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History of fusion projects (such as ITER) is a good example of the fundamental difference between a scientific and engineering project. Fusion technology is there and we know how to do it for scientific research.
What is not there is sustainable net-added sustainable fusion, where we're not only doing the fusion in the lab but actually have an *economically* viable way of *producing* energy. As opposed to expensive way of consuming it, which most of the science projects do :)