What is the fine-grained topic of the following text: Called Breakthrough Starshot, the project would aim to build a tiny, light-propelled robotic spacecraft that could make the 4-light-year journey to Alpha Centauri — the closest star other than our sun — in just two decades, according to a Breakthrough Initiatives statement. Only return the topic.
The Breakthrough Starshot project aiming to build a robotic spacecraft for a journey to Alpha Centauri.