sorry it took so long to get back to this thread..
I decided I did want to ditch the 15-hour trip through the atmosphere - it's just boring and serves no purpose.
instead, I was thinking like -10 miles above the surface. 2-3 hours is enough to see the tops of clouds, harassed by flying monsters etc...
as the surface below you gets so far away you can only see landforms. The pilot sees whispy lines coming down from the sky, one seems to lead towards the sun, and another two lead toward each of the moons. (or the visible stars if the players are doing this at night.) the pilot's mind gets too close to one of the threads. ( is going to be the normal moon, because I have a funny encounter in mind going that way)
The air seems to open up, and you briefly see the shape of a dome of air surrounding the ship, (90 ft away) and suddenly you are in the blackness of space, headed for the moon, you look back and the world is shrinking rapidly in size as you are flung out into space at an unimaginable speed, that you can't even feel.
But I'm thinking about this the wrong way again. What Do I want to happen and what do the players think/want to explore?
the players spent a lot of time being excited about designing ship weapons, improving maneuverability, and providing safety lines for the crew. --ie they want to swashbuckle from the deck of their ship. They are also worried about crew size and food.
So a short hop to the existing moon, a longer trip to the bad moon, and some space/air combat.
I want them to be close enough to the world to see the lights of 2 other civilizations, each about 1/3 of the way around the world, and that most of their world is covered in ice. I want them to be interested but not have the instant gratification of just being able to go over and see.
Perhaps they can learn that their solar system also contains a second inhabited world, surrounded by rings of fire.
Or a third "Shattered" world on the edge of the system that has spelljamming built in.
they already know both of these planets exist, from an imperial astronomer.
I plan on ending the campaign after the PCs deal with the moon. We can start over on the same campaign world, or one of the others in system. It will be a conversation. We may eventually return to the Spelljammer party, for a one-shot/short arc or full campaign.
they will end the game somewhere between level 11-13. It's time to start over with new heroes.