STORY WRITTEN FOR & USED WITH PERMISSIONPosted: February 10, 2005After weeks of internal debate, testing and analyses, NASA managers today selected four rudimentary tile and wing leading edge repair techniques to demonstrate during the first post-Columbia shuttle mission. Spacewalking astronauts will test tile and RCC repair concepts during STS-114. Photo: NASATwo of the repair procedures will be carried out inside the shuttleDiscovery's crew cabin, a so-called "overlay" technique that could proveuseful for fixing damage to heat-shield tiles and a "plug" procedure forrepairing larger holes in wing leading edge panels. A less sophisticatedtile repair technique, one intended for minor damage, will be demonstratedduring a spacewalk, along with a technique for repairing small cracks inleading edge panels.A tile repair technique that had long been considered a front runner wasruled out, however, and while two large backpacks and high-tech caulk gunswill be carried aloft aboard Discovery, they will not be tested in flight,according to NASA spokesman Kyle Herring.Instead, engineers will continue work to perfect the technique and if allgoes well it may be tested on the second post-Columbia mission.Today's Program Requirements Control Board was chaired by shuttle programmanager William Parsons. His decision will be presented to NASA'sSpaceflight Leadership Council a week from Friday for formal approval.Discovery is scheduled for launch on the first post-Columbia shuttlemission around May 15. Three spacewalks are planned, two devoted to spacestation repair and servicing and one to demonstrate repair procedures. Buttechnical questions and concerns have held up a decision on which repairtechniques to demonstrate and with time running out to complete crewtraining and equipment testing, Parsons, deputy program manager Wayne Haleand other senior managers heard final presentations today.Three options were on the table.The first option called for spacewalkers Stephen Robinson and SoichiNoguchi to use the cure in-place-ablator applicator - CIPAA - backpacks,loaded with a tile repair material known as STA-54, to fill in deliberatelydamaged tiles in Discovery's cargo bay.Questions about the reliability of the procedure surfaced last year whenengineers noticed the formation of air bubbles in the viscous STA-54material as the two compounds that made it up were mixed together in thebackpack. After extensive troubleshooting, engineers were able to reduce thebubbling but they have not yet eliminated it. The concern is that bubblescould migrate in weightlessness and form large voids as the material cures.Those voids could weaken the patch and its ability to shield againstre-entry heating.Chief astronaut Kent Rominger told CBS News last week that his officeopposed in-flight testing aboard Discovery's flight and sources said laterthat Discovery commander Eileen Collins agreed with that position.A second option debated today called for eliminating a repairdemonstration spacewalk altogether. Instead, the crew would demonstrate theoverlay tile repair procedure in the shuttle's cabin, along with the plugtechnique for repairing small holes in leading edge panels. By eliminatingthe spacewalk, the crew would have more time for external tile inspectionsand logistics transfers to the international space station.A third option, the one ultimately selected, was chosen because thetechniques in question were the most technically mature and offered the bestopportunity to collect useful in-flight data, Herring said.Robinson and Noguchi now plan to test a tile repair technique known as"emittance wash" in Discovery's cargo bay. Using a demonstration kit withdeliberately damaged tiles, the spacewalkers will paint exposed surfaceswith a material that will replace damaged or eroded coating and improve heatrejection.Columbia was destroyed two years ago by a hole in a reinforced carboncarbon wing leading edge panel that hot gas to burn its way into the wing'sinterior during re-entry. NASA still has no way to repair that level ofdamage, but Robinson and Noguchi will test a rudimentary technique in whicha heat-resistant material known as NOAX will be smoothed over small cracksin RCC material.NOAX, which stands for non-oxide adhesive experimental, will be squirtedfrom a caulk gun-like device and then smoothed out with trowels. Theoriginal procedure required the RCC to be heated prior to NOAX applicationand for the patch itself to be heated for a half hour after that to cure thematerial. Whether a heater remains part of the new spacewalk demonstrationis not yet known.Two mechanical fixes that would not be affected by exposure to vacuumwill be tested inside the shuttle's crew cabin, assuming a safety analysisdetermines the equipment poses no risk to the astronauts.The so-called overlay technique for tile repair calls for the astronautsto cover a panel of damaged tiles with a thin, flexible sheet ofheat-resistant carbon silicon-carbide that would be mounted atop a gasketand attached with fasteners similar to drywall bolts that would be screwedinto surrounding tile.The final repair procedure, aimed at fixing small holes in RCC panels,requires a flexible carbon silicon-carbide patch called a "plug." After fitchecks and application of a sealant, a plug would be inserted into a holeand held in place from behind by expansion bolts.Between 20 and 30 different plugs, each with slightly differentgeometries, would be needed in a real repair kit to ensure a good fitvirtually anywhere in the curving leading edge.See the Feb. 6 for the first take of a detailed overview of all the shuttle in-flight repair options.Ares 1-X PatchThe official embroidered patch for the Ares 1-X rocket test flight, is available for purchase.Apollo CollageThis beautiful one piece set features the Apollo program emblem surrounded by the individual mission logos.Expedition 21The official embroidered patch for the International Space Station Expedition 21 crew is now available from our stores.Hubble PatchThe official embroidered patch for mission STS-125, the space shuttle's last planned service call to the Hubble Space Telescope, is available for purchase. | | | | 2014 Spaceflight Now Inc.NASA plans Tuesday launch pending final test results BY WILLIAM HARWOOD