PERSPECTIVES
Sailing to the stars with photonics
SAILING TO THE STARS WITH PHOTONICS
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Jadon Y. LIN 1, C. Martijn DE STERKE 1, Boris T. KUHLMEY 1, 2,*
1
School of Physics and Institute of Photonics and Optical Science, The University of Sydney, Sydney, Australia
2
The University of Sydney Nano Institute, The University of Sydney, Sydney, Australia * boris. kuhlmey @ sydney. edu. au
https:// doi. org / 10.1051 / photon / 202513460
Probing nearby star systems would take thousands of years for today’ s spacecrafts due to the immense distances between us and our stellar neighbours. In recent years, lightsails have gained interest as physically realistic interstellar vehicles. Lightsails are envisaged to be thin, highly reflective and lightweight membranes accelerated by high-power lasers up to substantial fractions of the speed of light. This ambitious endeavour entails substantial challenges, the solutions of which are rooted in photonics.
About 4.2 light years away, our nearest stellar neighbour, Proxima Centauri, harbours a planet in an orbit compatible with the existence of liquid water. Could it be home to life? From our own solar system, we can only gather indirect evidence that often raises more questions than it answers. Sending an exploratory probe would only make sense if it could send information back within one or perhaps a few human lifetimes. This would require speeds exceeding 10 % of the speed of light, which simply cannot be attained by standard rocketry or by any spacecraft that carries its own source of energy and reactive mass. To reach relativistic speeds, an external source of momentum is needed.
From the beginning of electrodynamical theory, light was predicted to carry momentum, which could be transferred to matter upon absorption or reflection. The magnitude of this radiation pressure is small for everyday light intensities, and it is only with the advent of lasers and their extreme intensities that the effect could be exploited for applications on small length scales like optical tweezers and in fields of study like cavity optomechanics. On a larger scale, solar sails composed of highly reflective thin films can take advantage of the freely available light from the sun and its associated momentum. While its intensity at realistic distances is modest compared to lasers, the small radiation pressure can accumulate over long times to provide attitude and orbit control within the solar system. Several solar sail demonstrations have been successful, with a growing presence in the space community as a cheaper alternative for interplanetary exploration.
To go further, beyond our own solar system, the sun’ s intensity provides insufficient acceleration. The idea of lightsails, in contrast to solar sails, is that propulsion is provided by lasers with much higher intensities than that of the sun, enabling relativistic speeds. While first proposals became literally the work of science fiction [ 1 ], recent technological progress and“ Moore’ s law” for lasers are bringing lightsails and interstellar exploration within reach.
Every aspect of an interstellar lightsail mission represents an extreme engineering challenge, but all are possible within known laws of physics [ 2 ]. Project designs envisage an extremely low mass sail( 10 m 2 in area but less than 10 grams total), carrying a chip-like payload containing
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