"Weve been doing this for 18 or 19 years now, and Id like to eliminate the risk," said Anker Rasmussen, manager of post-flight operations for shuttle prime contractor United Space Alliance. "Thats why were looking at the submarines. Its a safety enhancement."

Generating 3.3-million pounds of thrust during Atlantis sunrise liftoff, the shuttles boosters fired for two minutes before peeling away from the ships external tank. Plummeting from an altitude of about 35 miles (56 kilometers), the two solid-fueled rockets then splashed down in the Atlantic, where two ships the Liberty Star and the Freedom Star were waiting.

Since the first shuttle flight in 1981, Rasmussen and his crews have recovered almost 200 boosters, towing them back to shore for refurbishment and reuse. Only the two boosters lost in the 1986 Challenger accident and a pair that sunk after a 1982 flight after parachutes failed to deploy were not recovered.

Considered hazardous duty, the retrieval work requires divers to descend more than 100 feet (30 meters). Then they must insert a special plug into the boosters nozzles and pump air inside to make them float horizontally.

Manufactured by Canadian-based Nuytco Research Ltd., the DeepWorker 2000 sub eventually could replace the five to eight divers now needed to fish each booster out of the ocean.

A booster riding the swells also presents a hazard for divers as it bobs and moves to and fro. Rasmussen said. About 25 feet (7.5 meters) of the booster shows above the surface

The divers only spend about 15 minutes in the water with the booster. The rest of the time is spent reeling in parachute shroud lines, retrieving the parachute and getting the booster ready to be towed to port along with other shipboard duties.

But fewer people in the water potentially means less risk and less chance divers will encounter health risks associated diving at the depths necessary to work with the boosters.

Weighing in at about 3,800 pounds (1,710 kilograms), the sub seats one person inside its acrylic dome-covered cockpit.

"People always ask if its claustrophobic, but its not," Rasmussen said.

It normally is equipped with four thrusters, but that number was doubled to give the sub more propulsive power during the pick-up test today. Rasmussen called it "extremely maneuverable."

In addition to carrying the plug for the end of the booster, the sub also has an attachment on its robot arm to cut parachute shroud lines if theyre tangled around the booster.

But even if the new high-tech machine is adopted for regular use, dont look for the divers to be completely out of a job.

"I dont have people just designated as divers," Rasmussen said. "They have all sorts of other jobs," Rasmussen said. "They may be mechanics, electronics or engineers."