[CliffStoll]

Showing my age: As an undergrad, in 1969, I read Dirk Brouwer's book, Methods of Celestial Mechanics; much of it over my head. I remember writing a Fortran program to solve Kepler's Equation and -- surprise -- getting the same answer as the textbook's analytic solution.

  Turned out to be really useful when I studied planetary science in grad school - just knowing the language of the coordinate systems and expansions.  

  Later, I picked up a copy of Mattias Soop's sweet monograph, "Introduction to Geostationary Orbits" ... even today, it's a joy to read.