Atlantis sits atop pad 39B awaiting liftoff to deliver the Joint Airlock to the international space station. Photo: NASA

NASA officials gathered on Thursday for the traditional Flight Readiness Review and affirmed July 12 as the launch date for Atlantis' 11-day mission. Liftoff is planned for 5:04 a.m. EDT (0904 GMT).

Delayed because of troubles with the international space station's new robotic arm, the flight will deliver the $164 million Joint Airlock to the outpost. The airlock, named Quest, will serve as the staging area for U.S. and Russian spacewalks from the station.

The robot arm had suffered a couple of problems, but NASA says the issues appear to be resolved. The most significant glitch -- a communications error in the shoulder pitch joint's backup electronics -- hasn't recurred in several weeks. Engineers determined a suspect computer chip is to blame. A software patch has since been developed that will tell the electronics to bypass the communications error message in the event the problem happens again.

The airlock will add an additional 1,200 cubic feet of volume to the station, bringing its size to about 12,000 cubic feet of volume. The six-and-a-half-ton module was built by Boeing at NASA's Marshall Space Flight Center.

"This mission will be a milestone for both the station and shuttle as we complete a major phase of the station's assembly," Space Shuttle Program Manager Ron Dittemore said. "A year ago, I said we would fly the most complex series of missions NASA has undertaken since landing on the moon -- now we're nearing completion of the first phase. The team has truly done an excellent job to get us here safely, successfully and on schedule."

Atlantis' five astronauts will suit up and board the space shuttle on Friday for the final three hours of a countdown dress rehearsal.

Led by commander Steve Lindsey, with rookie pilot Charlie Hobaugh and mission specialists Janet Kavandi, Mike Gernhardt and Jim Reilly, the astronauts are due to enter Atlantis' crew module starting at 8:15 a.m. EDT at launch pad 39B.

The astronauts and launch team in a Complex 39 Firing Room will participate in the mock countdown to practice their roles before the real liftoff day arrives. The test will culminate with a pretend ignition and shutdown of Atlantis' three main engines just after 11 a.m. EDT. The astronauts will then simulate an emergency evacuation from the shuttle.

The crew arrived at Kennedy Space Center on Tuesday and have spent the past couple of days learning about pad evacuation procedures, test driving an armored transporter they could use to escape the pad area and inspecting the payloads loaded aboard Atlantis.