An image made from NASA Television shows the space shuttle Endeavour as it does its fly-around of the International Space Station on Monday, May 30, 2011, before returning home from NASA's penultimate shuttle mission. The shuttle is viewed from the space station as it passes over Australia. (AP Photo/National Aeronautics and Space Administration)
The crews of the space shuttle Endeavour and the International Space Station gather for a joint news conference from the space station on Thursday, May 26, 2011. (AP Photo/NASA)
In this image from NASA television astronauts Mike Fincke, left, and Greg Chamitoff, make their way along the P3 Truss on the International Space Station as they make their way back to the quest airlock wrapping up the fourth spacewalk Friday morning, May 27, 2011. (AP Photo/NASA)
A photo taken by NASA's Mars Exploration Rover Spirit in 2008 shows the Martian landscape. NASA is ending efforts to revive the immobilized robot. (NASA via Associated Press)
This image provided by NASA televsion shows the space shuttle Endeavour's tiles being inspected early Saturday morning May 21, 2011, using both the shuttle's robot arm and the International Space Station's robot arm. (AP Photo/NASA)
This image provided by NASA on Saturday, May 14, 2011, and taken by an Expedition 27 crew member aboard the International Space Station on May 12, 2011, clearly shows the outlines of some heavily flooded agricultural fields on the Missouri side of the Mississippi River. The center point for this frame is just north of Caruthersville, Mo., and west of Ridgely, Tenn. North is toward the lower right corner of the image. (AP Photo/NASA)
Visitors to the Intrepid Sea, Air and Space museum watch as NASA announces that the museum will receive the retired space shuttle Enterprise on a 40 foot long video wall, Tuesday, April 12, 2011 in New York. Shuttles will be going to the Smithsonian Institution, the Intrepid Sea, Air and Space Museum in New York, the Kennedy Space Center in Florida and the California Science Center in Los Angeles. (AP Photo/Mary Altaffer)
This March 28, 2011 image provided by NASA shows composited images from Swift's Ultraviolet/Optical and X-ray telescopes of a gamma-ray explosion designated GRB 110328A. Scientists say this blast is unusual because the effects are long-lasting. More than a week later, they continue to see high-energy radiation spiking and fading at the source. Flaring from such an event usually lasts a couple of hours. (AP Photo/NASA, Swift, Stefan Immler)
This image provided by NASA is the first ever obtained from a spacecraft in orbit about the Solar System's innermost planet, Mercury. The image was captured early this morning, at 5:20 a.m. EDT,Tuesday March 29, 2011. The dominant rayed crater in the upper portion of the image is Debussy. The bottom portion of this image is near Mercury's south pole and includes a region of Mercury's surface not previously seen by spacecraft. On March 17, 2011 (March 18, 2011, UTC), MESSENGER became the first spacecraft to orbit the planet Mercury. (AP Photo/NASA)
