LightSail-2, shortly after deployment in 2019.
LightSail-2, an experimental solar sail built by the Planetary Society, finally ended its mission this week, with the test sail burning up in the atmosphere upon re-entry.
LightSail 2 was launched aboard a SpaceX Falcon Heavy rocket in June 2019, settling into an initial orbit at an altitude of around 720 km (450 miles). At that height, the Earth’s atmosphere is still thick enough to create drag, which would threaten to eventually pull the spacecraft down.
But that’s where the plucky little satellite’s special ability came in. Although it’s only the size of a shoebox, LightSail 2 unfurled a big reflective sheet, called a solar sail, about the size of a boxing ring. The idea is that photons from sunlight strike this sail and generate tiny amounts of thrust, allowing the craft to change its orbit.
And LightSail 2 demonstrated this concept beautifully. In three and a half years, the spacecraft completed around 18,000 orbits and traveled 8 million km (5 million miles), adjusting its orbit continuously to keep itself aloft. But all good things must come to an end, and sometime on November 17, drag finally won the tug-of-war and pulled the spacecraft back to Earth.
LightSail-2 was the third time a light sail had been flown in space, with the first, Ikaros, deployed by the Japanese in 2010 and flown in solar orbit through 2012. That mission was successful in using sunlight to accelerate the sail. This was followed by LightSail-1 in 2015. That mission has some communications problems, but eventually succeeded in its main engineering mission by testing the sail deployment system.
