LightSail 2 is poised to embark on its journey into space, realizing ambitions that have persisted for centuries. This groundbreaking spacecraft utilizes sunlight for propulsion, similar to how a sailboat harnesses wind. The launch is expected to occur during the late hours of Monday, June 24, at the earliest.

In contrast to conventional spacecraft that rely on rocket engines and thrusters, solar sail vehicles exploit the momentum of sunlight. The shiny silver sail of LightSail 2 consists of a Mylar sheet measuring over 32 square meters (344 square feet)—approximately the size of a boxing ring—yet it is only 4.5 microns (1/5000 of an inch) thick, making it thinner than a human hair. As sunlight strikes this sail, it propels the craft forward.

“A square sail turns out to be a pretty good starting point, a pretty good design. It has to have rigid booms—much like a sailboat—to extend the sails. We twist relatively quickly in Earth orbit to align with the Sun, rotating 90 degrees to catch the full sunlight, similar to a sailboat going downwind. We build orbital energy, then rotate again on the night side of the Earth, continuing this process,” Bill Nye, CEO of The Planetary Society, explained at a press conference on June 20, 2019.

The Historical Journey of Solar Sailing

LightSail 2 is equipped with booms made from cobalt alloy and features solar cells on both the exterior and interior of deployable panels. The craft will be maneuvered using gyroscopes, magnetometers, and magnetotorquers to orient itself relative to Earth's magnetic field. A DVD onboard carries the names of all Planetary Society members, donors, and supporters who registered via the organization’s website.

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In 1607, Johannes Kepler observed Halley's Comet and envisioned a future where courageous navigators would traverse space with sails. His insights arose from studying the comet’s tail, which always points away from the Sun, suggesting that sunlight exerts a force on the comet. Kepler, known for his contributions to early planetary mechanics, proposed that a specially designed sailboat could harness this force for propulsion, sparking dreams of sailing beyond Earth. The following year, he wrote to Galileo Galilei about his vision.

“Provide ships or sails adapted to the heavenly breezes, and there will be some who will brave even that void,” Kepler wrote.

In 1976, renowned astronomer Carl Sagan appeared on the Tonight Show, showcasing an early prototype of a light sail-powered vehicle. He became a passionate supporter of the LightSail initiative, motivating scientists, engineers, and advocates, including Bill Nye.

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“Back in the 1970s, when Bruce Murray directed the Jet Propulsion Laboratory, there was an initial study for a solar sail mission. Lou Friedman, one of our founders and the executive director for the first 30 years, contributed to that project. Unfortunately, it was canceled. The three founders then decided to establish The Planetary Society, which was not specifically dedicated to solar sailing but was a shared passion of all three,” stated Jennifer Vaughn, COO of the Planetary Society.

Lou Friedman, a visionary in orbital mechanics, devised plans for a solar sail spacecraft that could visit Halley’s Comet, but that mission was scrapped in favor of developing Skylab and the Space Shuttle.

In 2005, the concept of a solar sail was attempted with the launch of Cosmos 1, a collaboration between the Russian space agency and Cosmos Studios, but it tragically failed at liftoff, crashing into the Barents Sea.

Afterward, The Planetary Society consulted its members on how to move forward, and the response was a strong desire to try again. This led to the innovative idea of integrating solar sails with small satellites. CubeSats—compact spacecraft measuring 10 inches on each side—perfectly fit this concept. LightSail 2’s payload consists of three connected CubeSats.

In 2010, JAXA successfully launched IKAROS, a spacecraft powered by a light sail, into space. Its sail was ingeniously folded in an origami style for launch and unfurled in orbit through rotation.

LightSail 1 reached space in 2015 as part of a deployment test, although it was not intended for solar sailing. Engineers successfully launched the CubeSat, testing its radio, communication, and electronic systems. They managed to deploy the light sail and captured images of it in space.

“They even conducted maneuvers by reducing the sail’s reflectivity using liquid crystal panels embedded in the material. However, this method of steering is too slow for Earth orbit,” Nye explained.

LightSail 2 will be the most advanced spacecraft of its kind upon launch, which will occur via a Falcon Heavy rocket in the inaugural nighttime launch of this booster, designed by SpaceX. Accompanying LightSail 2 will be two dozen satellites, making it the most ambitious mission yet for Elon Musk’s pioneering company.

With a mass of only five kilograms (11 pounds on Earth), LightSail 2 consists of three CubeSats and a tightly folded solar sail prepared for its launch into space, where it will be deployed.

“In its own way, this is history in the making. LightSail 2 is set to significantly advance spaceflight technology, especially by demonstrating solar sailing as a feasible option for small, standardized CubeSat spacecraft,” said Bruce Betts, chief scientist and LightSail program manager at The Planetary Society.

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After launch, engineers will aim to elevate its orbit using sunlight-driven propulsion, testing the potential of the solar sail concept.

“The orbit-raising phase will span about a month. Eventually, atmospheric drag will overpower the thrust from solar sailing, concluding the primary mission. The spacecraft will continue to orbit Earth for roughly a year before reentering the atmosphere,” Jason Davis explains for The Planetary Society.

The Future of Solar Sailing Awaits

Bill Nye, popularly known as Bill Nye the Science Guy, currently serves as CEO of The Planetary Society, a space advocacy organization founded by the late Dr. Sagan. Nye was a student in Carl Sagan’s astronomy class back in 1977.

“This is a romantic notion with significant practical applications. Solar sails are perfect for several missions… There are discussions about using solar sails as cargo transporters to deliver materials to Mars and beyond,” Nye remarked.

The Planetary Society developed this spacecraft with seven million dollars in private donations. The comparatively low cost of these vehicles could encourage private enterprises and organizations to create a variety of new craft navigating the cosmos, powered by light.

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In the future, light sail-powered spacecraft could serve as more than just transporters; they might also be used for recreational purposes, akin to how people engage in boating as a pastime.

“Carl Sagan envisioned regattas—sailing races in space between solar sail craft. Perhaps a standardized solar sail model will emerge, similar to the regulations in sailboat racing, with uniform boats, sails, and crews,” Nye shared with The Cosmic Companion.

A significant hurdle for such futuristic regattas is the challenge of reaching space. However, it’s conceivable that all participants could be launched aboard a single rocket, minimizing potential traffic issues that could arise from multiple solar sail vessels navigating space simultaneously.

“Just the fact that we’re discussing this is thrilling. I can envision a solar sail that is so affordable that we could have races determining who can best manage their spacecraft's orientation to the Sun to win,” Nye expressed.

Despite the obstacles, such competitions may become a reality as technology progresses.

“Absolutely, it’s a possibility, but there’s still a long way to go,” Nye humorously commented.

Currently, The Planetary Society has no plans for a LightSail 3, but members, including Nye, hope that other organizations will embrace the concept of these economical craft.

This technology, initially imagined in the early 17th century, is now on the brink of becoming a reality. Thousands of years after the Phoenicians and Greeks first sailed the seas, humanity is ready to navigate the vastness of space.