Countdown starts for NASA's final space shuttle Atlantis (PHOTOS)

NASA spacecraft Atlantis is gearing up for the scheduled July 8 launch to the International Space Station. The STS-135 crew members climbed aboard the space shuttle for the countdown dress rehearsal.

The space shuttle Atlantis will carry a crew of four: Commander Chris Ferguson, Pilot Doug Hurley, and Mission Specialists Sandy Magnus and Rex Walheim.

As part of the Terminal Countdown Demonstration Test (TCDT), the astronauts are driven to Kennedy's Launch Pad 39A and then are strapped into space shuttle Atlantis to practice the steps that will be taken on launch day a couple of weeks from now.

Similar to the launch day, the four astronauts put on their bright orange launch-and-entry suits and traveled to Launch Pad 39A at NASA's Kennedy Space Center in Florida aboard the Astrovan. The crew climbed into the space shuttle Atlantis and participated in a countdown dress rehearsal.

The astronauts wrapped up their on-site training at Kennedy before departing Thursday afternoon from the Shuttle Landing Facility for the flight back to their home base at NASA's Johnson Space Center in Houston.

The crew members will continue their training at Johnson for the final space shuttle flight, the STS-135 mission to the International Space Station. The astronauts plan to return to Kennedy on July 4 in preparation for the targeted liftoff on July 8.

At the launch pad, work continued as technicians scanned the bottom portions of the stringers on Atlantis' external fuel tank with no issues being found. A mass spectrometer external leak check of the shuttle's engine No. 3's main fuel valve was completed, and technicians installed insulation. A full retest of the valve is set for this weekend.

The space shuttle will carry the Raffaello multipurpose logistics module to deliver supplies, logistics and spare parts to the ISS during STS-135, which is the last planned space shuttle mission since STS-1.

The mission will also fly a system to investigate the potential for robotically refueling existing spacecraft and return a failed ammonia pump module to help NASA better understand the failure mechanism and improve pump designs for future systems.

STS-135 will be the 33rd flight of Atlantis, the 37th shuttle mission to the space station, and the 135th and final mission of NASA's Space Shuttle Program.

Take a glimpse of the space shuttle crew performing countdown dress rehearsal: