LightSail 2 spacecraft completes solar sailing mission with flying colors
The LightSail 2 spacecraft will no longer ride on the sun.
The Planetary Society’s solar glider has re-entered Earth’s atmosphere on Thursday morning (Nov. 17) after nearly 3.5 years in orbit — more than three times the mission’s intended lifetime.
The LightSail 2 the team has not received any communication from the spacecraft since that date, leading them to conclude that the shoebox-sized craft finally gave up the ghost after completing 18,000 orbits and traveling about 8 million kilometers around our planet.
“LightSail 2 has disappeared after more than three glorious years in the sky, illuminating the wake of buoyancy and proving that we can defy gravity by gliding in space,” said science communicator Bill Nye, executive director of The Planetary Society in statement (opens in new tab). “The mission was funded by tens of thousands of members of the Planetary Society, who want to advance space technology.”
LightSail 2 was the first small spacecraft to demonstrate controlled solar sailing, using photons from the sun to adjust its orbit. (LightSail 2, however, was not the first spacecraft of any kind to sail solar into space; the Japanese Icarus probe did it in 2010)
While light lacks mass, its individual particles – photons – carry momentum that can be transferred to the reflecting surface to give it a small pressure.
LightSail 2 demonstrated that solar sailing is an efficient and sustainable method of propulsion for small spacecraft, including small satellites known as cubesatsteam members said.
LightSail program manager and chief scientist Bruce Betts wrote for the Planetary Society statement (opens in new tab) that diversion was always going to be LightSail 2’s destiny, although the mission’s fiery end took longer to manifest than anticipated.
The end of LightSail 2 was difficult
LightSail 2 launched in June 2019 on SpaceX Falcon Heavy rocket, tasked with a one-year mission to demonstrate controlled solar sailing in orbit. It began its operations at an altitude of about 450 miles (720 kilometers) above Earth – slightly higher than orbit International Space Station (ISS).
At this altitude, Earth’s atmosphere is still dense enough to exert a slight drag on the spacecraft, an effect that ultimately sealed LightSail 2’s fate.
Because of the large surface area of the spacecraft’s solar sail, which was 244 square feet (32 square meters)—roughly the size of a boxing ring—it experienced a greater drag effect than other spacecraft of its mass.
“Think of throwing a rock compared to throwing a piece of paper. Atmospheric resistance will stop the paper much faster than a rock. In our case, LightSail 2 is 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 every few weeks using rockets to compensate for drag.”
During its third year of operation, in which it demonstrated its most efficient solar sailing, LightSail 2 experienced increased atmospheric drag due to increased solar activity. This activity from the sun warmed the atmosphere, making the region LightSail 2 passed through denser.
“It marked the beginning of the end,” Betts wrote. “As solar activity increased even more, solar sailing was unable to compete with the increased drag due to the increase in atmospheric density.”
Over the past few weeks, LightSail 2 has fallen deeper and deeper into the Earth’s atmosphere, experiencing more and more drag, which in turn dramatically increased its rate of descent.
“The spacecraft was caught in an increasing snowball effect: as the spacecraft descended, the density increased, causing the spacecraft to descend even faster,” Betts wrote.
While LightSail 2’s mission may be over, there is still scientific work to be done. The team behind the mission continues to analyze the data collected by the spacecraft, which remained operational until its final moments.
This data will also be shared with future space missions that also use solar sails, such as NASA’s NEA Scout, which launched on the agency Artemis 1 mission on Nov. 16 and will ride in sunlight to travel to the Moon and then to a near-Earth asteroid.
“Despite the sadness of seeing it go, all those who worked on this project and the 50,000 individual donors who fully funded the LightSail program should consider this a proud moment,” Betts wrote.
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