Yes, there is screen time of varying quality. In our case, I really don’t mind and am relaxed if the media is in our heritage language.

We called it "getting screen sick." And we would say "you must have been watching videos for too long and got screen sick. Next time you should stop after 30 minutes."

They learn to either control the whiny impulses or have their screen time shortened.

I think it's better than watching non-educational stuff, but over an hour of screen time is still a lot if he's doing that on a regular basis.

If he loves to play basketball on the driveway, there would be a time when he has to stop playing and come inside for dinner. He might get grumpy too.

I don't think this is about screen time but about transitioning between activities. Google "activity transition kids" for some common methods.

I’ve long felt that screens are just another form of media. They’re not intrinsically evil. What matters is the content accessed through them. There’s some truly awful stuff that kids need to be shielded from, a lot of mediocrity, and some real jewels that can be great for kids. They can really open up the world (or in your child’s case, the universe).

Hoagies has links to enrichment for all subjects and ages. Here’s their page for space links:
https://www.hoagiesgifted.org/space.htm

While I don’t think there’s a problem with screens themselves, I do think it’s important with any activity to follow parental direction. At various times, my kids balked at putting away a toy or coming home from the park. While I addressed such incidents as they arose, I didn’t take away all toys and lock my kids in the house. I might have temporarily restricted that specific activity to reinforce that it was a privilege they could lose if they weren’t mature enough to handle it, and then I’d give them another shot and hope they learned their lesson, reinforcing as necessary.

I remember reading an article at one point about the different types of screen times and how they're not created equal, though I couldn't find the one I'm thinking about to post here.

It sounds like he has an interest in space & his watching these shows is fueling creativity which is really cool!

Re: the grumpiness factor, if it's really bad, you can just say something to him like: "Hey, I know you love these shows, but you do X, Y and Z after which is not okay. I want to keep letting you watch these, but we need to figure out a way to stop X from happening. Any suggestions?"

He's old enough to have a conversation about this and help problem solve.

DS6 is obsessed with space. He likes to put on YouTube videos of planets, stars, black holes, etc on our TV and pause the screen to draw the planet/star/etc on a piece of paper with colored pencils, label its name, and write whatever random facts appear on the screen (such as diameter—even though he does not clearly understand what “diameter” means). He can do this for more than an hour at a time without getting bored. We get the feeling this kind of screen time is not as bad as mindlessly and passively watching cartoons, but he still can get very grumpy when we turn the TV off and move on to the next activity, and it can put him in a bad mood which we have to deal with. Any thoughts? The emotional upset associated with this type of screen time is obviously not great.