The big advantage of Orion is that we're reasonably confident it would work, and could probably build one within the decade with a serious effort. Zubrin's NSW

The big advantage of Orion is that we're reasonably confident it would work, and could probably build one within the decade with a serious effort. Zubrin's NSW rocket, on the other hand, falls into the "hasn't yet been conclusively proved impossible" category. We're not sure if we can control the reaction, and we're not sure how much heat would be transferred to the rocket if we can.