After safely reaching its launch pad at NASA's Kennedy Space Center in Florida, space shuttle Atlantis now awaits liftoff for its target May 12 STS-125 mission to the Hubble Space Telescope.

Atlantis arrived at Launch Pad 39A at approximately 9:10 a.m. EDT Tuesday on top of a giant crawler-transporter. The crawler-transporter left Kennedy's Vehicle Assembly Building at 3:54 a.m., traveling less than 1 mph during the 3.4-mile journey. The shuttle was secured on the launch pad at 11:17 a.m.

Atlantis' 11-day mission is the final shuttle flight to Hubble. During five spacewalks, the shuttle's seven astronauts will install two new instruments, repair two inactive ones and replace other Hubble components.

The Science Instrument Command and Data Handling Unit that will be installed in the telescope arrived at Kennedy on Monday. The new unit will replace the one in Hubble that stopped working in September 2008 and delayed the servicing mission.

The result of the upgrades will be six working, complementary science instruments with capabilities beyond those now available and an extended operational lifespan of the telescope through at least 2014.

Scott Altman will command Atlantis. Gregory C. Johnson will be the pilot. The Mission Specialists will be John Grunsfeld, Mike Massimino, Megan McArthur, Andrew Feustel and Michael Good.

STS-125 is the 126th shuttle flight, the 30th flight for Atlantis and the fifth Hubble servicing mission.

Space shuttle Endeavour is scheduled to roll out to Kennedy's other launch pad, 39B, on Thursday, April 17. Endeavour will be prepared for liftoff in the unlikely event that a rescue mission is necessary following Atlantis' launch. After Atlantis is cleared to land, Endeavour will move to Launch Pad 39A for its upcoming STS-127 mission to the International Space Station, targeted to launch in mid-June.

Endeavour will roll over from Kennedy's Orbiter Processing Facility 2 to the Vehicle Assembly Building on April 10. In the assembly building, crews will attach the spacecraft to its external fuel tank and twin solid rocket boosters in preparations for its move to pad 39B.

NASA managers decided to proceed with the dual-pad approach after carefully reviewing the manifest options to complete the International Space Station and to ensure it is in the most robust condition possible following shuttle retirement.

The dual-pad approach requires one month less processing time than the single-pad approach and will help complete both STS-125 and STS-127. Endeavour will deliver the Japanese Exposed Facility and make the space station more robust to support cargo delivery for a six-person crew.

The Space Shuttle Program will continue to work with the Constellation Program to minimize the impact on the Ares I-X test flight which will use Launch Pad 39B later this year.