The panel's most recent report, which came out last March and included analyses by the six departed members, warned that work on long-term shuttle safety "had deteriorated."

For example, a NASA committee reported in 2000 that more money and staff members were needed to support operations critical to shuttle safety.

But in the years after that troubled Columbia mission, fears about shuttle safety continued to build.

In the week since the Columbia disintegrated over Texas, the relationship between shuttle safety and spending is once again the subject of great debate.

It hit one of the booster rockets, causing superficial damage, but was judged not to threaten shuttle safety.

Did NASA undercut shuttle safety by shifting money to other programs?

At the same time, needed upgrades to shuttle safety were not made, Mr. Nelson says.

This was treated as a maintenance problem, not a threat to shuttle safety.

A1 Science Times C1-14 Budget constraints raise concerns about shuttle safety.

The lasting message from the past two years of hand-wringing over shuttle safety is a deeper realization of just how risky space travel remains.