in a conventional ROCKET. The ion rocket has the great advantage that much higher EXHAUST VELOCITIES can be achieved than with chemical fuels. However, the amount of THRUST generated by such motors is small because the mass of material ejected per unit time is small. Ion rockets are quite incapable (in the present state of technology) of lifting themselves off the ground, but they are ideally suited to the situation where a small amount of THRUST is required for extended periods or, intermittently, for much longer periods (e.g. attitude-control thrusters in satellites or spacecraft). In the longer term, ion rockets operated in space may be used to provide a small continual THRUST over long periods so as to accelerate interplanetary spacecraft to much higher final velocities than may
be attained by chemical rockets at the present time. (See also IONIZATION.)
