Stellar Engines Explained: Shkadov Thruster and Kaplan Thruster for Moving the Sun Across the Milky Way

Overview

In this Future Factual video we explore how an advanced civilisation might steer the Sun across the Milky Way using megastructures. The two main concepts are the Shkadov Thruster, a giant mirror that uses solar photons for propulsion, and the Kaplan Thruster, a Dyson sphere powered space station that ejects a fast jet to push the Sun. The discussion covers practicality, potential timescales, and the implications for habitable worlds and interstellar exploration.

• Two stellar engines are explained: Shkadov thruster and Kaplan thruster.
• Engineering constraints include placing mirrors over the Sun’s poles and the mass requirements for fuel and shielding.
• Kaplan thruster offers faster solar system movement and potential galaxy-scale navigation.
• Concepts are framed as aeon-scale engineering suitable for future descendants.

Introduction: A Dynamic Milky Way

The video sets the scene with a Milky Way that is anything but static. Billions of stars orbit the galactic center, and our Sun sits roughly 30 000 light years from the center, completing an orbit about every 230 million years. This cosmic dance is chaotic rather than orderly, creating a hazardous environment in our stellar neighborhood. The piece argues that while vast interstellar distances help shield us, future close encounters with supernovae or massive objects could threaten Earth, potentially giving us thousands to millions of years to respond but offering little chance to avert disaster without moving the solar system itself.

The Concept of Stellar Engines

To reposition the solar system within the galaxy one must move the Sun, since the other objects are bound by gravity to it. The video outlines two theoretical engines grounded in current physics that could in principle achieve this, noting that for civilizations with Dyson sphere level technology such a project would be feasible, though extraordinarily difficult.

Shkadov Thruster: A Simple Yet Slow Approach

The Shkadov Thruster uses a colossal reflector positioned near the Sun. By reflecting up to half of the solar radiation, photons impart momentum to the Sun, providing thrust. The mirror must be lightweight and stable, resisting the Sun’s gravity through radiation pressure. A paraboloid shaped reflector is preferred over a full spherical shell to avoid redirecting light back into the Sun. The safe emplacement is over the Sun’s poles which allows vertical motion in the plane of the solar system. At full thrust, this engine could move the solar system by about 100 light years over hundreds of millions of years, offering substantial but slow control over the Sun’s galactic orbit.

Kaplan Thruster: A Faster, More Dramatic Design

To accelerate responses to threats like nearby supernovae, researchers designed a more ambitious engine called the Kaplan Thruster. It resembles a space station platform powered by a Dyson sphere that aggregates solar mass and uses fusion to eject a high velocity jet of material at nearly 1% of the speed of light. This jet pushes the Sun like a tugboat while another jet balances thrust by returning momentum to the Sun, preventing destructive torques. It requires enormous fuel flow, on the order of millions of tons per second, gathered by funneling solar wind and offloading mass from the Sun via fusion reactors. In practical terms, Kaplan could move the Sun by about 50 light years in a million years and redirect the entire solar system’s galactic orbit in around 10 million years. Remarkably this method could extend the Sun’s life by reducing the rate of fuel consumption and enabling long term colonization of nearby stars or even galactic escape, given enough mass and energy management.

Broader Implications

The video contends that stellar engines embody an ultra-long-term view of civilization, one that transcends human time scales. With such megastructures, future descendants could traverse the galaxy and possibly outlive their planetary origins, moving toward new suns and expanding spacefaring civilization far beyond current horizons.

Conclusion

Stellar engines represent a speculative but provocative branch of astrophysical engineering. The narrative invites reflection on humanity’s long-term future, interstellar exploration, and how we might adapt to the cosmic scale of time and space. The video closes on a note of curiosity about what could be achieved when civilizations think in millions of years rather than years or decades.