The International Sun-Earth Explorer was launched in 1978 but has been out of service since 1997. Until now.
On Thursday, ISEE-3 woke up and is now sending telemetry back to earth after a group of space buffs used crowdfunding to contact the satellite from a radio-telescope in Puerto Rico.
"We knew we could do this. It's a vindication," group co-director Keith Cowing told Science.
"It's sort of like reaching back in time to grab something that otherwise would have been lost," he continued.
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Members of the Reboot Project say they will check out the craft's scientific equipment and then initiate a burn with its fuel left on board.
Their goal is to move the satellite into an orbit that will allow the group to conduct further research.