That’s a good point about I~sp~ not mattering as much lower in the atmosphere. This isn’t my field, but I know enough physics and have played enough Kerbal to know what to look for on the board.

Just a fun aside, while I was in undergrad, we covered the rocket equation in one of my mechanics courses. The textbook we were using was quite old, so a bunch of the questions were about the US/USSR launching rockets at each other.