- Josh Spradling/The Planetary Society
- SpaceX launched its third Falcon Heavy rocket, the world’s most powerful operational launch system, at 2:30 a.m. ET on Tuesday.
- The rocket deployed 24 satellites into orbit around Earth, including an atomic clock for NASA, the ashes of 152 people, and LightSail 2, an experiment that could change how vehicles propel themselves to a destination in space using just light from the sun.
- The Planetary Society, which is spearheading LightSail 2, says it’s the first “solar sailing” spacecraft – powered by sunlight alone.
- Solar-sailing technology could help spacecraft achieve interstellar travel.
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One of the biggest impediments to traveling across the galaxy, or to a nearby star, is that our spacecraft can’t carry enough fuel to cross light-years of ever-expanding space.
But a new technology that headed into orbit aboard SpaceX’s Falcon Heavy rocket on Tuesday – along with 23 other satellites, including an atomic clock for NASA and a craft holding the ashes of 152 people – could help eliminate that obstacle to interstellar travel.
LightSail 2 is set to be the first spacecraft in Earth orbit propelled solely by sunlight. Spearheaded by The Planetary Society, the partially Kickstarter-funded “solar sailing” project took to the skies at 2:30 a.m. ET on Tuesday.
“The launch of the SpaceX Falcon Heavy was spectacular! Our #LightSail2 is up and on its way,” Bill Nye, the ubiquitous American science communicator and CEO of The Planetary Society, tweeted early Tuesday.
“This is history in the making – LightSail 2 will fundamentally advance the technology of spaceflight,” he added in a press release.
A multistep, crowdfunded mission launched with SpaceX’s Falcon Heavy rocket
LightSail 2’s mission to orbit the Earth has multiple steps.
The first was the launch of SpaceX’s Falcon Heavy rocket. Then another spacecraft named Prox-1, which is carrying LightSail 2, separated from the rocket.
In seven days, Prox-1 should birth LightSail 2, an 11-pound cube satellite that’s about the size of a loaf of bread. The floating cube should eventually deploy an antenna, solar panels, and the booms and solar sail itself.
All told, LightSail 2 is set to be in space for a couple of weeks before the solar sails unfurl.
Bruce Betts, the chief scientist and LightSail program manager at The Planetary Society, said in a press conference last week that a challenge in creating LightSail 2 “was to figure out how to cram all that stuff into a little tiny spacecraft.”
- Jason Davis/The Planetary Society
LightSail 2’s four triangular sails, which resemble in form and function the sails of water-skimming ships, are designed to merge to form one 344-square-foot square sail. The sails are made of Mylar, a tear-resistant, highly reflective fabric that’s thinner than a human hair.
The project, which cost $7 million, was funded in part by a 40,000-person Kickstarter campaign in 2015.
Using light to travel the cosmos
Most spacecraft traverse the cosmos using rocket fuel, which is finite. Once the propellant runs out, the rocket can no longer control its speed or direction, and it floats in the vacuum of space.
But a solar-sail craft has an unlimited supply of energy, according to Nye. That’s because it’s continuously pushed through space by the pressure of sunlight.
Sunlight consists of tiny particles called photons, which have no mass but gain momentum as they’re spewed from the sun. Even though each photon’s momentum is minuscule, the collective push is enough to get a solar sail moving.
As light reflects off the sail, it transfers momentum to the sail and pushes it.
“The total force on the sail is approximately equal to the weight of a house fly on your hand on Earth, to give you an idea of how small it is,” Betts said. “But again, the key is that it’s constant. It’s always there.”
Sailing through space
Part of what enables LightSail 2 to harness sunlight effectively is that the solar sail can change its orientation based on where the sun is. Rigid booms hold the sails out, and the craft uses magnetometers that read changes in the Earth’s magnetic field to orient itself. Then, using a series of gyros and a momentum wheel, LightSail 2 spins accordingly.
For each orbit around Earth, LightSail 2 has to make two 90-degree turns of its solar sail, so that either the sail is turned away from the sun (akin to sailing downwind) as the craft moves away, or perpendicular to the sun as it moves toward the light (much like tacking a sailboat).
But precisely what will happen to the sails in space is still a bit of a mystery, Nye said in the press conference.
“Will it billow like a square-rig ship?” he said. “Will take on a nice curve like a racing jib? Will it be something in between?”
Solar sailing has been more than 40 years in the making
In 1976, Carl Sagan appeared on “The Tonight Show” to talk about solar sailing, and the idea has percolated through the space community ever since.
Nearly 40 years later, The Planetary Society is bringing Sagan’s dream to life. The organization sent LightSail 1, LightSail 2’s predecessor, into low-Earth orbit four years ago. But the craft didn’t actually solar-sail.
“That was purely a deployment test,” Jennifer Vaughn, the chief operating officer of The Planetary Society, said at the press conference. “We sent the CubeSat up. We checked out the radio, the communications, the overall electronics, and we deployed the sail, and we got a picture of that deployed sail in space.”
- The Planetary Society
LightSail 2 is set to orbit higher and perform more complex maneuvers, with the goal of rising farther from Earth. Its shiny sail should be visible from Earth’s surface with the naked eye for about a year, the researchers said.
LightSail 2 could one day help make interstellar travel possible
If LightSail 2 is successful, it will demonstrate that spacecraft can cruise through space without needing fuel.
“It’s a game-changer,” Nye said in an explainer video, adding, “Maybe one day in the future we could even sail one to another star.”
- Jason Davis/The Planetary Society
Since the technology should allow researchers on Earth to maneuver the solar sail much like skippers steer their sailboats, craft like LightSail 2 could one day harness the sun’s rays to travel in any direction.
“Solar sails are just ideal,” Nye said at the press conference. “People have speculated on using solar sails as cargo ships to take material to Mars and so on.”
The solar sail could help us travel farther in space without running out of fuel, enabling humanity to reach nearby star systems sooner rather than later. That in turn would help scientists answer fundamental questions about our place in the cosmos.
“There are two questions everybody asks: Where did we all come from, and are we alone in the universe? And if you want to answer those questions, you have to explore space,” Nye said. Part of that mission is traveling to “asteroids, Mars, and Europa,” he added.
“And how are you going to get there? How are you going to send a spacecraft, especially to an asteroid, to look for primordial minerals?” he said. “Very likely, you’re going to use a solar sail.”