At the space shuttle’s orbital speed of roughly 28,000 kilometres per hour, the journey to Alpha Centauri would take about 165,000 years. Breakthrough Starshot proposes sending a gram-scale chip attached to a metre-wide sail—accelerated by Earth-based lasers—to make the same journey in just over 20 years.
At orbital speed, the space shuttle crossed a continent in minutes. It circled Earth about once every 90…
