<COMMENT>The ABI labs</COMMENT>
<P><B><JC>Spacecraft Propulsion
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<P>Propulsion methods can be classified based on their means of accelerating the reaction mass. There are also some special methods for launches, planetary arrivals, and landings.
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<P><B>Electromagnetic acceleration of reaction mass
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<P>Rather than relying on high temperature and fluid dynamics to accelerate the reaction mass to high speeds, there are a variety of methods that use electrostatic or electromagnetic forces to accelerate the reaction mass directly. Usually the reaction mass is a stream of ions. Such an engine requires electric power to run, and high exhaust velocities require large amounts of energy.
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<P><B>Pitch drive and bias drive
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<P>One method of achieving a "diametric drive", or possibly a "disjunction drive", is called the pitch drive. This method involves the employment of a "disjoint field" which eliminates the need for the field to be generated on the spacecraft itself.
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<P>One specific technique for creating such a pitch drive is called the bias drive. The bias drive is created by locally altering the value of the gravitational constant G in front of and behind the craft. To understand how this is possible, it might help to point out here that while the gravitational constant is indeed a fundamental physical constant in our current gold standard theory of gravitation, general relativity, its best known competitor, the Brans-Dicke theory of gravitation, does in a sense allow for a locally varying gravitational constant, so the notion of a locally varying gravitational constant has been seriously discussed in mainstream physics. One problem with the concept of a bias drive is that under certain circumstances it may create a singularity in the field's gradient located inside the vehicle. This issue has yet to be resolved.