Into the dark and cold

A Johns Hopkins University engineering professor helped guide an underwater vehicle this week to one of the coldest, darkest, most remote places on Earth.

Louis Whitcomb and his team - safe and dry aboard a research vessel in the western Pacific - guided the 18-foot-long robotic submersible Nereus by remote control as it plunged to the bottom of the Mariana Trench. The dive marked the first time since 1998 that man has probed so far into the crushing depths of the Earth's greatest abyss.

"It is a humbling experience to remotely pilot a vehicle into such an extreme, hostile, lightless environment," said Whitcomb, 47, one of three principal investigators with the expedition.

Tethered to the end of a miles-long fiber-optic cable, the Nereus touched bottom 35,761 feet below the surface on Sunday, eliciting a burst of cheers from the scientists and engineers at the controls far above.

"The temperature is [near freezing] and the pressure is 1,100 times the pressure we experience on the Earth's surface," Whitcomb said via e-mail from the research ship Kilo Moana, operated from Guam by the University of Hawaii.

The achievement came just days before French and Brazilian authorities rushed to the Atlantic to try to recover the flight recorders of an Air France jet that plunged into the sea. Those boxes might lie miles beneath the surface, and even if located, may be beyond the reach of all underwater craft except the Nereus.

"Nereus is capable of this task," Whitcomb said, but "it is not the ideal vehicle for this particular operation if, for example, heavy manipulation of wreckage is required."

Nereus' plunge into the Mariana Trench was purely for engineering tests and science. The researchers could not even be sure they had reached the deepest spot in the trench; scientists haven't mapped it well enough yet to know.

So the cheers aboard the Kilo Moana were brief, Whitcomb said. "After all, we had just arrived on the actual site of work." During the subsequent 10 hours on the bottom, he said, "we collected rock samples, tube cores of sediment samples, biological samples and extensive HD video and still imaging."

The geological samples will help scientists better understand the collision of vast slabs of the Earth's crust. The Mariana Trench formed where the Pacific plate is being driven deep beneath the adjoining Marianas plate. Nereus retrieved sediments from both plates and, for the first time, rock samples from nearby outcrops of the Earth's crust, said Patty Fryer, a University of Hawaii geologist on the expedition.

Only two other vehicles have made it to the bottom of the Mariana Trench and survived.

They include the Navy's bathyscaphe Trieste, which carried two men there in 1960; and the Japanese robotic vehicle Kaiko, which made a series of dives between 1995 and 1998.

Trieste was retired in 1965, and Kaiko was lost in 2003 when its cable snapped at sea. Since then, no other vehicle has been capable of diving deeper than four miles, according to the National Science Foundation, which funded most of the $8 million Nereus project.

"With a robot like Nereus we can now explore virtually anywhere in the ocean," said Andy Bowen, of the Woods Hole Oceanographic Institution, the craft's principal developer. "The trenches are virtually unexplored, and I am absolutely certain Nereus will enable new discoveries. I believe it marks the start of a new era in ocean exploration."

Engineering a robotic explorer to withstand the pressures of the deep ocean was a huge challenge. For example, the miles of cable needed to guide a tethered submersible had to support their own huge weight without snapping.

Nereus' designers chose a hair-thin fiber-optic cable that can be spooled out from coffee can-size canisters aboard the submersible as it descends. Nereus can also drop the cable to swim autonomously or float to the surface.

To withstand the tremendous water pressure, the craft's instruments are housed in sealed lightweight ceramic cylinders. Electric power comes from 4,000 rechargeable lithium-ion batteries.

Whitcomb's private time has been devoted to an old wooden sailboat and, with his wife, to the rescue of golden retrievers. At work, he directs Hopkins' Laboratory for Computational Sensing and Robotics, where he developed systems for guiding and scaling the forces applied by surgical robots.

"He's very committed to systems that have real-world impact," said Greg Hager, a Hopkins computer scientist and long-time friend.

Whitcomb'scontribution to Nereus was its navigation system.

The satellite signals used by global positioning systems don't penetrate the ocean, he explained, so underwater vehicles must track their own movements with a variety of sensors. These include sonar ranging, Doppler sonar, precision pressure sensors to measure depth, a gyrocompass for direction and accelerometers to measure movement - all integrated by a central computer that calculates the craft's position and speed, Whitcomb said.

Nereus' lightweight design sharply reduces the costs of deep-sea exploration, and should put it within reach of more researchers, scientists say.

"Our true achievement is not just getting to the deepest part of the ocean," said Tim Shank, a Woods Hole biologist on the Nereus team.

It also includes "unleashing a capability that now enables deep exploration, unencumbered by a heavy tether and surface ship, to scientifically investigate some of the most dynamically rich geological and biological systems on Earth."

Other Hopkins scientists assisting Whitcomb onboard include Stephen Martin, James Kinsey, Michael Jakuba and doctoral candidate Sarah Webster.

In addition to the NSF, the work is sponsored by the Office of Naval Research, the National Oceanic and Atmospheric Administration, the Woods Hole Oceanographic Institution and the Russell Family Foundation.



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