Robot Submarine To Dive Deep In the Caribbean
Roland Piquepaille writes "According to BBC News, a new UK autonomous underwater vehicle (AUV), Autosub6000, will soon start to explore the world's deepest undersea volcanoes, located in the Caribbean. Autosub6000 has a range of up to 1,000 kilometers and has a maximum operating depth of 6,000 meters. It is 5.5 meters long, has a diameter of 0.9 meters, and is equipped with a high-performance GPS unit. For these two expeditions, each close to a month long, Autosub6000 will be joined by the Isis remotely operated vehicle, which is able to operate at a depth of 6,000 meters and grab animal specimens. Researchers from the National Oceanography Center in Southampton will lead these missions. They expect that 'one in every two animals they come across will be a species new to science' once the robots reach a depth of 3,000 meters."
Specifications for the submarine (PDF) are also available.
GPS will work down to a foot or so if you have the right antenna.
Engineering is the art of compromise.
They're likely communicating with a surface bouys over a more appropriate frequency. The bouys then do the actual communicating with the satellites. See, eg: http://www.underwater-gps.com/uk/technology-GIB-concept.php
2^5
Many commercial AUVs are rated to, at most, 6000m. The tradeoffs there are business: basically none of the customers want it any deeper, because, like I said, that depth rating can handle almost the entire ocean. So if this group's main driver is availability of technology and components to work from to build their AUV, they're probably willing to focus on just the 3000m-6000m range to take advantage of that. This isn't to say it's not worth it at all, and there are vehicles that can go deeper. But the question was asked, "Why are these guys limited to 6000m?" It's not technologically infeasible to go deeper, but practically speaking, they don't need to in order to get the information they need. Tradeoffs.
The sub uses GPS for positioning on and near the surface. The rest of the way it's using inertial navigation. USL@NOC is also working on multibeam sonar so that the robot can assess its position using geologic features on the bottom (up to about 200m away I expect) for position keeping in a current.