I know that this has been discussed before (I personally participated in some of that), but, to my knowledge, it's been quite a while since it was brought up.
Currently, the three groups that seem to make the most sense for space exploration news are ~tech, ~science, and ~misc. Personally, I perceive ~tech as being best suited for general news about what's going on in the tech industry, more or less "hey, Google released this" or "these researchers are working on graphene batteries". Similarly, I understand ~science as a place for discussing scientific discoveries and "meta" discussion about science as a whole. I think that most would agree with me on those characterizations after looking at those groups when sorted by activity or new.
Space exploration, on the other hand, doesn't really fit in either. It's not exactly ~tech material, and it's also not really the right material for ~science, since much of it isn't about specific new discoveries or studies, etc. If we had an ~engineering, I would say that that would be the correct place for space discussion, but we don't have one.
If you look at what's been happening over the last few months in the realm of space exploration, I think that it's also pretty easy to see that there's enough going on to generate enough content and discussion for a dedicated group. There've been new launches on a weekly or biweekly basis, interesting moves made by different new entrants to the industry, all of the NASA Artemis news, plenty of things from SpaceX, etc.