Interstellar travel IV: Solar, magnetic, & directed-energy sails

Our series on interstellar travel continues with an exploration of more practical proposals that utilize radiation pressure and electromagnetism to create interstellar spacecraft. Solar sails, magnetic sails, and directed-energy sails are among the concepts being considered. Solar sails, which have been around since the early 20th century, offer a cost-effective way to explore the solar system without the need for fuel.

They rely on radiation pressure from the sun or lasers to achieve high speeds, and their theoretical foundation was laid by James Clerk Maxwell's research into electromagnetic phenomena. Russian physicist Pyotr Lebedev conducted the first experiment using a torsional balance in 1899, while Konstantin Tsiolkovsky first proposed using sunlight to propel a spacecraft in 1921.

In the following decades, various scientists and researchers, including Friedrich Zander, J.B.S. Haldane, Carl Sagan, Dana G. Andrews, and Robert Zubrin, proposed different designs and methods for solar sails. Magnetic sails, also known as magsails, were first proposed in 1988 by Dana G. Andrews and Robert Zubrin. These sails would require a superconducting loop with a 50–100 km radius and a mass of about 100 metric tons.

They would launch using either thrust against Earth's ionosphere or magnetosphere or by being accelerated by a fusion rocket to relativistic speed. More recent proposals include the Mini-Magnetospheric Plasma Propulsion (M2P2) design, the Plasma Magnetoshell concept, and an electromagnetic sail that combines magnetic and electric sails.

These concepts all aim to achieve interstellar flight within a human lifetime and in the near future, offering a promising alternative to nuclear fission, fusion, and antimatter propulsion methods.