2nd Test Flight

As bystanders and security guards watch, the Space Shuttle Discovery approaches the runway at the Kennedy Space Center in Cape Canaveral, Fla., to complete mission STS-121 Monday, July 17, 2006.

Space Shuttle Discovery touches down on the runway at the Kennedy Space Center in Cape Canaveral, Fla., to complete mission STS-121 Monday, July 17, 2006.

The crew of the Space Shuttle Discovery poses for photographers after arriving at the Kennedy Space Center in Cape Canaveral, Fla., at the completion of mission STS-121 Monday, July 17, 2006. From left: Mission Specialist Michael Fossum, Mission Specialist Lisa Nowak, Commander Steven Lindsey, Mission Specialist Stephanie Wilson, Pilot Mark Kelly and British born U.S. astronaut Piers Sellers.

The nose of Shuttle Discovery and part of the forward underside can be seen in this image provided by NASA as photographed by one of the Expedition 13 crewmembers from the International Space Station on Thursday July 6, 2006. )

Space Shuttle Discovery lifts off with a seven member crew from Pad 39B at the Kennedy Space Center, Fla., Tuesday, July 4, 2006. The mission will include docking with the International Space Center and dropping off European Space Agency astronaut Thomas Reiter of Germany.

The Space Shuttle Discovery lifts off at the Kennedy Space Center in Cape Canaveral, Fla., on mission STS-121 Tuesday, July 4, 2006. The weather finally cooperated after two attempts to launch were scrubbed and despite the discovery of a small crack in the foam insulation on the shuttle's external fuel tank.

The Space Shuttle Discovery STS-121 crew walks to the astrovan holding American flags at the Kennedy Space Center, Fla., Tuesday, July 4, 2006. From left to right, front row: Mission Specialists Stephanie Wilson, Lisa Nowak and Pilot Mark Kelly. Back row, left to right: Mission Specialists Thomas Reiter of Germany, Piers Sellers, Michael Fossum and Commander Steven Lindsey.

The space shuttle Discovery sits on Kennedy Space Center's Launch Pad 39-B Monday, July 3, 2006, in Cape Canaveral, Fla. Workers inspecting the shuttle's external tank discovered a crack in the insulating foam.

Piece of foam from discovery's external fuel tank that inspectors found on the launch platform. NASA managers were deciding Monday, July 3, 2006, whether to call off the scheduled July 4, 2006, launch. A crack in the foam insulation covering the shuttle's external fuel tank was also spotted during an overnight inspection.

NASA astronaut David Wolf points to the spot on a model where a crack was discovered in the foam covering a bracket on the external fuel tank of the Space Shuttle Discovery at the Kennedy Space Center in Cape Canaveral, Fla., Monday, July 3, 2006. NASA officials may postpone the July 4th launch of Discovery.

Storm clouds hover over Press Site 39 some 3 1/2 miles from the Space Shuttle Discovery on Pad 39B at the Kennedy Space Center in Cape Canaveral, Fla., Sunday, July 2, 2006. NASA officials were forced to postpone liftoff for the second straight day because of the weather.

Storm clouds dot the sky around the Kennedy Space Center and the Vehicle Assembly Building on Saturday, July 1, 2006 in Cape Canaveral, Fla. The launch of the Space Shuttle Discovery was scrubbed because of weather.

The space shuttle Discovery is surrounded by early morning fog at the Kennedy Space Center in Cape Canaveral, Fla., Friday, June 30, 2006. The crew of STS-121 is scheduled for launch aboard the space shuttle Discovery on Saturday, July 1, 2006. This marks the second shuttle mission since the Columbia disaster.

This undated photo provided by NASA shows the the STS-121 crew members: mission specialists Stephanie Wilson; Michael Fossum; commander Steven Lindsey; mission specialist Piers Sellers; pilot Mark Kelly; mission specialists Thomas Reiter and Lisa Nowak, from left. The seven member crew is scheduled to lift off Saturday, July 1, 2006, onboard the space shuttle Discovery.

Traffic passes by the sign announcing the next launch at the Kennedy Space Center in Cape Canaveral, Fla., Friday, June 30, 2006. The crew of STS-121 is scheduled for launch aboard the Space Shuttle Discovery on Saturday, July 1, 2006.

St. Petersburg Times photographer Steve Coddington prepares his remote cameras outside Pad 39B at the Kennedy Space Center in Cape Canaveral, Fla., Friday, June 30, 2006. The crew of STS-121 is scheduled for launch aboard the Space Shuttle Discovery on Saturday, July 1, 2006.

A small alligator swims among the reeds in a pond adjacent to Pad 39B at the Kennedy Space Center in Cape Canaveral, Fla., Thursday, June 29, 2006. The crew of STS-121 is scheduled for launch aboard the Space Shuttle Discovery on Saturday, July 1, 2006.

An alligator floats in a pond near the space shuttle Discovery, background, Friday morning June 30, 2006, at the Kennedy Space Center in Cape Canaveral, Fla. Seven astronauts are making final preparations for a planned liftoff on Saturday, July 1, 2006.

In this photo released by NASA, STS-121 Mission Specialists Lisa Nowak, left, and British born, U.S. astronaut Piers Sellers inspect cables in the mid-body of space shuttle Discovery on Launch Pad 39-B Thursday June 29, 2006, at Cape Canaveral, Fla. The seven member crew is making final preparations for the launch on Saturday, July 1, to the International Space Station.

STS-121 pilot Mark Kelly, left, and mission commander Steven Lindsey adjust their launch and entry suits after flying in the shuttle training aircraft Wednesday, June 28, 2006, at the Kennedy Space Center's Shuttle Landing Facility. Seven astronauts are scheduled to liftoff Saturday, July 1, onboard the space shuttle Discovery.