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Sailing through space in the solar wind? LightSail 2 will try

Navigating the cosmos is becoming a reality.

For centuries, it has been a dream: to travel through space driven solely by the solar wind. It was first imagined in 1600 by Johannes Kepler, the German astronomer. Centuries later, Arthur C. Clarke moved him to the realm of science fiction in "Sunjammer," a short story from 1964. Carl Sagan, the cosmologist and co-founder of the Planetary Society, thought it could be more than a speculative fantasy, and It began in the 1970s to promote the construction of solar sails for space exploration.

On Tuesday, solar navigation could take its next big step to become a proven technique for navigating the gaps between worlds.

Last month, the spacecraft of the Planetary Society, LightSail 2, traveled to space aboard a SpaceX Falcon Heavy rocket. After 10 years of planning and more than 40,000 private donations worth $ 7 million, the cube has reached a high enough orbit around the Earth and some technical problems have been solved by engineers on Earth. With the press of a button on the ground in California on Tuesday morning, mission controllers expect spacecraft sails to unfold, opening the curtain at the next act of spaceflight.

A limitation of space travel is that energy sources eventually run out.

But the sun is a constant source of energy. It is always releasing photons into space. While these particles have no mass, they have momentum. Solar navigation is based on the always gentle thrust of photons to push a candle forward, moving what is behind the candle in another direction.

Navigation could be one of the most efficient options in fuel consumption for space travel. While the force exerted on a solar sail is approximately the same as can be felt by the weight of a piece of paper in the palm of your hand, the momentum is able to accumulate, increasing the speed of the candle over time.

For example, NASA's Voyager twin spacecraft, which was flying with pure momentum because they ran out of fuel, needed more than 40 years from launch to reach the limits of our solar system. But if they had solar candles, the duration of their trips could have been reduced by almost half.

LightSail 2 aims to become the first adjustable solar sail launched in orbit around the Earth. It is a cube the size of a bar that carries a solar candle the size of a boxing ring. Made of a fine mylar material, these candles are designed to bloom as a space lotus and collect energy from the sun.

The cubesat has an impulse wheel, which allows the engineering team of the Planetary Society on Earth to guide its mylar sails. That will keep the spacecraft at a 90 degree angle to the sun at all times, not like the way a sailboat needs to turn towards the wind to move.

As LightSail orbits the Earth, ground engineers will attempt to extend the farthest point of its orbit, called apogee. To do this, the sail must get enough sun thrust and also rely on the direction from the ground.

"If everything goes perfectly, we should be able to raise the apogee by approximately 1,640 feet per day," says Dave Spencer, professor of aeronautics at Purdue University in West Lafayette, Indiana, and LightSail mission manager.

Tuesday at 11:40 a.m. in California, 2:40 p.m. Eastern Time, California engineers will send an order to orbit, and in about two minutes, LightSail 2 will deploy its sails.

During deployment, two wide-angle cameras in the cube will capture 32 images. "It will effectively give us a kind of movie of the candle display," said Dr. Spencer.

The main mission is to last about a month, and after that LightSail could orbit the Earth for a year. Sometimes it will be visible from Earth to the naked eye, and the Planetary Society will provide updates on where it can be seen.

Eventually, Earth's gravitational attraction will drag the cubes into the atmosphere, where it will burn.

LightSail 2 follows LightSail 1, released in 2015 as a test. While fulfilling some of its objectives, the test was hindered by a series of engineering problems.

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