Space shuttle Discovery soars on one last journey
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: February 24, 2011
After a last-minute Air Force computer glitch that threatened to derail launch, the shuttle Discovery, carrying an all-veteran crew of six, critical supplies and a final U.S. module for the International Space Station, blasted off with seconds to spare and vaulted into orbit Thursday to begin its 39th and final flight.
No obvious heat shield damage could be seen, but engineers will carry out a detailed analysis over the next several days to make sure.
Discovery's crew, running three-and-a-half months behind schedule because of work to address cracks in the shuttle's external tank cracks, strapped in just after 1:03 p.m. EST (GMT-to await liftoff at 4:50:27 p.m., roughly the moment Earth's rotation carried the launch pad into the plane of the space station's orbit.
But trouble with an Air Force range safety system computer put the launch in doubt as the countdown ticked into its final minutes. With the end of Discovery's short three-minute launch window approaching, Launch Director Mike Leinbach ordered engineers to pick up the countdown at the T-minus nine-minute mark and to press ahead in hopes the Air Force would be ready in time.
But the problem was not immediately resolved and the countdown entered an unplanned "hold" at the T-minus five-minute mark. Finally, with time running out, the glitch was resolved, the countdown resumed and Discovery blasted off at 4:53:24 p.m., just three seconds before the end of the available launch window.
"Well, it was kind of an exciting last few minutes of this countdown," Leinbach told reporters later. "Several of us have been around for many, many countdowns and this was one for the record books. ... This was Discovery's last (launch), a great way to go out. She gave us a little bit of a fit today, but it's a great way to get (commander) Steve Lindsey and his crew on orbit. I'm very, very proud of my launch team and all the rest of the people who worked so hard on Discovery."
Large crowds gathered along area roads and beaches to witness Discovery's final climb to space and the shuttle did not disappoint, putting on a dramatic show as it climbed away through a mostly clear sky.
Because of the tank repairs and extensive re-application of protective foam insulation, flight controllers were on the lookout for any signs of foam debris falling away from the tank during the first minute and a half of flight when the dense lower atmosphere can cause debris to hit the shuttle with a high relative velocity.
Live television views from a camera mounted on the side of the tank showed several relatively large pieces of debris, presumably foam, separating and falling away roughly four minutes after launch
The most aerodynamically dangerous period from a debris impact standpoint is the first two minutes and 15 seconds of flight. While several pieces appeared to hit Discovery's heat shield, no obvious signs of impact damage could be seen.
"We did see some foam losses that did occur," astronaut Charles Hobaugh radioed the crew later. "The primary one was noted right around four minutes, three minutes and 55 seconds. The time we have the most concern about is two fifteen, so it was well after that. Currently, we have no concerns for the vehicle or success. We'll find out more, of course, as we go through the ascent video with a finer tooth comb and also after we do the surveys. So we're looking forward to all that."
"OK, copy that," Lindsey replied. "So that foam loss that they saw was after (the aerodynamically sensitive regime)?"
"That is correct," Hobaugh replied. "About a minute and 40 seconds later."
Bill Gerstenmaier, director of space operations at NASA headquarters, said the timing of the releases was consistent with an understood phenomenon known as "cryopumping." Such debris typically comes from the upper regions of the hydrogen tank, the result of trapped air in the foam expanding as the tank empties and warms up, causing overlying foam to pop off.
Gerstenmaier said a quick look at the ascent video indicated the repaired areas of foam near the top of the intertank stayed in place.
"From the cursory look at what we saw today and what we saw in the ascent video, I think it's consistent with our experience base," he said. "The loss, although the size is fairly large, the mass is not very much of a concern to us and the fact that it's late and it's kind of an understood timing consideration doesn't cause us a lot of concern. But that doesn't mean we won't keep digging and looking and trying to understand."
Joining Lindsey on the shuttle's flight deck were pilot Eric Boe, ascent flight engineer Al Drew and astronaut Nicole Stott, a space station veteran. Physician-astronaut Michael Barratt and Stephen Bowen, a former Navy submariner, were strapped in on the shuttle's lower deck.
A veteran of two previous shuttle flights, Bowen joined Discovery's crew in January after Timothy Kopra, the mission's original flight engineer and lead spacewalker, was injured in a bicycle mishap near his home in Houston.
"It was actually a sad story," Bowen said in a NASA interview. "Tim had worked for well over a year putting this thing together and had an accident. He's unable to make the launch time frame (and) we needed to find somebody to fill his role. ... It was not what you expected, not what you want. Tim worked really hard."
Kopra plans to help out in mission control during the flight, providing advice as needed based on his extensive training experience.
The primary goals of the 133rd shuttle mission are to deliver critical spare parts, supplies and a U.S. storage module to the International Space Station as NASA completes the lab's assembly more than 12 years after construction began in 1998.
Only two more shuttle flights are planned, one by Endeavour in April and a final mission by Atlantis in late June, before all three of NASA's orbiters are decommissioned and turned into museum displays. A decision on where the shuttles will end up is expected later this year.
"Discovery's a workhorse, the fleet leader in number of flights, done a lot of famous flights, all the return-to-flight test missions," Lindsey said before the crew's initial launch attempt. "Yet when you walk inside Discovery, it still looks like a new car even after almost 30 years of service. It's a great machine, a great vehicle. It's a privilege for us to be able to fly it on the last flight."
For Leinbach, the end of the line for Discovery will come on the Kennedy Space Center runway when it rolls to a stop after its 13th and final mission to the space station.
"Landing day's going to be tough," he said. "Landing day of Discovery, and then Endeavour and especially Atlantis, the last mission, you'll see a lot of people on the runway who will probably choke up some. Because it's the end of a 30-year program that not only have we worked in and made our livelihoods in but we've grown to love and appreciate and feel like we're doing something special for the country and, really, the world."
He said Discovery is "a great ship. This is her 39th mission, we'd have quite a few left in her had the program been extended. But it wasn't, and so it's kind of bittersweet to get the last flight out of her. But she's going to perform perfectly fine on orbit and bring the crew home safely."
With it's on-time launch, Lindsey and Boe plan to oversee a two-day rendezvous with the space station. The crew will carry out a now-routine heat-shield inspection Friday before guiding the shuttle to a docking at the station's forward port around 2:16 p.m. Saturday.
Waiting to welcome the shuttle astronauts aboard will be Expedition 26 commander Scott Kelly, Alexander Kaleri, Oleg Skripochka, Catherine Coleman, Dmitry Kondratyev and Italian astronaut Paolo Nespoli.
Discovery is scheduled to spend seven days docked to the space station, departing on March 5 and landing back at the Kennedy Space Center around 12:45 p.m. on March 7.
But U.S. and Russian space managers are expected to approve a one-day mission extension for an out-of-this-world photo opportunity.
The idea is to insert a new flight day 10 in the crew's timeline -- March 5 -- so Kelly, Kaleri and Skripochka can undock in the Soyuz TMA-01M spacecraft and photograph the space station with the shuttle and a full complement of European, Japanese and Russian cargo ships and crew capsules attached.
Discovery's mission is the last time all of the international spacecraft will be docked at the station at the same time before the shuttle fleet is retired later this summer.
Assuming the fly-around is approved -- and no decisions are expected until after Discovery reaches the space station -- Discovery would undock on March 6 and land in Florida around 11:35 a.m. on March 8.
NASA originally hoped to launch Discovery in November, but in the wake of a Nov. 5 launch delay engineers discovered small cracks in vertical rib-like stringers used in the wall of the external tank's central "intertank" section.
The cracks were repaired, but work to understand what caused their formation required exhaustive tests and analyses. The analysis had to address two major questions: issues: the structural integrity of the tank and the likelihood of small cracks to cause foam insulation to pop off during ascent.
Engineers ultimately concluded the cracks were caused by temperature-induced stress near the tops of the stringers as the upper liquid oxygen tank, exposed to minus 297-degree propellant, contracted during fuel loading. That contraction causes the tops of the stringers to pull inward.
The tank is designed to accommodate that contraction, but a manufacturing review found that the aluminum-lithium alloy used in the stringers was from a lot that was more brittle than usual and more susceptible to fractures.
To provide additional strength, so-called "radius-block doublers" were riveted into place over the top few inches of 105 of the 108 stringers used in the intertank section to make them less susceptible to stress-relief fractures.
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