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‘Sunjammer Project’ will ride largest solar sail towards the Sun

NASA and the UK Space Agency are teaming up to launch a new spacecraft next year, dubbed the 'Sunjammer Project', which will fly towards the Sun using the largest solar sail ever built.

The concept of the solar sail has been around for about 400 years, since Johannes Kepler saw that a comet's tail always points away from the Sun, and various scientists and science fiction writers have discussed or used the concept since. The nickname 'Sunjammer' even comes from the title of a 1964 Arthur C. Clarke short story, where he coined the term 'solar sailing'. More recently, several spacecraft have already tested the concepts of the technology, and the Japanese satellite IKAROS was the first to successfully use a solar sail, on its mission to the planet Venus in 2010.

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Solar sails take advantage of something called 'radiation pressure', which is a force that light exerts on any surface it hits. The tiny photons that light is made up of have no mass, but they have momentum. When they strike an object, they transfer that momentum to the object, and this acts as a push. Any object floating around in space experiences this. It's a small effect, but it's there, and engineers and scientists can design spacecraft to take advantage of it.

In the case of Sunjammer, it will be flying to a point between Earth and the Sun as a test for a mission that will provide us with earlier warnings for solar flare activity and coronal mass ejections, using pressure from the Sun's light to help it maintain a position directly 'in front' of the Earth, while still being closer to the Sun.

The solar sail that Sunjammer will use is huge, over 1,400 square metres in area, but since it's made of ultra-thin material it has a mass of only around 30 kilograms.

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Once this test is completed, NASA and other space agencies are looking to use it for other purposes as well — orbital space junk cleanup, supply ferrying, or maintaining geosynchronous orbits over higher latitudes — any mission where long-term fuel supply is a concern. There's even thoughts of using solar sails for interstellar travel, since if you have a sail big enough, the constant push you get from the Sun's light would continue to add to a spacecraft's speed as it headed towards the outer solar system, and you could reach speeds faster than anything we've reached so far.

(Image courtesy: L'Garde/NASA)

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