After weeks of internal debate, testing and analyses, NASA managers met Feb. 10 selected three rudimentary tile and wing leading edge repair techniques to demonstrate during the first post-Columbia shuttle mission.

One of the repair techniques will be carried out inside the shuttle Discovery's crew cabin, a so-called "plug" procedure for repairing larger holes in wing leading edge panels. A less sophisticated tile repair technique, one intended for minor damage, will be demonstrated during the crew's first spacewalk, along with a technique for repairing small cracks in leading edge panels.

NASA originally planned for Robinson and Noguchi to use so-called cure in-place-ablator applicator - CIPAA - backpacks, loaded with a tile repair material known as STA-54, to fill in deliberately damaged tiles in Discovery's cargo bay.

But questions about the reliability of the procedure surfaced last year when engineers noticed the formation of air bubbles in the viscous STA-54 material as the two compounds that made it up were mixed together in the backpack. After extensive troubleshooting, engineers were able to reduce the bubbling but they could not eliminate it. The concern was that bubbles could migrate in weightlessness and form large voids as the material cured. Those voids could weaken the patch and its ability to shield against re-entry heating.

Chief astronaut Kent Rominger told CBS News his office opposed in-flight testing aboard Discovery's flight and sources said later that Discovery commander Eileen Collins agreed with that position.

A second option debated during the Feb. 10 meeting called for eliminating a repair demonstration spacewalk altogether. Instead, the crew would demonstrate a so-called overlay tile repair procedure in the shuttle's cabin, along with the plug technique for repairing small holes in leading edge panels. By eliminating the spacewalk, the crew would have more time for external tile inspections and logistics transfers to the international space station.

A third option, the one ultimately selected, was chosen because the techniques in question were the most technically mature and offered the best opportunity to collect useful in-flight data.

Robinson and Noguchi now plan to test a tile repair technique known as "emittance wash" in Discovery's cargo bay. Using a demonstration kit with deliberately damaged tiles, the spacewalkers will paint exposed surfaces with a material that will replace damaged or eroded coating and improve heat rejection.

Flight Day 5 highlights:

   DAY..EDT........DD...HH...MM...EVENT
   
   07/17/05
   Sun  04:51 AM...03...13...00...STS crew wakeup
   Sun  05:21 AM...03...13...30...ISS crew wakeup
   Sun  06:51 AM...03...15...00...EVA-1: EVA prep
   Sun  07:31 AM...03...15...40...ISS daily planning conference
   Sun  07:41 AM...03...15...50...SSRMS grapples lab module for EVA
   									support
   Sun  07:51 AM...03...16...00...Collins exercises
   Sun  08:21 AM...03...16...30...Kelly exercises
   Sun  08:21 AM...03...16...30...Transfer review
   Sun  08:21 AM...03...16...30...EVA-1: EMU purge/prebreathe
   Sun  08:41 AM...03...16...50...SSRMS ungrapples mobile base station
   Sun  08:51 AM...03...17...00...Camarda exercises
   Sun  09:11 AM...03...17...20...External stowage platform
   								  attachment device (ESPAD) setup
   Sun  09:21 AM...03...17...30...Lawrence exercises
   Sun  09:46 AM...03...17...55...EVA-1: Airlock depress
   Sun  09:56 AM...03...18...05...EVA-1: Egress and setup
   Sun  09:56 AM...03...18...05...14.7 psi cabin repressurization
   Sun  10:31 AM...03...18...40...ISS: Phillips exercises
   Sun  10:31 AM...03...18...40...ISS: Krikalev exercises
   Sun  10:31 AM...03...18...40...ISS ingress
   Sun  10:46 AM...03...18...55...MPLM clothes transfer
   Sun  10:46 AM...03...18...55...Lithium hydroxide changeout
   Sun  11:01 AM...03...19...10...EVA-1: Tile/RCC repair demo
   Sun  12:01 PM...03...20...10...ISS/STS meals
   Sun  12:26 PM...03...20...35...SSRMS positioned for ESPAD installation
   Sun  12:41 PM...03...20...50...EVA-1/MS1: ESPAD cable routing
   Sun  12:41 PM...03...20...50...EVA-1/MS2, on SSRMS, removes ESPAD
   Sun  01:16 PM...03...21...25...Transfer operations
   Sun  01:26 PM...03...21...35...EVA-1/MS1/MS2: ESPAD installation on
   									Quest
   Sun  01:56 PM...03...22...05...EVA-1/MS1: GPS antenna R&R
   Sun  02:11 PM...03...22...20...EVA-1/MS2: CMG get aheads
   Sun  02:21 PM...03...22...30...OBSS survey
   Sun  02:56 PM...03...23...05...EVA-1: MS1/MS2 secondary ESPAD cable
   									routing
   Sun  03:21 PM...03...23...30...EVA-1: MS1: payload bay cleanup
   Sun  03:36 PM...03...23...45...STS crew departs ISS
   Sun  04:01 PM...04...00...10...ISS: Phillips exercises
   Sun  04:26 PM...04...00...35...EVA-1: Airlock repress
   Sun  04:51 PM...04...01...00...ISS: Krikalev exercises
   Sun  04:51 PM...04...01...00...CMG EVA setup
   Sun  06:21 PM...04...02...30...ISS daily planning conference
   Sun  07:06 PM...04...03...15...Daily transfer tagup
   Sun  08:51 PM...04...05...00...STS/ISS crew sleep begins

NOAX, which stands for non-oxide adhesive experimental, will be squirted from a caulk gun-like device and then smoothed out with trowels. The RCC will be heated prior to NOAX application and the patch itself will be heated for a half hour after that to cure the material.

The final repair procedure, aimed at fixing small holes in RCC panels, requires a flexible carbon silicon-carbide patch called a "plug." After fit checks and application of a sealant, a plug would be inserted into a hole and held in place from behind by expansion bolts.

Between 20 and 30 different plugs, each with slightly different geometries, would be needed in a real repair kit to ensure a good fit virtually anywhere in the curving leading edge.

The crew of the shuttle Atlantis now plans to test the CIPA technique during the second post-Columbia flight in September. The crew also may test a promising tile overlay technique that calls for spacewalkers to cover a panel of damaged tiles with a thin, flexible sheet of heat-resistant carbon silicon-carbide. The sheet would be mounted atop a gasket and attached with fasteners similar to drywall bolts that would be screwed into surrounding tile.

"The way I interpret the CAIB, I think a practicable repair technique is a requirement," said James Adamson, a member of the Stafford-Covey Return to Flight Task Group. "I don't believe it needs to be certified. It's an emergency technique for an emergency situation. I don't think it necessarily has to have completed all its testing. It has to be reasonable, doable and practicable. And I think NASA's going to have that."

A former shuttle astronaut, Adamson said it's possible "we might disagree that they have met the full intent, or goal, of the CAIB recommendation and still be OK with them deciding that it's OK to fly because of this over-arching reduction of risk.

"But it's really not our call to say the shuttle's safe to fly," he said. "We're looking at a very tiny subset of all the things NASA has to consider to fly again so we really can't be in a position of declaring the shuttle safe to fly. That's their call."

NASA originally planned to stage all three Discovery spacewalks from the space station's Quest airlock module. but concern about contamination in a system used to recharge the crew's spacesuits between outings forced the astronauts to use the shuttle's airlock instead.

The change had a major impact on flight planning, preventing Robinson an Noguchi from using a Quest system to help remove nitrogen from their blood, a requirement to prevent the bends when working in the 5 psi spacesuits. Using the shuttle airlock, the astronauts must close hatches between Discovery and the station before each spacewalk so the orbiter's cabin pressure can be reduced to 10.2 psi as part of the bends prevention process. Once a spacewalk is underway, the hatches can be reopened.

PREVIEW REPORT PART 8 --->