Using the Sun to orbit the Earth

 By Peter Ward

In 1607, Halley’s Comet appeared in the skies over Europe. Back then it was unnamed, untracked and something of a mystery, but a 36-year-old German astronomer named Johannes Kepler observed the broad tail that streaked across the sky and determined that sunlight was heating the comet, propelling material from its surface…

Kepler’s theory turned out to be true, and now acts as the inspiration behind a new form of spacecraft—one propelled by the light of the sun. Kepler predicted that humans would one day harness the power of the sun to make for the stars, writing in a 1608 letter to Galileo Galilei: “Provide ships or sails adapted to the heavenly breezes, and there will be some who will brave even that void”. In the years since, the science behind Kepler’s claim has been proven, and the idea of a spacecraft using a solar sail has emerged at various points in history. The science behind the idea was established in 1865 when James Clerk Maxwell demonstrated light was made of packets of energy called photons. Maxwell showed when photons strike a reflective surface—like a solar sail, for example—they push it forward.

Solar Sail Johannes Kepler on its way to Jupiter, digital artwork by Frans Blok (

Building on Maxwell’s work, two Russian scientists proposed a sail. “For flight in interplanetary space I am working on the idea of flying, using tremendous mirrors of very thin sheets, capable of achieving favorable results,” engineer Fridrikh Tsander wrote in 1924. The idea next surfaced in a science fiction magazine in 1951, when an electrical engineer named Carl Wiley proposed a solar sail in the style of a parachute in an issue of Astounding Science Fiction. The parachute would be deployed to tow a spacecraft behind it.

The model of Fridrikh Tsander's rocket plane, designed in 1922, and shown at the 1927 Exhibition of Interplanetary Machines in Moscow (

In 1957, the Soviet Union became the first country to launch a satellite into space, and America’s answer, the National Aeronautics and Space Administration (NASA), researched solar sails as a possible retort. But after the Apollo-era ended and the Cold War cooled, NASA funding decreased and solar sails fell victim to cuts. Research was canceled, and the idea was in danger of never being realized. One engineer kept the prospect alive. Jerome Wright’s research at the Battelle Memorial Institute in the United States’ Ohio aimed to find out what it would take to send a solar sail to other planets. While crunching the numbers, Wright discovered a trajectory that could send a solar sail spacecraft to Halley’s Comet when it would return in 1986.
Wright teamed up with Louis Freedman of the NASA Jet Propulsion Laboratory (JPL), and with the support of Dr. Bruce Murray, JPL’s director, attempted to make the mission to Halley’s comet a reality.
Due to lack of funding, however, it never happened, but both Freedman and Murray went on to found the Planetary Society with Carl Sagan, a non-profit space advocacy group determined to make solar sailing a reality.

Carl Sagan, Bruce Murray and Louis Friedman, the founders of The Planetary Society. The fourth person is Harry Ashmore, an advisor, who greatly helped in the founding of the Society (NASA JPL)

Solar sailing uses the momentum of photons to push a spacecraft through space. Sails made of large, reflective material, such as mylar, are used, and the photons bounce off the sails, speeding up the sail in the opposite direction of the bouncing light. This system eliminates the need for rocket propellant to be carried into orbit, which reduces the weight of the craft and cuts launch costs. Sunlight is also unlimited, meaning that a perfectly running solar sail would have much less chance of becoming stranded in orbit and contributing to the already drastic space debris problem around the planet. Solar sails are also theoretically capable of reaching higher speeds than chemical rockets, as they provide a continuous slight thrust rather than a short powerful burst.

Chasing the orbit

After the Planetary Society took up the baton, there were one or two failed attempts at launching a solar sail spacecraft into space. An example was the Cosmos 1, which was supposed to be launched from a Russian submarine but didn’t reach its intended orbit due to a rocket failure. In 2009, the organization began working on LightSail, as it raced to put the first solar-sail spacecraft into orbit. However, in 2010, the Planetary Society was beaten to the punch by the Japanese space agency JAXA, which flew IKAROS and earned its place in the Guinness Book of Records as the first solar sail flight. In 2015, the Planetary Society finally got LightSail into space, launching aboard an Atlas V rocket and completing its test flight in lower Earth orbit. The follow-up mission is set to launch in June 2019. LightSail 2 will be catapulted into space aboard a SpaceX Falcon Heavy rocket, and will fly to a higher orbit than its predecessor. It will also attempt to raise its orbit with solar sailing. The main difference between the IKAROS spacecraft and LightSail is size, with the Planetary Society’s project being much smaller, utilizing cubesat technology.

Engineer Joel Steinkraus stands with both of the Mars Cube One (MarCO) spacecraft at NASA's Jet Propulsion Laboratory (NASA)

The LightSail 2 is about the size of a loaf of bread with its panels closed and the sails not deployed.
The Planetary Society will hope the crowdfunded LightSail 2 project can fulfill its main aim—to use solar winds to raise its orbit by a measurable amount, proving cubesats can be moved without the need of chemical rockets. This would bring down the cost of cubesats, allow more projects to be launched into space and make space exploration more accessible to all.

READ MORE: Privatising the race to space by Nicholas Newman

about the author
Peter Ward
Business and technology reporter based in New York. MA in Business Journalism at Columbia University Journalism School 2013. Five years experience reporting in the U.S., the U.K., and the Middle East.