And replace the heat-shield system with WHAT exactly?
DOES that not seem to be the crux of the problem here Reuters?
(Change the tires - NOT the car ...)
On the next vehicle, use carbon-carbon for the really hot spots and titanium elsewhere.
Given the amount of preliminary work done, I can't fathom why they need three years just to make a decision.
Having worked R&D for NASA, I can personally attest to the fact that the fleet needs to be rebuilt. Until 5 years ago, the processors in your VCR were more powerful than those in the shuttle. To add a single wire to the shuttle takes MONTHS. Believe me, I know, I added 4 inches of wire (rebent a paper-clip, actually) to the on-board printer to prevent paper-jams. It took MONTHS. Material sciences has grown considerably in the past 40 years, we can make a better, safer and more efficient vehicle today that we did 30 years ago. Supercomputers now exist (thanks Cray, IBM and others) that can model EXACTLY what the shuttle will encounter as it goes from vacuum to light atmosphere, to dense atmosphere. We can predict and better simulate and control today, than we could 30 years ago.
Add to the fact that the Spin-Off technologies from the shuttle have far exceeded the costs of the program. How many materials and metalurgical processes do we enjoy today, that were a spin-off from a NASA need? Computer chips got their start from NASA, as did various OS's. As we continue developing, improving and researching, the spin-off technologies initiated at NASA will pay back to the USA many times the investments.
Face it, sometimes it's easier to simply throw a project away and start fresh, than to continue using obsolete designs. Would you continue to throw money into a 1970 Chevy (bottom of the line, using parts made from the cheapest vendor), or buy a new car and start fresh?