This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Welcome back to our series on interstellar travel! In our first installment, we examined attempts to realize nuclear propulsion and how the technology could be used to reach the nearest star.
In our second, we examined how fusion power has also been considered a means of propelling spacecraft to relativistic speeds (a fraction of the speed of light). In both cases, these proposals paralleled Cold War developments in rocketry and nuclear armaments, as they did for most space age advancements. In our third installment, we looked at a truly exotic set of proposals that leveraged the discovery (and creation) of positively charged electrons (positrons) and antiprotons, also known as antimatter propulsion.
In our latest installment, we'll look at more practical proposals that seek to use radiation pressure and electromagnetism to create interstellar spacecraft. This includes solar sails, magnetic sails and laser-driven lightsails. Solar sails have long been considered a cost-effective way of exploring the solar system.
In addition to being relatively easy and cheap to manufacture, solar sails have the added bonus of requiring no fuel. Rather than using rockets that require propellant (which accounts for the largest share of a spacecraft's mass), solar sails, magnetic sails and lightsails rely on reflective or magnetized structures and radiation pressure from the sun (solar wind) or lasers to reach high speeds. Compared to nuclear fission, fusion and antimatter concepts, these concepts offer the prospect of achieving interstellar flight within a human lifetime and in the near future.
Scottish physicist James Clerk Maxwell's research into electromagnetic phenomena (1861–1864) showed that light has momentum and can exert pressure on objects, providing the theoretical foundation for lightsails. Russian physicist Pyotr Lebedev conducted the first experiment using a torsional balance in 1899, which was supported by a similar, independent experiment by Ernest Nichols and Gordon Hull in 1901. This was followed by Konstantin Tsiolkovsky, who first proposed using sunlight to propel a spacecraft in 1921.
He also suggested that interstellar flight could be realized by "using tremendous mirrors of very thin sheets to utilize the pressure of sunlight to attain cosmic velocities." In 1925, Latvian physicist Friedrich Zander published a technical paper that included an analysis of solar sailing, writing "applying small forces [using] light pressure or transmission of light energy to distances by means of very thin mirrors." In 1972, J.B.S. Haldane wrote that "wings of metallic foil of a square kilometer or more in area are spread out to catch the sun's radiation pressure" could propel a tubular spacecraft. Similarly, Carl Sagan popularized the idea of solar sails through his lectures, books and television shows (like Cosmos), describing how a spacecraft launched in the near future could rendezvous with Halley's Comet.
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