Diving deep: Robosubmarine going down

How low can you go? A freewheelin' robotic submarine developed by NASA and Carnegie Mellon may soon find out. The untethered sub will dive into a water-filled sinkhole in Tamaulipas, Mexico.

How low will it go? So far sonar's reached a depth of 270 meters. But then human divers have gotten down to 282 meters below the surface. No bottom in sight at the Zacaton sinkhole.

The robosub is pill-shaped and about seven feet across. It'll carry water sampling, sonar, a robo-arm and other scientific gear, take pictures and help map the walls and hopefully the bottom of the sinkhole. The sinkhole's large overhang makes the sub's self-navigation system crucial. It has to get near the walls but eventually return to the open water leading back to the surface. It's like diving into a gigantic narrow-topped vase.

Scientists and engineers at Carnegie Mellon developed the sub and its guidance and control software. So far they've been testing it in a known, 115-meter-deep sinkhole called La Pilita, five hours south of Brownsville, Texas. They plan to do the deep dive at Zacaton in May.

The submarine's official name is DEPTHX. That's a catchy acronym for Deep Phreatic Thermal Explorer.