Stellar engine

Stellar engines are a class of hypothetical megastructures which use the resources of a star to generate available work (or, in other words, to generate energy). For instance, they can use the energy of the star to produce mechanical, electrical or chemical work or they can use the impulse of the light emitted by the star to produce thrust, able to control the motion of a star system. The concept has been introduced by Badescu and Cathcart. The variants which produce thrust may accelerate a star and anything orbiting it in a given direction. The creation of such a system would make its builders a type-II civilization on the Kardashev scale. Stellar engines are different megastructures from the Dyson spheres, which are not specifically designed to generate available work. Three classes of stellar engines have been defined. One of the simplest examples of a stellar engine is the Shkadov thruster (named after Dr. Leonid Shkadov, who first proposed it), or a class-A stellar engine. Such an engine is a stellar propulsion system, consisting of an enormous mirror/light sail—actually a massive type of solar statite large enough to classify as a megastructure—which would balance gravitational attraction towards and radiation pressure away from the star. Since the radiation pressure of the star would now be asymmetrical, i.e. more radiation being emitted in one direction as compared to another, the "excess" radiation pressure acts as net thrust, accelerating the star in the direction of the hovering statite. Such thrust and acceleration would be very slight, but such a system could be stable for millennia. Any planetary system attached to the star would be "dragged" along by its parent star. For a star such as the Sun, with luminosity 3.85 W and mass 1.99 kg, the total thrust produced by reflecting half of the solar output would be 1.28 N. After a period of one million years this would yield an imparted speed of 20 m/s, with a displacement from the original position of 0.03 light-years.