The original Star Trek had the Enterprise on a 5-year mission of exploration and discovery. Which sounds like a long time, but not compared to a pair of its real-life equivalents, which despite not being human, are possibly the greatest explorers of all.
The Voyager 1 and 2 probes have been on task for so long they accomplished their primary mission more than twenty years ago. 33 years after beng launched, they are still discovering things in places people can't get to. Together with their immediate predecessors, among others the Pioneers (wiki), and their subsequent followers they represent one of those amazing technological accomplishments that has been taken for granted and almost forgotten about. To put it another way, the Voyagers accomplished something in my lifetime that had been dreamt about for centuries, if not millenia in their explorations of the outer planets.
Initially planned only to explore Jupiter and Saturn, they were designed for a five year operational life. Due to the planetary alignments at the time, and a carefully planned trajectory that used the various planet's gravity to not only attract the probe, but bend them and boost them on their way to the next encounter, a 'Grand Tour' was on. With the Voyagers still going strong it was decided to extend the programme and exploit the opportunity to explore Uranus and Neptune as well. Pluto wasn't part of the alignment so missed out, but the New Horizons probe is on its way there now.
I was a bit young to catch the Jupiter and Saturn fly-bys between 1979 and 1981, but remember the Uranus (1986) and Neptune (1989) encounters well. Two of the encounters nicely co-incided with my birthday. The scientific knowledge pay-off was enormous, both in expanding and confirming what was previously known or thought, and providing completely new discoveries and questions as well. Voyager 1 was deflected off the tour route to explore Saturn's moon Titan, but Voyager 2 completed the tour, performing way beyond expectations, and still transmitting data to this day. It's awesome for a machine designed and built in the mid 70's and about the same size and weight as my car.
I'm bringing this up now because Voyager 1 has now apparently reached one of the boundaries that separate the Solar System from interstellar space (story). Space being really really big, it is expected to take another few years to cross it, even travelling at 17 kilometres per second.
Voyager 1 is currently about 116 Astronomical Units from Earth (1 AU being the average distance from the Earth to the Sun). To put it another way, it takes a little over 8 minutes for light to get to us from the Sun. To get to Voyager 1 right now that same light will take more than 16 hours, with the Sun now appearing merely as an extra bright star rather than the disc we are familiar with. There are roughly 63,241 AU in a Light Year. And that isn't even moving beyond the front door in interstellar terms. When you start to look at numbers like this it quickly becomes apparent just how almost incomprehensibly vast the universe is. The next time either of the Voyagers will be within a couple of light years of a star will be in around 40,000 years from now.
Contact was lost with the last Pioneer a while ago, but the Voyagers are expected to remain in communication for another fifteen years or so. They are already the farthest flung human artifacts, and could potentially outlive humanity itself. If any machines could be argued to have souls, these travellers out in the cold and silent dim should surely qualify. With the main mission accomplished most of their systems are powered down now to extend the life of those still in use. Before the cameras on Voyager 1 were shut down for the last time in 1990, they were turned back toward home.
The result was the 'Family Portrait' image (wiki background, and detail). Earth, and all it's history, everything you have ever experienced, and everyone you have ever known, measures less than a quarter of a pixel across :)