The key for interstellar travel might be light

The implication, then, is that we will need something that is not a rocket, that is, something propelled by an external energy source. One idea is a high-power laser driving a light sail of low mass with photon momentum. It sounds like science fiction, and serious estimates of the practical requirements illustrate a series of immense challenges. Even so, it may be possible. According to a recent analysis, radiation pressure generated by very large but realistic arrays of lasers could accelerate a reflective light-sail spacecraft to speeds as high as 0.2c. Such a craft could reach Proxima Centauri in about 20 years (J. Y. Lin et al. Preprint at https://doi.org/10.48550/arXiv.2502.17828; 2025).

This is the idea behind the Breakthrough Foundation’s Starshot Initiative (https://breakthroughinitiatives.org/initiative/3), which aims to lay the groundwork for ultrafast, light-driven nanocrafts reaching the Alpha Centauri system (comprising Proxima Centauri and two other stars) within the next generation. The payload might be a small instrument able to carry out advanced imaging of the exoplanets surrounding the star, determining their habitability far more accurately than Earth-based measurements. The concept is straightforward; the challenges, as Lin and colleagues discuss, arise from a variety of practical needs — a lightweight and highly reflective sail to reach high speeds, efficient radiative cooling to protect against laser heating, and dynamical and structural stability to keep the craft intact and on course.