Laser‑Powered Solar Sails Face Photon Drag at 75% Light Speed

Scientists studying laser‑driven solar sails have discovered that at about 75% of the speed of light, scattered photons begin to exert a drag force on the sail. The effect, rooted in special relativity, means that the very light used to accelerate the sail can eventually slow it down. The finding suggests a practical upper limit for laser‑pushed interstellar probes and indicates that future missions will need to account for photon drag in their trajectory and power calculations. Engineers may have to redesign sail materials or increase laser output to overcome the drag, or consider alternative propulsion concepts.