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2007-08-15 Science & Technology

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Posted by 3dc 2007-08-15 20:20|| || Front Page|| [11130 views ] Top

#1 Any ideas as to the cause of the damage, 3dc? Looks to me like electric discharge machining.

Posted by twobyfour 2007-08-15 22:11|| 2007-08-15 22:11|| Front Page Top

#2 AP story sez: Endeavour's belly was smacked a minute after liftoff on Aug. 8 by a piece of debris about the size of a dishwashing sponge and weighing less than an ounce. NASA does not know if it was insulating foam or ice from the external fuel tank, or both. Whatever the material, the debris broke off a bracket on the tank, fell onto a lower tank strut, then shot up into the shuttle.

Posted by ed 2007-08-15 22:29|| 2007-08-15 22:29|| Front Page Top

#3 Ed, did get some NASA reports and the foam is blamed. Dunno, to me it seems very unlikely. Even a 10oz piece of ice would not make the dent, as ice is several orders of magnitude more fragile than thermal tiles, and besides, the relative speeds of a fragment and the craft are almost the same. The gash is rather odd-shapped and conforms more with electric discharge machining than with causes that NASA came up with so far. I submit that they are looking in wrong direction.

Posted by twobyfour 2007-08-15 23:05|| 2007-08-15 23:05|| Front Page Top

#4 The tiles are very fragile since they are mostly air. A hit by anything going several hundred miles an hour will do damage. From Wikipedia: the underside black HRSI tiles
The HRSI tile is basically a composite of high purity (99.8%) silica fibers (10%) and empty space (90%) that exhibits ceramic bonding. The high percentage of voids is the reason for the low density (9 lb/ft³) of the material making it light enough for spaceflight and strong enough to withstand the required G forces. The HRSI tiles have the black glossy appearance because of waterproofing coating made of tetrasilicide and borosilicate glass.

For comparision, water weighs 62 lb/ft³.

Posted by ed 2007-08-15 23:18|| 2007-08-15 23:18|| Front Page Top

#5 A hit by anything going several hundred miles an hour will do damage

No doubt. But that is not the case with relative speeds with approximately the same vector. The difference between the speed of a departing fragment and the craft is rather small.

Posted by twobyfour 2007-08-15 23:27|| 2007-08-15 23:27|| Front Page Top

#6 Space Shuttle Columbia Foam Impact
Investigators into the Columbia accident have estimated that the dislodged foam was about 19 by 11.5 by 5.5 inches (48 by 29 by 14 cm), weighed about 26.7 ounces, or 1.7 lb (0.75 kg) and impacted the Shuttle at nearly 530 mph (850 km/h). For the sake of a rough comparison, this block of foam would be about the same size and weight as a large loaf of bread.

Check out the foam impact test pictures. The wing leading edge RCC insulation is much tougher than the black thermal tiles.

Reinforced Carbon-Carbon (RCC). The light gray material which withstands reentry temperatures up to 2750 °F (1510 °C) protects the wing leading edges and nose cap. Each of the Orbiters wings has 22 RCC panels. These panels are about 0.25 inch to 0.5 inch thick. T-seals between each panel allow thermal expansion and lateral movement between these panels and the Orbiter's wing.

RCC is a laminated composite material made from graphite rayon cloth and impregnated with a phenolic resin. After curing at high temperature in an autoclave, the laminate is pyrolized to convert the resin to carbon. This is then impregnated with furfural alcohol in a vacuum chamber, then cured and pyrolized again to convert the furfural alcohol to carbon. This process is repeated three times until the desired carbon-carbon properties are achieved.

To provide oxidation resistance for reuse capability, the outer layers of the RCC are converted to silicon carbide. The silicon-carbide coating protects the carbon-carbon from oxidation. The RCC is highly resistant to fatigue loading that is experienced during ascent and entry. It is stronger than the tile and is used around the socket of the forward attach point of the Orbiter to the External Tank to accommodate the shock loads of the explosive bolt detonation.

Posted by ed 2007-08-15 23:59|| 2007-08-15 23:59|| Front Page Top

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