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.
(Photo : Wikimedia Commons/ Andrzej Mirecki)
What is Solar Sail?
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.
The concept of solar sail is not new, as it goes back to the 1600s when German astronomer and mathematician Johannes Kepler suggested the idea to Galileo Galilei. It was only during the 21st century when the Planetary Society created the Cosmos 1 solar sail spacecraft. It was launched in June 2005 but it ended in failure that prevented it from reaching orbit. On May 20, 2010, the Japanese Aerospace Exploration Agency launched the first successful solar sail called Ikaros.
Since 1905, it has been known that light is made up of tiny particles called photons. Although they do not have any mass, they do have momentum while traveling through space. Photons act like a tennis ball that hits a racket and transfers some of its momentum as it bounces off the strings. In a similar way, photons that hit a solar sail will transfer some of their momentum to the sail, giving it a small push. As more photons hitting the sail slowly build up, the spacecraft slowly accelerates.
While traditional rocket engines have limited lifespan based on fuel availability, solar sail is limited only by degradation in sail material. It has a life expectancy of around 10 years, although additional coatings can still be included to extend its lifespan.
READ ALSO: Interstellar Object Oumuamua Could Be Reached by Satellite with Solar Sail
Exploring Mercury With Solar Sail
In a proposed new mission called Mercury Scout, experts aim to take advantage of solar sails to explore Mercury. The mission will take advantage of this technology as its main propulsion once it has reached Earth orbit.
The main objectives for Mercury Scout are to map out the mineral distribution on Mercury's surface, to image down the surface to one meter resolution, and to illuminate shadowed craters for water deposit identification. Experts chose solar sail because it offers significant benefits that lower overall cost and reduce transit time to Mercury.
To propel the module, the sail will be 2500 square meters and 2.5 microns thick. It is made of aluminized CP1, similar to the one used in the heat shield of the James Webb Space Telescope. It has four separate quadrants which unfurl along carbon fiber support. Mercury Scout is expected to reach Mercury in 3.8 years, targeting a polar orbit on arrival and then spend 176 days mapping the planet's surface.
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