[yongjik]

I don't think scientists in the Manhattan project knew exactly how to do it. That's why they ended up having (at least) two totally different types of bombs, one with a Plutonium core using spherical implosion and another with a Uranium core using cannon-like ignition.

Why try one scheme when you can try two at twice the price?

[simonh]

But both worked fine. So yes, they really did know what they were doing. The reason to do two versions wasn't really in case one didn't work, they had very good reason to believe both would work. It was a matter of which would offer the best combination of efficient fission, weight, cost and reliability. We do not have two clearly viable different routes to practical fusion reactors. We don't even have one at this point.