The LightSail 2 is ready to journey to space, fulfilling dreams which began centuries ago. This revolutionary spacecraft does not use fuel, but rides on light from the Sun, as a sailboat harnesses the wind. Takeoff is scheduled to take place, at the earliest, during the late night hours of Monday, June 24.
Unlike traditional spacecraft capable of exploring the solar system, solar sail craft are not propelled by thrusters and rocket engines, but they take advantage of the momentum of sunlight constantly streaming from the Sun. The bright silver sail on this craft is composed of a square sheet of Mylar more than 32 square meters (344 square feet) in area — equivalent in size to a boxing ring, but the sail is just 4.5 microns (1/5000 of an inch) thick, thinner than a human hair. As light from the Sun impacts this sail, the craft is pushed along on its journey.
“A square sail turns out to be a pretty good starting point, a pretty good design. It has to have rigid booms, we use the term boom just like on a sailboat, to hold the sails out, because we’re twisting relatively fast in earth orbit so that we go edge on towards the sun, twist 90 degrees, go face on and get a full push like a sailboat going down wind. Building orbital energy, then twisting again on the night side of the earth, and twisting on the day side over and over,” Bill Nye, chief executive officer of The Planetary Society, explained during a press conference held June 20, 2019.
The Past and Future History of Solar Sailing
LightSail 2 features booms made of cobalt alloy, solar cells placed on the outside of the craft and on the inside of panels which deploy during the course of the mission. The vehicle will be controlled by gyros, magnetomoeters and magnetotorquers, capable of adjusting the orientation of the craft relative to the magnetic field of the Earth. A DVD aboard the craft contains the names of every member of the Planetary Society, as well as donors to the program, and those who signed up through the organization’s website.
In 1607, Johannes Kepler viewed Halley’s Comet, and spoke of days in the future when brave sailors would travel through space using sails. The idea came as the legendary astrophysicist studied the tail of Halley’s Comet. He noted that since the tail always points away from the Sun, then our star must be — somehow — pushing on the comet. Kepler, who would later become famous for developing early planetary mechanics, reasoned a specially-designed sailboat would be able to capture the same force, and harness it for propulsion. This vision ignited dreams of a new form of sailing, far beyond the confines of the Earth. The following year, Kepler wrote a letter to Galileo Galilei, describing his idea.
“Provide ships or sails adapted to the heavenly breezes, and there will be some who will brave even that void.” Johannes Kepler wrote.
In 1976, famed astronomer Carl Sagan went on the Tonight Show, showing off an early model of a vehicle powered by a light sail. Sagan went on to become an a strong advocate for the LightSail program, inspiring scientists, engineers, and science advocates to this day, including Bill Nye.
“Back in the 1970s when Bruce Murray was the director of the Jet Propulsion Laboratory, there was an early study for a solar sail. Lou Friedman, one of our other founders plus our executive director for the first 30 years, worked on that mission. Like so many things, that mission got scrubbed. At that point, the three founders got together and said, ‘Let’s start The Planetary Society.’ It wasn’t mandated that we were going to pursue solar sailing, but it was a passion of all three of the founders,” described Jennifer Vaughn, chief operating officer of the Planetary Society.
Lou Friedman, an intellectual icon of orbital mechanics, developed plans for a solar sail-driven spacecraft, capable of visiting Halley’s Comet (now called Comet Halley). This mission was canceled in favor of developing Skylab and the Space Shuttle.
In 2005, the idea of a solar sail came to fruition for the first time, with the launch of the Cosmos 1 Solar Sail. This vehicle, a joint project between the Russian space agency and Cosmos Studios, was lost on liftoff. The spacecraft never reached space, crashing in the Barents Sea, an Arctic waterway on the border of Russia and Norway.
The leadership of the Planetary Society asked their members how they wanted to proceed, and group responded with a resounding call to try again. Studying new ways to develop the program produced the idea of mating the sail with small satellites. CubeSats — small spacecraft measuring just 10 inches per side — fit the bill perfectly. Three CubeSats, affixed together, make up the payload of LightSail 2.
In 2010, the Japan Aerospace Exploration Agency (JAXA) launched IKAROS, a spacecraft powered by a light sail, into space. The sail on that vehicle was folded for launch in a style reminiscent of origami, and was unfurled in space by spinning the sheet.
LightSail 1 reached space in 2015 as part of a deployment test, although the mission was never scheduled to undertake solar sailing. The CubeSat was launched from Earth, and engineers tested the radio, communication, and electronic systems. The team successfully deployed the light sail, and took a picture of the deployed sail in space.
“[T]hey even did some maneuvering by dimming the reflectivity of the sail with liquid crystal panels embedded in the sails. But that type of steering is too slow for Earth orbit,” Nye explained.
When LightSail 2 launches, it will be the highest-performance spacecraft of its type ever launched. The vehicle will be sent into space aboard a Falcon Heavy rocket, as part of the first-ever nighttime launch of the booster, designed by SpaceX. Accompanying LightSail 2 on its journey to space will be two dozen satellites, making it the most challenging flight yet for Elon Musk’s innovative company.
The LightSail 2 spacecraft, with a mass of just five kilograms (11 pounds on Earth), is composed of three CubeSats, and a solar sail tightly folded for its launch to space, where it will be unfurled.
“[I]n its own way, this is history in the making. LightSail 2 is going to fundamentally advance the technology of space flight, particularly by demonstrating solar sailing as a viable option for a small, standardized CubeSat spacecraft,” said Bruce Betts, chief scientist and LightSail program manager at the Planetary Society.
Following launch, engineers will attempt to raise its orbit through propulsion provided by sunlight, testing the promise of the light sail concept.
“The orbit-raising phase of the mission will last about a month… Eventually, atmospheric drag will overcome the thrust from solar sailing, ending the primary mission. The spacecraft will continue to orbit Earth for about a year before succumbing to atmospheric reentry,” Jason Davis explains for The Planetary Society.
Racing to the Future of Solar Sailing
Nye, best known by his popular moniker Bill Nye the Science Guy, is currently chief executive officer of the Planetary Society, a space advocacy group found by the late Dr. Sagan. In 1977, Bill Nye was a student in Carl Sagan’s astronomy class.
“It’s really a romantic notion, everybody, that has tremendous practical applications. There are just a few missions that solar sails are absolutely ideal for… people have speculated on using solar sails as cargo ships to take material to Mars and so on,” Nye stated.
Developed by the Planetary Society, this spacecraft was funded with seven million dollars in private contributions. The relatively low cost of these craft could entice private industries and organizations to develop a myriad of new craft sailing through space, powered on by light.
In the future, spacecraft propelled by light sails could serve as more than ferries, bringing cargo from one place to another in space — people may utilize these vehicles for recreation, much the way people today take up boating as a hobby.
“Carl Sagan talked about regattas, having sailboat races between the earth, solar sail spacecraft races between the earth and other destinations in the solar system. [P]erhaps a standard solar sail package will emerge the same way they have standards in sailboat racing, where the standard boats with standard sized sails, standard crews, maybe that would take place,” Nye told The Cosmic Companion.
A major challenge to such futuristic regattas would be reaching space, but it is possible all the vehicles in such a race would be placed into space aboard a single rocket. Doing so could also reduce the number of traffic-control issues that might otherwise result from a number of solar sail craft heading through space together at the same time.
“[J]ust that we’re talking about it to me is very exciting that we can imagine a solar sail so inexpensive that we’ll have a race who can operate, who can control the pitch, yaw, and roll of a spacecraft well enough to optimize its orientation of the sun and win a race,” Nye stated.
Despite the challenges, such races might still happen, once the technology is further developed.
“[T]he answer is absolutely without question maybe, but it’s a ways off,” Nye joked.
The Planetary Society does not currently have any plans for a LightSail 3, but members of the organization, including Nye, hope the idea of these inexpensive craft is taken up by other interested organizations.
This technology, first envisioned at the beginning of the 17th Century, is now ready to take flight. Thousands of years after the Phoenicians and Greeks set sail on the water, the human race is ready to set sail through the vast expanse of space.
For more information about the science of solar sailing, take a look at this informative article from Rob Lea.