The Deep Phreatic Thermal Explorer (DEPTHX) is the brainchild of Dr. Bill Stone, CEO of Stone Aerospace in Austin, Texas and has been developed by his team in concert with Carnegie Mellon University, the Southwest Research Institute, the University of Texas at Austin, the Colorado School of Mines, and NASA Ames Research centre. The DEPTHX is designed to explore and map submerged areas while collecting water and core samples. Unlike the Mars Rovers, the incredible distance to Europa — roughly 5.2AU on average — and constantly changing aqueous environment preclude any sort of Earth-based control system. Instead, the DEPTHX will have to think for itself.
Bill Stone first had the idea for the DEPTHX in 1999 while working on an underwater survey project. By 2003 NASA had granted DEPTHX a three-year, $US5 million development project. For the next three years Stone's team worked through a multitude of initial designs before reaching the current egg shape in 2006. The DEPTHX is roughly 4m long and 2.4m wide. Packed into this frame are 54 sonars for navigation, 36 computers for information processing, six thrusters and twin battery stacks, a suite of accelerometers, velocity loggers, observational instruments including liquid and core samplers as well as an onboard microscope to hunt for microbial life.
It communicates with the the Valkyrie mother craft using a single fibre optic tether as well as Wi-Fi. And to keep all 1.3t of this machine floating, the DEPTHX employs two variable-buoyancy engines that sense the temperature, salinity and pressure of the water around it and adjusts the amount of water it takes on to adjust its relative buoyancy down to 1000m.
The most impressive feature of the DEPTHX is its self-guided navigation. An array of 54 sonars can locate objects within a 300m radius to map the machine's surroundings while the onboard accelerometers, velocity loggers and guidance instruments all help to inform the DEPTHX about its position within the space. What's more, the soar array performs double duty by generating a 3D map of what it senses ion real time. The technique is known as 3D Simultaneous localisation and Mapping (3D-SLAM) and allows the robot to navigate for itself.
The DEPTHX is, according to Stone Aerospace, "literally an all-seeing eyeball. Using forward and backward-looking range sensors and very sophisticated real-time mathematics, DEPTHX can locate itself within a geometric environment, even one that it just explored for the first time only seconds previously. The 3D-SLAM accuracy on DEPTHX is approximately one metre anywhere within a 500m cube about the vehicle." [Stone Aeronautics - Space - Wikipedia - How Stuff Works - Carnagie Mellon]