LightSail 2 orbiting Earth with solar propulsion

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LightSail 2 is using its reflective aluminised Mylar sail to become the first spacecraft that uses the light pressure from the sun for propulsion in Earth orbit.

LightSail 2 during sail deployment sequence. Image: The Planetary Society

The Planetary Society’s LightSail 2 launched from Kennedy Space Center, Florida aboard a SpaceX Falcon Heavy rocket on June 25, 2019, and deployed its square sail nearly a month later on July 23. The aim of the mission is to demonstrate solar sailing as a method for propelling CubeSats.

The spacecraft’s orbital high point (apogee) has since risen by about 2km, whilst the perigee (the low point of its orbit), has fallen away by a similar distance, which The Planetary Society said is consistent with pre-flight predictions for the effects of atmospheric drag.

LightSail 2 set to demonstrate solar sailing in Earth orbit

According to a statement, the mission team confirmed the apogee increase can only be attributed to solar sailing, meaning LightSail 2 has successfully completed its primary goal of demonstrating so-called ‘flight by light’ for CubeSats.

"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."

The milestone makes LightSail 2 the first spacecraft to use solar sailing for propulsion in Earth orbit, the first small spacecraft to demonstrate solar sailing, and the second solar sail spacecraft to fly, following Japan's IKAROS, which launched in 2010.

"For The Planetary Society, this moment has been decades in the making," said Planetary Society CEO Bill Nye. "Carl Sagan talked about solar sailing…in 1977. But the idea goes back at least to 1607, when Johannes Kepler noticed that comet tails must be created by energy from the Sun. The LightSail 2 mission is a game-changer for spaceflight and advancing space exploration."

The mission team will continue raising LightSail 2's orbit for roughly a month, until the perigee decreases to the point where atmospheric drag overcomes the thrust from solar sailing. During the orbit-raising period, the team will continue optimising the performance of the solar sail.

"We've been working since sail deployment to refine the way the spacecraft tracks the Sun," said LightSail 2 project manager Dave Spencer. "The team has done a great job getting us to the point where we can declare mission success. Moving ahead, we're going to continue working to tune the sail control performance and see how much we can raise apogee over time."

After LightSail 2's month-long orbit raising phase, the spacecraft will begin to deorbit, eventually re-entering the atmosphere in around a year.

Approximately 50,000 Planetary Society members and private citizens from over 100 countries, as well as foundations and corporate partners, donated to the LightSail 2 mission, which cost $7m.