The orbiting station is seen here silhouetted against the planet. Photo: NASA

The international space station currently is made up of four main habitable modules and two airlock modules - one Russian and one American. Think of the four main modules as a train moving through space. The U.S. laboratory module Destiny is in front, followed by a multi-hatch node called Unity that serves as a gateway to the Russian segment of the outpost.

Connected to the node on the opposite side from Destiny is a pressurized mating adapter, or PMA, leading into the Russian-built NASA-financed Zarya propulsion and storage module. Zarya, in turn, is connected to the Zvezda command module. The Russian Pirs docking and airlock module is attached to Zvezda's downward-facing, or nadir, port.

Russian Progress supply ships typically dock at Zvezda's aft port while Soyuz lifeboats can be docked at Pirs or a nadir port on the Zarya module. When Atlantis arrives, the Progress 9 cargo ship will be docked to Zvezda's aft port while the current Soyuz lifeboat will be docked to Zarya's nadir port.

Facing forward, the U.S. Quest airlock module is attached to Unity's right-side, or starboard, hatch. The Z1 truss, containing the lab's four massive U.S.-built gyroscopes, is bolted to Unity's upward-facing, or zenith, port. Mounted on top of Z1 is the P6 solar array, a huge set of electricity producing panels that ultimately will be moved to the port side of the solar array truss currently under construction.

The P6 array truss also includes a thermal control system to provide cooling until the main truss is completed. The solar wings stretch 240 feet from tip to tip, towering 90 feet above the main body of the station.

Atlantis' launching, like all flights to the space station, is timed to coincide with the moment Earth's rotation carries the launch pad into the plane of the station's orbit. That plane is tilted 51.6 degrees to Earth's equator.

The shuttle has enough power to launch five minutes to either side of the moment the pad is "in plane" with the station. For technical reasons, NASA only uses five minutes of that 10-minute launch window, taking off when the pad is essentially directly in the plane of the station's orbit.

Once in space, the plane of the shuttle's orbit cannot be significantly altered. Altitude, however, is another matter and the lower the altitude, the higher the spacecraft's velocity. Atlantis will launch into the station's plane but orbit at an initially lower altitude.

Atlantis will dock to the Pressurized Mating Adapter on the front of Destiny. The S0 truss, delivered in April, is in view. Photo: NASA

After a series of rocket firings to fine-tune the shuttle's approach, Ashby will begin the terminal phase of the rendezvous with Atlantis trailing the station by about 9.2 statute miles. From there, Ashby and Melroy will oversee a series of computer-controlled rocket firings designed to place the shuttle at a point 600 feet or so directly below the space station.

At about that point, Ashby will take over manual control and pilot Atlantis in a slow loop up to a point 300 to 400 feet directly in front of the lab complex as both spacecraft race through space at five miles per second.

Positioned directly in front of the station's long axis, Ashby will manually guide Atlantis in so the docking system in the shuttle's cargo bay can mate with its counterpart on a pressurized mating adapter attached to Destiny's forward hatch. After hooks and latches engage, the two spacecraft will be locked together.

In pre-flight NASA interviews, Ashby did not discuss the terminal rendezvous sequence. But Kenneth Cockrell, Endeavour's commander for NASA's most recent shuttle flight in June, provided a good description of the final series of steps.

"It's really a fun piloting task," Cockrell said. "It's like driving a ship. You make very small inputs that take a long time to occur; but once they occur, they're very hard to stop. So it's something you need to do very precisely and it takes a lot of practice.

Endeavour under the control of skipper Ken Cokrell during its approach to the space station in June. Photo: NASA

"So we go in very slowly and gradually, we slow down at about 30 feet away from the docking port and just look through a zoomed-in camera at the target. The target has a little set of alignment guides on it and we make sure that we're all lined up, that the two vehicles are exactly in plane.

"And then, from 30 feet in, we just hold a steady rate and we crash into the station," he joked. "That's a very slow crash. It's one-tenth of a foot per second. It's as slow as a snail would crawl."

After leak checks, hatches between the two spacecraft will be opened and station commander Korzun and his two Expedition 5 crewmates will welcome Atlantis' six astronauts on board. After a safety briefing, the combined crews will get down to work.

Along with installing the S1 truss, the shuttle crew plans to deliver about 1,000 pounds of supplies and equipment, along with a few tasty treats for the station's crew.

"They're looking forward to getting some apples and oranges and things of that nature," Magnus said at a pre-flight briefing. "There's a pecan pie that we're trying to get up there to them. But that's a secret, don't let them know, that's going to be a surprise!"

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