Posted: August 19, 2009As expected, senior NASA managers Wednesday formally cleared the shuttle Discovery for launch Tuesday on a space station resupply mission. While some engineers said they favored collecting additional data on the integrity of foam insulation on the shuttle's external tank - work that would trigger a lengthy launch delay - officials said no one objected to pressing ahead for launch at 1:36 a.m. EDT Aug. 25.
"We had lots of discussion about the foam," said Bill Gerstenmaier, chief of space operations at NASA headquarters in Washington. "Some folks wanted some additional testing, some folks had some different opinions about what the data was telling us. But it wasn't a contentious discussion, it was just really an engineering discussion about what we know and what we don't know. "In the end, we let everyone kind of state their opinions. No one chose to appeal the decision, but there were definitely some differing opinions amongst the group and I think that's really good, that's what we've been trying to get." Discovery commander Frederick Sturckow, pilot Kevin Ford, flight engineer Jose Hernandez, Patrick Forrester, John "Danny" Olivas, European Space Agency astronaut Christer Fuglesang and space station flight engineer Nicole Stott planned to fly to the Kennedy Space Center Wednesday evening to prepare for launch. Discovery's countdown is scheduled to begin at 11 p.m. Friday. The only technical issue still under discussion is a failure analysis to determine what caused a power controller aboard the shuttle to malfunction. The controller was replaced, but two similar units recently failed and engineers want to make sure the issue is understood before proceeding. The results of troubleshooting will be presented to NASA's Mission Management Team during an engineering review this weekend. The primary goals of shuttle mission STS-128 are to ferry Stott to the lab complex to replace outgoing flight engineer Timothy Kopra and to deliver more than seven tons of science equipment, hardware, food and other supplies. Three spacewalks are planned to replace a massive ammonia coolant system tank; to retrieve external experiments; to install a replacement rate gyroscope assembly; to deploy an external hardware storage mechanism; and to install wiring needed for the attachment of a new module next year. Assuming an on-time launch Tuesday, Discovery will return to the Kennedy Space Center for a landing around 8:40 p.m. on Sept. 6.
The official patch
A major topic in this week's executive-level flight readiness review was the integrity of the foam insulation on Discovery's external tank, ET-132. An unusual amount of foam fell away from the shuttle Endeavour's tank during launch July 15, most of it from the central "intertank" area separating the hydrogen and oxygen sections of external tank No. 131. A small amount of foam fell from the base of the left-side bi-pod strut that helps hold the shuttle's nose to the tank and another piece of debris fell from one of the so-called ice-frost ramps on the side of the liquid oxygen section. The bi-pod foam loss is an understood phenomenon and not considered a major issue. Addressing the intertank foam loss, engineers carried out nearly 200 so-called "plug-pull" tests to check the adhesion of the insulation and no problems were found. But Endeavour's launch was the second in a row in which foam fell from the same ice-frost ramp on the liquid-oxygen section of the tank. The ice-frost ramps are aerodynamically shaped areas of foam covering fittings that attach pressurization lines to the oxygen section of the tank. The foam loss during Endeavour's launch presumably occurred because of undetected voids in the insulation. Atmospheric heating during ascent can cause trapped air to expand, popping off overlying foam. Impact-related heat shield damage depends on the size and timing of a release, which can be difficult to model. NASA managers are extremely sensitive to foam issues in the wake of the 2003 Columbia disaster, but shuttle Program Manager John Shannon said the foam shedding under discussion following Endeavour's flight was minor in comparison. "I read a couple of comparisons that said this was similar to Columbia," he said. "And of course on Columbia, we had a 2.2-pound piece of foam come off and damage the wing. The loss we had on the last flight that generated all of this discussion over the last two weeks was 0.044 pounds, which is one-fiftieth the size of the Columbia foam. "That's how close we're looking, that's how sensitive we are. It generated four days of flight readiness review discussion, and a whole lot of work and additional testing. And that's exactly what we want the team to do, to look at it that closely. I feel extremely good about the results of the meeting. I think we have done absolute due diligence on the foam piece of it." The ramp in question on Discovery's tank was subjected to non-destructive terahertz inspections before the shuttle was moved to the launch pad and no significant voids were seen. But three other ramps, which have no history of foam loss, were not inspected. At a shuttle program review last week, some engineers recommended hauling Discovery back to the Vehicle Assembly Building for terahertz inspections of the other ramps, a move that would delay launch to around Oct. 17. Instead, managers ordered additional plug-pull tests and terahertz inspections of the ice-frost ramps on the next tank in the sequence, ET-133. The additional pull tests found no problems. The ice-frost ramp scans of ET-133 detected 10 very small voids, none of which would be expected to result in damaging foam losses. "Getting the data off the next tank and showing we don't have a big processing issue I think was key to the team accepting the condition," Shannon said. Characterizing the debate over the foam, Shannon said it was not so much dissension "as it was the team coming in and saying there are other data you can collect, or there are other ways you can slice the data and look at it." "And we rely on that in order to make a good decision," he said. "We try to reinforce that in the flight readiness process that that's what we expect, we want team members to come in and say there's additional data you can collect, there are additional ways to collect that data. And that was done, and I think that was very helpful."
The official patch
A major topic in this week's executive-level flight readiness review was the integrity of the foam insulation on Discovery's external tank, ET-132. An unusual amount of foam fell away from the shuttle Endeavour's tank during launch July 15, most of it from the central "intertank" area separating the hydrogen and oxygen sections of external tank No. 131. A small amount of foam fell from the base of the left-side bi-pod strut that helps hold the shuttle's nose to the tank and another piece of debris fell from one of the so-called ice-frost ramps on the side of the liquid oxygen section. The bi-pod foam loss is an understood phenomenon and not considered a major issue. Addressing the intertank foam loss, engineers carried out nearly 200 so-called "plug-pull" tests to check the adhesion of the insulation and no problems were found. But Endeavour's launch was the second in a row in which foam fell from the same ice-frost ramp on the liquid-oxygen section of the tank. The ice-frost ramps are aerodynamically shaped areas of foam covering fittings that attach pressurization lines to the oxygen section of the tank. The foam loss during Endeavour's launch presumably occurred because of undetected voids in the insulation. Atmospheric heating during ascent can cause trapped air to expand, popping off overlying foam. Impact-related heat shield damage depends on the size and timing of a release, which can be difficult to model. NASA managers are extremely sensitive to foam issues in the wake of the 2003 Columbia disaster, but shuttle Program Manager John Shannon said the foam shedding under discussion following Endeavour's flight was minor in comparison. "I read a couple of comparisons that said this was similar to Columbia," he said. "And of course on Columbia, we had a 2.2-pound piece of foam come off and damage the wing. The loss we had on the last flight that generated all of this discussion over the last two weeks was 0.044 pounds, which is one-fiftieth the size of the Columbia foam. "That's how close we're looking, that's how sensitive we are. It generated four days of flight readiness review discussion, and a whole lot of work and additional testing. And that's exactly what we want the team to do, to look at it that closely. I feel extremely good about the results of the meeting. I think we have done absolute due diligence on the foam piece of it." The ramp in question on Discovery's tank was subjected to non-destructive terahertz inspections before the shuttle was moved to the launch pad and no significant voids were seen. But three other ramps, which have no history of foam loss, were not inspected. At a shuttle program review last week, some engineers recommended hauling Discovery back to the Vehicle Assembly Building for terahertz inspections of the other ramps, a move that would delay launch to around Oct. 17. Instead, managers ordered additional plug-pull tests and terahertz inspections of the ice-frost ramps on the next tank in the sequence, ET-133. The additional pull tests found no problems. The ice-frost ramp scans of ET-133 detected 10 very small voids, none of which would be expected to result in damaging foam losses. "Getting the data off the next tank and showing we don't have a big processing issue I think was key to the team accepting the condition," Shannon said. Characterizing the debate over the foam, Shannon said it was not so much dissension "as it was the team coming in and saying there are other data you can collect, or there are other ways you can slice the data and look at it." "And we rely on that in order to make a good decision," he said. "We try to reinforce that in the flight readiness process that that's what we expect, we want team members to come in and say there's additional data you can collect, there are additional ways to collect that data. And that was done, and I think that was very helpful."
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Good Clear Skies
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Astrocomet
--
Colin James Watling
--
Astronomer and head of the Comet section for LYRA (Lowestoft and Great Yarmouth Regional Astronomers) also head of K.A.G (Kessingland Astronomy Group) and Navigator of the Stars (Fieldwork)
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Web: http://lyra.freewebsites.com/
Good Clear Skies
--
Astrocomet
--
Colin James Watling
--
Astronomer and head of the Comet section for LYRA (Lowestoft and Great Yarmouth Regional Astronomers) also head of K.A.G (Kessingland Astronomy Group) and Navigator of the Stars (Fieldwork)
--
Web: http://lyra.freewebsites.com/
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