The Lightsail 2 mission has been declared a success after the spacecraft raised its orbit around Earth, through the push of sunlight on it’s bright silver sail. The highest point of LightSail 2’s orbit (apogee) increased by 1.7 km (1 mile). This may not seem like an enormous distance, but it marked the first time a spacecraft changed its orbit through the power of sunlight alone.
When the Wright Brothers took off at Kitty Hawk, they were not alone in the quest to develop heavier-than-air flight. The big advantage they had was the ability to control their Wright Flyer. The lone pilot would warp the wings in order to maneuver the plane in flight. By raising the orbit of the LightSail 2, the Planetary Society demonstrated that their solar sail craft (funded by private donations) is also the most maneuverable vehicle of its type yet flown.
"For The Planetary Society, this moment has been decades in the making. Carl Sagan talked about solar sailing when I was in his class in 1977. But the idea goes back at least to 1607, when Johannes Kepler noticed that comet tails must be created by energy from the Sun. The LightSail 2 mission is a game-changer for spaceflight and advancing space exploration,” said Bill Nye, CEO of the Planetary Society.
Sailing can Definitely be Romantic
“This idea that you could fly the spacecraft, that you could get propulsion in space from nothing but photons is… it’s really counterintuitive. It’s surprising. And for me, it’s very romantic that you’ll be sailing on sunbeams,” Nye expressed at a teleconference announcing the mission success.
Like sailing the seas of Earth, sailing on light from the Sun holds a quaint appeal. Using some of the oldest technology on Earth (sails), we are able to explore the space between the planets.
For the foreseeable future, spacecraft soaring on solar sails only carry small CubeSat payloads. But, one day, much larger sails could be affixed to craft carrying human crews. Although the sails would need to be enormous to propel such a vehicle, such flights could propel both people and cargo around the Solar System.
“[T]he practical things of not getting hit with an asteroid, not getting slammed with a coronal mass ejection particle beam or a stream from the sun, those are important. But there’s a deep romantic thing.”
- Bill Nye
First envisioned four centuries ago by famed astrophysicist Johannes Kepler, solar sails are now within our grasp. Over the next few decades, solar sails could propel ships ferrying cargo between the Earth and Moon, or Mars and our home planet.
I’m Imagining Space Gondolas
LightSail 2 is just the second solar sail craft to fly successfully in space, following the launch of IKAROS in 2010. The 32-square-meter (345 square foot) sail was deployed on July 23. The four triangular sails sit between four cobalt-alloy booms extending four meters (13 feet) from a central spindle. Orbiting between 710 and 725 kilometers above the Earth, the vehicle maneuvers by using electromagnetic torque rods, which “push” on the magnetic field of the Earth.
Powered solely by sunlight falling on a aluminized Mylar sail, this mission was the first publicly-funded spacecraft to ever demonstrate a new form of propulsion.
“To reach a port we must set sail –
Sail, not tie at anchor
Sail, not drift.”
― Franklin D. Roosevelt
The Planetary Society does not currently have plans to develop future light sail craft, but other organizations could use light sails in a wide range of applications.
“The Planetary Society is built on this idea of providing a bridge between the public and real, meaningful space exploration. And LightSail exemplifies this so beautifully,” said Jennifer Vaughn, chief operating officer of The Planetary Society.
The future of spacecraft powered by light sails will encompass new technologies, shapes, and designs for light sails. Each design, modification, and update will advance light sail technology, and bring space a little closer to home.
“[I]t’s fascinating all the different shapes that people propose for solar sails, all the different ways to fold the sail, to make it deploy reliably… NanoSail-D, a NASA mission, had trouble deploying its sail… [Y]ou think about Icarus, that was deployed by spinning this origami-style packing, it’s really fascinating,” Bill Nye told The Cosmic Companion.
The booms that extend the sails of LightSail 2 stretch over 4 meters (13 feet) long, but using cobalt-alloy for booms much longer than this could present significant problems, including weight.
“[P]eople are looking at composite, cylindrical tubes that flatten and roll up… They’re looking at other solar materials… [W]ays to integrate electrical materials into the sail itself, induced electrical generation for materials in the sail,” Dr. Bruce Betts, chief scientist of the Planetary Society, explained to The Cosmic Companion.
The Bright Future of Light Sails
The IKAROS spacecraft, launched by Japan in 2010, was the first vehicle to ever perform controlled solar sailing. Using tiny CubeSats (just 10 cm or four inches on a side), LightSail 2 was much more maneuverable than the earlier craft. This robotic explorer had a mass less than two percent as great as IKAROS, with a sail 17 percent the size, giving LightSail 2 the ability to turn and alter its orbit and orientation.
Light sails are not propelled by the solar wind (charged particles from the Sun), but solely by the power of photons of light. This technology is a slow means of propulsion, but there may be a way, in the future, to produce significant speeds from the push of photons alone.
“[A] dream that people have talked about for decades is you get a solar sail that could tolerate the high heat and radiation of being near our sun. Then you could go in real close to the sun and get a great big push and send the spacecraft to all sorts of destinations at a much higher speed than we’re able to achieve right now,” Nye explains.
When NASA launches the Space Launch System on its journey to orbit the Moon, the Orion spacecraft will be accompanied by a smaller payload — the solar sail-powered NEA Scout. Once its solar sails are deployed, the vehicle will travel out to an asteroid to explore its surface.
Inexpensive solar sails could bring space travel to the masses, and clubs may hold regattas, racing their craft around the inner solar system.
The distant future could see solar sail spacecraft propelled over vast distances by lasers on Earth or the Moon, adding additional thrust to the vehicles as they race away from the Sun.
“Solar sails are also one of the only known methods that could someday be used to travel to the stars. In 2016, the group Breakthrough Initiatives announced an initiative to send a fleet of laser-powered solar sails to our nearest star, Alpha Centauri,” The Planetary Society reports.
Such a system could send a CubeSat to Alpha Centauri, the nearest star system, in just a few decades.
LightSail 2 will remain in orbit for roughly a year. Sometime around August 2020, the spacecraft will start to lose altitude. At that point, it may become visible to some Earth-bound observers at dawn and dusk. Even now, the spacecraft can be seen by sky watchers living within 42 degrees (north or south) of the equator, using a moderate amateur telescope. Using a radio tracker set to 437.025 MHz, it is even possible to track LightSail 2 as it transmits its call sign, WM9XPA, every 45 seconds.
The success of LightSail 2 also points the way to another future — one where ordinary people fund space missions and exploration directly through small donations. Over 50,000 people from 109 countries around the world donated to make the LightSail 2 mission happen. Through crowdfunding, private organizations, like The Planetary Society, can test new technologies and carry out missions in space.
“Space exploration brings out the best in us. It’s where we solve problems that have never been solved before… [O]ur ancestors who did not try to go over the horizon to see what was beyond, well, they’re not actually our ancestors. We’re descended from the people or organisms that did look over the horizon and find out more about their place in the world,” Nye surmised.
Until humans sail on light, the greatest romance of solar sail technology will be discovering the wonders of science through low-cast access to space for everyone.
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