CAPE CANAVERAL, Fla. - For the second time in two weeks, NASA is just hours away from launching the space shuttle Discovery, the agency's first space shuttle to fly since the Columbia catastrophe.
Discovery sits atop Pad 39B here at Kennedy Space Center (KSC) - its external tank filled with super-chilled fuel - as engineers carefully track readings from vital engine cut-off sensors inside the tank's liquid hydrogen section. It was one of those hydrogen sensors, ECO sensor No. 2, which failed a standard pre-launch countdown test during Discovery's initial July 13 launch attempt. Since flight rules call for four functioning sensors in order to launch, shuttle officials scrubbed the attempted space shot.
"We've gone through so much in the last couple of weeks, and it's discouraging," Discovery's vehicle manager Stephanie Stilson told SPACE.com. "It's impossible not to be discouraged when something you've been working for is postponed."
But today is a different story.
"It's going to be an very exciting time," astronaut Dave Wolf said of Discovery's second launch attempt, adding that while attention may have dropped after Discovery's first scrub, today's launch will be sure to make a mark. "The eyes of the world are going to be on KSC."
Mission managers believe that the extensive investigation into the fuel sensor glitch over the last two weeks has given them a good understanding of the anomaly, even if they still cannot fully explain it. During that time, pad engineers found and addressed wiring grounding issues inside the orbiter's ECO sensor electronics box, tested and retested potential sources of electromagnetic interference and rewired two of the ECO sensors - No. 2 and No. 4 - to better isolate the glitch should it occur again.
Two additional tests, spaced out throughout the countdown, should verify the sensors' performance, NASA officials said. The first will take place about 30 minutes after pad engineers begin loading the external tank with its cryogenic fuel. A second test is scheduled during a planned countdown hold at T minus 9 minutes, NASA officials said.
Mission managers have even drawn up plans to launch Discovery should the sensor glitch pop up again, so long as it does so according to specific guidelines which have been discussed exhaustively.
"I think we're all struggling with the ghost of Columbia," said Wayne Hale, deputy program manager of the shuttle program, during a pre-launch briefing late Sunday. "We want to do it right."
The space shuttle Columbia broke apart over Texas, its seven astronaut crew lost, during atmospheric reentry on Feb. 1, 2003. Investigators pinned the accident on launch debris that pierced Columbia's protective thermal shield, as well as a sense of complacency and schedule-mindedness pervading through NASA's internal culture.
The family members of the astronauts lost aboard Columbia, as well as relatives of those astronauts lost in the 1986 Challenger disaster, are expected to attend today's space shot, NASA officials said. Other dignitaries include First Lady Laura Bush, Florida Gov. Jeb Bush and family, Gen. Forrest McCartney - a Columbia accident investigator, as well as artist Barbara Erst Prey, Congressman Dave Weldon (R-Florida) and Sen. Tom Feeney (R-Florida) and others.
NASA has spent the last two and a half years working to address its internal culture and return its three remaining shuttles - Discovery, Atlantis and Endeavour - to flight status.
Commanded by veteran astronaut Eileen Collins, Discovery's STS-114 space shot is the first of two test flights - Atlantis' STS-121 mission is expected to follow in September - to shakedown new tools and procedures developed to increase shuttle flight safety. The orbiter bears a sensor-laden extension for its robotic arm, which STS-114 astronauts will use to check the orbiter's sensitive areas for damage. An extensive network of still and film cameras, as well as radar, is in place to scrutinize every phase of the launch. Even the astronauts aboard the International Space Station will play a part, photographing the orbiter
"I'm probably not quite as excited because [July 13] was the real one," Stilson said of the upcoming launch. "But it's building back up for me."
Meanwhile, Discovery's sistership Atlantis is mated to its own external-tank launch stack and primed to roll out to the launch pad on Aug. 3. The shuttle rolled out if its Orbiter Processing Facility and into the Vehicle Assembly Building on July 22.
Shuttle officials prepared the Atlantis for its STS-121 spaceflight in tandem with the work on Discovery in order to have a back up spacecraft to retrieve the STS-114 crew from the ISS. That rescue plan, known as Contingency Shuttle Crew Support (CSCS) or "safe haven," calls for Atlantis to launch on a mission dubbed STS-300 by Aug. 22 in the unlikely event that Discovery suffer extensive damage and is unable to return to Earth safely.
"We were processing for STS-121, for a [space] station flight...if in the slim chance we were called up for STS-300, we'd just go," Atlantis vehicle manager Scott Thurston told SPACE.com. "I dare say folks are more excited now than for STS-114 because now we have two shuttles ready to go...it's a good thing that we're flying again."
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