Preparations for undocking are on the way as the ISS flies over the Mediterranean Sea - Source: NASA TV

Yesterday, the STS-129 and Expedition 21 crew members parted ways with a change of command and farewell ceremony, where Expedition 21 Commander Frank De Winne handed over the command of the International Space Station to NASA’s astronaut Jeff Williams (@Astro_Jeff). After the farewell ceremony, the crews closed the hatches that divide the two spacecraft at 18:12 GMT.

The STS-129 and Expedition 21 crew members bid farewell. Photo credit: NASA TV

After 87 days spent in the complex, Expedition 20 and 21 Flight engineer Nicole Stott (@Astro_Nicole), officially, item number 914, became the last astronaut who used the Space Shuttle for a lift to or from the station (as a member of the station’s Expedition crew). If Atlantis lands as scheduled, she will have spent 91 days in space.

Space Shuttle Orbital Maneuvering System (OMS) is scheduled to execute the deorbit burn at 13:37 GMT on Friday, leading to landing at the Kennedy Space Center (KSC) Shuttle Landing Facility (SLF) runway 33 at 14:44 GMT.

Discovery Touchdown in HD - Source: NASA

UPDATE 1: HD video of shuttle Discovery landing is now available at NASA TV YouTube Channel.

Today at 19:13:17 UT, the Space Shuttle Discovery landed on Runway 15 at NASA’s Kennedy Space Center, Cape Canaveral in Florida, ending a 13-day mission to the ISS.

Discovery gliding towards Runway 15 - Source: NASA TV

Discovery moments before landing - Source: NASA TV

Discovery touchdown - Source: NASA TV

Discovery touchdown - Source: NASA TV

The STS-119 flight delivered the space station’s fourth and final set of solar array wings, completing the station’s truss. The additional electricity provided by the arrays will fully power science experiments, help support station operations and extend the station’s crew to six astronauts.

The newly installed S6 solar panel array - Source: NASA

During the mission, which lasted 12 days 19 hours 29 minutes and 33 seconds, the crew traveled 8.5 million kilometres (5.3 million miles). STS-119 was the 125th space shuttle flight, the 28th flight to the station, the 36th flight for Discovery and the first flight in 2009. Despite a few minor glitches and one relatively large one (mission specialist Joseph Acaba accidentally inserted a pin upside down jamming the deployment of an equipment storage platform outside the Japanese Kibo laboratory), the mission is viewed as a big success by bringing the station to full power. Eight flights to station remain before the shuttles retire in 2010.

Discovery deployed the landing "chute" - Source: NASA TV

Discovery deployed the landing "chute" - Source: NASA TV

Source: NASA TV

Source: NASA TV

With Discovery and its crew safely home, the stage is set for the launch of STS-125, targeted for May 12. Atlantis’ mission will return the space shuttle to NASA’s Hubble Space Telescope for one last visit before the shuttle fleet retires in 2010. Over 11 days and five spacewalks, Atlantis’ crew will upgrade the telescope, preparing it for at least another five years of research.

STS-119 T-0 Ignition - Source: NASA TV

STS-119 T+5 Ignition - Source: NASA TV

STS-119 Discovery Lift Off - Source: NASA TV

STS-119 Main Engine Cut Off (MECO) - Source: NASA TV

STS-119 External Tank Jettisoned - Source: NASA TV

Every mission carries out Detailed Test Objectives (DTO’s). STS-119 has 6 planned DTO’s. One will involve measuring pressure vibration during solid rocket boosts. Three are related to the International Space Station (such as measuring the effects of orbiter docking on the structure), the 5th will focus on research how could computer displays be made more readable during the launch, and the 6th is research on Boundary Layer Transitions.

Boundary Layer Transition is a process occurring during the shuttle re-entry as the smooth air flow along the shuttle’s heat shield becomes turbulent. The experiment will measure the heat difference between the air flow using sensors (thermometers) installed in particular tiles on the shield. A protuberance tile with a quarter inch (0.635cm) “speed bump” has been installed on Discovery’s heat shield. The tile will intentionally disrupt the smooth air flow. Several other tiles have been placed strategically on the shield to monitor the air flow before and after it hits the protuberance. The re-entry will also be captured by an infrared camera aboard US-Navy’s NP-3D Orion aircraft flying below the shuttle. This experiment will be continued during future missions with a varied height of the bump on the protuberance tile.

Shuttle re-entry - Source: NASA

Below is a short summary of today events with commentary for frame shots from NASA TV:

At 16:30 UT the external tank’s liquid hydrogen section has reached the point where a leak was detected on Wednesday. No leak was apparent today. Despite all efforts and tests carried out, NASA could not be 100% sure that the issue was fixed until the tank was refilled.

Earlier in the day a minor issue was discovered with the pressure valve that feeds helium into the “gap” area between the external tank and shuttle. This area, where liquid hydrogen and liquid oxygen lines run from the tank to the shuttle, is purged with helium to prevent the formation of ice and the accumulation of gaseous hydrogen and oxygen. Roughly at 11:45 UT, the “red team” of technicians reported that the issue with helium pressure was successfully resolved.

Launch Pad 39A from Kennedy Space Center's - Source: NASA/NASA TV

A few minutes after 20:00 UT the STS-119 astronauts departed the Kennedy Space Center’s Operations and Checkout Building. They boarded the Astrovan which took them to the launch pad 39A a few minutes away.

STS 119 crew is leaving the crew quarter - Source: NASA/Kim Shiflett

STS-119 In front of the Astrovan - Source: NASA/Kim Shiflett

At this point, astronaut are already wearing their pressure suites. Since the suites are closed to outside environment astronauts own body heat can warm up the insides pretty fast. The Astrovan is equipped with AC and other cooling systems to provide some comfort.

Astrovan stops at the Launch Control Center - Source: NASA/NASA TV

The Astrovan makes a stop at the Launch Control Center to let out flight managers accompanying the crew on its way to the launch pad. Also chief astronaut Steve Lindsey leaves  to conduct a weather recon mission for the launch as well as for emergency situations in which the shuttle would have to return.

Astrovan on its way to the launch pad - Source: NASA/NASA TV

In the image above, the Astrovan and its escort are just a few minutes away from the launch pad 39A. The wide road strips on the left are used by the Crawler Transporter to bring the shuttle to the pad.

STS 119 Pilot Dominic Antonelli being strapped into parachute harness - Source: NASA/NASA TV

The mission’s pilot Pilot Dominic Antonelli is being strapped into parachute harness in the White Room. The actual parachute is already in the seat aboard the shuttle. All astronaut are wearing a parachute in case the orbiter cannot reach a stable orbit and they need to abandon the shuttle.

At 21:48 UT the Closeout Crew got a “go” to close Discovery’s side hatch. Meanwhile the astronauts finished air-ground voice-checks and the shuttle’s weather officer Kathy Winters updated the chances of good weather from 80% to 100% for tonight’s launch (which means that there is no chance of weather prohibiting launch).

The Closeout Crew seals the Discovery's side hatch - Source: NASA/NASA TV

At 22:28 UT the countdown entered a 10 minute planned hold at T-20 minute mark. Discovery’s hatch is closed and latched and cabin leak checks are under way. Launch teams are not working on any issues that would interfere with launch.

At 22:49 UT the countdown entered a 45-minute planned hold at the T-9 minute mark, during which the Mission Management Team, and Launch Control team conducted polls to make final “go” – “no go” decisions for launch.

At 23:32:30 UT Discovery was given an official “go” for the launch.

At 23:34:44 UT the countdown resumed at the T-9 minute mark.

At 23:38:44 UT the Auxiliary Power Units started at the T-5 minute mark.

At 23:43:44 UT the Discovery space shuttle launched on the STS-119 mission.

At 23:52:07 UT The Main Engine Cut Off (MECO). The MECO sequence began about 10 seconds before cutoff. About three seconds later, the Space Shuttle Main Engines (SSMEs) throttled back by 10%/second until they reach 65% rated thrust, called the Minimum P. Minimum power was maintained for seven seconds, then the SSMEs shuts down.

The shuttle is now on a two day long chase to catch the ISS, which it will dock on Tuesday. Meanwhile, teams of experts will be looking at launch imagery for any debris that might have come off and hit the orbiter during launch. The next space shuttle lunch will be the STS-125 mission of Space Shuttle Atlantis to the Hubble Space Telescope (HST)  with launch scheduled on May 12, 2009.

Update #1: At 00:50 UT During the post-launch news conference NASA managers said that there were no obvious debris strikes on Discovery. The crew debris report will follow in hours after the launch. The designated team will be meticulously analysing the launch imagery and videos in the days to come.

Update #2: NASA Associate Administrator for Space Operations Bill Gerstenmaier expressed his thanks to the teams from the NASA centers that resolved the technical issues which delayed the launch. Mission Management Chairman Mike Moses remarked how smooth the launch countdown went and gave special thanks to the reusable solid rocket motor team celebrating their 100th launch since the Challenger redesign. NASA Launch Director Mike Leinbach said that this was the most visually beautiful launch he’s ever seen.

STS-119 crew attired in training versions of their shuttle launch and entry suits - Source: NASA

If Discovery launches on Sunday, the mission will last 13 days and include 3  spacewalks (EVA’s). The Mission Management Team will meet tomorrow at 17:00 UT to make the final “go” – “no go” decision. The meeting will be followed by NASA news conference (L-1 briefing). If everything goes according to the plan, the L-1 countdown will be restarted at 08:11 UT on Sunday; astronauts will suit up a few minutes before 19:00 UT and head to the launch pad. NASA’s Discovery Launch Coverage will start at 18:30 UT on NASA TV and shuttle commentary will be available 24/7 for the duration of the mission.

A nearly full Moon sets as the space shuttle Discovery sits atop Launch pad 39A at the Kennedy Space Center in Cape Canaveral, Florida, Wednesday, March 11, 2009 Credit: NASA/Bill Ingalls

All systems are “go” for space shuttle Discovery’s launch at 01:20:14 UT. The countdown picked up as planned at 09:55 UT. You can join the Astronauts aboard the space station, who will watch Discovery’s  launch live on NASA TV.