No matter what NASA does with the shuttle though, it will never be safe. Even for the fuel sensor problem alone, they said they tried fixing it from 200 possible causes, yet they still don't know if they fixed it.
Being that NASA's space shuttle is one of the most (if not the most) complicated machine built - to have one system go wrong every launch is not extremely surprising. So to have people state the shuttle has problems every launch is an extremely ignorant comment.
Foam has been hitting the space shuttle every launch. Period. There's usually been tile damage on every shuttle when they inspect it once it returns. Once had over 100 tiles damaged. NASA got the feeling though that "It happens and we're fine" and that's what doomed Columbia. If the foam had hit one RCC panel over, Columbia probably would've made it home. Instead, it hit in exactly the worse spot possible for it.
It seems that the problem was not fixed entirely from Columbia. They fixed the foam area from the bipod part where it fell off and hit Columbia, but it seems that it wasn't enough.
Like it or not, NASA will be working on a new shuttle for 2010. The current shuttle fleet will be retired by 2010 since as of right now they will have to be recertified to fly by 2010. To do this would mean to look at every possible system on the shuttle, inspect every piece...etc. The costs would be astronomical *no pun intended*.
A new system is needed for exploring space, but what that is I'm not sure. NASA did get a good backing from Congress recently on their budget, which has been a help for NASA. Figuring that roughly 5 cents of every tax payer's dollar went into the space program in the Apollo days, and now its less than once cent of every dollar goes into NASA, cost is a major issue.
Once they can get over that hurdle of a cost efficient vehicle then it will be smoother ground for the engineering crew. However, the shuttles will be used till the Space Station is finished, after that...then I'm sure we'll see a lot more movements against NASA starting a new vehicle. People think the money is being wasted, and right now the space station is one of the core reasons people feel the shuttles must be used - since its an international project. Once its complete, then I'm sure will start seeing movements against NASA. (Same way we saw it against NASA after Columbia)