NASA’s STEREO-A flies by Earth after a 17-year trip around the sun | Space

Like many NASA spacecraft, STEREO-A outlived its mission life span of two years. Instead, it traveled further and further away from Earth on a journey that became fraught with uncertainty as it passed behind the sun in 2015, temporarily severing contact with NASA. The same year, the agency lost contact with STEREO-A’s sibling vessel, STEREO-B, which was traveling a similar path.

But STEREO-A kept going. And its orbital trajectory around the sun meant that it had a chance to do what very few other NASA spacecraft could: eventually make its way back toward home.

That came to fruition earlier this month, when STEREO-A passed between the sun and the Earth for the first time since its launch in 2006, NASA announced. The flyby marked a milestone for the spacecraft and the team that has monitored its progress — and a chance for STEREO-A to prove its relevance almost two decades later. As it continues to pass by Earth, STEREO-A will be used to perform new research on the sun, aided by newer NASA satellites that have been developed since its launch.

“This is a point in time for this mission to shine again,” Lika Guhathakurta, STEREO’s program scientist, told The Washington Post.

The two STEREO spacecraft launched in October 2006 with an ambitious mission: to generate a 360-degree view of the sun by observing the star from two vantage points as they circled it on orbits that diverged from the Earth in opposite directions. STEREO-A maneuvered into an orbit around the sun ahead of Earth, and STEREO-B began circling the sun in the opposite direction behind the Earth.

The difference in perspective was groundbreaking, Guhathakurta said. Earthbound instruments can only ever observe one Earth-facing slice of the…