How to move stars: Stellar engine: Space travel using solar energy

STELLAR  ENGINE

Stellar engines are a class of hypothetical megastructures that use a star's radiation to create usable energy. Some variants use this energy to produce thrust and thus 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.

There are three variant classes of this idea

1.shkadov thruster( Class A) 

    One of the simplest examples of the stellar engine is the Shkadov thruster  Dr. Leonid Shkadov who first proposed it. 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 is 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 × 10²⁶ W and mass 1.99 × 10³⁰ kg, the total thrust produced by reflecting half of the solar output would be 1.28 × 10¹⁸ 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. After one billion years, the speed would be 20 km/s and the displacement 34,000 light-years, a little over a third of the estimated width of the Milky Way galaxy.

2.dyson sphere(class B)

  a Dyson sphere—of whichever variant—built around the star, which uses the difference in temperature between the star and the interstellar medium to extract usable energy from the system, possibly using heat engines or photovoltaic cells. Unlike the Shkadov thruster, such a system is not propulsive.

3.Caplan Thruster(class C)

stellar engine combines the two other classes, employing both the propulsive aspects of the Shkadov thruster and the energy generating aspects of a Class B engine.

A Dyson shell with an inner surface partly covered by a mirror would be one incarnation of such a system (although it suffers from the same stabilization problems as a non-propulsive shell), as would be a Dyson swarm with a large statite mirror (see image above). A Dyson bubble variant is already a Shkadov thruster (provided that the arrangement of statite components is asymmetrical); adding energy extraction capability to the components seems an almost trivial extension

The second type of Dyson sphere is the "Dyson bubble". It would be similar to a Dyson swarm, composed of many independent constructs and likewise could be constructed incrementally.

Unlike the Dyson swarm, the constructs making it up are not in orbit around the star, but would be statites—satellites suspended by use of enormous light sails using radiation pressure to counteract the star's pull of gravity. Such constructs would not be in danger of collision or of eclipsing one another; they would be totally stationary with regard to the star, and independent of one another. Because the ratio of radiation pressure to the force of gravity from a star is constant regardless of the distance (provided the satellite has an unobstructed line-of-sight to the surface of its star^[12]), such satellites could also vary their distance from their central star

Astrophysicist Matthew E. Caplan of Illinois State University has proposed a variant of the Dyson swarm of mirrors that uses concentrated stellar energy to excite certain regions of the outer surface of the star and create beams of solar wind for collection by a multi-Bussard ramjet assembly, producing directed plasma to stabilize its orbit and jets of oxygen-14 to push the star. Using rudimentary calculations that assume maximum efficiency, Caplan estimates the Bussard engine would use 10¹⁵ grams per second of solar material to produce a maximum acceleration of 10^-9 m/s², yielding a velocity of 200 km/s after 5 million years, and a distance of 10 parsecs over 1 million years. While theoretically the Bussard engine would work for 100 million years given the mass loss rate of the Sun, Caplan deems 10 million years to be sufficient for a stellar collision avoidance