The image is grainy and poorly lit, but the video camera mounted atop a small, tracked robot shows the robot's progress through a service corridor of the collapsed World Trade Center's second tower.
As the robot comes up to a rubble pile, the video shows the top of a corpse's head and a wristwatch.
The chilling image, recorded a week after the Sept. 11 attack, demonstrates both a strength and a weakness of the robots now available for urban search and rescue operations, said Howie Choset, a mechanical engineer at Carnegie Mellon University. The tethered robots, similar to miniature tanks, can search areas inaccessible to or unsafe for humans, but the inability to crane their necks or probe into rubble piles limits what they can see.
Imagine, Choset said, if the robot's camera was mounted on something akin to an elephant's trunk. The camera could peer over the edge of the rubble, or perhaps probe through spaces between the rubble to search for other, larger voids where survivors might be.
Or, separated from the tracked robot, the long, segmented device might slither like a snake deep into the rubble in its search for survivors.
The concept of snake-like robots isn't new, but Choset is leading a research effort to overcome problems with strength, navigation and locomotion that have restricted use of these robots.
His lab recently was awarded an $800,000 grant from the U.S. Department of Energy to extend the technology, perhaps making these "hyper-redundant" robots available for use in waste tank or bridge inspections, surveying of bio-terrorism sites or robotic surgery, as well as for search and rescue operations.
The beauty is both the ability of these robots to do what humans can't do, such as squirming through tiny gaps, and to simply do a lot of different things, from dipping its head into a coffee cup thought to contain anthrax to serving passively as a makeshift support amid shifting debris.
"Sometimes, it's more important to have something that's versatile, rather than to have something that does one task well," Choset said.
The potential value of snake robots became obvious in the aftermath of the Twin Towers' collapse.
Within 24 hours of the attack, researchers from several research centers and robot manufacturers were on the scene with about a dozen robots, varying in size from a shoebox to a suitcase. The remote-controlled robots ventured into areas too small or too unstable for human emergency workers.
By 8 a.m. the day after the attack, a robot had found its first human victim in the rubble, noted Robin Murphy of the nonprofit Center for Robot-Assisted Search and Rescue.
At Ground Zero, time was of the essence, as it is at any such urban disaster, such as building collapses caused by earthquakes. "You've basically got 48 hours to find survivors," explained Murphy, a roboticist at the University of South Florida. But it's hard to know where large voids that contain survivors might be in the rubble.
"You just don't have enough cranes and people to move everything," she added. "You have to know where to dig."
Within 10 years - and maybe in as few as five - robots will be as routine at search and rescue sites as dogs are today, Murphy predicted. By using a variety of types and sizes of robots, emergency crews might quickly identify pockets of survivors and perhaps even establish communication with them, or deliver food and medical supplies to them.