Oh yes, I have lots of memories playing this as a kid. I have not seen one since, but they had one at the Time Out arcade in the Springfield Mall in Springfield, VA way back in the day. It was indeed an EM. You sat on the seat and rotated around looking for UFOs in the viewfinder. Once you spot one you'd shoot it down.
I'd love to see one now just for the memories. I really liked this game for some reason.
Here's one from Knott's Berry Farm in the early 1980s taken by my friend Eddie Sotto. I'm assuming this was being removed from the arcade inside the building...