Reports to NASA Indicated Detatched Foam from External Tank Often Damaged Shuttle Tiles
Roger Hedgecock filled in for Rush Limbaugh yesterday on The Rush Limbaugh radio program. At the beginning of the show, Hedgecock reported that a NASA Engineer named Greg Katnik had reported that foam from the external tank had struck the Columbia orbiter on the STS-87 mission in 1997. According to an article found on a NASA educational web site:
...the extent of damage at the conclusion of this mission was not "normal."
The pattern of hits did not follow aerodynamic expectations, and the number, size and severity of hits were abnormal. Three hundred and eight hits were counted during the inspection, one-hundred and thirty two (132) were greater than one inch. Some of the hits measured fifteen (15) inches long with depths measuring up to one and one-half (1 1/2) inches. Considering that the depth of the tile is two (2) inches, a 75% penetration depth had been reached. Over one hundred (100) tiles have been removed from the Columbia because they were irreparable. The inspection revealed the damage, now the "detective process" began.
During the STS-87 mission, there was a change made on the external tank. Because of NASA's goal to use environmentally friendly products, a new method of "foaming" the external tank had been used for this mission and the STS-86 mission. It is suspected that large amounts of foam separated from the external tank and impacted the orbiter. This caused significant damage to the protective tiles of the orbiter. Foam cause damage to a ceramic tile?! That seems unlikely, however when that foam is combined with a flight velocity between speeds of MACH two to MACH four, it becomes a projectile with incredible damage potential. The big question? At what phase of the flight did it happen and what changes need to be made to correct this for future missions?
Also yesterday, RushLimbaugh.com pointed to an article that appeared in The San Francisco Chronicle about the danger of the so-called zipper effect and its effect on the integrity of the orbiters' heat shields. The zipper effect is a chain reaction of silicate tile damage that spreads from the initial loss of or damage to as few as one tile. According to the article, "This kind of damage might have conspired with some other, as-yet-unknown problem, experts said, to create the aerodynamic disturbances and heat-related system failures NASA observed during Columbia's final seconds."
The Chronicle article referred to a 1994 study by Paul Fischbeck and M. Elisabeth Pate-Cornell of problems with the management of thermal protection systems at NASA. It also points out the existance of a new thermal protection system, developed for the now cancelled X-33 space plane that is "billed as cheaper and more durable than fragile ceramic tiles."
Much of this information is picked up by The New York Times and The Washington Post in articles published today.