A kind of space travel imagined almost a century ago may soon get its moment in the sun. Solar sails could carry a spacecraft beyond our solar system in the next few years.
Solar sails harness light energy to propel an object through space. But the sails don’t work like solar panels on Earth do. They don’t capture energy and convert it for use through a battery system. Instead, the sails catch a particle of solar wind—like sailboat sails do down here below.
The plan is that in 2018, NASA will launch a small space probe into Earth’s orbit. The probe will unfurl a vast, ultrathin, square sail. It will be pushed away from Earth by a solar current.
Light from the sun is made up of moving photons—electrically charged particles flowing outward from the sun. These photons exert a tiny amount of pressure on everything they encounter. In space, free of gravity and atmosphere to slow the craft down, the photons will begin to push against the huge sail. That little push will move the probe away from the sun. The constant pressure of the photons against the sail will build velocity. The probe will gradually accelerate—all without the use of rocket fuel.
Solar sail technology was first explored in the 1990s. As electronics that equip spacecraft have become lighter and smaller, sail technology has also become feasible. In 2010, NASA and Japan both sent up test craft with solar sails. Japan’s model was released outside Earth’s orbit. It made history when it sailed past Venus on the power of photons from the sun.
The planned 2018 NASA probe is called the Near-Earth Asteroid Scout (NEA Scout). It will be sent to explore an asteroid called 1991 VG, which isn’t so near to Earth as you might expect. NEA Scout will begin to float ever so slowly away from Earth and the rocket that takes it up initially. But as the sail continues to catch pressure from the sun’s photons, the craft will accelerate to a speed of more than 63,000 miles per hour! Even then, it will take about 2.5 years to reach the asteroid.
Even though a solar sail uses no rocket propulsion, it can eventually far exceed the speed of rockets in space—as long as it has enough time to build up acceleration, and as long as the sun keeps shining!
