Nearly two years ago while undergoing in-flight testing, the STEREO-B spacecraft lost communications with ground stations on Earth. Like in a script of a science fiction movie, it sent one last message containing only a few clues before the stricken craft fell silent. Now, 22 months since last contact, NASA has found its wayward spaceship.
The STEREO-B spacecraft is one of two (the other is STEREO-A) that were launched in 2006 to study the Sun and solar flares. They were put in orbits around the Sun nearly identical to Earth’s, but one was slightly outside our planet’s orbit, and one was slightly inside. This caused one to trail Earth (outside), and one to move more quickly (inside), which resulted in Earth and each of the STEREO spacecraft to slowly spread apart from each other. Eventually this gave visibility to all sides of the Sun at once. Because of this, the two spacecraft could end up on the far side of the Sun and out of communication for long periods of time. Just prior to one of those periods, the guidance equipment on STEREO-B failed, and contact was lost.
For 22 months, STEREO-B drifted alone in space until it was found. Now the Missions Operation team will try to assess how to get it fully operational again. They believe they know the problem, but nearly two years is a long time to be exposed to space in a manner that is potentially outside of normal operations. Subsystems may have failed, the craft could be damaged. Any number of things could have happened that would make the small spacecraft a derelict in space. Only time will tell.