> My understanding is that closer to the equator is better, with some caveats.

For this project, I don't think it matters. They even said they will orient the launcher vertically.

The reason you normally want to be closer to the equator is that you get some sideways velocity from the rotating earth, and that is faster nearer the equator. This is important for low earth orbits because the sideways velocity is very high.

However, in this case they don't really care much about sideways velocity. They want to reach escape velocity. As you go higher, the sideways velocity needed to stay in orbit gets smaller, until finally it's practically zero. So, any gain they would get from being near the equator wouldn't be needed.

I think.