I'd be surprised if they haven't tested at least one engine in vacuum. You can build a test apparatus for that. Only learned how when I saw this video: https://

I'd be surprised if they haven't tested at least one engine in vacuum. You can build a test apparatus for that. Only learned how when I saw this video: https://www.youtube.com/watch?v=hrLyzpTV7GU https://www.youtube.com/watch?v=hrLyzpTV7GU