OT - Train Guy - more on shuttle tire theory from Houston Chronicle:
If a breach in Columbia's left wing were heating up its wheel well, the temperature wouldn't have had to rise much to cause a catastrophe.
According to current and former NASA engineers, the tires would have exploded violently at just 340 degrees Fahrenheit.
Temperatures outside the shuttle as it descended were as high as 3,000 degrees.
"Have you ever seen an airplane tire blow? That's a bomb," said a retired Johnson Space Center engineer who worked on systems in the wheel area.
The force of the explosion would easily blow the door off the wheel well and probably the top off the wing, he said.
NASA said Thursday that accident investigators have concluded that Columbia's left side was breached during the superhot re-entry into Earth's atmosphere Feb. 1. Where the break occurred is not yet known, but wherever it was, it was beginning to heat up the wheel well when contact with the shuttle was lost.
The heat certainly could have destroyed the orbiter's airframe on its own, but the wheel well is also a snake pit of combustible items.
Least likely to cause problems would be the hydraulic lines feeding the area, several engineers said. NASA uses hydraulic fluid in the landing gear struts that has a flash point below 300 degrees.
And there probably was not enough oxygen at the altitude Columbia was flying to allow the fluid to combust, even if heat had ruptured a line, according to several experts.
Another problem area might seem to be the pyrotechnic charges located in the wheel well, but at least one former JSC engineer, who asked not to be named, said that is unlikely.
Shuttle pilots normally don't drop the landing gear until an altitude of 250 feet. If the spacecraft's normal gravity-drop system jams, the explosive charges force the gears down.
The pyrotechnic initiator, normally triggered by an electric current, contains zirconium-potassium perchlorate, or ZPP. It will ignite on its own at 1,050 degrees.
That triggers another pyrotechnic powder called BKNO3, boron/potassium nitrate, which auto-ignites at 600 degrees. The BKN03 pushes a piston opening the wheel-well door. If the door was opened at the wrong time, it could lead to the destruction of the spacecraft.
NASA officials have said they don't believe the landing gear dropped before contact with Columbia was lost, which would seem to rule out auto-ignition of the charges.
The tires almost certainly would have blown out first, the engineers said.
Market Data 
Markets 
AI
