Space Shuttle Endeavour’s heat shield is damaged more than NASA engineer’s originally thought. The 3 1/2 inch gouge, caused by a chunk of insulation that shuttle at high velocity during lift-off, goes all the way through the tiles and exposes the felt layer between the heat shield and the aluminum fuselage.
Now I certainly am no expert in aeronautics or space flight, but I know enough from my reading on the subject to realize that this is bad. Not only does the shuttle encounter extreme temperatures during reentry (upwards of 3000 degrees), it also has to endure the mechanical stress of reentering the atmosphere at high speed.
The space shuttle’s TPS (thermal protection system) is excellent at insulating against heat, but is extremely fragile to the point that individual tiles can be crushed in one’s bare hand. While the system is reusable, it is difficult to maintain and there is little redundancy. As mentioned above, there is so secondary thermal protection underneath the tiles, and where the tiles are only an inch thick, the matter of structural integrity is especially daunting in the event that the TPS was compromised.
While a metal heat shield would have mitigated this, it would have made the shuttle much heavier. (Compare, for example the Apollo reentry spacecraft, the heat shield of which comprised 1/3 of the total weight.)
Repairing the TPS system in space poses its own problems. As the tiles are extremely fragile, they can be easily damaged further on accident during a repair excursion, exacerbating the dangers further.
Evidently, when designing the shuttle, redundancy in the heat shield was something that didn’t seem important.
What is especially troublesome is that NASA engineers are debating whether the gouge needs to be repaired. Considering that temperatures as low as 350 degrees Fahrenheit will cause structural failure in the shuttle, I don’t see how this repair can be merely optional.
Posted by -kf 
