On the big day, no human eyes will see it. It will make art history, but there will be no campaign to prevent it leaving the country. Its final gallery will be windy, freezing and lit by two moons. And the spot painting – a colour calibration chart destined for a scientific experiment – will put Damien Hirst on the map as never before. It will be the first commissioned design, aboard the first British lander, ever to touch down upon another planet.