The user who closed A cure for the 'Kessler Syndrome'? (gold tag badge holder) also referenced How to efficiently deorbit space junk, tagged reality-check space orbital-mechanics space-constructs and itself closed as a duplicate of Dealing with space debris and Kessler Syndrome.
Generally speaking, question X is a duplicate of question Y if, and only if, any valid answer to question Y is an equally valid answer to question X. Typically, question Y should also exist on the site before question X is posted, but exceptions sometimes exist.
Compare Does [hard-science] imply [science-based] imply [reality-check]? as well as Should our default position be that answers should be science-/logic-based, rather than magic-based? and A hard-science ultimatum, along with the hard science notice:
This question asks for hard science. All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See the tag description for more information.
Ignoring for a second that A cure for the 'Kessler Syndrome'? probably should be retagged with kessler-syndrome and possibly other tags to aid discovery via categorization by tags, my question is simply:
Given that hard-science questions place specific requirements on answers that neither science-based nor reality-check questions do, can a question tagged hard-science ever validly be a duplicate of a non-hard-science question?