It appears to be all smooth sailing for The Planetary Society's LightSail 2, with the history-making CubeSat now propelling itself through space on sunlight alone. The nonprofit announced today that after unfurling its solar sail last week, the tiny spacecraft has successfully leveraged photons from the Sun to shift its trajectory in Earth orbit, a landmark moment in the history of space exploration.

The idea that sunlight exerts pressure on objects and could therefore, theoretically at least, offer a form of propulsion dates back to the 17th century, when German astronomer Johannes Kepler spotted comet tails blowing about by what he believed to be a solar breeze. More recently, Carl Sagan began throwing the idea of solar sailing around in the 70s, and in co-founding The Planetary Society in 1980, hoped to explore the concept as part of a wider mission to further our understanding of space.

All of which is to say that this moment has been a long time coming for The Planetary Society, and the scientific community as a whole. Other spacecraft have used forms of solar propulsion before, such as NASA's Mariner 10, which ran out of fuel on the way to Mercury and used solar arrays to control its orientation.

In 2010, The Japan Aerospace Exploration Agency's (JAXA) IKAROS became the first spacecraft to demonstrate solar sailing technology in interplanetary space, as it made its way toward Venus. But weighing around 60 times less and with a sail six times smaller than IKAROS, LightSail 2 is a different story altogether.

The objective of its mission is to demonstrate the solar sailing potential for CubeSats, which are smaller and simpler spacecraft that therefore keep the costs of delivering payloads to space to a minimum. In LightSail 2's case, it is around the same size as a loaf of bread, which doesn't leave much room for propulsion systems, only the boxing-ring-sized solar sail that it deployed last week.

While the thrust provided by the Sun's photons is roughly equal to the weight of a paper clip, by making slight adjustments to the orientation of the sail mission control is able to set the spacecraft on a slightly different path, swinging it to higher and higher altitudes and in effect demonstrating a form of controlled flight.

The Planetary Society today confirmed that its first attempts at doing so have proven successful. Over the past four days, the spacecraft has lifted its orbital high point by around 2 km (1.2 mi), while its low-point has dropped by a similar distance. This is in line with the team's pre-flight simulations and predictions.

"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."

LightSail 2 is now the first spacecraft to use solar sailing for propulsion in Earth orbit, the first small spacecraft to do it anywhere and the second spacecraft of any type to do so, after IKAROS. It will spend the next month drifting into higher and higher orbits with the team keeping a close eye on proceedings to optimize its performance.

The plan is to have it circle the Earth for around one year before burning up in the atmosphere, with the data gathered throughout hoped to enlighten other missions involving solar-sailing propulsion, such as NASA's NEA Scout mission that is scheduled for launch next year.

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