From baDBob:

As seen on this "Space Shuttle Program Development Roadmap":

http://spaceflight.nasa.gov/shuttle/...es/roadmap.pdf

...the number 1 goal of shuttle upgrades was "Fly Safely", and the
very first safety upgrade on this schedule was the MMOD/WLE fix which
was to strengthen the Wing Leading Edge RCC panels.

Maybe I just don't see it. Where did you see WLE on that chart?

Go to the "Orbiter" row on the left (under "Shuttle Upgrades").
Follow this line to the right past the little orbiter diagram...

....and the very first upgrade listed is "MMOD", which addressed the
threat of debris impact. The two block drawings to the right are the
two aspects of this upgrade, one being "WLE", Wing Leading Edge - RCC.

There is a line connection from the "MMOD" block up to the "Fly
Safely" line at the top. A clear interpretation of this slide is that
upgrading the WLE RCC was the first safety priority at the time.

(If anyone has a better resolution version of this slide, I'd be very
interested in obtaining a copy.)


There's lots more info in the Congressional Record for anyone
interested in digging further to see how the WLE upgrade got axed
while the MEDS upgrade got funded.


~ CT