Reaching bottom after a 2-hour-and-36-minute descent, the National Geographic explorer and filmmaker typed out welcome words for the cheering support crew waiting at the surface: "All systems OK."

Folded into a sub cockpit as cramped as any Apollo capsule, the National Geographic explorer and frilmmaker is now investigating a seascape more alien to humans than the moon. Cameron is only the third person to reach this Pacific Ocean valley southwest of Guam (map)—and the only one to do so solo.

Hovering in what he's called a vertical torpedo, Cameron is likely collecting data, specimens, and imagery unthinkable in 1960, when the only other explorers to reach Challenger Deep returned after seeing little more than the silt stirred up by their bathyscaphe.

After as long as six hours in the trench, Cameron—best known for creating fictional worlds on film (Avatar, Titanic, The Abyss)—is to jettison steel weights attached to the sub and shoot back to the surface. (See pictures of Cameron's sub.)

Meanwhile, the expedition's scientific support team awaits his return aboard the research ships Mermaid Sapphire and Barakuda, 7 miles (11 kilometers) up. (Video: how sound revealed that Challenger Deep is the deepest spot in the ocean.)

"We're now a band of brothers and sisters that have been through this for a while," marine biologist Doug Bartlett told National Geographic News from the ship before the dive.

"People have worked for months or years in a very intensive way to get to this point," said Bartlett, chief scientist for the DEEPSEA CHALLENGE program, a partnership with the National Geographic Society and Rolex. (The Society owns National Geographic News.)

"I think people are ready," added Bartlett, of the Scripps Institution of Oceanography in San Diego, California. "They want to get there, and they want to see this happen."

(Video: Cameron Dive Is an Exploration First.)m

Rendezvous at Challenger Deep

Upon touchdown at Challenger Deep, Cameron's first target is a phone booth-like unmanned "lander" dropped into the trench hours before his dive.

Using sonar, "I'm going to attempt to rendezvous with that vehicle so I can observe animals that are attracted to the chemical signature of its bait," Cameron told National Geographic News before the dive.

He'll later follow a route designed to take him through as many environments as possible, surveying not only the sediment-covered seafloor but also cliffs of interest to expedition geologists.

"I'll be doing a bit of a longitudinal transect along the trench axis for a while, and then I'll turn 90 degrees and I'll go north and work myself up the wall," said Cameron, also a National Geographic Society explorer-in-residence. (Listen: James Cameron on becoming a National Geographic explorer.)

Though battery power and vast distances limit his contact with his science team to text messaging and sporadic voice communication, Cameron seemed confident in his mission Friday. "I'm pretty well briefed on what I'll see," he said.

Bullet to the Deep

To get to this point, Cameron and his crew have spent seven years reimagining what a submersible can be. The result is the 24-foot-tall (7-meter-tall) DEEPSEA CHALLENGER.

Engineered to sink upright and spinning, like a bullet fired straight into the Mariana Trench, the sub can descend about 500 feet (150 meters) a minute—"amazingly fast," in the words of Robert Stern, a marine geologist at the University of Texas at Dallas.

Pre-expedition estimates put the Challenger Deep descent at about 90 minutes. (Animation: Cameron's Mariana Trench dive compressed into one minute.)

By contrast, some current remotely operated vehicles, or ROVs, descend at about 40 meters (130 feet) a minute, added Stern, who isn't part of the expedition.

Andy Bowen, project manager and principal developer of the Nereus, an ROV that explored Challenger Deep in 2009, called the DEEPSEA CHALLENGER "an extremely elegant solution to the challenge of diving a human-occupied submersible to such extreme depths."