A "lost and found" story.
From,
http://www.nasa.gov/feature/goddard/saving-nasas-stereo-b-the-189-million-mile-road-to-recovery
December 11, 2015
On Oct. 1, 2014, NASA mission operations lost communication with one of
the two spacecraft of the Solar and Terrestrial Relations Observatory,
or STEREO, mission, just as the spacecraft was about to orbit around
the other side of the sun. Though they haven’t heard from the Behind
spacecraft , also known as STEREO-B, in over a year, the spacecraft has
finally emerged into a region where it can once again receive radio
signals. Scientists have a plan to get it back-and their chances
only get better with time...
Fast forward
From,
http://www.nasa.gov/feature/goddard/2016/nasa-establishes-contact-with-stereo-mission
On Aug. 21, 2016, contact was reestablished with
one of NASA's Solar Terrestrial Relations
Observatories, known as the STEREO-B spacecraft ,
after communications were lost on Oct. 1, 2014. Over
22 months, the STEREO team has worked to attempt
contact with the spacecraft . Most recently, they have
attempted a monthly recovery operation using
NASA's Deep Space Network, or DSN, which tracks
and communicates with missions throughout space.
The DSN established a lock on the STEREO-B
downlink carrier at 6:27 p.m. EDT. The downlink
signal was monitored by the Mission Operations team
over several hours to characterize the attitude of the
spacecraft and then transmitter high voltage was
powered down to save battery power. The STEREO
Missions Operations team plans further recovery
processes to assess observatory health, re-establish
attitude control, and evaluate all subsystems and
instruments.
Communications with STEREO-B were lost during a test
of the spacecraft ’s command loss timer, a hard reset
that is triggered after the spacecraft goes without
communications from Earth for 72 hours. The STEREO team
was testing this function in preparation for something
known as solar conjunction, when STEREO-B’s line of
sight to Earth-and therefore all communication -
was blocked by the sun.
STEREO-A continues to work normally.