by The LightSail 2 spacecraft will no longer run on sunshine.
The Planetary Society’s crowdfunded solar sail craft was once again in the running the Earth’s atmosphere on Thursday morning (Nov. 17) after nearly 3.5 years in orbit — more than three times longer than the mission’s planned lifetime.
The Light sail 2 The team has not received any communication from the spacecraft since that date, leading them to conclude that the shoebox-sized craft had finally given up the ghost after completing 18,000 orbits and traveling approximately 5 million miles (8 million kilometers) around our planet.
“LightSail 2 is gone after more than three glorious years in the sky, blazing a trail of lift with light and proving we could defy gravity by tacking a sail in space,” said science communicator Bill Nye, CEO of The Planetary Society, in one pronunciation (opens in new tab). “The mission was funded by tens of thousands of members of the Planetary Society, who want to advance space technology.”
Related: LightSail 2 takes beautiful pictures of the Earth from space
LightSail 2 was the first small spacecraft to demonstrate solar-powered controlled sailing, using photons from the sun to adjust its trajectory. (However, LightSail 2 was not the first craft of any type to sail through space on solar power; Japan’s Ikaros probe did so in 2010.)
Although light has no mass, its individual particles — photons — carry momentum that can be transferred to a reflective surface to give it a little push.
LightSail 2 has shown that solar powered sailing is an effective and viable propulsion method for small spacecraft, including small satellites known as cubesatssaid team members.
LightSail program manager and chief scientist Bruce Betts wrote in a Planetary Society pronunciation (opens in new tab) that deorbiting would always be LightSail 2’s fate, though the mission’s fiery end took longer than predicted.
The end of LightSail 2 was a drag
LightSail 2 was launched in June 2019 aboard a SpaceX falcon heavy rocket, tasked with a year-long mission to demonstrate controlled solar sails in orbit. It began operations at an altitude of about 450 miles (720 kilometers) above Earth — slightly higher than the orbit of the International Space Station (ISS).
At this altitude, Earth’s atmosphere is still dense enough to exert a slight drag on a spacecraft, and it’s this effect that ultimately sealed LightSail 2’s fate.
Due to the large area of the craft’s solar sail, which measures 244 square feet (32 square meters) — about the size of a boxing ring — it experienced a greater drag effect than other spacecraft of its mass.
“Imagine throwing a rock compared to throwing a piece of paper. Atmospheric drag will stop the paper much faster than the rock. In our case, LightSail 2 is the paper,” Betts wrote. “A spacecraft like the ISS is huge but also massive, more like a rock. But even the ISS has to be boosted higher every few weeks using rockets to compensate for drag.”
During its third year of operation, demonstrating its most efficient solar powered sails, LightSail 2 experienced increased atmospheric drag due to an increase in solar activity. This activity from the sun warmed the atmosphere, making the area through which LightSail 2 passed denser.
“That was the beginning of the end,” Betts wrote. “As solar activity increased even more, solar powered sailing could not compete with the increased drag due to the increase in atmospheric density.”
Over the past few weeks, LightSail 2 had sunk deeper and deeper into Earth’s atmosphere and was experiencing increasing resistance, which in turn dramatically increased the rate of its fall.
“The spacecraft entered into an ever-expanding snowball effect: As the spacecraft lowered, its density increased, causing the spacecraft to lower even faster,” Betts wrote.
While LightSail 2’s mission may be over, scientific work still needs to be done. The team behind the mission continues to analyze data collected by the craft, which remained operational until the last moments.
This data will also be shared with future space missions that also use solar sails, such as NASA’s NEA Scout, which launched Nov. 16 on the agency’s Artemis 1 mission and piggybacked on sunlight to travel to the moon and then to a asteroid near Earth.
“Despite the sadness to see it go, all those who worked on this project and the 50,000 individual donors who fully funded the LightSail program should look back on this as a moment of pride,” Betts wrote.
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