NASA says Hubble plans not threatened by pad repairs
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: June 12, 2008
Serious damage to the "flame trench" at launch pad 39A during the shuttle Discovery's May 31 takeoff will require extensive repairs, officials said today, but engineers believe the work can be completed in time to support the planned Oct. 8 launch of shuttle Atlantis on a long-awaited flight to service the Hubble Space Telescope.
During Discovery's climb out, the exhaust plume from the shuttle's two solid-fuel boosters blew out about 5,300 heat-resistant bricks lining one side of the flame trench below the orbiter's launch stand. Blasted out like shrapnel, bricks and fragments littered the pad perimeter and severely damaged a heavy duty security fence some 1,800 feet away.
The shuttle was not struck by any debris and Cain said a re-assessment of the environment in the flame trench during launch that was carried out after DIscovery's take off confirmed there is virtually no chance for debris from inside the trench to ricochet or otherwise overcome the exhaust plume to strike the orbiter.
Recommendations on what sort of repair work might be needed will be presented to shuttle Program Manager John Shannon on June 26. Cain said he did not want to provide details of proposed fixes until the engineering team has had time to fully assess the options. But he said engineers believe enough time is available to implement any of the repair scenarios under discussion.
"By the end of this week I think we're going to be done inspecting in the pad A area and we're going to get to work in earnest on doing the cleanup work and on putting a repair in place after we hear it at the program board," he said. "We're going to better understand this problem, obviously, as a result of all this.
"We will be able to repair the pad A flame trench damage that we've sustained here and it's going to be in time to support the STS-125 Hubble mission. There's no reason for us to look at going to pad B for that mission, we have high confidence in being able to go do this."
NASA has set up two teams to assess the pad damage and its implications. John Casper, a veteran shuttle commander and program manager who is participating in the damage assessment, told CBS News today he agrees with Cain's optimism about getting repairs done in time for the Hubble flight. But he described the work as "a big job."
"It's amazing when you think about what those pads have been through," he said. "They've really held up remarkably well."
NASA's two shuttle launch pads, LC-39A and LC-39B, were built by the U.S. Army Corps of Engineers in the 1960s to support the Apollo moon program and later, launches for the Skylab space station and Apllo-Soyuz Test Program. The pads were modified in the mid 1970s to support the space shuttle.
First used in 1967, pad 39A has withstood 12 Saturn 5 launchings, including the first Apollo moon landing mission, and 70 shuttle flights. Pad 39B, first used in 1969, supported one Saturn 5 launch, four Saturn 1B flights and 53 shuttle missions, including Challenger's final flight.
The pads are built around long rectangular flame trenches that measure 490 feet long, 58 feet wide and 42 feet deep. The space shuttle, mounted atop a mobile launch platform, is positioned directly above the flame trench. Exhaust from three hydrogen-fueled main engines and two solid-fuel boosters passes through cutouts in the mobile launch platform and into the trench. A flame deflector, shaped like an inverted V, is positioned directly below the MLP openings to divert engine exhaust to one side of the pad and booster exhaust to the other.
The pressures and temperatures in the main engine section of the flame trench are much less than what the structure must endure from the shuttle's boosters. At ignition, each booster generates some 3.3 million pounds of thrust and a 5,000-degree exhaust plume.
Each brick measures 6-by-3-by-13.5 inches and features a half-moon-shaped groove on one surface and an opposite protrusion on the other. The protrusion on one brick fits into the groove on the one above or below to lock them together. The epoxy was used to help hold the bricks to the underlying concrete wall.
For added protection from the heat of booster ignition, Fondu Fyre covers bricks in the floor and side walls of the trench from the flame deflector out to about 20 feet. After that, the trench walls are bare brick.
During Discovery's launching, some 5,300 bricks on the northeast side of the flame trench were blown out, leaving bare concrete in an area roughly measuring 20 feet by 75 feet. While engineers later found signs of ricochets in the flame trench, video and still images show nothing came close to hitting the shuttle and no dents were found on the underside of the mobile launch platform.
But engineers soon discovered the metal clips that help hold the bricks to the walls of the flame trench were severely rusted and corroded, possibly due to decades of exposure to the acidic byproducts of booster exhaust. Inspectors also found areas where the absence of trowel marks indicates the epoxy intended to help hold the bricks to the underlying concrete wall was not uniformly applied. Subsequent "tap tests" have indicated voids behind 30 percent of the bricks that are still in place.
Engineers suspect similar problems may be lurking at pad 39B. Inspections and tap tests are ongoing.
A variety of repair options are being assessed for pad 39A. The original brick vendor, A.P. Green, has inspected the pad, along with representatives of Atlantic Firebrick and Supply Co. Molds of the original bricks are still available, officials say, but there is no existing stockpile. New bricks can be made, but not in time for the October launching.
"We have talked to the original vendor," Cain said. "The brick contracting company and the original vendor were on site to evaluate this issue for us. There apparently are no applications similar, or necessary, today and so they don't make this kind of brick. Whether or not it could be done, I don't know if we know the answer to that yet."
Among the options under consideration are removing all the bricks and spraying the underlying concrete with a thick coating of Fondu Fyre or a similar material; removing the bricks and leaving bare concrete; and leaving the bricks in place and using Fondu Fyre to fill in the damaged areas.
"As an old structural engineer, I can't see how we'd launch with any of the existing bricks in place," said one senior manager. "Maybe on the (main engine side), but not on the SRB side. The little clips that hold the bricks to the steel beams imbedded in the concrete wall are rusted badly. Many (are) gone. So even the ones behind the bricks that are still standing must be in the same shape."
Cain declined to provide any details about possible repair options, saying "I don't want to talk about that today because I don't want to get out in front of the team that's working on all those options."
"But fundamentally, it's fair to say one of the options is looking at spraying the areas where we've lost brick," he said. "Possibly removing more brick and spraying would be a different option, or doing something other than spraying Fondu Fyre in the areas where we've lost brick to preserve those areas.
"What we're really saying is any of those options doesn't look like, in terms of time and schedule and resources, that they would be an issue for us to complete them. We just have to go figure out which ones make the most sense given the problem we're facing today."
Casper said the near-term goal is to come up with a fix in time for the Hubble mission that would carry over through the 2010 end of the shuttle program. A longer-term fix, possibly using a fresh batch of firebricks, may be implemented for the Constellation program's Ares rockets that will replace the shuttle.
NASA plans to haul Atlantis to the launch pad on Aug. 29 to prepare the ship for blastoff Oct. 8. If possible, Casper said, NASA would like to complete any spraying of Fondu Fyre or similar material before the shuttle is moved to the pad. But engineers are looking into the possibility of spraying after rollout if required.
The Hubble flight is the only mission left on the shuttle manifest that does not go to the space station. Because Hubble is in a different orbit than the lab complex, the crew of the servicing mission cannot take advantage of "safe haven" aboard the station if any major problems develop that might prevent a safe re-entry. As a result, NASA Administrator Mike Griffin decided early on to have a second shuttle prepped and ready for takeoff from nearby pad 39B if an emergency rescue mission is needed.
If so, the rescue flight would be launched from pad 39B as soon as possible. Otherwise, Endeavour will be moved to pad 39A for launch on a space station resupply mission currently targeted for launch Nov. 10.
Complicating the end-of-year schedule, NASA cannot launch shuttles to the station between around Nov. 27 and Dec. 17 and between Jan. 27 and Feb. 11 because of thermal issues related to the angle between the sun and the plane of the station's orbit. Because NASA wants to avoid missions extending from one year to the next, the so-called "beta angle cutout" effectively means no launches between the end of November and the first of the year.
It takes about a month to prepare the launch pad for another flight. If the Hubble mission is delayed more than three weeks or so, the November shuttle flight could be delayed into next year, extending Chamitoff's stay in space well beyond the currently planned six months.
"We've looked very hard at that, that is right in the middle of our radar screen, with the large beta cutout that we have at the end of this calendar year," Cain said. "I asked the team to look at that before this mission launched, actually."
The result, he said, is that if Atlantis takes off by Oct. 27 or thereabouts, NASA could still launch the STS-126 station mission from pad 39A before the beta cutout begins. Just barely.
"We have almost three weeks, essentially, to get HST launched before it's going to begin to impinge on our ability to get 126 launched before the beta cutout," Cain agreed.