There are quite a number of question topics that could fit on either. Do we have thoughts on what will make a question better fit here or on Physics?

If it asks for mathematics, does that make it a physics question? Does it have to refer to actually using those equations to navigate/calculate thrust to be on-topic here?

  • $\begingroup$ What happens when it's space physics? My question on sound in space is considered off topic but a question on if artificial gravity in space is possible is not? $\endgroup$ Jul 17, 2013 at 20:02
  • $\begingroup$ Sound in space feels more physics - it has nothing to do with exploration. And in fact there is a question on physics on this exact topic. $\endgroup$
    – Rory Alsop Mod
    Jul 17, 2013 at 20:20
  • $\begingroup$ Would the question "Could two astronauts in space walk communicate between each other without transmitters?" be a valid question. $\endgroup$ Jul 17, 2013 at 20:21
  • 1
    $\begingroup$ It still isn't exploration - so to me it feels off topic. $\endgroup$
    – Rory Alsop Mod
    Jul 17, 2013 at 20:22

4 Answers 4


The border is incredibly soft.

The more diverse SE sites exist, the more complicated it becomes to put a question into a specific category. Was it ever considered at SE to implement "cross-posts" in any way? Let's say, a question is asked here in space exploration, but it is listed by the author in e.g. astronomy and physics too? From my point of view, eventually this is going to make a lot of sense. (I somehow imagine special tags for cross-posting.)


The border is soft, but here's where I draw the line.

If it is about spacecraft operations, or engineering, it belongs here.

If it is a very general physics question, then it could best go there.

Some questions could fit in to either category (How does an Ion Engine work).

Space Exploration

  • How much fuel do I need to get to go to __?


  • What is the source of the 11 year solar cycle?

Either site

  • What is the optimal transfer orbit?
  • How does an Ion Engine work?
  • $\begingroup$ I'd say the ion engine example would go to Physics. $\endgroup$
    – user12
    Jul 17, 2013 at 15:37
  • 8
    $\begingroup$ @Undo: It's an engineering and a science question, don't see why it couldn't go to either. In fact, I'd say it's probably more on topic here... $\endgroup$
    – PearsonArtPhoto Mod
    Jul 17, 2013 at 15:49
  • 1
    $\begingroup$ ...especially that Physics.SE got a very strong 'theoretical physics' slant and doesn't like questions that lean on engineering. Especially if you want hard numbers in the answer, don't count on Physics.SE. $\endgroup$
    – SF.
    Jun 3, 2018 at 21:19

I would say that the utility of the answer is another consideration. In cases where one thinks that a good answer could be found to be helpful, useful, or instructive to readers coming to the site for on-topic learning in the future, then try to refrain from reflexively reaching for the insta-close button.

If for example the question is about astronauts shooting at the Sun, and several well-received answers with instructive insight on principles of astrodynamics and orbital mechanics appear quickly, then perhaps refraining from reflexive insta-closeing was the right course of action.

Alternatives, especially in low to moderate question-rate sites include helpful comments or possibly in some cases proactive edits, with discretion of course.

  • 1
    $\begingroup$ While I get what you are saying, the general guidance is not to keep a question that would otherwise be migrated just because it has answers which are on-topic. This is because visitors search on questions, not answers. A good answer does not usually save a bad question. $\endgroup$
    – Rory Alsop Mod
    Mar 29, 2018 at 8:21
  • $\begingroup$ If the answers are on-topic, then it's more worth to edit the question on-topic. Off-topic questions must be closed or migrated due to what @RoryAlsop said. $\endgroup$ Mar 29, 2018 at 10:23
  • $\begingroup$ @derwodamaso sometimes the true nature of the question, (including its on-or-off-topicness) evolves as answers are worked out. Pre-closing before letting others explore the implications of the question by answering can kill a question, as the closing prevents people from answering and looking at each others' answers. Off-topic-ness is not a simple, self-evident boolean, sometimes it takes a bit of time and people working together to come to a consensus. Drive-by close-voters can block this also. Communicating via comments is not the same as reading others' answers and then commenting on those. $\endgroup$
    – uhoh
    Mar 29, 2018 at 10:31
  • $\begingroup$ In a medium to low question rate site this kind of collaboration happens all the time. In these cases the quick-closers lower the effectiveness of the community effort. $\endgroup$
    – uhoh
    Mar 29, 2018 at 10:37
  • 3
    $\begingroup$ Regarding editing questions to fit answers, please see @Gilles answer here: meta.stackexchange.com/a/89373/154443 as well as other posts on Chameleon Questions on meta. Key line: "If all of the answers would still be ok after your edit, then yes, go ahead." $\endgroup$
    – Rory Alsop Mod
    Mar 29, 2018 at 11:35
  • $\begingroup$ I agree with you on the point of not closing questions instantly. In this case, I did not vote for closing instantly and keep giving you upvotes ;-) Still I think the question must be edited on-topic, by someone who has time to do so ^^ $\endgroup$ Apr 2, 2018 at 8:03
  • $\begingroup$ @derwodamaso one can't "give upvotes" especially to me since I didn't post there. Anyway thanks for your comment! $\endgroup$
    – uhoh
    Apr 2, 2018 at 8:18

I would say that if it is directly related to Space Exploration, let it stay. If it is something like

How much fuel would I need in rocket x to get to planet y?

Then it's probably on-topic here.

If, on the other hand, it's something like this:

What makes an ion engine work?

Then it should go to Physics.


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