A solar sail is a spacecraft propulsion method that uses the pressure of sunlight to push a spacecraft through space. It works based on the principle of radiation pressure, which is the force exerted by photons (particles of light) when they strike an object. The force exerted by sunlight on a solar sail is relatively small but can be continuous and cumulative, allowing a spacecraft to gradually accelerate.
The formula that describes the force exerted on a solar sail due to sunlight is:
Where:
- F is the force exerted on the solar sail (in newtons, N)
- is the radiation pressure (in pascals, Pa), which is equal to the momentum flux of sunlight.
- P=2*P0​/c
- P0 is the Solar Constant, or the intensity of sunlight
- c is the Speed of light=299,792,458
- A is the effective area of solar sails exposed to sunlight
The effective area  is the area of the solar sail that interacts with sunlight and can be defined in terms of its physical dimensions.
Solar sails are typically made of lightweight and highly reflective materials, such as metallized polymer films, to maximize the radiation pressure effect. The continuous pressure from sunlight imparts acceleration to the spacecraft, allowing it to reach high speeds and explore deep space without the need for conventional rocket propulsion or fuel. Solar sails have the advantage of being very efficient for long-duration missions in the vacuum of space, as they can continue to accelerate over time.