Long-Running Underwater Robot Lost At Sea 132
this_boat_is_real writes "Somewhere off the coast of Chile a pioneering underwater robot named Abe lies in a watery grave today. The Autonomous Benthic Explorer was one of the first truly independent research submersibles, being both unmanned and un-tethered to its launching ship. While on its 222nd research dive on Friday all contact with the craft was lost, the Woods Hole Oceanographic Institution has announced."
they where right! (Score:2, Informative)
Re:floaties? (Score:5, Informative)
Touché, vulgar anonymous poster.
The people that design these things are smart. Smarter than the average poster here in their field. If Joe Armchairengineer can think it up, I'm pretty damn confident that the engineers behind ABE thought of it too.
In fact, from the WHOI release, there's this nugget:
Re:they where right! (Score:5, Informative)
That, or the fact that 'benthic' is an adjective referring to the bottom of the ocean.
http://www.merriam-webster.com/dictionary/benthic [merriam-webster.com]
Re:Cthulhu strikes again! (Score:2, Informative)
Re:I have to assume there will be a followup desig (Score:2, Informative)
The replacement for ABE is Sentry. http://www.whoi.edu/page.do?pid=38095
The cost of running support ships limits the number of subs used and the amount of science which is done.
Re:they were right! (Score:2, Informative)
Film. The camera ran out of film.
You kids...
Re:floaties? (Score:5, Informative)
Air doesn't work because of the enormous pressure involved. A 3000 psi scuba tank could only inflate a balloon down to about 2000 meters. Below that, the water pressure is greater than that inside the tank, and opening the valve would result in water forcing the balloon into the tank, rather than air inflating the balloon. A 10000 psi high pressure tank would work at 5000 meters, but would only result in about a 30% increase in volume, meaning you'd need a very big tank to be able to raise the entire craft in a catastrophic failure. Furthermore, the air would expand as the craft rose, risking rupturing the balloon. That's why the buoyancy control uses an oil bladder - oil is relatively incompressible.
Dropping the ascent weight helps raise the craft at the end of a mission. But usually they're relatively lightweight so you can attach them manually. The 17-inch glass spheres [benthos.com] typically used to house equipment provides over 50 pounds of buoyancy. The failure of one of these spheres at a depth of 3000 meters (~4500 psi) would release (4500 psi) * 4/3 * pi * (8.5 inches)^3 = 1.3 MJ of energy. A stick of dynamite is about 2.1 MJ, so losing one sphere is pretty much guaranteed to cause all the other spheres to fail. If the remainder of the craft somehow survived all that energy release, the loss in buoyancy would overwhelm what buoyancy you'd get by dropping the ascent weight.
Re:they were right! (Score:2, Informative)
Re:floaties? (Score:3, Informative)
Right. I wasn't saying the balloon idea was impossible, just explaining why it's inferior to oil and static pressure sphere buoyancy.
One of the Benthos reps (actually, he was one of the founders of the company) gave us a presentation which touched on sphere failures. It's an implosion which almost instantly turns the glass sphere into powder. The energy released goes into pulverizing the glass, and generating an inverse pressure wave which spreads outward disrupting or destroying any nearby equipment.
He also mentioned one unusual case where the vacuum valve for the sphere failed. If you didn't read the link I gave, the spheres is actually two hemispheres placed atop each other (this lets you put equipment and stuff inside). There's a small quarter-inch hole with a valve on it used to pump the air out of the sphere. The vacuum allows ambient air pressure to hold the two halves together. As it turns out, one of these spheres used only for floatation had this valve fail at depth. Instead of destroying the sphere, the water pressure simply filled the sphere very rapidly with water. All the netting which had been outside the sphere was forced through the quarter-inch hole into the sphere.