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Cassini, the little spacecraft that could, had all the attributes of Wall-E, Pixar’s plucky waste compacting robot.

Busy, isolated, reliable, undeterred. It was this anthropomorphic cross-over, I presume, that teased the tear to my eye when the faithful workhorse smashed into the planet that it had been observing for 13 years in an emotional climax of its extended 20-year mission.

Low on fuel and out of time, Cassini took its final plunge on September 15, sending back images “until its last breath” – doing science until the end. Those who worked on the project gathered to watch the radio signal fade and die, like the ominous long beep of an electrocardiogram in Holby City.

Some had spent their careers working in tandem with the bus-sized orbiter and they looked to the heavens wondering what would happen now, up there in space and here on Earth, where the void was equally marked.

As we discovered in Horizon’s breath-taking Goodbye Cassini – Hello Saturn (available on iPlayer), a similar suicide job on the moon of Enceladus would have proved more controversial. For Enceladus, one of the planets many and varied satellites, has a liquid water ocean and all the conditions for life. Should Cassini crash and burn there, and life be discovered by a later mission, doubters would suggest Cassini as the seed.

A blacklit Saturn taken from Cassini, with Earth one of those tiny dots of light, bottom right

A blacklit Saturn taken from Cassini, with Earth one of those tiny dots of light, bottom right (Image: Nasa)

Better still, for comic books, if the nuclear battery of Cassini turbo-charged the subterranean amoeba of Enceladus then vengeance-seeking blob monsters would surely make the journey to Earth that Cassini never did.

Our knowledge of the potential of Enceladus, the Death Star look of Mimas, the methane lakes of Titan and the paper-thin rings of Saturn are the legacy of Cassini, which spent seven years reaching the planet and the next 13 orbiting the environment carrying out tests that sent scientists in similar circles of giddy glee. In a hundred years’ time, there’ll still be work to be done on the findings, we were told. This mission was the poster child of space exploration.

Some of the pictures have become iconic, not least a image past the backlit planet to a small dot in the heavens far in the distance – Earth, hanging there in the nothingness, looking vulnerable.

The marvel of Cassini

That Cassini could take pictures, fly through 500km water spumes, reveal chemical compositions and execute all sorts of tests is a marvel of modern science. That it could beam back the information through the wastes of our solar system with such detail that it captured subtle changes of gravitational pull is a miracle of modern engineering.

Imagine a funfair grabber with an arm a billion miles away, travelling at 19,000mph and a 90minute time lag on action and result. I’ve just dumped my four-year printer because the print drum has broken and it was right there, on my desk. I could poke my fingers in and jiggle the cogs.

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Cassini stayed reliable at a distance for two decades, in a system hurling rock and ice and oblivious to the romance of the interloper’s presumptions. The extent of the human and mechanical endeavour defies superlatives. Little wonder that sober-minded scientists attending the “grand finale” party had tears in their eyes and champagne in their glasses – a funeral and a celebration.

Manager Earl Maize said into the PA: “This has been an incredible mission, an incredible spacecraft and you’re all an incredible team. I’m going to call this the end of mission.”

Silence, except the plopping of tiny methane tears on Titan.