Beaming Up a Breakthrough for Navy Subs : Point Mugu: A laser system may allow the vessels to send and receive messages while remaining deep below the surface.

After Navy aircraft swept the area clear of intruders, a green beam of light descended from the heavens, pierced through the clouds and plunged deep into the sea about 80 miles off Point Mugu.

Moments later, a beam of blue light emerged from the murky depths and disappeared into the clouds above. A round of cheers erupted inside a nondescript building at Point Mugu’s Pacific Missile Test Center.

The dueling laser beams connected an aircraft flying at 20,000 feet to a submerged Navy submarine in the first sea test of space-age technology that promises to revolutionize naval communications.

Navy and Pentagon officials are poring over the results from late May tests of the Tactical Airborne Laser Communications (TALC) program in the Navy’s Sea Test Range near San Nicolas Island.

If proven successful, supporters in the Pentagon and on Capitol Hill say, new laser technology could remove the Achilles’ heel of the U.S. Navy submarine fleet: the need to surface so they can communicate over conventional radio frequencies.

“The beauty of this is that you could talk to submarines at operational depths,” said Bob Davis of the House Appropriations subcommittee on defense. “They could operate at several hundred feet. The precise number is classified.”

The Naval Ocean Systems Center, a research lab in San Diego, selected the testing area 30 miles southwest of San Nicolas Island because it has sufficient depth to evaluate the laser’s effectiveness, Navy documents show. It is at least 3,000 feet deep in the testing area.

The site is also heavily monitored by the Pacific Missile Test Center. Navy radar and surveillance aircraft routinely sweep the 35,000-square-mile Sea Test Range to maintain secrecy of weapons tests and prevent harm to non-military airplanes, ships and pleasure boats that venture into restricted areas.

The laser tests were controlled by a research team at Point Mugu’s range operations center, a building filled with banks of radar monitors and screens resembling those of NASA’s Mission Control.

When the submarine’s beam of blue light shot into the sky, two dozen men and women broke into cheers. “It was like a NASA launch. People started jumping up and down,” said project director Ed Munn of the Naval Ocean Systems Center. “I guess, when you put that much time into a project and it works, everybody gets pretty excited.”

Over the past three years, Congress has set aside more than $50 million to develop new technology that could establish laser communications between attack submarines and pilotless aircraft designed to be used in regional battles.

Pentagon and Navy officials envision laser communications on a much larger scale, however. They contend that the new solid-state lasers could be magnified to work from low-flying satellites.

“We think satellites have the greatest overall potential,” said John Davis, chief scientist of the Navy Space & Electronic Warfare directorate at the Pentagon. “When we say satellite, we mean global. We mean tactical as well as strategic submarines.”

Under current technology, the Navy relies on very low frequency (VLF) radio transmissions relayed by aircraft from shore to communicate with its ballistic missile and attack submarines dispersed around the globe.

But these VLF signals can penetrate only a few feet of seawater and require submarines to trail long antenna wires near the ocean’s surface. The closer to the surface, the more vulnerable the sub is to detection.

The Navy also uses extremely low frequency (ELF) radio signals that can penetrate seawater to depths of several hundred feet. But these signals, transmitted from huge antennas in Michigan and Wisconsin, must be sent at very slow speeds and can only be used for short messages.

To return messages, submarines must punch through the surface of the water with an antenna. Typically, they use ultra high frequency radio waves to send messages in seconds and then dive to depths safe from detection.

Laser beams in blue and green wavelengths can penetrate several hundred feet of seawater and are difficult to intercept or jam. But they too are quite slow--about the speed of a Teletype--and many Navy submariners worry that enemy sensors might be able to detect a submarine by following the blue or green lighted path.

“That was one of the main reasons of the submarine tests: to determine how much of a problem that would be,” Munn said. “At this stage, it is very difficult to say.”

Three hours before the tests, which began the evening of May 22, a P-3 Orion surveillance aircraft took off from Point Mugu Naval Air Station to scour the area for boats and planes, and whales and other marine mammals. Navy officials kept a lookout for marine life because an environmental study concluded that fish, sea lions, whales or other sea animals could suffer eye damage if they were caught in the laser beam within 155 feet of the submarine and happened to look at the source of the light.

In its 66-page study, the Navy determined that the chances of eye damage were remote--a conclusion accepted by state and federal wildlife officials. Nevertheless, naval officials decided they would suspend testing if marine mammals were found in the area.

“It happened only once,” said Calvin Jacobs, a Sea Test Range supervisor at Point Mugu. “We heard them on the acoustic system from the sub.” When the submarine crew heard the animal sounds, they thought they were whales, Jacobs said. “But it was a school of dolphins. We flew over and confirmed it.”

Jacobs said he suspected the submarine roused the dolphins’ curiosity. But they soon became bored and left the area. The tests then resumed, he said.

To conduct the experiments, defense contractors developed a new lightweight, solid-state laser that emits green light and mounted it in the belly of a Convair 580 aircraft. The research plane was also equipped with a new optical receiver designed to be four times as sensitive to detecting blue light as its predecessors.

The Navy had a division of Allied Signal Inc. in Westlake Village develop a blue-light laser for the Dolphin, a deep-diving submarine from San Diego.

The laser, about the size of a footlocker, was installed inside the submarine and pointed straight up through a double set of thick glass windows.

A laser receiver was mounted outside the hull on the bow of the submarine. It too was pointed straight up, even though the aircraft beamed messages from a variety of angles during the week of tests.

The underwater laser receiver takes advantage of the “manhole effect,” one of the peculiarities of nature. In the phenomenon, light takes the path of least resistance and essentially heads straight down. Scuba divers are familiar with the manhole effect, which makes the sun appear as if it is straight overhead even at sunrise or sunset.

“The manhole effect sure makes it a lot easier for us,” said Larry Stotts, manager of the laser communications program for the Pentagon’s Defense Advanced Research Projects Agency. “It simplifies the tracking system for the optical receiver. It sticks straight up.”

Over the course of a week, the submarine and aircraft sent laser messages from a variety of angles at different altitudes and depths. The tests continued day and night, Munn said. Although the laser beams are not invisible, no one was able to see them with the naked eye, he said.

Surveillance aircraft from Point Mugu patrolled the area and warned any ships or airplanes to stay out of the laser test area and avoid using binoculars that could magnify the potential for eye damage.

“We didn’t have any aircraft come through,” Munn said. “We had a couple of merchant ships that came by, and they didn’t come close enough to be a problem.”

The Navy has long been interested in satellite-based laser communications. But the projected multibillion-dollar cost of putting heavy xenon chloride gas lasers in space bogged down the program.

Last month’s tests provided the strongest evidence yet that a solid-state laser can penetrate the ocean depths. A solid-state laser is smaller, lighter, more power-efficient and has a longer life than a gas laser.

“When you look at all of the breakthroughs, it is quite an accomplishment in two years,” Stotts said. “We are very happy with the results.”

Navy leaders have begun to talk more about laser communications. Vice Adm. Jerry O. Tuttle, Navy director of the Space & Electronic Warfare directorate, has emerged as a cheerleader of the concept.

Although he is awaiting final test results--due in about three months--Tuttle has been nudging the defense community to consider advances in solid-state lasers and the potential for installing them on low orbiting satellites that operate a few hundred miles above the Earth.

Tactical Airborne Laser Communications

Experimental laser technology enabled an aircraft last month to send messages through a green beam of light to a submarine deep in the ocean. The submarine responded over the blue-light spectrum from depths required for stealth maneuvers. Under current technology, U.S. Navy subs must raise an antenna above the surface to communicate over radio frequencies.

Sources: Naval Oceans Systems Center and Defense Advanced Researched Projects Agency