FEATURE - Foam still vexes NASA after fixes to shuttle

CAPE CANAVERAL, Fla. (Reuters) - It's been 3.5 years and hundreds of millions of dollars since the space shuttle Columbia disintegrated. Yet NASA faces the same vexing problem that doomed the orbiter when it tries to launch shuttle Discovery on Saturday. 

Insulation foam -- it seems a trivial part of launching a complex spacecraft. But the problem of falling foam has perplexed the U.S. space agency capable of doing what no other country does, landing a space freighter like an airplane.