A solar-sailing mission is now marking three years of spaceflight, but is unlikely to celebrate a fourth anniversary.

The Planetary Society's LightSail 2 is a crowdfunded solar sail that launched June 25, 2019. It was expected to last a year in an assessment of how well a spacecraft could perform using only the power of the sun.

Now tripling that expectation, the spacecraft continues to work well but is in a fight with atmospheric drag. Molecules of the Earth's atmosphere are slowly pulling the spacecraft back to our planet, with re-entry expected in perhaps a few months, according to a Planetary Society update (opens in new tab).

"We have continued to work to learn more and sail more efficiently as part of itsextended missionincluding itssecond yearin orbit as well as this last year, its third year," Bruce Betts, the mission's project manager, wrote Friday (June 24) on the Planetary Society's website.

Related: LightSail 2 captures stunning photos of Earth from space

Like any long-running mission, the spacecraft has met a few challenges. Last summer, engineers recalibrated the gyroscopes on the spacecraft to account for drift, but the gyros "began returning data that measured incorrect spin rates," Betts wrote.

"We developed techniques to calibrate the gyros on orbit, and updated the onboard flight software to enable corrections to the gyro bias parameters. The update improved our sail control, thus improving our solar sailing."

The change allowed the altitude to rise by 328 feet (100 meters) per day for a few months, but as of today the average altitude is about 390 miles (627 kilometers). That's compared with 446 miles (718 km) at mission start.

The altitude fell for a few reasons, Betts explained, including communications trouble with the spacecraft due to ground station components breaking (and requiring replacement), ongoing atmospheric drag, and increased activity in the 11-year solar cycle puffing up Earth's atmosphere and moving more molecules higher.

That said, the Mylar sail material remains in good condition and the spacecraft has no major component failures, which Betts said is "an amazing testament to the many tens of people over the years whove worked on it."

He added the team plans to "make the most out of the next several months" before LightSail 2's eventual re-entry, but the data collected will remain useful essentially forever after the mission. The team plans numerous mission analyses, paper publications and conference publications for LightSail, as well as continuing their connections with other space missions planning on using solar sails themselves.

In the meantime, the LightSail team continues to publish updates through technical publications (opens in new tab) and, while the mission is active, you can view key parameters through the mission control dashboard (opens in new tab).

Follow Elizabeth Howell on Twitter@howellspace. Follow uson Twitter@Spacedotcomand onFacebook.

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LightSail 2 marks 3rd anniversary as end of mission approaches - Space.com