Sunday, August 30, 2009

Live In Orbit: Jet Failure Triggers Docking Challenge

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WATCH IT LIVE: Discovery just entered the final stages of its rendezvous with the International Space Station, and you can watch live at 8 p.m. as the shuttle goes through an eight-minute backflip after it reaches a point about 600 feet below the statuon at 8 p.m. Click the NASA TV box at the right to launch our NASA TV viewer and refresh this page for periodic updates.

Discovery astronauts are zooming toward an unprecedented final rendezvous and docking at the International Space Station, one triggered by a failure that took out all six of the shuttle's small nose-and-tail vernier thrusters.

For the first time ever, shuttle astronauts instead will rely solely on larger, more powerful primary jets that will sound like howitzers booming as mission commander Rick "C.J." Sturckow guides Discovery toward a 9:04 p.m. docking at the outpost.

Leroy Cain, chairman of NASA's Mission Management Team, said the alternate means of flying the shuttle will be "slightly more challenging" than previous docking operations, which typically make "extensive" use of the smaller thrusters for precision piloting.

The cannon-like booms from the larger jets -- especially those on the nose of the orbiter -- will be quite "noticeable" to the astronauts in Discovery's crew cabin -- "even impressive," Cain said.

But the back-up mode is one that is fully certified and one which all station-bound crews train for prior to launching to the outpost.

"So we don't have any concerns for that," Cain said.

Discovery blasted off from Kennedy Space Center at 11:59 p.m. Friday, setting sail on a ground-up rendezvous with the station. About 4.5 hours after reaching orbit, a leak was detected in one of two small jets on the nose of the shuttle.

The shuttle is equipped with 38 primary jets that each produce 870 pounds of thrust and six smaller thrusters that each produce 24 pounds of thrust.

The failure of the single forward jet prompted NASA flight controllers to shut down both the small jets in the orbiter's nose as well as the four small thrusters in the tail, or aft, of the orbiter. The concern is that a leaking jet might spew toxic rocket propellant on the station's solar wings, degrading their ability to produce electrical power.

No primary Reaction Control System rendezvous and docking has ever been done at the station, Cain said. The alternative mode has been evident during course corrections the Discovery crew has been making during the early stages of today's rendezvous.

As viewed by station cameras from more than 41 miles away, Discovery appeared as a bright star and an additional burst of light could be seen like a brief halo around the spaceship.

The final stages of rendezvous and docking will begin around 6:25 p.m. as Sturckow and pilot Kevin Ford perform a "Terminal Initiation, or TI, burn as Discovery pulls within eight nautical miles of the station.

Discovery will fly a Rotational Pitch Maneuver -- the now-standard back-flip -- about 8 p.m. so station flight engineer Michael Barratt and outpost commander Gennady Padalka can take high resolution images of the thermal tiles on the underside of the orbiter.

Docking remains scheduled for 9:04 p.m.

You can watch live here in The Flame Trench. Simply click the NASA TV box on the right side of the page to launch our NASA TV viewer, and be sure to refresh this page for periodic updates.

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