There are some good astronomy and phyiscs lessons to be had in space and plenty of pictures from NASA to help.

One thing to do is to show how empty space is: stand on one asteroid and you can't see the next one, never mind needing to dodge it.

Plus standing on an asteroid means that they don't have artificial gravity, so there is the demonstration that weightless doesn't mean there is no inertia and the lack of friction to hide Newton's laws of motion: how does a floating spaceman get back to the spaceship?

And a small asteroid makes it easier to demonstrate orbits because orbital and escape velocities are so low - the SF story of the spy in a spacesuit vs a spaceship comes to mind.

With Traveller ships you get to cheat (jump space and normal space drives, as well as contra grav) so you can go chasing radio messages. You can also see the difference between driving to orbital altitude at 100mph and being in orbit at 7.8km/s - there are lots of things moving very rapidly to dodge if hovering in low orbit altitude using CG. Also the fact that the Earth is round and isn't stationary: it's moving rapidly around the sun.