You can abandon the largely useless stack exchange search capability and use duckduckgo, which supports the negation operator much better than google.
falcon -spacex -heavy -9 -9s site:space.stackexchange.com works pretty well.
You can exclude certain terms with the - operator, as described in the Help Center. In this case, since the keywords you want to exclude, you have to make them exact matches with ". Searching for
"falcon" -falcon-9 -"falcon-heavy"
gives 133 results; it looks like it returns both posts using the word 'Falcon' on its own, and also 'falcon-1'. (I say looks ...