Original URL: http://www.theregister.co.uk/2011/06/28/biological_xbts/
US Navy invents 'Zero-Power Autonomous' ocean probe
Crafty bacterio-buoyancy underwater podule triumph
US Navy and Marine Corps boffins are chuffed with themselves today, after inventing a crafty underwater probe podule which can be dropped into the sea, sink to a pre-programmed depth, remain there for weeks or months and then at some point rise to the surface again - all without using any electrical power.
This last is a good feature as generating power underwater is no simple matter. The conventionally-fuelled generators used in surface ships and equipment aren't an option: batteries can't hold much juice for a given amount of weight and money. This is why big navies use nuclear-powered submarines, despite the expense and bureaucracy involved.
Nuclear power isn't a realistic option for a small instrument package, however, and one which is intended to go underwater can't use ordinary renewables such as wind and solar. At the moment, as a result, it's common to use a thing called an eXpendable Bathythermograph (XBT) to measure water temperatures down through the depths. The one-shot XBT plunges downwards, sending information back up to the deploying ship along very thin wires unreeling as it goes, and when the wires run out it is abandoned.
But now US naval boffins have come up with a crafty means of controlling buoyancy over long periods which doesn't involve expensive, unreliable long-duration batteries. Instead they have designed what they refer to as an "inoculated gas production vessel", a small cylinder with bacteria inside which produce hydrogen gas. This then escapes to fill a flotation chamber which will bring the instrument to the surface at a predetermined time.
The invention is known as Zero Power Ballast Control (ZPBC). According to a statement  issued yesterday by the Naval Research Laboratory:
With an ultimate goal of producing simple, small, power-efficient data harvesting nodes with variable buoyancy the device will be able to monitor ocean temperatures with a stay time ranging from weeks to months and eventually years, providing a longer term than other mechanisms such as the Expendable Bathythermograph (XBT).
In the future, the ZPBC will provide input for robust modeling of ocean temperatures and other parameters. The ZPBC could also be used to provide in-water optical data to enhance models for underwater visibilities, laser penetration depths, diver and target vulnerability assessments, electro-optical system performance predictions, and refining numerical models.
"Preliminary trials were successful in many ways," says Dr Justin Biffinger, NRL boffin. "The device surfaced and submerged periodically as designed via hydrogen gas produced from the microbial inoculum and growth medium, proving the device generated gas in sufficient quantity to produce buoyancy."
The US navy lab boys describe the test devices as "Autonomous Zero-Power Bathythermograph sensors" and believe that they could replace XBTs and similar instruments used in support of naval antisubmarine operations, mine-clearance, frogman attacks and more. ®