Robot Submarines Go To War. Part 2: The Navy's AUVs

One of the vehicles military planners believe might someday be able to destroy mines is the Surf Zone Crawler, an unusual AUV being developed at the Navy's Coastal Systems Station in Panama City, Florida. These small, square, tank-like vehicles are less then a foot tall and have wide tracks that enable them to negotiate rocky ocean terrain. The crawlers aren't as vulnerable to ocean currents as swimming AUVs, which makes them ideal for close-range identification of mines. But they're a long way from being ready. "When it comes down to it, we put our robots in the water and sometimes we get stuck in the mud," says Chuck Bernstein, a Coastal Systems Station engineer.




Another problem: AUVs that are used to blow up mines are likely to be destroyed in the blast. Wernli believes it makes sense to sacrifice one Remus or similar vehicle for every mine destroyed: "If I can take out a mine for $100,000, that's worth it." But until now the Navy has been accustomed to building complex manned craft it does not want to lose, so the idea of creating expendable vehicles represents something of a paradigm shift. And it becomes a problematic notion as AUVs get more sophisticated, sporting new kinds of sensors and communications systems. The more gear an AUV possesses, the more it costs, and the less appropriate it is for kamikaze missions. Simmons' rule of thumb: "Don't put it in the water if you can't afford to lose it."




One solution to the problem is a concept known as cooperative autonomy. In a mine-sweeping scenario, for example, high-end AUVs could release cheaper, more primitive machines that could install themselves next to the targeted mines and wait to be told to blow up. "You can still do the job, but each vehicle doesn't have to be as smart," says Bernstein.




Communications will be a key component of such cooperative arrangements. Willcox says Bluefin is outfitting the BPAUV to act as a subsurface server, capable of receiving new mission plans from a ship and relaying them to AUVs down below. The BPAUV will communicate with the submerged vehicles through short-range acoustics, but when it needs to transmit or receive mission-critical information, it will employ a new long-wavelength antenna that transmits radio waves just above the ocean surface. With this capability, the BPAUV could quietly talk to a ship up to 60 nautical miles away.




Another way to economize is to create modular AUVs that perform many functions, rather than a panoply of specialized craft. SPAWAR engineers are designing a mission-reconfigurable AUV. The goal is a versatile and far-ranging vehicle, launched and recovered from a sub's torpedo tubes, that would be capable of anything from communications to reconnaissance work. If sub operators want to monitor radio signals near a hostile shoreline, "you equip it with an antenna to listen, collect intel, and then come back out to the safety of deep water to dump the information to those who can use it," says SPAWAR engineer Barbara Fletcher. Change the payload and the vehicle could conduct mine neutralization or track enemy submarines. A preliminary version of this next-generation AUV is expected to join the fleet in 2009.

NEXT STEP: TECH HURDLES

Autonomy is probably the most challenging aspect of the robot sub. AUVs will have to avoid potential threats, assess incoming information, and adapt mission priorities, all without direct human intervention. For all this to happen, sensors -- sonar, magnetic and optical -- will have to be improved so that AUVs can gather higher-resolution images at even greater distances. One technology that could get them there is synthetic aperture sonar, an underwater adaptation of a technique used in radar. For a given point on the ocean floor, a side-scanning sonar sends out and receives a single ping, but synthetic aperture sonars pelt the same spot over and over as the vehicle moves along. In effect, this widens the aperture of the sonar from 12 inches to 100 yards. Enson Chang of Dynamics Technology in Arlington, Virginia, says the new technique could resolve wallet-sized objects a kilometer away.