Why is that something that we should not worry about? (I am not being sarcastic, honestly asking, nuclear physics is not my primary expertise.) Yes many of them seem to have short half-lives but one of them has a half life of 1.5 million years.

Also I am not sure these are the only iron isotopes. This seems to be a list of "naturally occurring" iron isotopes which usually means "naturally occurring on Earth".

Also another thing to worry about is the isotopes of platinum and platinum group metals that seem to be the main and most lucrative target of space mining.

> Yes many of them seem to have short half-lives but one of them has a half life of 1.5 million years.

Which means it's completely safe. If it has a half-life that long, it won't be releasing radiation at a very high rate. Hardly enough to register above background. The isotopes you have to worry about are the ones with in-the-middle half lives- long enough that they don't deplete themselves in a conveniently short period, but short enough that they produce a dangerous power output.

That depends on concentrations of the isotope in the metal and the amount of metal we will be using. I have no idea what the concentrations of iron isotopes in meteors are and which iron isotopes are there, but I do not think it is correct to automatically say that radioactive isotopes with long half-lives are completely safe.