Researchers at Beihang University have proposed a novel method for deflecting a potentially hazardous asteroid by using a new type of solar sail. This technique involves sending a spacecraft to collide with the asteroid head-on at speeds up to 100 km/s, potentially delivering more energy than previous methods. The study, published on the arXiv preprint server, suggests that this approach could be more efficient than NASA’s DART mission, which used a kinetic impactor to strike an asteroid at about 6 km/s. The key challenge is maneuvering the spacecraft into a retrograde orbit—opposite to the asteroid’s orbital direction—which traditional chemical rockets cannot achieve due to physical limitations. Solar sails offer a potential solution. These spacecraft use the pressure from sunlight, specifically the force of photons, to propel themselves without the need for fuel. The idea of using solar sails for such maneuvers was first proposed in the 1990s by Italian engineer Giancarlo Vulpetti, who suggested an H-reversal trajectory. This involves slowing the spacecraft’s angular momentum and then using the sun’s gravity to pull it into a retrograde orbit. However, traditional solar sails—designed like large mirrors—require extreme tilting to achieve this, which limits their efficiency. To overcome this issue, the researchers explored the use of diffractive solar sails. These sails use microstructured optical gratings to bend light sideways without the need for the sail to rotate. This design allows the sail to maintain its full exposure to sunlight while generating sideways thrust, making attitude control simpler. Simulations showed that diffractive-reflective sails were the most effective for achieving the H-reversal trajectory. This technology could be applied to real-world scenarios, such as the asteroid Apophis, which is expected to come within 38,000 kilometers of Earth in 2029. The researchers simulated the use of this technology on Apophis, a 340-meter-wide asteroid. Both configurations of the diffractive sail were able to deliver a 100 km/s impactor to Apophis in approximately 200–300 days from launch. This significantly reduces the mission time compared to traditional reflective solar sails, highlighting the potential of this new approach for asteroid deflection missions.