Since the 1957 launch of the first space satellite, Sputnik, tens of thousands of spacecraft have been sent into space. Many of them are no longer in operation — they're basically zombies continuing to float through space with no purpose.

Last week, a group of citizen scientists was able to make contact with a satellite that hasn't been used in 17 years. It's called the International Sun Earth Explorer or ISEE-3 and it was launched by NASA in 1978.

Here to tell us why they made contact is Keith Cowing, co-founder of the ISEE-3 REBOOT Project and a former NASA scientist.