The French PicSat
scientific satellite, which also carries an amateur radio transponder, has come
back to life after four years of silence. Its signals were first picked up on
June 21 by Vlad Chorney, EU1SAT, and subsequently by other radio amateurs as
well. The PicSat team reported on its website that it was able to send commands
to the satellite and get responses. 
The PicSat satellite prior to
launch (from PicSat website)
The AMSAT News Service reports that PicSat was launched in January 2018 but fell silent just three months later. The team reports that it hopes to continue its astronomy mission and activate the satellite’s telescope, even though the specific event it was launched to observe is long past. At press time, there was still no indication of what might have caused the satellite’s transmitter to shut down four years ago, or why it suddenly decided to come back to life.