Sunlight is essentially electromagnetic radiation, mainly composed of visible light and a small amount of infrared light and ultraviolet light. Light has wave-particle duality, and the pressure exerted by light on the irradiated object is called light pressure. The existence of light pressure indicates that electromagnetic waves have momentum. ?

In space far from the atmosphere, there is no medium that affects the light pressure. The light pressure per square meter on the solar sail is 0.48× 10-6 tons. The solar sail area of Cosmos 1 is 530.93 square meters, and the thrust obtained by light pressure is 255 grams. ?

If the diameter of the solar sail is increased to 300 meters, its area is 70686 square meters, and the thrust obtained by light pressure is 0.034 tons. According to theoretical calculation, this thrust can make a spacecraft weighing about 0.5 tons fly to Mars in more than 200 days. If the diameter of the solar sail is increased to 2000 meters, it will get a thrust of 1.5 tons, which can send a spacecraft weighing about 5 tons outside the solar system. Because the light from the sun provides endless energy, a spacecraft equipped with a large number of solar sails can travel at a speed of 240 thousand kilometers per hour. This speed is four to six times faster than that of a rocket-propelled spacecraft. ?

Why can the thrust less than the weight of the spacecraft still push the latter to accelerate? Because the spacecraft running in space is in weightlessness and has no air resistance, the direction and speed of motion will change as long as a little force is added. For example, when launching a geostationary orbit satellite, the satellite first enters the large elliptical geosynchronous transfer orbit. When it runs to a height of 36,000 kilometers above the equator, the remote control commands to start the apogee engine on the satellite, which generates only a few tens of kilograms of thrust, but can move the satellite weighing several tons into the geostationary orbit and reach the predetermined position. The reason is that the increased thrust makes the satellite produce a new speed, which is combined with the original speed to form the final speed. The apogee engine will be turned off after completing the mission, and will be re-ignited and reset only when the satellite deviates from the predetermined position. The solar sail is subjected to light pressure, which can not only change the orbit of the universe 1, but also accelerate its flight. ?