Hi Steven,
Thanks for telling your story. My 22 year old son has Autism. You have inspired me to have another go in trying to involve my son in astronomy. Sadly after a while we tend to fall into a rut and just settle for coasting along, keeping the piece. As you said it is very difficult to get him interested in something new. It’s very difficult for him to understand the concept involved in something like this, or most things really.
Don’t know how old your son is (the younger the better), but as you are able to share and interact with him in something together you are surely helping his development for the future.
Stay out of the ruts, I'm sure you will.
All the best
Richard