Ah, a Fortran joke. That's not just "technologists". That's old farts.
(In Fortran 66, variables didn't have to be declared. They would be integer if they began with I, J, K, L, M, or N. Otherwise it would be floating point [REAL, in Fortran parlance]. To this day it's why for loops usually use "i". With the bonus joke that God is real unless declared integer.)
Maths is the reason for loops use i. Fortran defines variables starting with those letters to be integers because maths has used those letters for iteration, counting, indexing, etc. for centuries. It was natural for a formula translating system to follow suit.
Probably the most appropriate one. The ESA is not quite part of the EU and has non-EU member states (including _Canada_), so .eu would be inappropriate (the EU is itself a member of ESA, but most EU member states are also members in their own right.)
I think esa.int is probably one of the more popular .int domains on HN: https://news.ycombinator.com/from?site=esa.int