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LightSail 2 Unfurls Sails, Next Step Toward Space Travel on Solar Winds LightSail 2 Unfurls Sails, Next Step Toward Space Travel on Solar Winds
(about 3 hours later)
Sailing across the cosmos is finally becoming a reality. The ability to sail across the cosmos, powered by the energy of the sun, is finally becoming a reality.
For centuries, it has been a dream: traveling through space powered only by the solar wind. It was first imagined in the 1600s by Johannes Kepler, the German astronomer. Centuries later, Arthur C. Clarke moved it into the realm of science fiction in “Sunjammer,” a 1964 short story. Carl Sagan, the cosmologist and co-founder of the Planetary Society, thought it could be more than a speculative fantasy, and began in the 1970s to promote building solar sails for space exploration. Engineers in California pressed a button on Tuesday that unfurled the sails on a satellite that can be steered around Earth, advancing long held hopes for an inexhaustible form of spaceflight and expanding the possibilities for navigating the voids between worlds.
On Tuesday, solar sailing took its next major step to becoming a proven technique for navigating the voids between worlds. For centuries, it was only a dream: traveling through space propelled by the solar wind. It was first imagined in the 1600s by Johannes Kepler, the German astronomer who described the laws of the planets’ orbits. In 1964, Arthur C. Clarke moved it into the realm of science fiction in “Sunjammer,” a short story. Carl Sagan, the cosmologist, believed it could be more than a speculative fantasy, and in the 1970s began promoting the building of solar sails for space exploration.
Last month, the Planetary Society’s spacecraft, LightSail 2, traveled to space aboard a SpaceX Falcon Heavy rocket. After 10 years of planning and over 40,000 private donations worth $7 million, the cubesat has reached a high enough orbit around Earth and some technical issues have been worked out by engineers on Earth. With the press of a button on the ground in California on Tuesday morning, the mission’s controllers unfurled the spacecraft’s sails, opening the curtain on what they hope will be the next act of spaceflight. After 10 years of planning and over 40,000 private donations worth $7 million, that idea took flight on Tuesday, as LightSail 2, a spacecraft built for the Planetary Society, co-founded by Mr. Sagan, began what its creators hope will be a year of sailing around Earth.
One limitation of space travel is that power sources eventually run out. “This is still one of the most feasible pathways to have real interstellar space travel in the future,” said Sasha Sagan, a writer as well as the daughter of the astronomer.
But the sun is a source of constant energy. It is always releasing photons into space. While these particles don’t have mass, they have momentum. Solar sailing relies on the ever so gentle nudge of photons to push a sail forward, moving whatever is behind the sail in another direction. [Sign up to get reminders for space and astronomy events on your calendar.]
If it succeeds in its mission, it will contribute to overcoming one of the greatest limitations on the outer bounds of space travel — that the power that steers spacecraft, usually hydrazine fuel, eventually runs out.
In contrast, the sun is a source of constant energy. It is always releasing photons into space. While these particles don’t have mass, they have momentum. Solar sailing relies on the ever so gentle nudge of photons to push a sail forward, moving whatever is attached to the sail in the desired direction.
Other fuel sources, such as solar power and ion propulsion, can power spacecraft for decades, but solar sailing could eliminate their need for fuel altogether.
“There is a limitless supply of solar pressure,” said Dave Spencer, an aeronautics professor at Purdue University in West Lafayette, Ind. and LightSail’s mission manager.
Sailing could be one of the most fuel efficient options for space travel. While the force exerted on a solar sail is about the same as you might feel from the weight of a piece of paper in the palm of your hand, the momentum is able to build, increasing the speed of the sail over time.Sailing could be one of the most fuel efficient options for space travel. While the force exerted on a solar sail is about the same as you might feel from the weight of a piece of paper in the palm of your hand, the momentum is able to build, increasing the speed of the sail over time.
For example, NASA’s twin Voyager spacecraft, flying on pure momentum since they ran out of fuel, needed more than 40 years from launch to reach the boundary of our solar system. But if they had solar sails, the lengths of their trips could have been nearly cut in half. For example, NASA’s twin Voyager spacecraft, flying on pure momentum since they ran out of fuel, needed more than 40 years from launch to reach the interstellar medium. But if they had been powered by solar sails, their trips could have been completed in just over half that time.
LightSail 2 aims to become the first steerable solar sail ever launched into orbit around Earth. It is a loaf-sized cubesat carrying a boxing-ring-sized solar sail. Made from a thin mylar material, these sails are designed to blossom like a space-lotus and collect the sun’s energy. Japan’s space agency, JAXA, experimented in 2010 with the first solar sail spacecraft, Ikaros. That probe traveled past Venus, but lacked mechanisms for steering. It is orbiting the sun and was last heard from in 2015.
The cubesat has a momentum wheel, which allows the Planetary Society’s engineering team on Earth to guide its mylar sails. That will keep the spacecraft at a 90-degree angle to the sun at all times, not unlike the way a sailboat needs to tack into the wind to move. NASA is also experimenting with the technology. Early in the next decade, it plans to launch Near Earth Asteroid Scout. That small cubesat will use a solar sail to visit and study an asteroid.
As LightSail orbits Earth, engineers on the ground will attempt to extend the farthest point in its orbit, called apogee. To do this, the sail must get enough of a push from the sun, and also rely on steering from the ground. For now, space agencies will be watching the performance of LightSail 2, a cubesat that is about the size of a loaf of bread.
“If everything goes perfectly, we ought to be able to raise the apogee by about 1,640 feet per day,” says Dave Spencer, an aeronautics professor at Purdue University in West Lafayette, Ind., and LightSail’s mission manager. The spacecraft was launched last month by a SpaceX Falcon Heavy rocket, and has since been orbiting Earth while its managers on the ground prepared to unfurl its sails like a space-lotus.
At 11:40 a.m. in California, 2:40 p.m. Eastern time, the mission’s managers sent an order to orbit, and received readings indicating that LightSail 2 had successfully unfurled its sails.At 11:40 a.m. in California, 2:40 p.m. Eastern time, the mission’s managers sent an order to orbit, and received readings indicating that LightSail 2 had successfully unfurled its sails.
During the deployment, two wide-angle cameras on the cubesat were to capture 32 images. “It will effectively give us a kind of movie of the sail deployment,” Dr. Spencer said. Those pictures are to be sent back to Earth in the coming hours. “I’m really excited, things went just perfectly” said Dr. Spencer.
Watch a video stream of the team below. During the deployment, two wide-angle cameras on the cubesat were to capture 32 images. “It will effectively give us a kind of movie of the sail deployment,” Dr. Spencer said.
The primary mission is to last around a month, and after that LightSail could orbit Earth for up to a year. Sometimes it will be visible from Earth with the naked eye, and the Planetary Society will provide updates on where it can be seen. LightSail 2 is the first steerable solar sail ever launched into orbit around Earth. Its solar sail is about the size of a boxing ring, and made from a thin mylar material. It blossomed on Tuesday, and began to collect the sun’s energy.
The cubesat has a momentum wheel, which allows the Planetary Society’s engineering team on Earth to guide its sails. That will keep the spacecraft at a 90-degree angle to the sun at all times, not unlike the way a sailboat needs to tack into the wind to move.
“It’s a much more agile solar sail than has been flown before,” Dr. Spencer said.
As LightSail orbits Earth, engineers on the ground will attempt to extend the farthest point in its orbit, called apogee. To do this, the sail must get enough of a push from the sun, and also rely on steering from the ground.
“If everything goes perfectly, we ought to be able to raise the apogee by about 1,640 feet per day,” said Dr. Spencer in an interview before the deployment.
The primary mission is to last around a month, and after that LightSail 2 could orbit Earth for up to a year. Sometimes it will be visible from Earth with the naked eye, and the Planetary Society will provide updates on where it can be seen.
Eventually, Earth’s gravitational pull will drag the cubesat back toward the atmosphere, where it will burn up.Eventually, Earth’s gravitational pull will drag the cubesat back toward the atmosphere, where it will burn up.
LightSail 2 follows LightSail 1, launched in 2015 as a test. While accomplishing some of its goals, the test was hindered by a number of engineering snags. As the spacecraft’s name implies, LightSail 2 follows LightSail 1, launched in 2015 as a test. While accomplishing some of its goals, the test was hindered by a number of engineering snags.
The very first solar sail spacecraft, Ikaros, was launched in 2010 by the Japan Aerospace Exploration Agency. Although it was not steerable, it traveled past Venus. It entered orbit around the sun and was last heard from in 2015.
Early in the next decade, NASA plans to launch NEA Scout or, Near Earth Asteroid Scout. This small cubesat will use a solar sail to visit a near-Earth asteroid to collect data and send it back to Earth.