Mary Ross was one of the people working on those problems.

The Handbook That Mars And Venus Required

The most concrete and well-documented example of her work in this area is a technical publication known as the NASA Space Flight Handbooks, specifically the Planetary Flight Handbook, produced in the early 1960s.

The Planetary Flight Handbook was a serious technical document addressed to a serious technical problem: how, mathematically, would you actually plan a mission to another planet?

What were the specific calculations an engineer would need to perform?