In the cold darkness of interstellar space, way past the Kuiper belt, Voyager 1 is continuing its journey out as far from Earth as it can go. Right now, it's over 20 billion kilometres (13 billion miles) from our planet - around 140 times the distance between the Sun and Earth.
And yet we can still communicate with it. Last week, mission scientists from NASA sent instructions to activate backup thrusters that have been dormant for 37 years. And it took 19 hours and 35 minutes for them to hear back from the spacecraft.
For over 40 years, since Voyager 1's launch on 5 September 1977, attitude control has been the work of the main thrusters.