One of the members of my club let us know that Epic Games is making their Kerbal Space program software FREE until Jan 12. I had heard of it, but never did look into it. Looks complicated but addicting from what I am told by others.
Link:
https://store.epicgames.com/en-US/p/kerbal-space-program
Link:
https://store.epicgames.com/en-US/p/kerbal-space-program