Even after 30 months in space, The Planetary Society's LightSail 2 mission continues to successfully "sail on sunbeams," demonstrating solar sail technology in Earth orbit. The mission is providing hard data for future missions that hope to employ solar sails to explore the cosmos.
LightSail 2, a small cubesat, launched in June 2019 on a SpaceX Falcon Heavy, as a demonstration mission to test how well a solar sail could change the orbit of a spacecraft. A month after launch, when LightSail 2 unfurled its ultra-thin 32-square-meter Mylar sail, the mission was declared a success because the sail raised the orbit of the small, loaf-of-bread-sized spacecraft.
"We're going to a higher orbital altitude without rocket fuel, just with the push of sunlight," The Planetary Society's (TPS) CEO Bill Nye said at a press conference following the deployment. "This idea that you could fly a spacecraft and could get propulsion in space form nothing but photons, it's surprising, and for me, it's very romantic that you'd be sailing on sunbeams."
[...] Solar sails use the power of photons from the Sun to propel spacecraft. While photons have no mass, they can still transfer a small amount of momentum. So, when photons hit the solar sail, the craft is pushed very slightly away from the Sun. Over time, if a spacecraft is out in space without any atmosphere to encumber it, it could potentially accelerate to incredibly high speeds.
A spacecraft with a solar sail wouldn't need to carry fuel and so could theoretically travel for longer periods of time, as it wouldn't need to refuel.
But LightSail 2 is in orbit around the Earth. As the spacecraft swings its sails into the sunlight, it raises its orbit by as much as a few hundred meters a day. But the small spacecraft doesn't have the means to tilt the sails precisely enough to prevent lowering its orbit on the other side of the planet. Eventually, LightSail 2 will dip far into the Earth's atmosphere to succumb to atmospheric drag. It will deorbit and burn up.
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As early as next Monday night, a SpaceX Falcon Heavy rocket will launch a cluster of 24 satellites for the US Air Force. Known as the Space Test Program-2 mission, the rocket will deposit its payloads into three different orbits. Perhaps the most intriguing satellite will be dropped off at the second stop—a circular orbit 720km above the Earth's surface. This is the Planetary Society's LightSail 2 spacecraft.
After a week in space, allowing the satellites deposited in this orbit to drift apart, LightSail 2 will eject from its carrying case into open space. About the size of a loaf of bread, the 5-kg satellite will eventually unfurl into a solar sail 4 meters long by 5.6 meters tall. The Mylar material composing the sail is just 4.5 microns thick, or about one-tenth as thick as a human hair.
This experiment, which will attempt to harness the momentum of photons and "sail" through space, is the culmination of decades of work by The Planetary Society. "This goes back to the very beginning, to Carl Sagan, Bruce Murray and Lou Friedman," the organization's chief executive, Bill Nye, told Ars in an interview. "We are carrying on a legacy that has been with us since the founders. It's just an intriguing technology because it lowers the cost of going all over the place in the Solar System."
There were two prior attempts by the Planetary Society at deploying light sails. In 2005, the first stage of the rocket launching Cosmos 1 failed. In 2015, LightSail 1 was able to achieve orbit but experienced several technical difficulties from which lessons were learned and used to inform the design of this upcoming attempt with LightSail 2.
More details about the process can be found at the Planetary Society.
The space advocacy organization The Planetary Society recently confirmed that its LightSail 2 spacecraft has sent its first signals home from space.
The roughly 11-lb. (5 kilograms) cubesat is designed to prove that solar sailing is a feasible way of keeping satellites moving. Fuel is a costly and heavy commodity, and if LightSail 2 can prove that the solar-powered technique works well, perhaps future missions into the deep reaches of the solar system and beyond can be propelled by the charged particles released by the sun.
The project launched into space last week (June 25) from the Kennedy Space Center in Florida aboard a SpaceX Falcon Heavy megarocket. On Tuesday (July 2), the bread-loaf-size LightSail 2 experiment left Prox-1, its carrier vehicle. LightSail 2 will ultimately open up its ultrathin four-panel sail to achieve a surface area about the size of a boxing ring.
[...] Once the cubesat deploys its solar sail early next week, the rays from the sun will give LightSail 2 a gentle push. The goal is to observe LightSail 2 over the course of a month to see if it shifts in its orbit by a measurable amount, according to The Planetary Society officials. That will help demonstrate that solar sailing is an effective satellite-propulsion technique.
In other news, 'Oumuamua is not an alien light sail, probably.
See also: What's the Difference between LightSail 1 and LightSail 2?
First Contact! LightSail 2 Phones Home to Mission Control
See the Latest Data from LightSail 2 on Our New Mission Control Dashboard (here)
Previously: Planetary Society's "LightSail" Solar Sail Test Launch on May 20
Lightsail Update: Back in Communication
Planetary Society's LightSail Has Finally Deployed After Multiple Setbacks
One Legacy of Carl Sagan May Take Flight Next Week—a Working Solar Sail
Falcon Heavy to Launch STP-2; 4-Hour Window Opens @ 2019-06-25 2:30am EDT (2019-06-25 0630 UTC)
LightSail 2 has successfully deployed its solar sails. Shortly after 12:00 pm PST The Planetary Society tweeted that the sails were deployed, and that the spacecraft was sailing with sunlight. We can all enjoy their success and start to wonder how solar sails will fit into humanity's plans for space exploration.
[...] This is a dramatic moment for LightSail 2 and for The Planetary Society, the world's largest non-profit space organization. LightSail 2 is the third spacecraft in their LightSail program. It was launched on June 25th, and has been in orbit since then, preparing for sail deployment and sending us some sweet pictures of Earth.
[...] LightSail 2's sail is actually a system of four smaller triangular sails that make one large square when deployed. Once deployed, the sail measures 32 sq. meters, or 340 sq. ft. Once it's deployed, it can be used to raise the spacecraft's orbit, demonstrating the power and usefulness of solar sails.
[...] In some ways, the solar sail is exactly like a sail on a boat. The sail can be aimed at angles, to direct the travel of the spacecraft. If the sails are aimed directly at the Sun, the spacecraft will travel directly away from the Sun. But by tacking, or changing the angle of the sails, a spacecraft using solar sails can steer and propel itself through the Solar System and beyond.
Years of computer simulations. Countless ground tests. They've all led up to now. The Planetary Society's crowdfunded LightSail 2 spacecraft is successfully raising its orbit solely on the power of sunlight.
Since unfurling the spacecraft's silver solar sail last week, mission managers have been optimizing the way the spacecraft orients itself during solar sailing. After a few tweaks, LightSail 2 began raising its orbit around the Earth. In the past 4 days, the spacecraft has raised its orbital high point, or apogee, by about 2 kilometers. The perigee, or low point of its orbit, has dropped by a similar amount, which is consistent with pre-flight expectations for the effects of atmospheric drag on the spacecraft. The mission team has confirmed the apogee increase can only be attributed to solar sailing, meaning LightSail 2 has successfully completed its primary goal of demonstrating flight by light for CubeSats.
"We're thrilled to announce mission success for LightSail 2," said LightSail program manager and Planetary Society chief scientist Bruce Betts. "Our criteria was to demonstrate controlled solar sailing in a CubeSat by changing the spacecraft's orbit using only the light pressure of the Sun, something that's never been done before. I'm enormously proud of this team. It's been a long road and we did it."
[...] After LightSail 2's month-long orbit raising phase, the spacecraft will begin to deorbit, eventually reentering the atmosphere in roughly a year. The aluminized Mylar sail, about the size of a boxing ring, may currently be visible for some observers at dusk and dawn. The Planetary Society's mission control dashboard shows upcoming passes based on user location, and includes a link to a page that highlights passes when the sail is more likely to be visible.
Roughly 50,000 Planetary Society members and private citizens from more than 100 countries, as well as foundations and corporate partners, donated to the LightSail 2 mission, which cost $7 million from 2009 through March 2019.