I just asked this question and I took the liberty of adding two tags. One is failed-missions. Can this be interesting for filtering and for discussing causes and details about failed missions? With failed I mean at any phase: at launch-pad, in orbit, re-entering and so on.
Since the use of plural in tag names could potentially suggest that broad questions are fine (they're not), I suggest we rather use tag names in singular, e.g. this one would then be failed-mission. If we used the plural failed-missions, we might invite questions that discuss multiple failed missions, or even request lists of them, which is often counterproductive.
In case singular and plural versions aren't semantically different, then I favor the singular versions. They still imply the same thing, even if the question later refers to it in plural, but is not necessarily so the other way around.
Otherwise, I think the tag is fine. We'll inevitably have also tags with a negative connotation, and failed-missions is not even as strong as some others we might see added in the near future, such as casualty, death, e.t.c.