When Hollywood director Ridley Scott filmed astronauts looking for aliens in his 2012 movie Prometheus, little did he know that it would one day inspire a Network Rail drone project.
But, bizarrely, that's exactly what has happened. Network Rail, which owns and maintains most of the railway infrastructure in Britain - from vast stretches of track to thousands of bridges, tunnels and level crossings - has long sought cheaper and easier ways of surveying the many underground caves and abandoned mines dotted around its property.
Engineers must account for "shallow" subterranean voids when doing building work or moving heavy machinery, because the caverns might collapse and cause the ground above to shift. There are more than 5,000 shallow voids in Britain.
At an innovation workshop in 2018, Network Rail's principal mining engineer Neal Rushton found himself seated at a table with electronics experts and robot researchers. He sketched a simple drawing of the sort of device he was looking for - something that could travel down a 15cm borehole, enter an underground cave and map its interior.