Deep space travel is not a cheap mission, since it takes a lot of money to get a spacecraft beyond Earth's orbit. In a recent astronomical feat, NASA has developed a solution, called solar sail, which utilizes the radiation pressure from the Sun to power the propulsion system.

Driving a sailing boat relies on wind which is made up of countless gas particles that move in the same direction. Upon hitting the sail, these particles bounce off and start moving in another direction. This mechanism is an application of Newton's third law of motion, where a change of momentum for the wind produces a corresponding change of momentum for the boat, driving it forward.

The same system is used in a solar sail, where ultra-thin polymer "sails" leverage the photons from the Sun to propel a spacecraft. This method of spacecraft propulsion uses the pressure exerted by the Sun on large surfaces. As the sail gets closer to the Sun, its efficiency increases.

Conventional rocket engines require fuel, which itself adds weight and subsequently requires more fuel. Meanwhile, solar sails are far more efficient, as they allow spacecraft to be made much lighter and able to carry larger payloads.

Great for intra-solar system travel with very light payloads. But not much good for anything more ambitious.

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