Voyager 1 and 2: Still operating after 40 years in the depths of space. Voyager 1 is currently some 20 billion kilometres from Earth travelling at 15.5 kilometres a second. It takes 19 hours for a signal from the spacecraft's 20 watt transmitter to reach home. Voyager 2 is 17 billion kilometres away and will soon leave the Solar System.

Retired NASA astronaut Ron Garan meets many of the original team still working on the mission, nursing the twin spacecraft through their final years.

Photo: The Voyager 2 spacecraft passes by Saturn in 1981 Credit: NASA