Spaceflight Now





Shuttle Discovery will shoot for launch Thursday
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: November 3, 2010


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Despite threatening weather, NASA managers Wednesday cleared the shuttle Discovery for launch Thursday on its 39th and final mission, deciding an electrical glitch that prompted a 24-hour delay was not a threat to flight safety. Liftoff was targeted for 3:29:43 p.m. EDT.

 
Credit: Justin Ray/Spaceflight Now
 
NASA's mission management team reviewed an engineering assessment that concluded the electrical problem was most likely caused by "transient contamination" in a circuit breaker. Critical equipment on that circuit operated normally after the breaker was cycled several times and there have been no other signs of trouble.

"At the end of the day, I'll kind of cut to the chase and say we wrapped up with a unanimous poll out of the MMT, no dissenting opinions, no requests for additional data, everybody was very comfortable with the story that came together today," said Mike Moses, chairman of the mission management team.

"Really, the rationale there is all the evidence points to this being a circuit breaker problem, a power supply feed problem, it's not a controller problem so it's not a main engine controller. So no worries there the main engine controller itself is going to have problems later on."

While Discovery appears to be in good shape, dismal weather is on tap Thursday with high winds expected Friday and Saturday.

With a frontal system moving through the area, forecasters are predicting an 80 percent chance of low clouds and rain that would prohibit a launching Thursday. High winds are expected Friday and Saturday, with forecasters putting the odds of acceptable weather at 60 percent and 40 percent respectively.

The shuttle's current launch window runs through Sunday. After that, the angle between the sun and the plane of the station's orbit would result in higher-than-allowable heating of the shuttle after docking. The year's final shuttle launch window opens Dec. 1 and closes five days later.

Hoping for the best, engineers were cleared to roll a protective gantry away from Discovery late Wednesday, after a delay because of a lightning advisory, setting the stage for the start of fueling at 6:04 a.m. Thursday.

Mission managers will meet at 5:30 a.m. to assess the weather.

"The weather still looks really bad for tomorrow," Moses said. "But we're going to go ahead and go down to the tanking telecon in the morning. ... If the forecast tomorrow morning is still as bad as it is today, there's a chance we might decide not to spend one of our (launch) opportunities tomorrow. But it's too early to make that call right now."

Hoping for the best, Discovery's six-member crew -- commander Steven Lindsey, pilot Eric Boe, Michael Barratt, Nicole Stott and spacewalkers Timothy Kopra Alvin Drew -- plans to begin strapping in around 12:09 p.m. to await liftoff.

Assuming an on-time launch, Lindsey will guide Discovery to a docking with the International Space Station around 11:29 a.m. on Nov. 6. Spacewalks by Kopra and Drew are scheduled for Nov. 8 and 10. If all goes well, Discovery will undock from the lab complex around 5:27 a.m. on Nov. 13, setting up a landing back at the Kennedy Space Center at 10:24 a.m. on Nov. 15.

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Engineers started Discovery's final countdown Monday after working through the weekend to replace and retest leaking quick-disconnect fittings in the shuttle's right-side orbital maneuvering system rocket pod. That work forced NASA to delay launch from Monday to Tuesday and, eventually, to Wednesday.

Launch was delayed 24 hours to Thursday after engineers ran into problems with a circuit associated with a control computer mounted on one of Discovery's three hydrogen-fueled main engines. One of the controller's two channels did not power up when a switch was thrown. An hour and 45 minutes later, the controller powered up on its own.

Engineers then powered down the controller and cycled the circuit breaker five times. They also turned the controller off and on. A switch was then cycled five times and then re-powered the controller. There were no problems.

An hour and 45 minutes after that, however, telemetry indicated a 5-volt drop in the circuit for a brief 180 milliseconds. The drop was within design specification, but it was unusual and mission managers ordered a 24-hour delay to gain a better understanding of the overall issue.

As it turned out, Moses said, the engineering analysis showed that short voltage drops are not unusual and that very slight changes in the operation of other equipment on the circuit can produce similar signatures.

"Another big piece of data that got us comfortable today was the fact that it's not all that uncommon," he said. "And so again, when we laid it all out it all racked up to be pretty clear that our most probable cause here is we had contamination on that circuit breaker, that we slowly cleared it off by scrubbing (cycling) it. In fact, after we left last night, we scrubbed it five more times. Those power-up signatures were perfect.

"So, pretty good proof that we knocked the contamination off. Our history shows us that once we do that, that is a solid connection and it's not going to change and therefore we had pretty good acceptance rationale today to go fly."

Each main engine is equipped with a controller that monitors engine operation -- valve positions, temperatures, pressure, vibration and other factors -- 50 times per second. Those data are fed to the shuttle's flight computers and if a problem develops, an engine can be safely shut down before a catastrophic failure occurs.

If a controller channel fails before launch, a countdown hold or an on-pad abort would result. If a controller channel fails after liftoff, the affected engine would continue operating with a single channel. A second failure, however, would trigger an automatic engine shutdown and abort.

But the engineering review determined the electrical anomalies in the backup channel of main engine No. 3's controller were most likely the result of transient contamination in a circuit breaker located in the shuttle's cockpit behind the commander's seat.

"Given history of contamination issues in circuit breaker operation, signature of failure seen in this launch countdown is most probable cause," according to an MMT presentation.

"System behavior following last circuit breaker cycling indicates a strong conducting contact surface across all three phases."

Spaceflight Now Plus
Additional coverage for subscribers:
VIDEO: TUESDAY MORNING'S COUNTDOWN STATUS CHECK PLAY
VIDEO: DISCOVERY'S PRE-LAUNCH NEWS CONFERENCE PLAY
VIDEO: COUNTDOWN PREVIEW BRIEFING AND WEATHER FORECAST PLAY
VIDEO: ANOTHER 24-HOUR DELAY ORDERED TO FINISH REPAIRS PLAY
VIDEO: LAUNCH DELAYED 24 HOURS BY LEAK REPAIRS PLAY

VIDEO: ASTRONAUTS ARRIVE FOR LAUNCH PLAY | HI-DEF

VIDEO: FLIGHT READINESS REVIEW SETS LAUNCH DATE PLAY

VIDEO: SHUTTLE AND STATION PROGRAM BRIEFING PLAY
VIDEO: THE STS-133 MISSION OVERVIEW PRESENTATIONS PLAY
VIDEO: PREVIEW BRIEFING ON MISSION'S SPACEWALKS PLAY
VIDEO: IN-DEPTH BACKGROUND ON ROBONAUT 2 HUMANOID PLAY
VIDEO: THE ASTRONAUTS' PRE-FLIGHT NEWS BRIEFING PLAY

VIDEO: PAYLOAD BAY DOORS CLOSED FOR LAUNCH PLAY | HI-DEF
VIDEO: CREW LEAVES KSC FOR TRIP TO HOUSTON PLAY | HI-DEF
VIDEO: ASTRONAUTS INSPECT THE PAYLOAD BAY PLAY | HI-DEF
VIDEO: SHUTTLE EVACUATION PRACTICE PLAY | HI-DEF
VIDEO: ASTRONAUTS EGRESS SHUTTLE AS SEEN LIVE PLAY
VIDEO: ASTRONAUTS BOARD DISCOVERY PLAY | HI-DEF
VIDEO: SUN RISES ON LAUNCH PAD 39A PLAY | HI-DEF
VIDEO: LAUNCH DAY REHEARSAL BEGINS PLAY | HI-DEF
VIDEO: COMMEMORATIVE WALL SIGNING IN VAB PLAY | HI-DEF
VIDEO: CREW BRIEFED ON EMERGENCY PROCEDURES PLAY | HI-DEF
VIDEO: IN SHUTTLE TRAINING AIRCRAFT'S COCKPIT PLAY | HI-DEF
VIDEO: TEST-DRIVING AN EMERGENCY ARMORED TANK PLAY | HI-DEF

VIDEO: PRE-LAUNCH INTERVIEW WITH STEVE LINDSEY PLAY
VIDEO: PRE-LAUNCH INTERVIEW WITH ERIC BOE PLAY
VIDEO: PRE-LAUNCH INTERVIEW WITH AL DREW PLAY
VIDEO: PRE-LAUNCH INTERVIEW WITH TIM KOPRA PLAY
VIDEO: PRE-LAUNCH INTERVIEW WITH MIKE BARRATT PLAY
VIDEO: PRE-LAUNCH INTERVIEW WITH NICOLE STOTT PLAY

VIDEO: PAYLOADS INSTALLED INTO DISCOVERY PLAY | HI-DEF
VIDEO: MISSION PAYLOADS ARRIVE AT LAUNCH PAD PLAY | HI-DEF
VIDEO: CANISTER HAULING PAYLOADS TURNED UPRIGHT PLAY | HI-DEF
VIDEO: MODULE HOISTED INTO SHIPPING CANISTER PLAY | HI-DEF
VIDEO: WEIGHING NEW SPACE STATION MODULE PLAY | HI-DEF

VIDEO: GANTRY PLACED AROUND DISCOVERY PLAY | HI-DEF
VIDEO: SHUTTLE ATLANTIS REACHES PAD 39A PLAY | HI-DEF
VIDEO: CROWDS WATCH DISCOVERY'S FINAL ROLLOUT PLAY | HI-DEF

VIDEO: SHUTTLE HOISTED FOR ATTACHMENT TO TANK PLAY | HI-DEF
VIDEO: CRANE ROTATES THE ORBITER VERTICALLY PLAY | HI-DEF
VIDEO: DISCOVERY DEPARTS ITS HANGAR PLAY | HI-DEF

VIDEO: TIME-LAPSE SHOWS DISCOVERY ASCENDING IN VAB PLAY
VIDEO: TIME-LAPSE SHOWS THE MOVE TO ASSEMBLY BUILDING PLAY

VIDEO: DISCOVERY'S MAIDEN FLIGHT: FIRST TRIP TO VAB PLAY
VIDEO: DISCOVERY'S MAIDEN FLIGHT: ROLLOUT TO PAD 39A PLAY
VIDEO: DISCOVERY'S MAIDEN FLIGHT: TEST-FIRING ENGINES PLAY
VIDEO: DISCOVERY'S MAIDEN FLIGHT: ASSORTED VIEWS OF FRF PLAY

VIDEO: THE HISTORY OF SHUTTLE DISCOVERY PLAY
VIDEO: THE HISTORY OF SHUTTLE ENDEAVOUR PLAY
VIDEO: THE HISTORY OF SHUTTLE ATLANTIS PLAY

VIDEO: INSPECTION OF THE MISSION PAYLOADS PLAY | HI-DEF
VIDEO: ROBONAUT ARRIVES AT KENNEDY SPACE CENTER PLAY | HI-DEF
VIDEO: SPACE STATION'S SPARE THERMAL RADIATOR PLAY | HI-DEF
VIDEO: BLANKETING LEONARDO WITH INSULATION PLAY | HI-DEF
VIDEO: RACK INSERTED INTO LEONARDO FOR LAUNCH PLAY | HI-DEF
VIDEO: LEONARDO RETURNS FROM ITS PREVIOUS FLIGHT PLAY | HI-DEF
VIDEO: STATION'S SPARE PARTS DEPOT ARRIVES PLAY | HI-DEF

VIDEO: ORBITER'S PAYLOAD BAY CLOSED FOR ROLLOUT PLAY | HI-DEF
VIDEO: ASTRONAUTS VISIT THEIR SPACECRAFT PLAY | HI-DEF
VIDEO: CREW INSPECTS LEONARDO MODULE PLAY | HI-DEF
VIDEO: DISCOVERY RECEIVES ITS MAIN ENGINES PLAY | HI-DEF
VIDEO: FUEL TANK MATED TO SOLID ROCKET BOOSTERS PLAY | HI-DEF
VIDEO: HOISTING FUEL TANK INTO CHECKOUT BAY PLAY | HI-DEF
VIDEO: EXTERNAL FUEL TANK UNLOADED FROM BARGE PLAY | HI-DEF
VIDEO: MISSION'S FUEL TANK ARRIVES AT SPACEPORT PLAY | HI-DEF

VIDEO: POST-FLIGHT DESERVICING: OMS POD PLAY | HI-DEF
VIDEO: POST-FLIGHT DESERVICING: OBSS BOOM PLAY | HI-DEF
VIDEO: POST-FLIGHT DESERVICING: ENGINES PLAY | HI-DEF
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