[Diogenesis]

2.5 pound debris hits at 1500 mph a surface which is damaged by a human fingernail.

Can't find the cause? Really?

[Zavien Doombringer]

Imagine a 4oz lead ball (.50) flying at 900fps ripping your arm off, what 2.5 lbs at 1500mph would do to anything!

Can you say crater...

[tort_feasor]

You have to use the theory of relativity. The relative speed of the objects at they struck.

Pre foam break off - the foam and shuttle travel at same speed, foam breaks off and falls what 100 feet? it's not going to have lost too much forward velocity but enough so that the shuttle strikes it.

In a sense the debris was probably still going forward but because the distance was so short a small change in velocity caused it to "fall back"

[Cold Heat]

More like 150MPH.

[Charles Martel]

2.5 pound debris hits at 1500 mph a surface which is damaged by a human fingernail.

Hey, you'd think NASA would be eager to blame this on the insulation impact at launch. The film of that is as damning as the plume of flame escaping past Challenger's SRB o-ring.

However, the chunk of insulation was not hovering there in the sky for Columbia to hit, it was moving at the same speed and only began to lose velocity (relative to the orbiter) for a second or so before impact. The tiles are fragile, but for NASA to be veering away from the "easy explanation" is at least interesting - and unexpected.

[tm22721]

2.5 pound debris hits at 1500 mph

Remember the shuttle is also going 1500 mph. It is the delta velocity between the debris and shuttle that is important. Delta velocity is pretty low that is why NASA discounted this as a problem.

BUMP

[clamboat]

2.5 pound debris hits at 1500 mph a surface which is damaged by a human fingernail.

1500 mph!?! Back that up with a shred of evidence. Maybe you're someone who never took a basic physics course in 8th grade, or if you did you weren't listening.

The debris (whatever it was) fell off the top of the main fuel tank. That fuel tank may have been travelling at 1500 mph, but so was the debris, and so was the shuttle strapped to the tank.

Upon impacting the wing, the debris would have had a relative velocity equal to how much it slowed since falling, plus however much the shuttle itself accellerated in the time it took the debris to go from the top of the fuel tank to the wing.

You are suggesting that the debris decellerated to 0 mph so the shuttle wing could hit it at a full 1500 mph? Or perhaps you suggest that in that fraction of a second, the orbiter and the attached fuel tank accellerated an extra, say 1000 mph, to meet the decelerating debris at 1500mph?

[Tandem]

Both the foam and the shuttle were going at 1500 mph, so the foam didn't hit at that speed. Once it came loose, it started to slow, while the shuttle continued to accelerate. In the second or so after it separated, the estimate was that the difference in speed was 500 mph or less. The engineers doubled that, for sake of analysis, and looked at the strike at 100 mph. It still didn't appear to be a "fatal" strike, as it was a glancing blow.

[rickmichaels]

2.5 pound debris hits at 1500 mph a surface which is damaged by a human fingernail.

I'm not so sure about that. The external tank was obviously travelling upward at the same speed as the shuttle itself. When that piece of foam broke loose, the wing indeed smashed into it because the shuttle was now travelling faster than the piece of foam, although the foam still had upward momentum. The foam was still travelling upward, although not as fast as the shuttle meeting up with it. The wing didn't hit a stationary object at 1500 mph.

[foghornleghorn]

The debris would not hit at 1500 mph, but more like 32 ft/sec, since it fell about 32 feet. The tank is traveling at the same speed as the shuttle and the foam covering, when it breaks away, essentially falls like any object subject to gravity. The air, if there was much at that altitude, would affect it somewhat also. But it struck the shutle at nowhere near 1500 mph.