The STS-121 mission has ended and the crew of space shuttle Discovery have returned home to Texas. STS-121 Commander Steven Lindsey, Pilot Mark Kelly, Mission Specialist Mike Fossum, and Mission Specialists Lisa Nowak, Stephanie Wilson and Piers Sellers were given a hero's welcome by hundreds of colleagues, friends, family and members of the public. In turn, the crew thanked those who made the flight successful.

Discovery flight commander Steven Lindsey recalls NASA's two major objectives. One is to complete the 'Return to Flight' test objectives and the other is to get up to the space station, prepare it for assembly, fix whatever's broken, and deliver critical supplies to the crew. Both objectives were achieved and Lindsey acknowledged the support of the mission control teams in Houston:

"Every single minute we were awake and every single minute we were asleep, they flew the mission with us. They were up there with us every day. We were talking to them all the time. I can't count the number of times during the mission that these teams made critical decisions that made the difference between succeeding on a timeline or failing on a timeline. And they just did a superb job."

The STS-121 astronaut crew are due back on Earth at 9:14 a.m. EDT (1314 GMT) today at the Kennedy Space Center's  Runway 33. And everything looks just fine! “We’ve inspected the vehicle and we understand the [heat shield] more than we have on any other mission,” NASA’s reentry flight director Steve Stitch. “The vehicle is totally clean for reentry.”

Everything except the weather, that is. “Hopefully the weather will be great in Florida tomorrow,” pilot Mark Kelly. Mission controllers are hoping the skies would clear up despite forecasts of rain showers close to a 30-mile (48-kilometer) zone around the shuttle's landing site. The Discovery cannot land under rainy conditions because of possible damage to the thousands of black ceramic tiles that protect the orbiter’s belly from the searing heat of reentry.

If all goes well, Kelly and STS-121 commander Steven Lindsey will fire Discovery’s engines at about 8:07 a.m. EDT (1210 GMT) slowing it down for its hour-long drop toward Earth. But if weather conditions do interfere, NASA could could order the delay of the Discovery’s reentry for about 90 minutes. That's enough for the crew to make one last circle around Earth before firing Discovery’s engines for its second attempt at 9:43 a.m. EDT (1343 GMT) for a landing at 10:50 a.m. EDT (1450 GMT).

If Discovery fails to land as scheduled, flight controllers will activate the alternate landing sites at Edwards Air Force Base in California’s Mojave Desert and the Northrup Strip at White Sands Space Harbor in New Mexico. NASA said they expect to bring the shuttle home by Wednesday at the latest. Discovery’s planned landing activities will be broadcasted live on NASA TV beginning at 1:08 a.m. EDT (0508 GMT).

The Discovery crew began their long journey back to Earth Saturday as the shuttle cast off from the International Space Station (ISS) after eight days of orbital work. Discovery pulled away from its berth at the end of the station's Destiny laboratory at about 6:08 a.m. EDT (1008 GMT) to begin its planned two-day trip back to Earth.

The STS-121 astronaut took some final parting snapshots before hatches linking their spacecraft to the ISS were closed at about 4:00 a.m. EDT (0800 GMT). “We have physical separation,” Discovery’s commander Steven Lindsey said as the 100-ton orbiter pulled away from the 200-ton space station 223 miles above and off the coast of New Zealand.

Meanwhile, the three astronauts aboard the ISS watched their departing comrades after a busy week of restocking the space station's supply, testing an orbital inspection boom for use as a repair platform and evaluating a heat shield crack repair method. “This moment came so fast,” ISS Expedition 13 commander Pavel Vinogradov. “Have a safe trip, soft landings, and we’ll see you on the ground in a few months,” was ISS Expedition 13 flight engineer Jeffrey Williams' message as the shuttle pulled away.

Discovery will hover about 40 nautical miles (74 kilometers) from the ISS today while STS-121 mission specialists Lisa Nowak and Stephanie Wilson complete a final check of the orbiter’s nose cap and starboard wing leading edge. Back on earth, engineers continue to study a potential hydrazine fuel leak in one of Discovery’s three auxiliary power units. Flight controllers will test the small leak on Sunday to determine if the APU should remain in operation during Monday’s planned landing. Discovery is set to to land in Cape Canaveral, Florida at NASA’s Kennedy Space Center on July 17 at about 9:14 a.m. EDT (1314 GMT)

NASA is now more confident it can make minor in-flight repairs to a shuttle’s heat shield in orbit after the successfully testing of the repair techniques during the Wednesday spacewalk outside the Discovery.  According to Tony Ceccacci, lead shuttle flight director for the STS-121 mission, the preliminary results are positive. However, the repair technique will likely be limited to the types of repairs they performed.

During a seven-hour and 11-minute spacewalk, Piers Sellers and Michael Fossum tested application methods for a sticky, black material dubbed NOAX (non-oxide adhesive experimental). The space age material was formulated to fill in cracks and gouges to the carbon composite panels lining a shuttle’s nose cap or wing leading edges. Using spatulas and caulk gun-like tools, they applied NOAX to squares of reinforced carbon carbon used to protect the shuttle nose and wings from reentry temperatures. Then they spent three hours testing the technique by perching themselves on the space station’s robotic arm and a shuttle foot restraint to recreate the types of positions that would likely be used in the event of an actual repair.

Today’s spacewalk adds to the initial tests conducted during NASA’s STS-114 astronauts in July 2005 to determine the basic behavior of NOAX under actual flight conditions. “For STS-114, the conditions that we did the NOAX repair was more of a science project to see if we could throw it on the piece of RCC and determine what the results were,” Ceccacci said. “For 121, these guys went through a lot of work to determine exactly how you would repair [damage].”

The six astronauts of the Discovery shuttle passed the midpoint of their spaceflight as they spent their 8th day in orbit. NASA’s STS-121 astronauts commanded by Steven Lindsey, and the just arrived ISS crewmember Thomas Reiter, are pushing ahead with transferring the cargo between the station and Discovery. Space cowboys Piers Sellers and Michael Fossum are also gearing up for their third and final spacewalk of the flight. The two astronauts will step outside the space station’s Quest airlock to test a heat shield crack repair method inside Discovery’s payload bay. That spacewalk is expected to take about six hours.

STS-121 mission specialist Lisa Nowak, and crewmate Stephanie Wilson will conduct a final round of heat shield inspections after undocking from the ISS on Saturday to scan for any damage from micrometeorites or debris. Meanwhile, Discovery’s STS-121 astronauts and the ISS Expedition 13 crewmembers are busy filling the cargo module known as Leonardo with trash and unnecessary items for the return trip to Earth.

Many of Discovery’s astronauts are confident that with the success of their mission, NASA can resume construction flights to the ISS. Discovery’s STS-121 spaceflight is aimed at completing many of the return to flight objective that started with the STS-114 missions.

Amidst all the work that the guys and gals of STS-121 have to do, they of course still have time to engage in some friendly and encouraging banter with the President of the United States. Nine crew members are responsible for transferring two tons of cargo (obsolete equipment, tools and other unnecessary items) between the shuttle Discovery and the International Space Station.

On the lighter side of things, President Bush was able to speak with the astronauts during a private ground-to-orbit telephone call. The President told the astronauts that he watched closely as STS-121 spacewalkers Piers Sellers and Michael Fossum worked outside their spacecraft, and invited the astronauts and their families to the White House. The President was also proud of the fact that Fossum is a graduate of Texas A & M University.

Discovery will return about 5,421 pounds (2,458 kilograms) of material to Earth, more than 4,000 pounds (1,814 kilograms) of which will be stowed in Leonardo during the descent, NASA has said. Among the first things to be unpacked were 82 containers of food and about 187 pounds (85 kilograms) of other provisions for the European Space Agency’s (ESA) astronaut Thomas Reiter, who joined station commander Pavel Vinogradov and flight engineer Jeffrey Williams as a member of the ISS Expedition 13 crew. Mr. Reiter obviously doesn't pack light (kidding)!

Also, astronauts Fossum and Sellers readied their U.S.-built spacesuits for one last spacewalk outside Discovery. They will spend roughly 6-7 hours working inside Discovery’s payload bay to test an experimental black, heat-resistant non-oxide adhesive (NOAX) material for use in repairing small cracks in the carbon composite panels that line the shuttle’s wings and nose. They will also test a new infrared camera by recording about 20 seconds of video of the carbon composite panels along Discovery’s wing edge. Let's wish these two brave men the best of luck as they spacewalk today!

The second of three spacewalks for the STS-121 mission was done last yesterday, July 10. To stow a spare cooling system pump and replace a broken cable reel for the ISS' Mobile Transporter, STS-121 spacewalkers Piers Sellers and Michael Fossum spent seven hours outside the station. The tasks will give NASA the green signal for a precisely choreographed series of 16 space shuttle missions (STS-121 included) that will complete the orbital laboratory and man it with six full-time astronauts.

August 28 will see the launch of NASA's first ISS construction mission since 2002 and it will deliver a pair of new solar panel wings and the massive truss mast to the orbital library. And to continue the orbital ISS construction effort, NASA also hopes to launch in December the STS-116 aboard Discovery.

Although the spacewalk was successful, it was not without complexities. Lead ISS flight director for NASA's STS-121 mission Rick LaBrode shared that the astronauts needed to work through stuck bolts, a stubborn spring that prevented initial attempts to install the new cable reel, and a lot of bumping - all of which made the task more complicated.

Tomas Gonzalez-Torres, lead spacewalker officer for the STS-121 mission however said that he wasn't worried at all; adding that he had a crew who can handle the job. "I couldn’t have asked for a better crew. These guys were fantastic," shares Gonzalez-Torres.

NASA mission controllers gave the go-signal for a third spacewalk and an extra day in space for the shuttle Discovery crew. “It’s a done deal,” according to lead shuttle flight director for Discovery’s STS-121 mission Tony Ceccacci. “We’re going to tell them we’ll step up to do a 13-day mission and we’ll plan accordingly.”

The extra day will give spacewalkers Piers Sellers and Michael Fossum a chance to test additional crack repair methods in the reinforced carbon carbon panels lining the shuttle wing leading edges. Ceccacci said the extra mission day will also give Discovery’s crew extra time for the cargo transfer operations and make heat shield repairs in case any damage is seen.

NASA set aside four hours today for the STS-121 crew to examine a gap filler jutting out near Discovery’s starboard external tank door, a gap filler along the forward section of the orbiter, a white spot that appears similar to bird droppings on the nose cap, two scuffs on a right wing RCC panel and a dark spot on another RCC panel on the same wing.

Sellers and Fossum are preparing for the first spacewalk to make repairs to the station’s railcar-like Mobile Transporter and test the stability of the orbital boom as a work platform.  The spacewalk starts at 9:13 a.m. EDT (1313 GMT) and can be viewed live on NASA TV.

The International Space Station (ISS) became the happiest place on Earth, err, in space when the seven crew members of the Discovery came aboard. This was Mission No.1 accomplished for the the STS-121 spaceflight. Tony Ceccacci, lead shuttle flight director for the Discovery mission said the orbiter’s docking at the ISS marks the start of a spaceflight marathon for the shuttle’s crew.

Veteran space cowboy and Discovery’s STS-121 mission commander, Steven Lindsey, eased the 100-ton shuttle into a berth at the end of the ISS Destiny lab at 10:52 a.m. EDT (1452 GMT) today. Less than two hours later, Lindsey and his six STS-121 crewmates were exchanging handshakes and hugs with ISS Expedition 13 commander Pavel Vinogradov and flight engineer Jeffrey Williams.

Among the major achievements during the orbital rendezvous was Discovery’s orbital back flip executed while flying 600 feet below the ISS. During that time, Vinogradov and Williams took 350 still images later relayed down to Earth to be analyzed to determine the state of the Discovery’s heat shield.

The Discovery crew also oriented a thruster heater towards the Sun to keep it warm and made fine adjustments with the engine. Aside from those issues, Discovery’s STS-121 mission – and its crew – are sailing quietly along. “You know, it’s boring to us that it’s quiet, but that’s a good thing,” Ceccacci said. “That means everything is going well.”

NASA sighed with relief as data from Discovery show no concerns over the health of the vehicle. NASA’s deputy shuttle program manager John Shannon, said early image analysis of the space shuttles external tank, nose cap and heat shield-lined wing edges revealed items of interest but nothing to worry flight controllers or the crew. “Right now it’s zero,” said Shannon, "We’ll get the truth data tomorrow.”

After arriving at the International Space Station (ISS) on July 6, two Discovery astronauts will conduct a high-resolution photographic survey of the orbiter’s tile-lined belly during the spacecraft's back flip maneuver. The images from that survey will complete the health check of Discovery’s heat shield.

Earlier today, STS-121 mission specialists Lisa Nowak and Stephanie Wilson, put Discovery’s sensor laden orbital boom to work, scanning the heat-resistant reinforced carbon carbon (RCC) panels along the orbiter’s wing leading edges. These scanning revealed nothing that could impact heat shield performance. The boom survey did find a protruding gapfiller jutting out a half-inch from the underside of Discovery’s port wing - an area where gapfillers presented no concern.