Dive for the stars

The robot was jammed 25m down, just under the roof of one of the the world’s deepest flooded caves at the El Zacaton complex in Mexico.

On its way back from a four-hour mission, the robot — DepthX — had a problem with its sonar processing and drove itself into a wall. The only way for the team on the surface to rescue its £2.5m ($5m) investment was to don scuba equipment and dive down into the inky blackness to help nudge it free.

DepthX (Deep Phreatic Thermal Explorer) is a fully-funded NASA project which hopes to develop a robot that will be capable of searching for life in the lakes hidden beneath the ice of Jupiter’s most Earth-like moon, Europa.

But while the money may be NASA’s, the project itself is undeniably the brainchild of engineer, explorer and prodigious polymath, Bob Stone. Little hiccups along the way, like robots that get stuck, are all part of the development process, according to the man who has not only produced more than 200 peer-reviewed scientific papers but is also arguably the world’s foremost cave-explorer.

‘There are over 100,000 lines of autonomous behaviour software in this thing so there’s going to be a bug somewhere,’ said Stone of the recent minor scrape. ‘But that is why we are doing all of these smaller missions, to iron out all of the little problems.’

In this recent test, DepthX completed the second of three planned missions at El Zacaton. It was the first stage of a long process that will eventually result in an autonomous robot capable of mapping and analysing the water on Europa — the place scientists reckon is the most likely to contain life in our solar system.

Europa is covered by a global ocean of liquid water submerged beneath a layer of ice estimated to be up to 10km (just over six miles) thick. The moon, about the same size as Earth’s Moon, is slightly heated by the friction of tides, meaning its water is in liquid form. And it is this that may well contain our nearest alien neighbours.

The idea for an autonomous under- water robot began with an early prototype Stone and his team had built to map the underwater caves they had explored all over the world. Stone has a track record of developing technologies to fit his expeditionary needs and was the inventor of the closed circuit ‘re-breather’ scuba system that removes carbon dioxide from exhaled air and re-circulates it for re-use. It is now considered standard issue for extreme cave-divers. Stone himself claims to have spent a total of 353 days in caves deeper than 1,500ft (457m).

After developing his human-operated mapping robot, Stone heard that NASA was looking for ideas for its lander for a planned mission to Europa. This was his type of challenge, and together with a team of researchers — including microbiologists and electromechanical engineers — he began work on what was to become DepthX.

The robot’s distinctive mushroom-like shape is designed to maximise its unique geometry-based navigation system. Instead of using radio referencing or even GPS like other robots, the locations in which it will be operating meant that a new mapping engine had to be developed. This simultaneous localisation and mapping (SLAM) algorithm will be the navigation device that DepthX will rely on when operating in unexplored areas. It means it can create 3D maps of its location and then use these stored maps to navigate itself out of any labyrinthine series of underwater caves.

‘It’s like an all-seeing eyeball which gets geometric lock on the features that surround it to work out its position,’ explained Stone. Powered by a lithium ion battery, the vehicle’s six thrusters, two of which are positioned vertically, and four horizontally, enable it to carefully pick its way through the underwater world.

While its 3D mapping and navigation skills are extremely advanced, DepthX has another role, that of autonomous robotic microbiologist — like a floating robotic David Attenborough. As well as its sonar and wide-field camera it is also equipped with a one-metre extension probe fitted with a high-resolution camera, an altimeter and a series of sensors for measuring water samples.

After creating a 3D map of its environment, the robot begins to characterise its surroundings by analysing variables such as pH, salinity, conductivity and dissolved oxygen present. Using complex intelligent algorithms DepthX then divides its vision of the world around it into virtual cubes into which it can split the information it has gathered. Currently, this information is then post-processed back at the base and analysed to see whether the data gives indication of any life in a certain area of the cave. However in future missions, Stone said that all of this analysis will be done on board the robot in real-time.

‘The robot can then follow the gradient of a trace, such as hydrogen sulphide, back to a wall or floor to find its source. Microbiological life likes to be on surfaces rather than in the water column.’