NASA announced on Monday that it has finally reestablished contact with the STEREO-B space probe after losing contact almost two years ago.
NASA's STEREO Mission was launched in November 2009, and it consisted of a pair of spacecraft called STEREO-A and STEREO-B. The goal was to use these two craft to observe the sun, looking for coronal mass ejections (CME), or large eruptions of plasma from the sun's surface.
A CME can pose significant danger to our electronics and communications grid if it is directed at the Earth, but it can be hard to tell which direction a CME is moving or how fast it's traveling just by observing it with telescopes. With the two STEREO spacecraft, NASA could observe any CMEs from multiple angles, essentially letting them see the CME in 3D.
However, in 2014, during a routine test of STEREO-B's timer, NASA lost contact with the spacecraft. Although the STEREO team tried regularly to reestablish contact, they were unsuccessful—until Sunday, when, miraculously, STEREO-B's signal was picked up by NASA's Deep Space Network.
The STEREO team is currently running diagnostics on the spacecraft, attempting to determine what kind of state it's in. Following that, the team will try and get STEREO-B up and running again, and continue the original mission after this two-year hiatus.