Sending Signals Under the Sea
The cables are high-tech, but the way to lay them hasn't changed in 130 years
NEWINGTON, N.H. — WHEN Hurricane Bob knocked out power lines in New England in August, utility crews worked day and night for more than a week to restore electricity in the region.But to Jeffrey Sanders, captain of the world's biggest undersea-cable-laying ship, repairing power lines on land is easy compared with fixing cable lines at sea in stormy weather. Right now Captain Sanders is somewhere in the northern Atlantic, one of the most inhospitable regions in the world, laying the telecommunications industry's newest fiber-optic cable system, called TAT-9. It is a $347.5-million project involving a consortium of 39 companies. Once this slender cable is laid to depths of more than two miles, TAT-9 will transmit 80,000 calls simultaneously, compared with 40,000 calls for TAT-8, the first transatlantic fiber-optic cable system, installed in 1988. A brief conversation with the captain reveals why he seems suited to be the man chosen for this sensitive and dangerous job. Sanders tells of a November 1989 voyage in which he and his C.S. Long Lines ship (owned by American Telephone & Telegraph Corporation's Transoceanic Cable Ship Company subsidiary) traveled to the frigid waters off Iceland to fix a transmission problem on an undersea fiber-optic cable. When the ship arrived on station, a typhoon was kicking up 20-foot waves. Despite the storm, his crew recovered the damaged cable 2 1/2 miles below. But with the storm rising to 70-knot winds and 40-foot waves, he became concerned about the safety of his crew, some of whom had to be strapped to the deck to avoid being swept overboard. He abandoned the operation. Three days later, with the weather still bad, he managed to finish the job.
A 5,750-mile 'garden hose' Sanders and his crew can expect to stay busy with the likes of the new TAT-9 system coming on line. More than 5,000 nautical miles (5,750 miles) long and only an inch in diameter, TAT-9 will connect shore installations in Manahawkin, N.J., and Nova Scotia with landing sites in Goonhilly, Britain; St. Hilaire, France; and Conil, Spain. With its new fiber-optic cable, TAT-9 can transmit 1,120 megabits (million bits) of information per second). With this capacity, an entire 24-volume set of the Encyclopedia Britannica, equivalent to 13 million words, can be transmitted in less than a second over 4,000 miles. AT&T spokesman Rick Brayall says that TAT-8 could not meet the rising demand for overseas calls, so the company decided to add additional undersea fiber-optic systems. "Since the late '60s and early '70s, it has been a question of providing additional capacity on a continuous basis to try to stay ahead of demand," says Derek Willson, spokesman for British Telecom, an undersea cable-laying giant along with AT&T. Fiber-optic cables use hair-thin glass fibers to transmit voice, data, and video signals with pulses of laser light. They can carry more data than the heavier and thicker (four inches in diameter) coaxial copper wire formerly used. The ship can lay the entire TAT-9 system in just one trip. Because of a copper cable's bigger bulk, it would have taken four trips to cover the same distance, Sanders says. Before TAT-8 was installed, the maximum volume of a copper-wire cable was 10,000 calls, says Deepak Swamy, an analyst for Kessler Marketing Intelligence, a fiber-optic research firm in Newport, R.I. Sanders's ship docked in Newington, N.H., two months ago to load 3,000 miles of fiber-optic cable for TAT-9 from the Simplex Wire and Cable Company. Six workers spooled the garden-hose-sized cable into the ship's holds by hand for three weeks, working day and night. This is the same method used by the British, who, in 1858, laid the first transatlantic cable, which carried telegraph lines between Newfoundland and Ireland, Sanders says. Manned by a crew of 94 (including five women) and 20 technicians from AT&T, the Long Lines left for Manahawkin, N.J., July 29 to start the first part of the TAT-9 system. When the ship arrived at Manahawkin, the first job was to find the end of the cable line that was ready to be connected from the New Jersey coast. Instead of using divers to lift the line, Sanders employs a technique that was used by the British 130 years ago: The ship drags one of several special hooks, which weigh from 40 to 400 pounds, until it grabs a cable on the ocean bottom. While this is not a difficult operation in shallow water, the crew often must perform this procedure to repair a damaged cable laid nearly four miles deep. "It is like standing on top of the Empire State Building with a fishing rod and trying to grab a piece of straw on the sidewalk," Sanders says. "I hope to get it in the first drag," he says. "If not, I'll be out there until I do." Aside from his successes with Long Lines, he recalls catching by mistake an old telegraph cable laid in the 1800s, an abandoned military cable, and 200 pounds of coral in Panama. The procedure for laying the TAT-9 cable is a familiar one to Sanders. Once it is picked up, the ship begins to lay it nonstop at a speed of five knots until it reaches connecting points in Canada, France, and Spain, and its final destination in England. At this speed, the cable begins to hit the bottom of the ocean 20 miles behind the ship, says Sanders. By using a special scanner, oceanographers avoid sharp peaks or volcanic ranges on the ocean floor. If the weather is agreeable, the entire operation will be completed by Oct. 13, the captain says.
Expensive 'repeaters' For TAT-9, a special device called a repeater is used every 100 kilometers (60 miles) of cable to amplify the lightwave signals. This is necessary because the strength of a lightwave weakens as it travels. For the TAT-8 system, the repeater was installed every 60 kilometers (37 miles). If a cable is damaged, engineers replace the broken section with a new one. The major expense, however, is in replacing repeaters, which cost $800,000 apiece. But the undersea fiber-optic cable systems such as TAT-8 and TAT-9 are built to last at least 25 years, says Richard Mondello, department head of undersea systems laboratory at AT&T's Bell Laboratories. He says repeaters are likely to fail three times during that period.
More cables planned To prepare for a possible transmission problem, AT&T has a "self-healing" backup system. If a transmission problem develops on the TAT-9 system, all overseas calls will automatically be rerouted to other systems. Besides TAT-9, other undersea cable systems will be installed in the near future. Next year, TAT-10, which connects the United States, Germany, and the Netherlands, will be launched. From 1993 to 1996, three more systems linking the US, Britain, and France will be installed. In 1995, AT&T is planning to use an optical amplifier - segments of optical fiber containing the rare element erbium - to boost lightwave signals without using expensive electronic repeaters. The optical amplifiers will be installed every 20 to 30 miles, allowing simultaneous transmission of 600,000 telephone calls, 7 1/2 times the capacity of TAT-9. Despite the technological breakthrough in fiber optics, cable-laying technology hasn't changed much in 130 years, Sanders says. "This is very labor intensive and there is no way to eliminate it." Good crews and coordination of work are keys to success in this business, he adds.