During the second world war the British not so famously (it's not like it's something you brag about) spent a lot of money and effort building extremely heavy tanks or assault guns designed to help a spearhead a breach of the Siegfried line. They turned out to be mostly unnecessary due to a combination of factors that can be roughly summed up as "quantity has a quality all its own" and the projects were steadily cancelled as the war in Europe wound down.

It's likely that some of these big unknown problems will similarly evaporate or prove to be easily solved once we actually do stuff like put humans in deep space ad on the moon for serious chunks of time.